Spi + planing hull = ?

I recently heard from a very experienced cat sailor/racer that it was his experience that flying a spi in 15 kts singlehandedly on a cat with "planing" wave piercing hulls caused the bows to bury and made the cat difficult to control even though the boat's handling characteristics in all other conditions was great. In contrast, he said that flying a spi in similar winds singlehandedly on a different cat with "plowing" wave piercing hulls the bows didn't bury as much. He summarized his comment by saying something like "spi + planing wave piercing hulls don't mix!". Clearly this is one experienced guy who likes to push the limits, but it would be nice to know that if the wind builds that you could still control your cat while flying a chute. This was the first time I had heard this issue raised in this way and stated so clearly.

My questions are:
1) Has anyone else seen this? Cat and windspeed?
2) Has anyone seen this on cats with "plowing" hulls? Cat and windspeed?
3) Why does this happen to "planing" and not to "plowing" hulls?
4) If others have observed this, how is it influenced by boat weight and hull length (and why) - ie, would the same phenomenon be seen on A-cats, FXOne, and planing F16's such as Stealth/Blade (but not seen on I17 and T4.9)?
5) In picking a new boat, how important is this issue?

Jerry

It'd be interesting to see a planing cat despite the fact that its a displacement boat.

Just exactly what is a planing wave piercing cat?
Can you tell us the boat models that were discussed???

Hi MauganH17,

Just to clarify, by "planing" hull I was referring to cats with flat bottom hulls like the Flyer A-cat which tend to jump over waves (also called "slappers" by some) vs "plowing" hulls which tend to more smoothly cut through the waves with rounder or v-shaped bottoms. I think everyone agrees all cats are primarily displacement boats with brief periods of planing caused by dynamic lift. I didn't mean that flat bottomed hull designs truely plane and that others don't and are displacement only. See discussion in prior posts under "Singlehanded Cat Sailing"...

Jerry

We realy should be starting to descriminate between different types of wave piercers (I dislike that description as well by the way.) We have several shapes right now after the Flyer introduced the concept. And the Flyer hull is different from teh FX-one which is different from the Bimare shapes which in turn can not be compared to that of the Blade. Some designers try to design "wave piercer hulls" by reducing bouyance fore and aft in the hull. Others by moveing this bouyancy away from the extremeties towards the centre under the main beam. And another implements this by only redistributing the bouyancy in the vertical direction while keeping the destribution in the horizontal sense unchanged. The different paths lead to the boats behaving differently under certain conditions. There is even a difference between the Hobie Fox and the Hobie FX-one in my personal experience. Therefor I don't think it can be stated that :"spi + planing wave piercing hulls don't mix!". It dependent on the design path followed.

The same must be set about displacement boats however. An Inter-18 is different from a Nacra F18 in this respect as well despite the fact that neither are regarded as "Wave piercers".

My questions are:

1) Has anyone else seen this? Cat and windspeed?
2) Has anyone seen this on cats with "plowing" hulls? Cat and windspeed?

No further comment on these points, I'm too involved.

3) Why does this happen to "planing" and not to "plowing" hulls?

It can to happen to both depending on the individual design of the boat.

4) If others have observed this, how is it influenced by boat weight and hull length (and why) - ie, would the same phenomenon be seen on A-cats, FXOne, and planing F16's such as Stealth/Blade (but not seen on I17 and T4.9)?

In your list of examples you have actually listed boats under "don't" that do and visa versa


Wouter

Wouter,

Thanks for your input. A few clarifications:

Can we agree on terms?
1)plower = cutter and planer = hopper
2)we don't mean plane as true planing or plow as displacement only
3)most cats share both of these characteristic depending on many factors including sailor weight position but some cats due to hull design show one of these characteristics to a greater degree much of the time

I had said:
"4) If others have observed this, how is it influenced by boat weight and hull length (and why) - ie, would the same phenomenon be seen on A-cats, FXOne, and planing F16's such as Stealth/Blade (but not seen on I17 and T4.9)?"

And you replied:
"In your list of examples you have actually listed boats under "don't" that do and visa versa"

I'm assuming you're referring to which boats are plowers/cutter vs planers/hoppers?

But in an earlier post "Single Handed Cat Sailing" you had said:
"The cutters more smooth and silent. The Taipan is a cutter and I believe the I-17 is so as well. The FX-one, Stealth F16 and Blade F16 are more of a hopper ... With respect to F16's ; Taipan 4.9/F16 is definately a cutter, Blade F16 and Stealth F16 are planers."

I had thought I was classifying the boats as you did; did I misunderstand you?

One of the reasons I raised the original question of spi + planing hull is related to another comment you made during the same post:

"With regard to the term planing. No cat planes fully and probably never will. It is indeed more like "having a (small) portion of its weight carried by dynamic forces created on the hull. I personally believe that such surfaces allow you to drive the boat harder without picthpoling and that explains more of the (possible) speed increases than the actual "plaining"."

So I had thought that a cat with planing hulls would be more resistant to pitchpoling and not less so while flying a spi and driving it hard. Yet the experience of one cat sailor goes against this. Which brings up a related question: how much of the pitchpoling characteristic of any hull design is due to boat setup/tuning? You and others have showed previously how changing the tuning of a boat can dramatically change sailing characteristics (ie, in reference to BroBru's I17). How much of this one cat sailor's experience might have been due to the boat he was sailing not being tuned well for the challenging conditions - and if so, what can one change on a cat to allow it to be driven hard off the wind cat rigged or spi that would help it avoid pitchpoling?

Speaking of tuning, one unrealted question: when you sail a cat such as a T4.9 or I17 cat rigged vs sloop vs spi, is it generally necessary to adjust standing rigging (ie, mast rake) or otherwise retune the boat for each configuration in order to allow it to sail properly (ie, balanced helm, pitchpole resistance)?

Thanks for the great input,

Jerry

Mast rake can have a large effect on stuffing. For hull shape, boats with more bouyancy forward are generally harder to stuff.

RBJ wrote

"4) If others have observed this, how is it influenced by boat weight and hull length (and why) - ie, would the same phenomenon be seen on A-cats, FXOne, and planing F16's such as Stealth/Blade (but not seen on I17 and T4.9)?"

And you replied:
"In your list of examples you have actually listed boats under "don't" that do and visa versa"

I'm assuming you're referring to which boats are plowers/cutter vs planers/hoppers?


No I'm not. I'm refering to diving under spi or remaining relatively stabil. Thus answering the original point of your post.

I all dependent on the hulls and also tuning setup. But I know hullshapes that most of the sailors call wave piercing that confirm the comment that you heard from an experienced racer and I also know a wave piercer hull that doesn't. Therefor the link between wavepiercer lable and diving under spi is not a good one.

This is mostly the result of an explosions of flyer copies which are all called wavepiercers but may be very different in behaviour just the same.

>>I had thought I was classifying the boats as you did; did I misunderstand you?

I was comment on the wavepiercer and spi don't mix; I wasn't at all refering to planing or plowing (or which other synonimes are used for this)


>>>One of the reasons I raised the original question of spi + planing hull is related to another comment you made during the same post:

"With regard to the term planing. No cat planes fully and probably never will. It is indeed more like "having a (small) portion of its weight carried by dynamic forces created on the hull. I personally believe that such surfaces allow you to drive the boat harder without picthpoling and that explains more of the (possible) speed increases than the actual "plaining"."

So I had thought that a cat with planing hulls would be more resistant to pitchpoling and not less so while flying a spi and driving it hard. Yet the experience of one cat sailor goes against this.


I think I have an idea on which boat the sailor making the comment has sailed but I can not comment on specific boat types in this manner in public.

I'll repeat what I stated earlier I know of "wavepiercers' doing well under spi and of wavepiercer not doing well. Visa Versa for "plowers" and spi. Therefor I think the comment made by the sailor is type specific and not "wave piercer" specific.

Of course I still think wave piercer is by now a useless term. It has been highjacket by several producers who make cosmetic changes to their boat to make it look like one but in all honesty don't understand what is really going on with the orginal wavepiercers. Others however do know and here the boats are better behaved.


>>Which brings up a related question: how much of the pitchpoling characteristic of any hull design is due to boat setup/tuning?

Mast rake can be important in the ease in which you initiate a dive, however hull shape determines whether this ends in a pitchpole or not. Therefor I would answer your question with tuning is not very important in pitchpoling and you can't trim it out of the boats without trimming away power or efficiency.

Fast and efficient boats are the ones that allow a boat to recover fully and with ease when it finds itself in a dive. The better the recovery the more powered up a boat can be trimmed and more to the edge you can sail it. Having said this I also know of a boat that can be sailed right up to its edge under full power without much diving or even bow down attitude BUT that will disappear from under you when you step over the edge. It is superior to others all the way up to the edge but you pay for it by having to learn the exact location of its limit.

This may not be the answers you are looking but this setup is a multivariable equation and simple rule often don't do it justice.


>>You and others have showed previously how changing the tuning of a boat can dramatically change sailing characteristics (ie, in reference to BroBru's I17). How much of this one cat sailor's experience might have been due to the boat he was sailing not being tuned well for the challenging conditions - and if so, what can one change on a cat to allow it to be driven hard off the wind cat rigged or spi that would help it avoid pitchpoling?


In general flying a spi on a catamaran will make it less dive sensitive. Quite a number of crews overhere pull spis in big wind not because of performance but because they feel they have a better controlled boat with it. I share this experience. It is weird to see a boat being actually worse off. I know the Dart 18 didn't take well to the spi. The only reason I can think of that would cause a cat to dislike a spi is that a hull doesn't have sufficient bouyancy in the bow and/or stern in relation to the leverage of the rig. I know some builders tried to imitate the wavepiercer concept by remove bouyancy at both ends without changing much else in the hull shape. I would look at these designs first if I had to name designs that could suffers under spi.


>>>Speaking of tuning, one unrealted question: when you sail a cat such as a T4.9 or I17 cat rigged vs sloop vs spi, is it generally necessary to adjust standing rigging (ie, mast rake) or otherwise retune the boat for each configuration in order to allow it to sail properly (ie, balanced helm, pitchpole resistance)?

I personally just trimmed the boat to an good average between modes and leave it like that. However, this does mean you can get some extra out of the rig by retrimming it when you are sure in which your are going to sail. I didn't really experience much problem with helm or pitchpole resistance. You know which boats I sailed and none appeared to be very sensitive to changes in setup. All cats with spi have leehelm, however I don't think this is a bad thing. After all the safety zone for sailing under spinnaker is to your lee and not to your luff as is the case when going upwind. It may not be excessive but that is logical.


Thanks for the great input,

Jerry

Wouter,

As usual, thanks for an extraordinary and very clear reply. I've read your comments previously that all wave piercing hulls are not created equal, but didn't make the connection to this specific behavior under spi.

What has become abundantly clear after getting great input from you and others is that to properly evaluate a cat it is really necessary to understand it's sailing characteristics (either in person or via experiences from others who you trust) for each possible mode (ie, cat rigged, sloop, spi, and sloop/spi), with each mode sailed under a very wide range of wind and wave conditions. So in this regard, even the usual good advice often given of "sail each cat once before you buy a new one" should be taken with a grain of salt since you might get a very incomplete understanding from a limited test sail under only one sail plan in non-stress test conditions. I don't like to be surprised!

I am so impressed with the quality of contributors to this forum and the enthusiasm with which everyone shares their experiences, expertise, and ideas. Only in this kind of forum would it have been possible to hear from one experienced sailor "this is what I observed" and get an insightful analysis from another "this is why he may have observed that".

Guys, what can I say but thank-you!

Jerry

Going back to the original question.

My first thought would be that the spin pole is too short on the boat that is burying.

Next I would look at mast rake (WAG 0 to 1 ft aft) and the look for water in the hulls.

Finally I would try to take both boats side by side and if one was still burying, I would swap spins to see if that was it.

The torque from the spin in winds over 10 knots is pretty big in comparison to the torque from the bouyancy at the bows for boat under ~20 ft. So, in general the spin is set to lift the bows. The longer the spin pole, the qreater the lever arm to torque the bows up and the greater the percentage of the force of the spin force that goes into lift.

This even works on boat that have no bows like Waves.

My $0.02's

Carl,

Great points.

Regarding the spi lifting the bows for boats under ~20 ft and 10+ kts: is the lifting torque influenced by spi tack sheet trim? If you trim this do you do it only for power/efficiency related to point of sail or do you do it to influence bow lift and associated boat handling characteristics?

Also, from what I understand, on pole-end snuffer systems you usually can't adjust tack sheet trim at all since the spi tack is usually shackled to the pole end; also on mid-pole snuffer systems using a single halyard to set spi head/tack you can't trim spi tack independently of spi head. What kind of snuffer do you use and do you ever concern yourself with trimming the spi tack?

Finally, at the risk of showing my ignorance, what's "WAG 0 to 1 ft aft"?

Jerry

Hi Jerry,
Don't get too carried with the technical information you get on this forum. There are some who speak loudly and don't know what they are talking about. They have never built a boat and never done scientific studies. Never put instruments on a beach cat and taken measurements upon which to base sound conclusions.
The man from Texas is right. If a spinnaker makes a boat dig its bow, the pole is too short. Aluminum tubing comes in 12ft lengths. Therefore many spin poles are 12ft long. It doesn't matter if that is the correct length pole for the boat or not; it is the length that is readily available so that is what is sold/used. A spinnaker that lifts the bows flies from a pole that is 45% to 50% of the mast height. A spinnaker flying in this mechanical arrangement will lift the bow no matter what the bow shape. The flying spinnaker unloads the bow no mtter what the bow shape.
"All boats that fly spinnakers have lee helm". Only boat designs that place the daggerboard in the classical position, approximately at the shroud chainplate, have lee helm with the spinnaker up. This is a system design that has ignored the spinnaker during the design phase of the boat development and the designer/manufacturer expects the sailing public to put up with it. There is a sail/boat design system that does take this CE migration into account. The design system is called "shared lift" and it is incorporated into ARC products. It has to do with shifting the board location forward so that the CE with spin up cannot get in front of the board. Then down sizing the board and up sizing the rudder so that the shared lift between the board and rudder is in the correct effective location for sailing the boat as sloop.
Good Sailing,
Bill

Bill,

Thanks for your comments. I understand there are differences in opinion on many issues but I have leaned from and respect the views of the prior posters (as well as your many insightful posts). I'd like to discuss any differences in opionion constructively.

I'll look into the mast height vs spi pole lengths to see if this contributed to the problem. I had actually thought they were fairly comparable but not sure of this. Your point regarding the moveable CE and how this can be address with a "shared lift" approach sounds innovative. The comparison I mentioned was between conventional daggerboard catamarans. But you do raise a related question: the majority of cats being sailed don't attempt to compensate for a spi induced forward movement of the CE; in fact, going downwind they usually raise their daggerboards moving the CLR even further aft in relation to forward moving CE.

Two questions:
1) Althogh they have some lee helm as a result I've not heard spi sailors complain about this so why is it a problem?
2) As catamarans sail fast downwind and are headed by their own apparent wind does their "spi migrated" CE shift aft somewhat as a result reducing the effect on lee helm? I've read on windsurfers in high apparent wind conditions and/or gusts the sail shape can change moving the CE aft even on their battened sails.

Jerry

Bill,

What instruments can you/have you put on a beach cat. How well do they work.

Gareth

Hi Jerry,
1)Cat sailors don't complain about lee helm with spinnakers up for two reasons. One is that there is nothing they can do about it; they have already bought their boat. Two is the other boats have the same problem so live with it.
Other examples of this attitude: H16s tack so poorly that the time and distance lost due to tacking usually outweighs the advantage of a new tack, so why tack? Who complains? It is the same for everybody in a H16 race, so what the heck.
H16s pitchpole easily on a reach so you can't be too aggressive and drive the boat hard in a breeze or you will pitchpole. Who complains? It is the same for everybody in a H16 race, so what the heck.
I see nothing but praise for the H16 on this forum. In West Palm Beach, Florida two sailors have lost their lives because of the unsafe characteristics, easy pitchpole tendency, of the H16 design. It is the same for everyone sailing a H16 so, what the heck.
2) With spinnaker up and sailing downwind, a given boat design sails to a constant relative wind angle depending on the wind strength. The direction of the boat may change in the puffs but the sailor tries to hold relative wind angle constant at max VMG downwind. If relative wind angle is held constant, then sail trim is held constant and CE does not move around once the sails are set and the boat is up to speed. When the CE goes in front of the daggerboard, you've got lee helm. So what, it is the same for everybody, what the heck.
Bill

I've kept my mouth shut for so long on this...

but Bill, you just can't help but take cheap shots at other boat designs can you?

EVERY post of your has a smart-assed remark about how such-and-such design blows goats compared to the ARC. While this may be true, is it necessary to sit there and talk sh*t about every catamaran under the sun? Its exactly like a politician who wont stop running a negative attack campaign. Frankly I'm sick of it. I really respect you for what you've done for our sport, but I'm seriously considering writing a script that removes your comments from everythread (on my end, don't worry Rick) just so I don't feel dirty after I read them.

Hi Gareth,
The instrumentation that I use for testing is made up of a compass and speedometer and slip angle measurement. I also carry a windspeed instrument. Frequently during a test the boat is turned head to wind and the windspeed and direction are recorded. The data is usually recorded on a pocket tape recorder so comments and special circumstances are noted in the data.
Bill

Hey MauganH17,

Chill out! This is a forum. Everyone gets his say. We listen to you right. I enjoy Bill's posts. I actually learn something on here when he speaks. Come to Round the Island next year in Ft. Walton beach and check out some of Bill's handy work. I believe last year he and his crew ( there were two I think ) were triple trapped on the downwind run at about 25 knots.

Happy Sailing

Tom

ps. Seems to me he is just stating some facts about the ole H16 that everyone pretty much knows.

Bill,
What is 'slip angle measurement' ?
How is it calculated or measured?
Thanks,
Chris

I think what Maugan is saying is that you don't have to tell a man his wife is ugly, even if it is a "fact."

I'm calm, I just "speak" (type) whats on my mind. I like Mary's analogy though, made me chuckle.

Perhaps Maugan was a bit strong...but the manufacturer and designer bashing is wearing on me too. If everybody else is so bad why do they sell so many boats? Bill, I don't think anyone doubts that you have designed some great boats but there are a lot of boats out there designed by other smart people too.

>>The instrumentation that I use for testing is made up of a compass and speedometer and slip angle measurement. I also carry a windspeed instrument.


And I thought your were talking about gyroscopes, GPS units and stress sensors. Everybody carries a compass on board and speedometers are outdated. Just use a GPS unit with tracking ability and make sure there is no current on the body of water you're sailing on. Having a reference boat around with reference crew helps a lot as well.

Talking about GPS tracking here is one from my personal archive. Note how the top speed (30 km/u=16 knots) of the sloop rigged craft is reached on ALL courses !

But then again I'm not a real designer.

Wouter

Hi Chris,
Slip angle is the angle between the boat centerline and the path of the boat through the water. It is simply a weather vane that runs in the water and the base is clamped to the boat. The vane is connected to a pointer just above the clamp/bracket that indicates the direction of the vane in the water as the boat sails. The difference in the vane indicated direction and boat centerline is the slip angle.
I have done alot of sailing with instruments on my boats because I don't have another boat to sail against so I sail against the instruments. This has helped me develope boats that are the fastest US Sailing has on record and cost 1/15th as much as a Formula 40 boat for example.
Bill

Hi Magee,
I'm only stating facts,not rhetoric. If you don't like them, I'm sorry. I wrote the comments that you don't like in the style I did for emphasis. I think boat safety is NUMBER 1 in order of importance. That is why the SC/ARC boats are the shape they are, elliptical hull cross section shape. That is why all SC/ARC boats come with a righting system from the factory. As soon as you leave the shore on a beach cat and the water is over your head, you are "at risk" and your beach cat put you there. Your beach cat better be able to take you out of an "at risk" situation, like a turn over.
SAFETY, SAFETY, SAFETY is NUMBER 1 in order of importance in any boat design.
And by the way, Magee, some day all beach cats with spinnakers will have the daggerboards close behind the main beam or maybe just in front of the main beam. It is just going to take a while for them to get there.
Some day all beach cats will have self tacking jibs. It is just going to take a while for them to get there.
Some day all beach cats will come from the factory with righting systems. It is just going to take a while for them to get there.
Good Sailing,
Bill

You are right, Wouter, you are not a real designer. You are a buyer and a user and a talk abouter. Back in the 1970s and early 1980s when I was doing my basic beach cat design/study work, there were no GPSs. What would you suggest I do; wait until the 1990s to gain understanding about the design and performance of beach cats using a GPS? The last clean sheet design I did on a beach cat was 1979, the RC27, winner of the Bol De Or race in 1989.
Dream on, Wouter.
Bill

Bill,

What have I done to deserve :"Wouter, you are not a real designer. You are a buyer and a user and a talk abouter" ?

Apparently I'm also a GPS user taking measurements upon which to base sound conclusions IN 2003 !

Not 1978.

And who exactly were you refering to in :

"... who speak loudly and don't know what they are talking about. They have never built a boat and never done scientific studies. Never put instruments on a beach cat and taken measurements upon which to base sound conclusions ..."

I get the funny feeling that that "who" is somebody I know personally.

Wouter

Hello to EVERYONE,

...just so you know,..I learn from ALL OF YOU!

...just so you know,.. diversity and different points of view is what drives innovation

..you all are just great,.....except for one ting, mon

...you should be packing up your boats to come sail down here....Rolex in St. Thomas is last week in March, 5 days later is BVI Regatta

...we can sail all day......

regards,
Bruce
St. Croix

ps; my next boat is a ARC 27,...I need something a little bigger down here

Man oh man. I love the islands. If I don't get a job with the FAA, My Wife and I are just going to sell everything and move there. I'll figure out where to work once I get there.

Hi Bill,

What you (and others) said about lee helm under spi (without CLR correction) sounds both obvious and right and is concordant with many peoples experience; however, I still wonder if it's as simple as you say because today when I discussed this very issue with an experienced I20 racer he SWORE to me that he has a nearly neutral helm under spi (as well as upwind as a sloop).

Why?

Could it be that when one raises their boards off the wind and significantly reduces the magnitude of their CLR the migration of the CE becomes a non-issue (ie, they are not seeing lee helm because they are side-slipping downwind on their broad reach)? This effect might be pronounced on cats with flat bottomed (semi planing) hulls and not observed on cats with deeper hulls - hence different sailors observe different amounts of lee helm. Also, at speed, couldn't the rudder/aft hull be generating sufficient lift to compensate for some forward sail CE migration (when their boards are raised)? Finally, wouldn't the very presence of a spi augment the mainsail's lift (ie, slot effect) effectively moving the aggregate CE back somewhat? (I hope my inexperience and/or naivete isn't showing too badly...).

Who else out there has spi experience on an I20: do you see lee or neutral helm? Anyone else out there on any other (non ARC/SC) spi cats ever see neutral helm?

Jerry

Jerry

I have followed this discussion with interest since I am the designer/builder of the Stealth F16, one of the boats mentioned.

Most of the posters are right, and are actually agreeing with each other, but unfortunately the argument has become a personal one and the answers to your questions are a bit lost in the mud that's flying around.

Your question about whether spinnakers produce dificulties in certain types of boats.

Well I think that it is too simplistic to put cats into these two camps of Hoppers and ploughers, my experience is that all the cats around today are pretty easy to sail with spinnakers. Some respond better than others but I suggest that the main difference is in the developement that has gone into the boat in the first place so that it is more a question of refinement rather than, the effect that the hull shape has.

next on the point of weather helm or lee helm

It is a simple fact of life that if you stick up a spinnaker you move the centre of effort forwards, now if you have a balanced boat to begin with you will end up with lee helm, if the boat is balanced with the kite up, there must have been weather helm before you put it up. You cannot have a balanced boat both ways unless you mave the daggerboards forward when you put the kite up.

Some boats, the I20 is one, have very balanced rudders, so that you cannot tell if there is weather or lee helm, but it is still there.

Bill is right in that his design will make a more neutral helm when the kite is up, but he failed to mention that his design must have more weather helm when the kite is down, its just that he has balanced rudders so you can't feel it.

The real question is whether or not any of this is a problem, and the answer is that it is not, just select a boat that has been designed by a good company, and develeloped with the spinnaker on it and you will have no problems with any of this.

Any of the boats you are looking at will do in this case

Bill,

I have some questions on slip angles going to WINDWARD, and ballpark numbers are good enough, for as they say 'government work'. What kind of relative numerical difference between board vs boardless?


For say SC20 catamaran (which I have had the pleasure to sail on):


Is slip angle more practical as a design tool, than for practicing by yourself to improve VMG?

The slower you go the higher the slip angle, and the converse, the faster you go the slip angle approaches zero to the same true wind angle?

Going to windward, what angle to the true wind will the slip angle begin to zero out?
(mathematically never, but for practical use go to windward)

Is there a boat speed at which point the slip angle almost zero's out?

Did anything supprise you, while you were doing your research on SA?
ie. the rate of change of slip angle from 1kn to 10kn.

Using a slip angle you can determine the optimum amount of board to use for a given wind speed? and if so, any comments?

The higher a cat points into the wind the higher the SA? For practicing to improve VMG would you sail lower angles to the true wind until SA plateau's out? If so when does it plateau out?

Bill, should I buy North's SA meter-z1, or Elvstrom's SA A04-meter? (LOL)
Thanks again,
Chris

Thanks for making the answer so clear, John, as with all your advice. A while back I asked how to get rid of lee-helm, the answer came from John : Rake the mast back until the lee-helm is neutral, or at least not too unmanageable. Then rake rudders forward so that the weatherhelm upwind from increased mast rake is not a problem. It`s still there, it still loads up the rudders, but it isn`t transferred to the tiller, so you get to keep your shoulder joint in one piece. Apparently some weatherhelm helps the boat track upwind as the loaded up rudders create lift. (If I`m mis-informed here please don`t kill me, I spend my time designing buildings, not boats, and very seldom consider the hydrodynamic properties of concrete, although I imagine they`re not worth discussing. No, this is not an invitation to ressurect the thread about concrete canoes ).
Although my boat was designed without a spinnaker in mind, I`ve found that this advice has helped tame the rudders.

Cheers
Steve

“Perhaps Maugan was a bit strong...but the manufacturer and designer bashing is wearing on me too. If everybody else is so bad why do they sell so many boats?”

Come on Jake…you already know the answer to that one…LOL…MARKETING!!!! More than quality of design... More than quality materials... More than after the sale support...it’s all about MARKETING! If you can get a person emotionally involved with a product, logic goes out the window.

What do you think was the cause of Hobie selling so many H16? A stellar beach cat design? Or the most brilliant advertising campaign in catamaran history selling the “Hobie way of life”?

How can you get mad at Bill for stating known facts about the H 16?? How can we move toward better catamaran designs if everyone pretends “it doesn’t get any better than this”, and ignores the glaring short comings of past designs? They call that denial…LOL

What I see in this thread is, logic clashing with emotional brand loyalty.

Bob

FYI:

I'm far from brand loyal to hobie. In fact, I'm still quite bitter about quite a few things about my boat, and feel that hobie should have given me a more straight forward answer about it.

Which is why my next boat is non-hobie. Its actually manufacturer-free, which I love.

Hi Jerry,
In answer to your first question: A balanced rudder, a rudder swept forward until 20% of the rudder area is in front of a line through the pintle axis, will feel neutral, light touch, no matter what the side load on the rudder.
Further discussion:
How did we get where we are? Why are CB trunks on beach cats located at or very close to the shroud chainplates? Answer: Because that is where the CB trunk should be located relative to the CE for the SLOOP rigged sail plan. Now add the spinnaker. Does anything change relative to the CE and CLR locations? I think so and the proof of it being so is that so many boats have lee helm with spinnakers up. What can be done about this? Lean the mast back which moves the spinnaker aft. This moves the whole sail plan CE aft and brings the CE and CLR into better alignment with spinnaker up and may be sufficient to get close to a neutral helm for most spinaker sailing situations. Now, how does this leave the CE/CLR situation without spinnaker or sloop rigged? We have moved the CE well aft from the normal position with the large amount of mast rake. We have unloaded the daggerboard and loaded up the rudder. (Remember the N6.0s, Worrell boats, with spinnakers; the masts were raked way way back. This was the correct trim because they were going to sail all day with spinnakers up.) This will make the rudder prone to stall sailing to windward but once you know it is touchy, you can live with it. A larger rudder would be an improvement in this trim/balance situation because the rudder is carrying a larger side force than it was originally designed for.
This situation of trying control the CE migration due to adding the spinnaker to the sloop rig led me to the CLR design scheme that I call "shared lift". The increased sharing of sail generated side force is being sharred between the centerboard and an oversize rudder. Instead of running a large amount of mast rake to move the CE aft, I have chosen to move the CB trunk forward and run a more normal amount of mast rake. The rudder side load increases with more mast rake or moving the CB trunk forward so the rudder is upsized in both cases. The CB side load has been reduced; it can be downsized. Sizing the centerboard and rudder to match the loads they carry will reduce the drag they generate due to making lift.
Good Sailing,
Bill

Hi Bill,
I have often wondered why there are not good slip (call them leeway) indicators on the market. They give information that is not unavailable from a GPS and a compass in practice. An inexpensive flux gate compass might be within 2 or 3 degrees - just no good at all for measuring leeway.

One tough part is keeping the vane perpendicular to the water. A pendulum seems like a good way, but then you have to damp the swing somehow (maybe use an Airpot?) AYRS once had plans for a leeway indicator but it mounted to the bottom of the hull, and did not remain vertical. Maybe there is an updated version. Now, if you could indicate apparent wind direction on the same display...

I really appreciate the technical portions of your posts.
Thanks for taking the time.

Talk to you later
-colin

Bill,
What I understand from your post is that putting a larger rudder set on the boat will have the same effect of "load sharing" whether you move the CB forward, or rake the mast back ?
If you upsize the rudders, is it necessary to make the CB`s smaller in area ?
Obviously can`t move my cb cases forward, so I`ll go with the "more rake" option.

Steve

I think you guys are making this way more complicated than it needs to be.

All older designs that add a chute end up with lee helm because there COE was not designed to work with a chute. Some people try to correct for this some by raking the mast waaayyyy back but it can't correct for all of the lee helm.

New boats like the I20 have Neutral helm upwind and downwind because they were designed to balance the helm. They moved the front crossbar forward to balance the boat. The I18 is also designed like this.

However the Hobie Tiger still seems to suffer from lee helm issues. However that lee helm doesn't seem to slow the Tiger down any as it is competitive with any F18.

I just heard this past Sunday that Performance Catamarans has a larger rudder now available for the I17R. It is not class legal yet but is available.

As it is now, I can only rack back so far until I get some rudder stalling problems going to windward.

Tom Turlington

I17R #124

Hi Colin,
Here's a trick; things are easier than they seem. The compass gives the direction the boat is headed. The GPS gives the direction of the path of the boat. The difference is the slip angle.
Good Slipping,
Bill

Hi Jerry,

I have been sailing/racing my I-17R since spring 2000. I have adjusted my rudders between neutral (no weather helm) going to weather and having "some" weather helm. In both modes, I experience some lee helm after raising the spinnaker. The amount seems minimal. I prefer the neutral setting going to weather...there are times I want to set the helm down to do something else. Under these conditions, I can set the helm down going downwind and not suffer significant change in speed or direction, although I try to minimize the time that I am not holding the tiller. I always let the tiller go when taking the spinnaker down, usually very close to the leeward mark. The I-17R behaves beautifiully all around the race course! In my 23 years of racing catamarans, 19 years on single-handed Catamarans, nothing is as much fun to sail as the I-17R!

Regarding Tom's comments on the new rudders, I would like to have the new rudders also! Although I have had my rudders stall, I have been able to get them to re-attach by oscillating the tiller. I think they would help with coming out of tacks, too (anytime the boat is going very slowly). We should contact Performance and get it made Class legal. Just join the I-17R Class first...they are the only ones who get a vote! Membership runs from 1-Jan thru 31-Dec, no matter when you join!

Hi Tom,
I think you now understand why this larger rudder is being made available.
Bill

Bill,

Exactly! I understood as soon as I read your post. I immediately thought about trying to get my rudders out of a stall once they went in.

I stopped getting too technically involved in the boat a couple years ago and decided instead to concentrate on the " nut on the tiller. " If I am in the ball park on setup, I am happy. But it sure is nice to know what causes what on some things. Thanks for taking the time to explain terms easy to understand.

Tom Turlington
B.A.History; Memphis State

I thought a small degree of weather helm upwind was a good thing on a boarded boat. Countering the helm with the rudders puts a slight angle of attack to the daggerboards making them generate lift to windward and compensate for some of the leeway.

Hi Steve,
Up sizing the rudders will help the rudder stalling problem when sailing to windward. You do not have to downsize the CBs. Leave them alone. My comments about upsizing and downsizing parts is for boat designers and sailors who build their own stuff.
Good Sailing,
Bill

Hi Bill,

Well, it is not quite that easy. Your leeway sensor idea is a much better idea. Ignoring the obvious problem of current there is an accuracy problem.

The bearing accuracy of a good commercial flux gate compass is plus or minus 2 degrees. The bearing repeatability is typically plus or minus 1 degree. I am interested in measuring leeway with greater accuracy than a 2 degree range, and certainly better than a 4 degree range (really absolute accuracy is what matters comparing to a GPS track). Four degrees is right around the leeway angle I am expecting when the hull just starts to fly on a close reach. I also want to be able to read leeway angle while sailing.

I know comparing course and heading works for finding the set and drift of ships with enough accuracy for navigation.
Sailboat performance is a different problem.

Talk to you later
Best regards
-colin

Thanks, John, for the great input.

I actually wasn't sure that all of these boats were designed for a spi (and balanced as such).

Still, lee helm aside, it does seem to be the experience of some good sailors that a modern spi equipped design can have a tendency to bury it's bow (and pitchpole) in heavier air (under spi) whereas others will not.

Jerry

Bill,

Thanks for your insights. One question, though:

You said "A balanced rudder, a rudder swept forward until 20% of the rudder area is in front of a line through the pintle axis, will feel neutral, light touch, no matter what the side load on the rudder"

Why is it that sweeping a rudder forward only 20% in relation to the pintle axis will fuly neutralize the helm (regardless of the load)? I understand why this shift in rudder position has the effect that it does, but would have guessed that it would be necessary to end up with closer to 50% of the rudder surface area in front and 50% behind the pintle axis to get the balanced helm you describe independent of rudder load.

Jerry

Hi Mike,

Good input. Do you know if the I17 was designed like the I18 and I20 with a more foreward front beam? And, in your (or other's) experience does the I17 have a neutral helm under spi like the I20 without over raking the mast and rudders?

Jerry

Jerry,
If a boat burys its bow with the spin up, the pole is too short. I have found from testing that the spin pole needs to be half as long as the spinnaker hoist. Also look at the Australian dinghys. These guys have been sailing/developing very high performance boats with spinnakers for 50 years. They know how to do it and they know what the proportions of the mechanical arrangement should be. Their poles are 50% plus as long as the hoist of the spinnaker and they lift the bows of their dinghys high. No more questions; no more argument. I'm convinced!
Bill

Sparky,

I appreciate hearing about your experience with the I17. If I understand you correctly, with an overall "neutral helm" (non-spi) you feel comfortable briefly letting go of the tiller even on a broad reach while snuffing the spi? Do you ever need to let go of the tiller going upwind?

Jerry

Thanks, Bill

Jerry

Hi Colin,
I think much of the error you are concerned about can be eliminated with proper testing technique. First repeat each test several times.
Take the same measurements on both port and starboard tacks.
When setting/approaching a position for taking a data point, approach the point from both sides and take data on point. That is sail low and rotate the boat clockwise to test point and then sail high and rotate the boat counter- clockwise to test point. I think this will wash out most of the errors you are concerned about.
Good Testing,
Bill

RBJ,

Like an aeronautical wing (or any basic foil shape), the rudder's center of lift is generated at it's thickest cross section (chord)...a dirty estimation would place this 1/3 of the way behind the leading edge.

Hey Jerry,

You ask if the I17R has neutral helm with spinnaker flying. It better! Think about it a second. We have no crew. We are lowering the spinnaker as we approach " C " mark. My boat will track straight after I have dropped the tiller and am in the process of lowering the spinnaker. Sometimes the damn think will get stuck or the halyard will tangle and I have to fix it all this being done while the boat is sailing itself.

Another thing, I'll let the engineers explain the why's and wherefore's, but the I17 does great in heavy air with the spinnaker up! Actually, the only reason boats were flipping during the heavy wind days at the Nationals was because the wind direction was jumping around so much after the front had gone through!

Tom

ps. The big bows on the I17 have save me on countless occasions however. I have buried the boat half way to the front beam and brought it back out before due to a wind change while flying the spin. This was because of the boat not me!

Thank you Bill,

I think I figured out a cheap way to measure leeway directly. Sorry for straying off topic. Thank you for the suggestions.

Best regards
-colin

Tom and Les,

Please descibe this 'stalling' of the rudder upwind,....this is the 3rd year I am sailing my 2000 I-17normal( no-spin, heck, I can barely handle this, as it is!),.......and we sail every week of the year here,.... and we get some light airs in the summer ( between hurricanes, you know..)

What exactly happens..?

What are you doing with your boards at this time?.....are they full down?

I have not seen this,.... yet.

regards,

Bruce
St. Croix

Bill,

Since we seem to be getting alot of Uni rig sailors asking questions here,....can you make a comment about the design of your 17?

Specifically in respect to what you decided to do with board placement?

regards,

Bruce
St. Croix
I-17n
ps.....it was 83 f again today,....13 E mph

Bruce,

It usually happens when the wind is up a bit. I cannot explain it though. The rudders just don't work right. I usually have to head up to get them to come out of the stall which slows the boat........not good. Of course, as we have learned, it is due to mast rack. I would tell you where my rack is but I am now running the single forestay setup so it would not help. If I was still running the two bridle wires ( I think they call them that ) I could tell you where the boat stalls out. At what setting.

I guess you could rack the hell out of your mast, like top hole and try it when the wind is 14-15 or so. But you have the shorter mast. Might not work!

Tom

Hey Bruce,

Rack = rake. It's been a long day.

Tom

Bruce,

I was suppose to have a date tonight, but I hurt my back in the gym trying to get ready to race in a couple weeks. Couldn't go. Guess I just have " a nice rack " on my brain.

Tom

Tom and Les,

Ok,..14-15,...this is the point where my stock sail ( 160sf) is;
1. full downhaul,
2. max mainsheet,
3. outhaul max tight,
4. mast rotation ( check groove at mast base, not arm[it bends and gives you a false reading]) just forward of rear beam,
5. traveler out 6-8 inches,
6. dagger-board up 12 inches
7. and the top 3 foam battens are replaced with solid fiberglass one ( no power from top part of sail)

....you can get all this data from the f-16 forum here, Wouter and the Austrailian T-4.9 sailers actually have a database of past articles,..plus they are very responsive to help out,.....to date, I can find no I-17 database such as this.

8. At 15 +, down goes the stock 160sf sail,..up goes the Charle Ogletree 150sf Pentax,...6 inches cut off the luff,..head to foot.........the boat goes from handleing like a pitbull on a short lease,...back to a sweet sailing machine,...and just rips full throttle,.

.....never has the rudders done anything but be 'finger-light'.

9. Since I canot get you guys to come sail down here, and I do not have to sail against you ...I gave you my research for the last 2 years,...90% came from the F-16 Forum gang.

10. a Aussie T 4.9 champ shared with me,..once I touch the mainsheet, I am changing the draft and shape of the sail, and am guessing as to what is going on,...all bad things in solo Uni sailing upwind.
Since then,....I never touch the mainsheet from max tight,..even in 30+ storm conditions,...I just travel down until the boat gets'happy'...

Again,....what are you doing with your boards?

regards,

Bruce
St. Croix

Hi Bruce,
The ARC 17 is a beginner's boat, no boards, a true beach cat. It does have "shared lift" between the forward half of the hull and an oversize rudder which in actual practice could be called a steering daggerboard. The objective of this hull design was to have a "beach cat" with a better underwater lift to drag than other boardless beach cats so it would go faster and a boat that would tack easily and quickly. These goals were acheived. The underwater part of the ARC 17 hull is a deep Vee hull shape forward which transitions into a round bottom shape at the transom. The deep Vee forward acts like a low aspect ratio daggerboard and provides 50% of the sideways lift force while sailing to windward. The other 50% of the sideways lift force comes from an oversized high aspect ratio rudder. The result is a much higher effective underwater aspect ratio lifting body and less induced drag due to generating side force than the full length assymetrical hull shapes. The other benefit of this hull design concept is that since the hull shape near the transom is round, it can slide across the water sideways with ease. When the rudder exerts a sideways force on the transom, the hull spins right around. On a beach cat hull shape that carries the hard corner and assymetrical hull shape right into the transom, when the rudder exerts a side force to turn the boat, the rudder and hull near the transom get in a fight. The rudder is pushing the aft end of the hull sideways and the hull is saying, "no, I am designed not to go sideways" and there is a large hull drag increase and the boat comes to a stop about half way through the tack. Now the jib must be backed to complete the tack and the boat backs up and this causes the rudders to have to be reversed as the boat backs up and finishes the turn. Now with no forward speed coming out of the tack, if the mainsheet hasn't been let out, the rudders stall and the boat goes into irons. What a complicated mess it is when tacking can be so simple with proper design.
Relative to the spinnaker:
With the effective sideways lifting part of the hull being in the front half of the hull, the ARC 17 handles a spinnaker very nicely, no lee helm. The 17 was my very first "shared lift hull design". The ARC 17 is the only boardless beach cat that will carry a spinnaker without lee helm for the above reasons.
Good Sailing,
Bill

Hi Bruce,

You asked "Please descibe this 'stalling' of the rudder upwind"...

I've never experienced this on a catamran but the same thing does happen when windsurfing, there it's call spin-out and it happens for the same reason - the "skeg" (which is like a fixed rudder) stalls... loses it's ability to develop lift and loses it's diretional stability. What does it feel like? It feels like you've lost your skeg, ie, like the rudder fell off... time for the warp factor six face plant if you're unlucky!

Jerry

Thanks, Tom.

I've heard the I17 handles spi well in heavy air but how the heck to you launch it when it gets that windy without going over?

Jerry

Jerry

Perhaps I oversimplified it when I said that boats designed for spinnakers...etc.

If the spinnaker has been properly developed you should have no problem, the boat I had in mind was a Dart 18, we've got loads of them over here, about 5 years ago the manufacturer just stuck a spinnaker on them, it was not good, the boat has skegs and as the boat pitched back and forward, the CLR would move back and forth making the boat want to luff one minute and bear off the next, add some rudders that were very swept back and the boat was very dificult.

Bill is right about pole length, but what that really means is the angle of the spinnaker luff, the more swept back this is the greater the lift, so, I suspect the problems encountered by your friend are more down to lack of developement of the overall package rather than just the spinnaker acting on the hull shape.

The fact is that with sufficient developement you can make anything work well. Just look at a Porsche 911, no-one would build a sports car these days with the engine behind the rear wheels, but 30 years of developement and it's a superb car.

Jerry,

For launching in heavy air..............


We just head a little lower after rounding " A " mark............... be a little conservative while setting in heavy air. Then after it's up, you can power up as you please. This is when these single handed uni's are so fun. You are driving the boat, setting the main, and handling the spin sheet at the same time don't forget downhaul, mast rotation, outhaul and boards.

Oh, speaking of boards, Bruce, with all that I just mentioned my boards usually end up all the way down even if I start with them up 4" to 6". I ripped out a couple a those well cushions when I first got the boat because I couldn't move the boards. Have been re-epoxying sections in as needed. Usually ends up a bit on the loose side though which I like in case I hit bottom. It's real pain hitting bottom with the spinnaker up and know one to go forward to wrestle with the board.

Tom

To continue, because of all that is going on with the spinnaker up, most of us have move our mast rotator line cam cleats back aft of the boards. Also, we have added a cam cleat for the spinnaker. While distance racing in " safe " conditions ( inside, not out in the gulf ) we lock in our spinnaker sheet, move to the back of the boat and trap out. We then control the boat with the main traveler/sheet only (mainly traveler). If the wind is up, the boat will simply fly!!! And the spinnaker will make this moaning sound.......on my boat anyway. It's great. Other guys have customized their boats in other ways. That's what makes the I17R so much fun. You sit around and try to figure out how to make things easier for yourself with so much going on.

Tom

ps. I have had some rather spectacular pitchpoles on this boat...............usually because I got tired and wasn't paying attention. This boat will work you!!

Tom

Hi John,
I just returned from sailing in the Tradewinds Regatta in thr Florida Keys. I saw many different types of boats with spinnakers. Most boats have poles that are too short. When the spinnaker fills, the bows dig and the skipper and crew head for the back of the boat. I think that the reason for the short pole is that the longer pole pushes the CE further forward and requires even more mast rake than we see today to get rid of lee helm with spinnaker. Now take the spinnaker down and the sloop rig CE is so far aft that it stalls the rudders. So what do you do??? Go with a short pole and small spinnaker and less mast rake and live with it. You can "get by".
A better solution is go with the long spinnaker pole that lifts the bows and move the centerboard trunk forward a couple of feet to trim the boat out with spinnaker. Now without spinnaker, this will automatically reduce the side load on the forward located centerboard and increase the side load on the rudder. Therefore downsize the centerboard until it is carrying the boat's original design point lift per square foot of board area and upsize the rudder until it is carrying the boat's original design point lift per square foot of rudder area. This puts the centerboard and rudder back to operating at their respective design point loadings which results in the these foils operating at their highest level of lift to drag ratio while the boat is sailing to windward.
The other scheme of raking the mast back and balancing the rudders and "live with it" is a second level of performance compromise, a slower boat to windward.
Bill

Bill

Yes I agree, I have always used the shared lift idea in my boats, both those I build and when I sailed T's and others, Whether the boards are forward or not, the same efect can be got with what ever size boards/rudders are chosen, its just about the position of CLR against CE of the rig, however with existing classes obviously board position is fixed.

With the boats we build, we go down the raking the mast back route to load up the rudders, and rake back the spinnaker luff, however we do have large rudders, one thing that compromises most boats that now carry spinnakers is that most class rules limit pole length to 80cm beyond the bow, I don't know why they do this, but Formula 16, formula 18, Formula 18Ht, Tornado and Formula 20 all do this, most manufacturer class boats just toe this line as well, hence the reason why poles are generally short on cats compared to skiffs, also skiffs have a neat way of getting around the lee helm problem, they sail them upright upwind and lean them to leeward downwind, the rig, and hull shape then creates a torque screwing the boat upwind which goes some way to balancing the leehelm effect of the kite way out front, cats obviously aim to fly a hull as much as possible so they can't do this.

I think the fact is that we are both singing from the same hymn sheet on what makes boats go well, we just have different ways of achieving this. Funny isn't it when you put time into developing things, even when you are on different continents and in different decades, you still end up in pretty much the same place, I guess now the internet is around it will stop all this repetition of work!!

Bill,

No doubt that having a longer pole gives you a more vertical component to the drive produced by the spinnaker. But I don't recall seeing any spin boats bury a bow even in the 15-20 mph breeze at Tradewinds on Sunday. It was the least of our worries on the Inter20 and never even presented the remotest of possibilites. I did hear tale of 6.0 driving under but they weren't flying a spinnaker. The inter20 does have a relatively short pole. My 6.0 has a 14' pole and a 28' hoist height and I'm less concerned about burying a bow with the spinnaker than without it. You do have an extreme angle on the luff on the SC17 and I remember remarking how similar the SC17 spinnaker angle looked to that of the Aussie style skiffs (not that there's anything wrong with that).

Would you agree that if your pole is too long that too much of the force generated from the spinnaker would be lost to lift? For example if you take this to the extreme and come up with a spinnaker flying with the luff horizontal - it would not provide any forward drive and would only lift the boat and provide a healing moment. Point being, if the luff is at too much angle, you would not be getting the full benefit of all that sail area. Hence, the less angle at which you attach your spinnaker (and still handle it without driving a bow under) the deeper you can drive it and the faster you'll get to C.

Jake

In regards to pole length, the problem is in how the classes are spec'ing pole length.

In simple terms, Tornado's and 6.0's have long bows so spec'ing the pole 80 cm in front of the bow gives you a long pole. F16 have a 4 ft shorter bows so you end up with a shorter pole. On a Wave you would end up with 4-5 ft pole, if you did this.

I tested pole length on a Wave and found you were into diminishing returns at 50% hoist length


The pole length is dependent on hoist height. If you have a one design class like the Tornado, you know hoist height, so you can spec a pole that works with the sails you tried

One of the reasons Tornado spec'ed like this is it can be enforced and it probably eliminates some of the really weird ideas without going into a detailed explanation of how to measure the pole. For example, if the rules said "the tack can be no more than 12 ft from the crossbeam when measured on the beach." I might try bending the pole so that it was 12 ft and nearly touching the water at rest but extended to 14 ft under load. Historically, with Tornados, unless you say you can't do it, somebody will probably try.


For boats like the F16 where there could be wide variations in optimum hoist height, I think the rule is too restrictive. It indirectly restricts sails, mast height, and mast placement. For example if I wanted to push the front crossbeam forward for some reason, I could have some real problems

Personally I feel bad idea's have their own penalties, I would open it up and keep my camera handy for the guy who tries to use his spare mast as a spin pole.


Also Bill is very right in one respect. I learned a lot about this in designing my own boat from scratch and knowing I was committing my own money and time to my theories. There is nothing like knowing you are committing your time and money to make you conservative.

I've got two bent H17 masts laying around that you could try and use.

I think it would throw the balance of your rig off though

>>In simple terms, Tornado's and 6.0's have long bows so spec'ing the pole 80 cm in front of the bow gives you a long pole. F16 have a 4 ft shorter bows so you end up with a shorter pole.


This is wrong. The F16 rules specify that the pole can be 3.50 mtr measured along the pole. No 80 cm past bow or anything. And your explanation is of as well. Sure the pole is shorter in a F16 than on a say a F18 BUT its hoist height os proportionally smaller as well and the also the area is (proportionally)^2 smaller as well.

The F16 spi setup is actually the same as taking a picture from a F18 setup and then photoshop it to x % size. Therefor the lifting and pitching moments have exactly the same effect.

You guys are looking at boat design like a person that thinks only coins are money. Exchange the coins for a banknoted and this person think he has lost money.

THAT is cherry picking boatdesign.


>>The pole length is dependent on hoist height. If you have a one design class like the Tornado, you know hoist height, so you can spec a pole that works with the sails you tried

What is the difference to the F16 rules ? You know the hoist height here as well and just as the tornado the pole length is given.


>>One of the reasons Tornado spec'ed like this is it can be enforced and it probably eliminates some of the really weird ideas without going into a detailed explanation of how to measure the pole.

Yep that is why we, the F16 class, do it in the same way.


>>For boats like the F16 where there could be wide variations in optimum hoist height,


HUH !? Did you read the rules at all ? From the beginning the Hoist height of the spi is 7.5 mtr. above mainbeam.


>>It indirectly restricts sails, mast height, and mast placement. For example if I wanted to push the front crossbeam forward for some reason, I could have some real problems.


Sorry ? But now you go from bad to worse. Mast height is 8.5 mtr max + max 0.075 mtr for the crane. Mast placement ? Absolutely NOT ruled upon. You can even put the forebeam behind the rearbeam if you want to. This is really complete nonsense you're are writing up.

The only thing that ruled upon in a varying way are the sailarea of the jib and that of the mainsail. It allows some differences in area and lufflength so that the net power remains the same. So here you are right, but how does this qualify as "too restrictive ?" . Isn't that a bit meaningless when ALL other classes except A-cat are more restricted in this ?


>>Personally I feel bad idea's have their own penalties, I would open it up and keep my camera handy for the guy who tries to use his spare mast as a spin pole.

And you would also by one of these boats ?

>>Also Bill is very right in one respect. I learned a lot about this in designing my own boat from scratch and knowing I was committing my own money and time to my theories. There is nothing like knowing you are committing your time and money to make you conservative.

And Bill is the only one having done so since 1978 ?

Really !


Wouter

I'm afraid we are flying alright where we should be standing with both feet on the ground.

>>one thing that compromises most boats that now carry spinnakers is that most class rules limit pole length to 80cm beyond the bow, I don't know why they do this, but Formula 16, formula 18, Formula 18Ht, Tornado and Formula 20 all do this,

Formula 16 does not.

Formula 16 specifies a pole length of 3.50 mtr in front of the beam. This is 1 mtr in front of the bows. And no matter what skiff lovers say the cats beat them fair and square. A 49-er with spi has a rating about equal to a Prindle 16 without a spi.


>>hence the reason why poles are generally short on cats compared to skiffs,


I don't know about that, the 49-er spi tack isn't much further in front of the mast than the F16's. Same for 29-er and javelins (I think cherubs as well) and lets not even start on 505, 470 etc. Only the int 12 ft, 14 ft, 16 ft and 18 ft classes are unrestricted in this and have those massive poles. Look up those ratings if you have the time. Not very impressive. Only the 18's would impress a catsailor.

What am I saying here ? That I think it is funny that we are taking advice from a design concept that has yet to outperform Prindle 16's and Hobie 16's when having massive amounts of sailarea and almost no weights.


>>also skiffs have a neat way of getting around the lee helm problem, they sail them upright upwind and lean them to leeward downwind, the rig, and hull shape then creates a torque screwing the boat upwind which goes some way to balancing the leehelm effect of the kite way out front, cats obviously aim to fly a hull as much as possible so they can't do this.


This is not true. Take the 49-er again. Come to think of it I'm probably the only skiff sailor in this discussion group. Anyway. The 49-er has MASSIVE weatherhelm that is fully camouflaged by a balanced rudder. It is the reason why it is a non-kickup rudder setup. Leaving the beach and landing is a real pain in b*tt. And I know because I do it regulary. You can hardly pull in the main as that will weather vane the boat. It is also easy on the 49-er to overload the rudder and get a spin-out. Rapid and big turns need to be accompanied with significant mainsail sheeting. The RS 800 and laser X*1000 use kick-up rudders. Man ! do you learn to hate those. The rudder only needs to slip a little and all that weathelm is right on your tiller. Eventually we learned to lay the boats on their ear right after leaving the beach and to jam the rudder as far forward as we could and TIE it into place. And to top it out the 49-er may still have lee helm under spi. It is a BIG spi.

And one more point. I'm standing far more to the rear under spi than I do on upwind or even reaching courses. Does this imply a net lifting force of the spi ? Or that the spi actually presses the bow down that I push up again with my weight ?

Wouter

Hi Bill,

Regarding the migrating CE problem, why not design cat hulls with two sets of CB trunks rather than one "comprimise" position - shift the boards when spi is up, no need for oversized rudders, less drag? If you didn't want two sets of CB's you could use "rubber slats" to automatically seal the bottom of the unused CB trunks to keep flow non-turbulent there as they do on retractable CB windsurf boards.

Jerry

Hey Bill, John, and you other engineer types,

Check out that picture that MauganH17 has posted. The boards are WAY forward.

Tom

Bill,
thanks for the info on your new ARC17,......I went back to your site and looked at it alot closer......

.......looks like a great boat.

Of course,..I had to check out the ARC 27 too,.....definately on my wish list!.


regards,

Bruce
St. Croix

Jerry,
You are not with me yet. The spinnaker up causes a CE migration, we all agree. With spinnaker up lean the mast back to get the CE at or behind the centerboard to balance the boat, no lee helm. This is what is done today, we all agree. Now take the spinnaker down and the CE of the sloop rig is well behind the centerboard much closer to the rudder. Now the rudder is overloaded and prone to stall. This is what we put up with today.
Here's another way to solve this problem: With the spinnaker up and the CE moved forward, move the centerboard forward to bring the boat in proper balance. Don't rake the mast back. Now we are in good shape with spinnaker up. Now let's take the spinnaker down. The CE moves aft a couple of feet from where it was with spinnaker up. This loads up the rudder and unloads the forward located centerboard. Now, reduce the centerboard area the same percentage that the load on the centerboard has been reduced because of its forward location. This is going to be a number like 10 to 20%. The reduced load on the centerboard now falls on the rudder as an increase in load. Therefore increase the rudder area, rudder balanced, in direct proportion to the increased load it now carries. Now the centerboard is happy and so is the rudder and lee helm with the spinnaker up has been solved. The CE migration dragon has been captured and put in a cage under our control. This will place the centerboard immediately behind the main beam or if you feel bold and run a long spin pole and put the centerboard just in front of the main beam. As the centerboard is located further forward, it is becoming smaller in area and the rudder is becoming larger in area and the system is kept in balance on all points of sail. No more radical mast rake required and no more overloaded rudders with a hair trigger ready to stall sailing to windward.
Bill

Hi Bill,

Thanks, but I understood you the first time regarding how shared lift solves the CE migration problem when flying a spi. What I was asking was why an alternative approach wouldn't work just as well if not better. So, without raking the mast, when flying a spi, why not just move the daggerboard forward to a second daggerboard well to match the new CE? And when taking the spi down, why not just move it back to a more aft position? Although it would be an extra step during changing from upwind to downwind, it seems like it would give a balanced helm in all conditions just as well as the shared lift approach. I'm not a boat designer with your years of experience; I'm just trying to understand why this alternative approach is not used.

Jerry

OK Bill,
Explain something to me.
ALL Supercats, SCs and ARCs were and are sold WITHOUT A STANDARD SPINNAKER.
How long has Aquarius even offered the OPTIONAL SPINNAKER?
You told us that to make the ACR 22, you merely added two feet to the bows of the old SC20.
You have continually stated that a spinnaker boat MUST have daggerboards relocated and different rudders in order to handle the change in sail CE.
How is it that your boats are immune to that "Bill's law of physics"?
Is Aquarius selling unbalanced, poorly designed boats which need a spinnaker or unbalanced, poorly designed boats which aren't designed for a spinnaker?
Are your boats designed for spinnakers or not?

P.S. You never have told us the name of the other "boardless 17foot beachcat" that yours is so much better and faster than.

Wait a minute Bill...you moved the board forward to counter lee helm induced by the spinnaker and agree that the rudder loading is increased upwind. To that point you can make the daggerboard smaller but the rudder bigger. Somehow you conclude that the forward daggerboard placement also helps prevent rudder stalling upwind. But you just said the rudder loads are higher upwind now as a result of the daggerboard placement - did I miss something?

Supose we took an I20 and moved the boards forward as you prescribe (this boat runs very little mast rake and it's forward beam is very far forward on the boat). This would only make the windward rudder stalling problem more severe.

Hi Jerry,
Two daggerboard positions would work fine.
Bill

Hi Jake,
With the forward located CB and spin up everything is in balance and no lee helm. Now take the spinnaker down. The CB is still forward. Therefore the CB will be exposed to and carry less of the side load from the sail because the sail CE is now further behind it. What other foil can carry side load? The rudder! Now the rudder will carry its norman side load plus the additional side that the CB is not carrying because of its forward location. The next step is to match the CB and rudder areas to the loads they are carrying. Therefore relative to their base sizes, the CB can be made smaller and the rudder should be made larger. This results in the same effective CLR location as the base boat configuration but with the forward CB location, the CE cannot get in front of it, spin up, to cause lee helm.
Jake, the forward daggerboard placement does not help prevent the rudder from stalling. The increased rudder area helps prevent the rudder from stalling. The trem is called rudder loading and its units are force per unit area or for example pounds per square foot.
Bill

We're looking for solutions of problems that don't exist.

Why does Bill think that leehelm is a "dragon" ? Moreso than weatherhelm ?

Does any of you realize why a boat is setup for weatherhelm upwind ? It appears that the want for weatherhelm has become a dogma that must be satisfied at all costs.

-1- You have weatherhelm on big boats because that is the safety zone for them and because tacking becomes difficult without it.

-2- On smaller boats you have it in order to get some positive return on an item that otherwise only introduces drag.

On downwind the first point is useless; the safety zone here is to lee. How about weatherhelm when singlehanded doucing the spi ? You rather want the boat to track downwind then weathervane up. BLa bla bla Balanced rudders, bla bla bla. IT IS STILL WEATHERHELM ! Put your rudders sligthly of centre and you're gone.

Point 2 is totally mute on downwind legs. Good crews pull up their boards because alot of lateal resistance is really not needed on downwind legs. They leave a smaller area in place to keep some minimal sensitivity to steering. This moves CLR forward as well as on all boats the CLR component of the hull alone is forward of the daggerboard.

I can honestly say that I have never met a leehelm dragon while sailing a cat that was designed to sail with a spinnaker. And to complete it ; I never saw that dragon after adding a spi on other boats except the Dart 18 and a handfull exceptions as well.

I did experience the downsides of shared lift on the 49-er skiff and the downsides of long spi poles.

Excessive mast rake due to spinnaker then ? Nop, haven't seen it or even needed it on my own boats. Mast rake on Hobie 16 or even Taipan 4.9 then ? That is for other reasons and we can't really say that it is holding these boats back CAN WE, Bill ?

Spi pole length at 50 % of hoist height spi to prevent diving ? Great ! F16 runs poles of 3.5/7.5 = 47 %. What a difference those 50%-47% = 3 % makes ! That just doesn't fly with me. So I see really no need to put a longer pole on my F16.

What else was introduced to make the ARC-17 appear superior to all other designs ? Ohh yeah shared lift.

Massive tiller loads when the rudder kick up or when leaving the beach with the rudders trailing (unbalanced rudders !)

In my surf ? No, thank you !

Not using shared lift on other boats makes them slow or slower ? Hum, ARC-17 with spi = rating 70.2 ; Taipan 4.9 WITHOUT spi = 68.1 and to show that there are no ill feelings between us we'll just forget about those 26 % in more (main+jib) sailarea that Bill has put on the ARC-17.

I say that sums it up quite nicely. Thank God Bill uses shared lift on the ARC-17 or else it would be sailing of a rating of 75 and be looking over its shoulder for the fastest Hobie 16's I suspect.

A while back Bill also chastized all other designers for designing overweight boats and you'd expressed F16's were nothing special at 107 kg including all sailing gear !

Well, didn't he prove us all wrong by making the ARC-17 = 126 kg EXCLUDING the weight of the sails (min 8 kg) and spi package (min 5 kg). This puts you on a level with the 1976 Dart 18 design which is of equal length.

To daggerboard wells then : one for upwind sailing and one for downwind sailing ?

I will garantee you that you'll be at the leeward mark behind all boats that use only one daggerboard well.

How much time does it take to move the two boards from one well to another ? 10 seconds ? That is quite fast.

10 seconds that you could already be travelling at full speed under spinnaker = 50 - 100 meters less distance travelled ?

I can assure you that you will never be able to compensate for this loss even if the new position of the boards would make your craft more effecient.

As it is right now in the F18 a 3 second delay in setting the spi at the A-mark is enough to loose you 1 to 5 places in the field.

A lot of crews don't even readjust the jib sheet and outhaul of the main in tight racing as that takes to much time in which they can easily loose a tactical beneficial position. Most of the time they do that later in the leg during a lull or when the skipper has one hand free. Getting the spi up quickly is the most important thing. Repositioning the boards is not what you want to do if that delays the setting of the spi. That is even IF it would be necessary

BECAUSE

The balancing of the rudders that Bills shared lift needs to get rid of the weatherhelm feel on the upwind legs will ALSO remove the feel of the leehelm on downwind legs that other boats MAY have.

So the whole discussion comes down on wether having leehelm on downwind legs (not the feel of it as that can be taken away by balanced rudders) is a SIGNIFICANTLY bad thing performance wise ? If leehelm is assumed to be present, that is.

This does not appear to be the case. And untill a newly designed shared lift ARC F18 starts beating all other F18's on the course I think we'll be at a loss to proof that it does significantly influence performance in a bad manner.

Wouter

Jerry,

I let go of the tiller if I am going forward to adjust downhaul because holding the tiller while moving around on the boat causes me to veer all over the place. Occasionally, I will pull the mainsheet with both hands while on the wire, so I set the tiller down, sheet in, and pick the tiller up. I also put the tiller to rest if adjusting outhaul, mast rotation, or board position. Any one of these is a brief interlude of letting the tiller rest unattended.

Bruce,

I run my boards about 8" up all the time. If I thought I could afford the time, I might pull them another 12" when going downwind but for now, feel that it does not provide enough benefit for my "'round the bouys" racing to take my mind off steering the boat to go play with the boards up and down at A and C marks. I have not seen any difference upwind with my boards up 8" and all the other I-17R's with their boards all the way down.

Hi Wouter,
I saw a T4.9 at the Tradewinds Regatta two weeks ago for the first time. That boat looks like a great design. Did you design that one? It reminds me of Poison Ivy.
Good boat design has weather helm for two reasons: 1) From a boat performance point of view you always want weather helm. The daggerboard is always generating lift to windward. When the rudder is lifting in the same direction, the induced drag from the two foils is a minimun. If the rudder is producing lee helm, opposite the daggerboard, then the daggerboard must generate lift equal and opposite the sail side force plus generate additional side force to windward to overcome the negative side force the rudder is generating, lee helm. This situation, lee helm, makes the daggerboard work harder, generate more lift, which makes more drag. 2)Helm satbility. You want the helm to always to be pulling lightly in the same direction from the skipper for ease of handling. You do not want the helm to reverse between weather and lee helm, especially unexpectedly. This makes the boat difficult to sail well and it is draggy underwater; a slower boat results.
I'm not going to address the rest of your comments because I see an ugly attitude and your goal here is not to help anyone.
So long,
Bill

Hi Sam,
All SCs were sold without spinnakers. That was before 1992, 1978 through 1991. In 1992 the product name was changed to ARC products and spinnakers and self tacking jibs etc became an option or standard on all products, the 22, the 27 and the 30. See the Aquarius-Sail.com web site for this information. These products were/are designed with spinnakers.
>I'm sorry I forgot, the 22 also has the CB trunk located right behind the main beam to prevent lee helm with spinnaker up.
>I am saying that moving the CB forward is a better way to trim a boat out with spinnaker than raking the mast back which leaves the rudder overloaded and the CB underloaded sailing to windward without spinnaker. The boat will sail to windward like this but the induced drag from the CB and rudder is greater than it could be. The boat is out of trim sloop rigged.
>A boat with centrboards moved forward to accomodate the forward migration of sail center of effort due to the spinnaker and downsized boards to match the smaller side load they now are expozed to in this new forward location and upsized rudders to match the new increased side load they are exposed to due to the forward located centerboard HAS THE SAME CENTER OF LATERAL RESISTANCE as the boats original CB/rudder arrangement. The advantages here are: 1) that the centerboard is so far forward that the sail CE with spinnaker up cannot get in front of the centerboard and cause lee helm. 2) With spinnaker down the centerboard and rudder are sized to match the loads they are exposed to and this results in minimum induced drag from the CB and rudder, a faster boat to windward.
> At the recent Tradewinds Regatta I sailed an ARC 17 against several other boats for my first time in 25 years. We sailed poorly, went three times around the long course when I should have sailed two times around the short course, in the first heat. Then on Sunday my crew, who had never sailed on the boat or with a spinaker before, thought we shouldn't try the spinnaker in the 20 knot winds so we didn't. We still won the open class on corrected time and did finish a couple of heats first boat across the finish line. Our assigned PN was 70.2. That number is coming down as a data base is developed for the ARC 17 with spinnaker.
Good Sailing, Sam,
Bill

Mate..
Only 12s are unrestricted these days..
14s have a hoist height of 7626mm with rule 13.e.1 stating "The foremost end of the spinnaker boom, including end fitting(s), shall not extend more than 2743mm beyond the foremost vertical extension or transverse extension of the bow.").
With 16s the rule is 7.12 which states the maximum length of the assymetric spar may not exceed 2700 mm measured from the stem..
There are two 18 foot skiffs these days the "Bethwaite" camp and the "Murray" camp..
The league 18s have rule 11 which states in part "Any pole has a maximum length of 3.8m (12ft 5in) from the stem."

In regard to rigs many 14s do in fact have rigs that are adjustable uphill and down.. Cranking on the stays tightend the uppers and pulls the rig tip back..Some even have an adjustable setup that allows the rig to lay back as required.. Ie adjustable forestay and side stays..
As do many Javelins and Cherubs.. The old 18teens did as well but with Bethwaites strict one design rules these were basically banned.. The 16teens walked the same path as Bethwaites's 18teens..
I dont believe the any 12s have an adjustable rig.. But then I wouldnt like to be trying to adjust much with that much rag up..
But no matter which skiff it is one will find the rig is designed to be far more gust responsive than any cat rig..

Yes skiffs are slower than a cat when one looks at the ratings.. Apart from the 18teens vs a 18 foot cat.. But Im sure a 12 footer crew will also tell you that its far more lively than any cat..
I will stick my neck out here and suggest..
Any of the top 12 footer crews could easily jump on a Tornado/F18/F18HT/F16/M20/F20/F20HT and take her around a course without swimming.. In fact it would be a cake walk.. I would further suggest there isnt one top cat crews who could do the reverse (unless they have a reasonable amount of skiff experience)..

just my thoughts..

I would agree with that assumption...Personally, I don't want anything to do with trying to keep one of those skiffs upright!

With respect to Mr. Robert's implementation of the "shared lift" concept:

1) Would increasing rudder size also increase the apparant "load"(for lack of a better term) on the driver? After about 70 miles, even the "finger touch" tillers tend to cause fatigue. Yanking pizza-pan sized rudders could certainly kill off the weak over 500 or 1000 miles!

2) I can visualize the advantages you describe in windward/leeward sailing (around the cans), but would there be any advantage in a distance format that ends up being primarily close-reaching (no spin)?

Hi!
Are the skiff sailors better SAILORS than the cat sailors? No.

Would the best 12-foot crew have a chance in the Tornado Worlds if you put them on a Tornado? NO. (If they raced the Tornado a couple of years they might be able to give the Austrailian top sailors Forbes/Bundoc a match.)

The differance is that the cat is stable when sailed gently and the skiff isn't. Each boat requires more or less training before you can handle it without swimming. When you stopped swimming and have good speed in most conditions the major thing left is tacktics.


cheers
hakan

Wouter,

Thanks for your comments.

In my limited experience with spi's on a monohull, I have to agree with you that some lee helm downwind isn't a bad thing, although if it's too much I would guess it might set you up for an accidental gybe if you let go of the tiller for too long at the wrong time, especially in waves.

I agree with you that two CB wells would take too much time to manage if you were racing usual courses and if you tried to do it at the time you hit the mark; I acknowledged in my post that it would take more time to change over from upwind to downwind. This is, of course, unless the change was done on the flying hull well in advance of hitting the mark when there's time to do it and at which time it would't have adverse consequences.

Actually, in my original post, I was curious if two wells would work well for cruising, recreational sailing, and long distance racing where it might offer a very light touch both upwind and downwind for long legs avoiding any strain on the skipper, and in the case of long distance racing, might offer a slightly lower drag and more efficiency which could add up to slight performance gains over the times and distances involved.

Jerry

Hi Les,

Thanks for clarifying when you steer "look ma, no hands!".
I've done a lot of tuning on my monohull to be able to do the same thing and I have to admit that it's an awsome feeling when I let go of eveything (albeit briefly in order to attend to something) while the boat remains fully powered up and on it's intended course sailing itself. I guess that is something folks with large keelboats do all the time, but I find the feeling of doing it on a small boat even more fun due to the higher speeds involved.

Jerry

Hi Waterbug,
1)The side load on the rudder is increased with "shared lift". The force to hold the boat straight or turn the boat is not increased. This is acheived by balancing the dynamic forces on the rudder. Most boats already do this today. Note the forward swept leading edge on the rudder.
2) There is no advantage or disadvantage to shared lift while close reaching.
"Shared lift" is a design method to accomodate the large migration in sail center of effort asociated with adding a spinnaker to a high performance beach cat where the spinnaker is sailed primarily on a relative wind reach and the boat is aimed much lower than that relative to the absolute wind direction. The boat sails at roughly twice the speed of the wind tacking downwind.
Bill
Bill

The hull needs to be strong where the centerboard well is located. Two centerboard wells on each hull means more weight. The empty well will create turbulence.

/hakan

Attached is a photo (I don't know the source) of an ARC 21. Check out the placement of the boards as well as the relative size of the boards vs rudders. This shows the unusual balance that Mr. Bill is talking about.

Wow!

Thanks David. That's a big help. Notice the aspect ratio of that unloaded daggerboard. One could not build a board with that aspect ratio with the board in the normal position, shroud chainplate, because carrying very nearly 100% of the sail side force and double trapeze would break the board with that aspect ratio.
Bill

Les,

Thanks for the info on your boards being up on your I-17R

Works that way for me to (..in my winds)

I always wondered, again, I am a driver,..is it possible for the entire I series, ( I-17, I-18 and I-20),..to have the same daggarboard ?

Builders, Designers,...what do you think?

Bruce
St. Croxi

Hi Harkan,

Thanks.

You said:
>>The hull needs to be strong where the centerboard well is located

I'd have to agree... except that the hull is already strong where the well is already placed in the aft position on most cats and since the forward position would be close to the main beam, I would guess its already pretty strong there as well so although it might need some reinforcing it shouldn't be a major obstacle...

You also said:
>>Two centerboard wells on each hull means more weight

I'd have to agree... except on long legs of a course or cruise the relatively small amount of additional weight that would be introduced might be easily offset by modestly increased efficiency and drag reduction not to mention that a less fatigued skipper might end up being a better skipper when at the helm for extended periods in these conditions further compensating for slightly increased weight...

And finally you said:
>> The empty well will create turbulence.

I'd have to agree... except in my original post I said:
>> you could use "rubber slats" to automatically seal the bottom of the unused CB trunks to keep flow non-turbulent there as they do on retractable CB windsurf boards

I don't know if you're familiar with this approach but it works very well - two thin but tough sheets of rubber running along the length of the centerboard well, each attached along the outside edge as well as fore and aft, "kissing" in the midline. When the board is pushed down, the rubber parts and allows free sliding (also gives just the right amount of friction to hold the board where you want it) but when the board is raised, the slats close and present a very flush surface to the water minimizing any turbulence.

Jerry

Hi Bruce,
I don't think so. Board area usually varies directly with sail area. They might use the same board section and vary imersed depth with sail area. This should work, but I don't think they would literally use the same board on three boats with different sail areas.
Bill

Lets try again Bill.

>All SCs were sold without spinnakers. That was before 1992, 1978 through 1991. In 1992 the product name was changed to ARC products and spinnakers and self tacking jibs etc became an option or standard on all products, the 22, the 27 and the 30. See the Aquarius-Sail.com web site for this information.
SE- You need to talk to the people at Aquarius Bill.
According to their website, as of five minutes ago, NO Aquarius boats are sold with a standard spinnaker.

>These products were/are designed with spinnakers.
SE- Then why are they sold with out spins?

>I'm sorry I forgot, the 22 also has the CB trunk located right behind the main beam to prevent lee helm with spinnaker up.
SE- So the non-spin SC 20 had the boards directly behind the front crossbar? Are the ARC 22 boards different from the SC 20 boards?

>I am saying that moving the CB forward is a better way to trim a boat out with spinnaker than raking the mast back which leaves the rudder overloaded and the CB underloaded sailing to windward without spinnaker. The boat will sail to windward like this but the induced drag from the CB and rudder is greater than it could be. The boat is out of trim sloop rigged.
SE- Why did you intentionally design many of the Supercat and SC boats "out of trim".

>A boat with centrboards moved forward to accomodate the forward migration of sail center of effort due to the spinnaker and downsized boards to match the smaller side load they now are expozed to in this new forward location and upsized rudders to match the new increased side load they are exposed to due to the forward located centerboard HAS THE SAME CENTER OF LATERAL RESISTANCE as the boats original CB/rudder arrangement. The advantages here are: 1) that the centerboard is so far forward that the sail CE with spinnaker up cannot get in front of the centerboard and cause lee helm. 2) With spinnaker down the centerboard and rudder are sized to match the loads they are exposed to and this results in minimum induced drag from the CB and rudder, a faster boat to windward.
SE- Which boat are you referring to, The ARC 22,27,30 or the ARC 21?

> At the recent Tradewinds Regatta I sailed an ARC 17 against several other boats for my first time in 25 years.
SE- The ARC 17 came out in 2003 and you raced a number of times last year on ARCs.

We sailed poorly, went three times around the long course when I should have sailed two times around the short course, in the first heat. Then on Sunday my crew, who had never sailed on the boat or with a spinaker before, thought we shouldn't try the spinnaker in the 20 knot winds so we didn't. We still won the open class on corrected time and did finish a couple of heats first boat across the finish line. Our assigned PN was 70.2. That number is coming down as a data base is developed for the ARC 17 with spinnaker.
SE- Such a sad story.
Speaking of the ARC 17, someone was asking about racing an ARC 17 under iF18.
This begs the question, why did you come out with an ARC 17 instead of an ARC 18, built to iF18 Class rules?
Or an ARC 21 instead of an ARC 20 built to F20 Class rules?
Why do you and Aquarius continue to hide from Class competition?
Do you actually think you will sell more oddball ARC 17s than you would sell ARC F18s?
Well, if ARC F18s lost every race then you probably wouldn't sell many.

What about an ARC F18HT? You brag about “state of the art” construction.

iF18 Class - 63.5 dPN, 397lbs, 183sf main, 44.7 jib, 226sf spin
ARC 17 - 68.3 dPN, 350lbs±, 206sf main, 51.0 jib, 290sf spin
F18HT - 60.0 dPN, 287lbs, 215sf main, no jib, 215sf spin

The ARC 17 weighs 11.8% less and has a 12.6% larger main, a 14.1% larger jib, a 28.3% larger spin, (20.6% larger sail area overall) than an F18.

The ARC 17 has a sail area(sf) to weight(lbs) ratio of 1.563, the F18HT is 1.498, the F18 is 1.143.
The ARC 17 has a higher “horsepower” to weight ratio than the F18HT and iF18 and yet it competes with a dPN of 70.3.
What do you prove when you "win" a regatta with a totally bogus handicap number?


I repeat this question:
> P.S. You never have told us the name of the other "boardless 17foot beachcat" that yours is so much better and faster than.

You are looking to find a solution for a problem that doesn't exist. Bill says that it does exist on non ARC boats like I-17, I-20 and Stealth while various I-17, Stealth, I-20 etc sailors and designers have said that it doesn't.

It now all comes down to who you believe most.

I had enough of the shared lift farytale. I think John Pierce said it right, we are really talking about the same thing here.

Loading up the rudders by mast rake or loading up the rudders by placing the daggerboards forward both lead to the same end result.

>I was curious if two wells would work well for cruising, recreational sailing, and long distance racing where it might >offer a very light touch both upwind and downwind for long legs avoiding any strain on the skipper

You have begun to buy into the Fairytale. Don't you see ? Why can you balances the rudders to remove the feel of the big weather helm that is part of "shared lift principle" as a direct result of the board placement but can't use the same principle of balanced rudders to relieve the stain on the skippers of other boats as well.

There is really no difference here. Just smoke and mirrors.

Wouter

Wouter,

Thanks for your input. Maybe I am missing something so help me see the light:

You said:
>> Loading up the rudders by mast rake or loading up the rudders by placing the daggerboards forward both lead to the same end result.

But I was talking about placing the boards back under cat rigged/sloop and forward under spi. It was my understanding (and maybe I'm wrong here), that by doing this one would NOT be loading up the rudder either upwind or downwind. If this is true, wouldn't an unloaded (or minimally loaded) rudder be more efficient? Less drag? Less likely to stall? Now, if unloaded rudders don't offer any benefit or if really matching CE/CLR doesn't unload the rudders, then that is what I needed to know regarding why this approach would have no value.

You also said:
>> You have begun to buy into the Fairytale. Don't you see ? Why can you balances the rudders to remove the feel of the big weather helm that is part of "shared lift principle" as a direct result of the board placement but can't use the same principle of balanced rudders to relieve the stain on the skippers of other boats as well.

It was my assumption that if the CB is placed properly for each sail configuration to balance CE/CLR then you wouldn't need to balance/rake the rudder for either big weather helm or big lee helm. This sounds more efficient to me; if it's not really more efficient, then that is what I wanted to know!

Finally, please understand, I'm not disputing that the current approach "doesn't work" - in fact it works quite well. Does that mean it can't work slightly better? That's what I am trying to understand. Fortunately you guys have far more experience than I!

Jerry

Jerry

Let's see if we can put this one to bed.

1.) Everyone agrees that some weather helm helps boats performance to windward, therefor it is more efficient. Lets be clear about this we are probably talking about less than 1 % gain.

2.)This weather helm can be made so that it does not create a load on the tiller by balancing the rudder

3.) when the spinnaker goes up the centre of effort goes forward, so the weather helm will go, and can produce lee helm,

4.) Again a balanced rudder will make it so that you do not feel much of this load.

5.) having two centreboard slots will lose much more than any gain, since the only gain is removal of the lee helm downwind, and the loss due to this is microscopic. But the losses are:

turbulence from the slot:greater than 2%, slot gaskets work well with rotating c/boards, jam with daggers,

time taken to change boards, loss of at least 10 seconds each change,

Extra expense, you could spend the money elsewhere where it would make genuine gains.

Hope this helps.

The point is skiffs are unstable.. Thus skiffies are more attuned (as are their rigs) to the weather.. Make a slip, miss a gust or lull and you swim.. As you seem to agree this isnt the case for cats.

As for skill levels..
Could a skiffie get on a tornado and win.. Hmmm... well F& B are flipping good.. It will take any crew some years to develop the skills to match them..
But before F&B reign on the Australian scene.. A couple of skiffies did get on a T and won for almost a decade.. Including Au T olympic selection and either a 3 or 4th at the Olympics.. Dont know what that means but...

Oppsss off point.. Skiffies enjoy the challenge of keeping their crafts upright and they have the best ride downhill.. Even if a cat may be faster than all but the 18teen..

Stewart

Thanks for questioning the SC-17 PN#. I sailed open class on my stock H-20, I was first over the line 4 0r 5 times out of 8 races and still got clobbered on PN. The course was relatively short but the format was great. The Arc 17 was very fast, I was usually on 20-30 seconds ahead at the A mark. It is much faster than the assigned 70 #. I was suprised that it won.

It is a beautiful boat, full of innovation and goodies, sqaretopm Main, spin, selftacking jib, trick main traveler set up jeez what did I miss.

>>I was first over the line 4 0r 5 times out of 8 races

You were first over the line in 3 out 8 races.

See the results attached

Wouter

What happened in race 2 the differences between the boats are way to big for such a short course.

Wouter

I did some slacking on the 49-er in my other post BUT I wouldn't want to go without one.

I really like sailing the skiff but for totally different reason why I like sailing a cat. With the Skiff the joy is in getting the handling right and show of your skill by making it look easy. (Still a long way off)

With a cat it is the power and the simple form of racing. Seastate, winds it doesn't matter with a cat you can race all in all conditions and have a bloody good fight for hours on end.

With a skiff you can drain yourself within 30 minutes and go swimming because you can't keep the level of concentration up.

Skiff rigs are an interesting topic in their own right, but are optimized for the limitations that are encountered on a skiff. This probably makes application of such a rig on a cat less optimal.

Sail both enjoy both.

Thanks for the heads up on the skiff 12,14,16 rules

Wouter

Hi Sam,
We have one gaint communications problem.
As to spinnakers and ARC boats: Spinnakers and spinnaker poles and all the gear, blocks,ropes, etc, you need to go with it are an option on all ARC boats. Some ARC22s and most RC27s and 30s are sold as non racing boats and the buyers don't want spinnakers, they daysail the boats, so the spinnaker is left as an option. In US Sailing PNs the 21, the 22, the 27 and 30 are all rated with spinnaker.
>All of these boats are designed with spinnakers and sold both with and without spinnakers.
>The old SC20, 1978 thru 1991, had the CB back by the shroud chainplate, same as other 20 ft cats.
The old SC20 boards and the new ARC22 boards are the same size. The SC20 had 275 sqft of sail area on a 33 ft mast and the ARC 22 has 350 sqft of sail area on a 38.5 ft mast. The sail area is up by 27% on the 22 and the boards are located forward just behind the main beam where they are exposed to 27% less side force from the sails. Therefore in effect the 22 boards are downsized 27% per sqft of sail area relative to the old 20 installation. The boards feel the same side force on the 22 as on the 20 even though the 22 sailplan is 27% larger.
SE- Why did you intentionally design many of the Supercat and SC boats "out of trim".
> The SC boats and other centerboard cats, slop rigged, are in trim when they run a normal amount of mast rake like 5 degrees or so. When the top of the mast is raked back an additional 3 to 4ft to trim the boat out with spinnaker and then you sail this larger mast rake to windward, the boat is out of trim.
SE- Which boat are you referring to, The ARC 22,27,30 or the ARC 21?
> Each one of them, Sam. All of these boats have the CB right behind the main beam.
SE- The ARC 17 came out in 2003 and you raced a number of times last year on ARCs.
> An ARC17 was on the water in Mn undergoing development in 2003. I never set foot on the boat until it was in Florida a couple of weeks before the Tradewinds Jan. 2004. I raced/crewed on an RC30 in 2003.
SE- Such a sad story.
> Right, Sam. There was another communications problem. The race comittee held up a race course sign with an L on it. Some sailors in the open class took that to mean sail the long course. As it turned out it ment sail the shorter course.
> Sam, the ARC17 is a beach boat, a beginners boat, a boat without boards. It is not a performance boat. It is a one person boat or a two person boat. It comes unirig or with a self tacking jib. You can even add a spinnaker with launcher to it. It is a totally flexible boat for the beginning beach cat sailor. This is a different approach from anything anyone else builds and hopefully some newcomers to our sport will find this boat attractive and purchase it.
>As to your question about an ARC 20: If you or anyone wants an ARC20, it can be built in a heartbeat. Use the 22 tooling and move the transom forward 2ft. Then you have a 20ft boat built for ocean racing. The tall elliptical bows are forgiving in big waves and or a near pitchpole situation. (Look at the picture of the SC20 during the Steeplechase race. The foredeck is underwater and the boat is ripping. The sailors are in their normal positions. You don't see rear ends and elbows as the sailors scramble for the back of the boat. These guys know that this hull design is not in difficulty at this point.) Building a 20 in the 22 tooling would place the mast 2ft aft of the hull mid point. Again moving the CG further aft and allowing the sailors to apply more horsepower, drive the boat harder, while reaching downwind with chute. In 1980 the SCs had a simple on the water mainsail reefing system that could be employed in 5 minutes. This would allow a high powered boat to depower quickly on the water. A long distance race ocean race winner is sitting on the shelf up there in Mn.
SE Why do you and Aquarius continue to hide from Class competition?
The tooling for the 22, 27 and 30 were all built before there was any of this Formula class stuff. In about 1988 when the 22 was designed, other builders were building boats longer than 20ft. There was the H21 which was 21.5ft long and Stiletto was building a 23ft boat. I did a 22ft boat to sort of split the difference. As it turned out the H21 and Stiletto were slower than some 20ft boats. Only the 22 continued the progression of faster boats as they got larger. The 22 has set the chinning bar. Why won't anyone else step up to the 22. Everyone else, the competition, has retreated.
> As to your last comments: You probably did not know the 17 is a boardless beach cat for the beginning sailor. It is not aimed at performance. It is a simple boat, a very safe boat with tall bows and righting system and the rig is totally flexible to the owners desires. You can buy the boat as a one person boat. If things change and you want to sail with two people, no problem. Add the self tacking jib. When you get good and are feeling your oats, add the spinnaker, no problem again. You don't have to buy a new boat everytime your circumstances change.
Good Sailing, Sam
Bill

You've got it right, Carl and those boys from down under have known about this and incorporated it into their skiffs at least 50 years ago. We're just learning.
Bill

Just to (hopefully) clarify, it helps to realize from a drag perspective, all things being equal and ideal, that the optimum is two boards (1 rudder + 1 dagger) of the exact same size, at the same angle of attack.
Also, this necessitates the center of effort intersecting the middle of a line directly between the two boards. The further apart the two boards, the less effect the shift in CE has, the more "balanced" the boat. Voila.
Of course this all gets screwed up by the hull and daggerboard being locked together, the board being adjustable in area (unfortunately proportioned to aspect ratio), and the rudder being of fixed area, but adjustable in attack angle, and wind strengths varying.
Humbly Submitted by a Talkerabouter.

Sorry guys, I stand corrected, Wouter is correct. However, look at race one...The Dart seems to have been sailing the inside(yellow)course. There was also alot of confusion revolving aroung the general recal of the I-20's and susequent course change on the open class restart. As Bill noted earlier, we all seemed to have sailed an extra lap in at least one race.

Wouter, I still maintain my earlier comments regarding the ARC 17 PN #.. Bill, nothing personal, that boat was fast. Had you had experienced crew and flown the chute down wind the PN # would be open to even more scrutiny. You are extremely intelligent, you know the number needs work. Benefit from it while you can....
I am still hooked on that trick traveler and straifgt jib track.....

Hi Eric,
As you know I have nothing to do with the level of any boats' PN. When a boat starts out new, the initial PN is a guess. The ARC17 PN was based on the SC17 and adjusted for square top main and spinnaker and boat width. At Tradewinds Rick did the calculations. He used a spinnaker adjustment factor of 0.972. I think US Sailing uses 0.96 but, he is the boss at Tradewinds. Anyway, race data will bring it in where it belongs quickly. Tom just needs to sell a few and get them out there racing.
Good Sailing,
Bill

Thanks, Jonn.

Now THAT was what I wanted to know (expecially the magnitude contribibuted by each element)!

Jerry

Bill,
I know..Perhaps this brewhaha with "H" will bring some new Arcs into NAMSA. Let me know if any 20' to 22' "used" Arc become available. I think a new one is out of reach for me but I love the set up, really simple and clean.

>It now all comes down to who you believe most. <
>I had enough of the shared lift farytale. I think John Pierce said it right, we are really talking about the same thing here.<

You MISPELLED farytale (fairytale), your getting as bad as Bill, in the drama department. So you like to use drama, too?



>Loading up the rudders by mast rake or loading up the rudders by placing the
daggerboards forward both lead to the same end result.<

I disagree. Same result, but from my experience there is a difference you may NOT have considered (luff perpendicular)? There is a difference in acceleration, and top speed is basically the same (hull speed). Over ten years of R/C sailing mast rake (>5deg) has been slow accelerating out of tacks (& starts). Model boats normally tack on every shift, on average 6-12 per weather leg. So you gain 6-12 seconds which is all you need say if you are match racing. The model boat is extremely sensitive to adjustments of CE and is done by moving the mast base 1/4"-1/2" fore or aft, NOT mast rake. I don't see America's Cup boats using a huge amount of mast rake (>5deg) for tacking, so I believe scaling this up to larger boats applies? In a light wind with moderate chop where acceleration and power is needed the boat with the mast rake (>5 deg) would loose.





>There is really no difference here. Just smoke and mirrors.<
Is this a professional comment? I'm SUPPRISED to read a comment such as this coming from a person I regarded.

>>..., the ARC17 is a beach boat, ... It is a one person boat or a two person boat. It comes unirig or with a self tacking jib. You can even add a spinnaker with launcher to it. It is a totally flexible boat for the beginning beach cat sailor.

>>This is a different approach from anything anyone else builds and hopefully some newcomers to our sport will find this boat attractive and purchase it


A different approach from anything anyone else builds ?

Cognitive dissonance is running rampant.

Wouter

Hello Sail7seas,
Here's what John Pierce, builder of the Stealth, had to say about "shared lift and CE migration and how to live with it".

Bill

Yes I agree, I have always used the shared lift idea in my boats, both those I build and when I sailed T's and others, Whether the boards are forward or not, the same effect can be got with what ever size boards/rudders are chosen, its just about the position of CLR against CE of the rig, however with existing classes obviously board position is fixed.

With the boats we build, we go down the raking the mast back route to load up the rudders, and rake back the spinnaker luff, however we do have large rudders, one thing that compromises most boats that now carry spinnakers is that most class rules limit pole length to 80cm beyond the bow.
John Pierce and I agree, Sail7seas. We are on the same page.
I don't know why one poster wants to say that when you put an additional sail up in front of the mast on a pole that sticks out well beyond the bows and has an area equal to or greater than the base sail area of the boat, it does not move the center of effort forward significantly when in use. This is putting your head in the sand. It is not a farytale. It really happens.
>Loading up the rudders by mast rake or loading up the rudders by placing the daggerboards forward both lead to the same end result.<
This is a true statement but incomplete. Raking the mast back or moving the CBs forward will trim the boat out properly with spinnaker up. This is fine, AOK.
The problem is "what are you left with when the spinnaker is down and now you are sailing to windward sloop rigged"?
If you have chosen the "rake the mast back route" you are left with an overloaded rudder and underloaded centerboard and this is draggy underwater. If you go with "move the centerboard forward and downsize it and upsize the rudder", you eliminate leehelm with spinnaker up and the centerboard and rudder are in balance, less drag, sailing to windward with spinnaker down. I'm getting out of breath saying this, Sail7seas. I hope we are communicating.
I have no experience with model boats and model boat testing. On any sailboat there are many interactions with changing mast rake. It is a complex subject.
Good luck with your model boat racing,
Bill

Hi Wouter,
We live in two different worlds/populations when it comes to catamaran sailing. I saw two T4.9s for the first time in my life two weeks ago. This F16 class stuff must be big in Europe but where I sail, it is so small I can't see it. I understand the T4.9 is a one or two person boat. That's fine, but again where I sail, I don't see them. No US builder builds a one or two person boat, boardless beach cat, that I know of. Hopefully both classes will prosper.
Good Sailing,
Bill

C'mon Bill,
While wouter does act like he is from a different planet, cat sailing is not that different in europe.
There are more f16s in the U.S than europe. The European Class president doesn't even own one(wouter).

Your claiming all of these unique options for the ARC 17 or any other SC/ARC is typical of your bull.
The ARC 17 is sold like a Chevy pick-up, any combination of parts and accessories.

>>..., the ARC17 is a beach boat, ... It is a one person boat or a two person boat. It comes unirig or with a self tacking jib. You can even add a spinnaker with launcher to it. It is a totally flexible boat for the beginning beach cat sailor.
>>This is a different approach from anything anyone else builds and hopefully some newcomers to our sport will find this boat attractive and purchase
it

How it that different from me buying a Tiger and sailing it double-handed without spinnaker,
Or D-H without jib,
Or single-handed, w/self-tacking jib and spinnaker ?
Or S-H, w/spinnaker, no jib
Or S-H w/self-tacking jib
Or S-H, Uni-rig?
Or, gosh, I could sail it D-H, w/self-tacking jib and spin and race in the Tiger Class and the NAF18 Class and take honor in any victories.

No Bill, the difference is not how the ARC 17 is built, it is how it is sold.
The SC/ARC 17 has no Class rules, no Class association, no Class events, no Class competition.

Are there ANY Class rules for ANY Supercat/SC/ARC boats?
Where is the Class Association and who are the Class officers?

>Are we communicating?< 'give me break, I'm on your side'
I got it two days ago, I was wondering what instigated Wouter to use comments
like "farytale" and "smoke and mirror" and "cognitive disonance".

If I were to choose between John P's design or your design.
With ALL else being EQUAL for a balanced design.
(solving the problem two different ways)

It would be yours, Bill. sorry John.
For two reasons, first, larger sweet spot for CE migration.
Secondly, Luff perpendicular for more acceleration
based on my model testing of mast rake (see previous post)

More cognotive disonance, please (opps, can't use that, it's Wouter's phrase)

Hello Bill,

Of course the F16 and Taipan classes can only hope to sell as many boats as the ARC-17 and SC-17 class have sold so far.

Without this great 17 foot product line many of us would never have seen the light of starting up a class for the sailor looking to singlehand and doublehand a high performance spinnaker boat.

It seems thought we have made a mistake by opting to allow boards. A boardless design like the 17's is indeed superiour. Our mistake but we can't have everything, can we.

And of course we in Europe have the nacra 5.5 sloop and uni which the US hasn't so indeed you must be the first US builder to offer such a flexible boat.

It is also our wish that both classes will prosper. Although it is already a given that the ARC-17 will be extremely succesful. The F16 class will have a lot of catching up to do with respect the 17's. This omni present class has indeed set the benchmark to which we may only strive to achieve as well.

It is also great to see that Yves Parlier ( http://www.parlier.org/site02/accueil/1024x768.html ) has taken a good look at your SC-17 testbed of 10 years ago ( http://www.catsailor.com/wwwboard/messages/63230.html )and learned from it so that he now can try to expand on the planing hull idea to the French ORMA cirquit. It has been long overdue that the French got off their love for conservative designs and tried something new.

Lets hope he does not forget to bring a compass along to take the necessary measurements.

I'm sure that in a 100 years the SC-17 and ARC-17 product line will be viewed as the mother of all modern high performance catamarans. They will be present in all nautical musea as the prototype beach catamaran and sure enough it will be THE catamaran in the olympics.


Good Sailing,

Wouter

Maybe all has been said about it and the only thing left to do is for somebody to build such a superiour design under the A-cat, F18, F16 or F20 rules and proof the theory.

I for one, am very interested to find out how efficient a lift providing rudderboard is while travelling in the wake of the hull and daggerboard. But that is just my university hydrodynamics course speaking.

Wouter

Sam Evans wrote this bit : "The ARC 17 weighs 11.8% less and has a 12.6% larger main, a 14.1% larger jib, a 28.3% larger spin, (20.6% larger sail area overall) than an F18."

Wow. Sounds like a really powerful boat.
But then Bill says it`s a beginner`s boat, NOT built for performance ? Take a Hobie Tiger, reduce the weight by 11.8%, and increase the sail area by 20.6%, and you have a really tame beginner`s boat.
Ok, I get it, aimed at the American market, where either they have no wind, or the sailors are REAL heavy.
My guess is it gets really interesting with the kite up in around 15 knots, looking at the sail area comparison made by Sam. I`d love to see one, but in a nice 25 knot Cape South Easter. I hope the underside of the trampoline is made from UV-protected material, `cos it`s gonna see a lot of sunshine !
Please Bill, be honest about the intended design - It`s meant to be fast & hairy, don`t try flog it off to beginners. Some of them might be fooled by your marketing campaign, buy one & be scared off of cat-sailing for life.
Tell us it`s faster than a Tornado, a F18 or whatever you like, just don`t tell us it`s for two teenage girls who are just getting out of Optimists.
I`m sure it`s a great boat, just seems a pity that it was designed to purposefully fit nicely between both Formula classes, that way it doesn`t have to compete with either. It`s interesting that some folks will buy into the "in-betweener" rather than something that can be raced against boats of very similar designs.
I`m also confused by the fact that it was designed for use as unirig, double-handed, spinnaker or non-spinnaker use, yet this discussion thread is highlighting how critical the CLR position is for each use. Does this mean that the CLR is along the entire length of the hull, as the Dart 18 was meant to be ? If so, my comment on the Dart 18 is that it`s really crew-position sensitive, as well as mast-rake sensitive, and is sailed with a lot of aft rake by the faster guys. It has a deep-v shaped hull along the full length to provide lateral resistance, yet still goes sideways almost as fast as it goes forward, and can`t handle a spinnaker, and also steers like a pig (my nickname for my Dart was in fact "pig". I did love her though.)
I hope you`ve managed to overcome all these obstacles in designing symmetric hulled boardless hulls - in my experience these boats aways have very heavy steering tendencies. Like I said, I`d really love to see one, sounds like a good fast boat suitable for scaring the living daylights out of beginners with.

Cheers
Steve

From my limited experience sailing on an original SC-17 it was about the easiest cat to sail I can imagine.

You really could submerge the bows without worrying about pitchpoling. The boat hardly slowed down. It was smooth, quiet dry and the steering was as light as on a laser. The hull shape was comfortable for trapezing and hiking. There were no sharp edges anywhere as I recall. The boat tacked easily. It seemed to sail best upwind trimmed down by the bow somewhat. It was fast, but deceptively so. That sounds like a good beginners boat to me.

It makes perfect sense that the boat should balance well with many different sailplans. The center of pressure on those hulls should be located very far forward due to their shape. If the rudder angle is close to zero the center of lift is far forward. As rudder angle increases the center of lift will move aft.

I have not sailed a new one yet. It looks like an ideal cruising boat for the Chesapeake Bay.

Talk to you later
colin pitts

All boats are a compromise…The SC/ARC 17 is just one of those rare breads that walk the razors edge with uncanny finesse…Yes there are faster boats, yes there are other well built boats, Yes there are many other board less boats around, yes there are other easy to sail boats out there…but no one to my knowledge has combined this level of performance, very forgiving sailing characteristics, complete flexibility of solo/double/W/WO spinnaker with a board less design.

I have never sailed the ARC 17 but I did own a SC 17 for a number of years (and I just bought another one). Unless you have sailed this boat you don’t have a clue…It makes sailing…and sailing fast….soooo easy.

The vast majority of cat sailors are not racers. For the people who just want to go out for an afternoon and enjoy the water….going fast with their spouse/girlfriend/boyfriend/son/daughter….this is “The Boat”…near bomb proof construction…no dagger boards to spit open your hull if you run up on a sandbar…easy to launch through the surf…eats up rough water like candy…easy to right…holds a lot more crew weight than most it’s size…no pitch polls! If you find over complicating things enjoyable, then this is not your boat…if tweaking an endless number variables is what you are all about, then look else where.

As far as SC/ARC avoiding competition…you must be joking right?…the SC 17 has been out since at least 1981 that I know of…maybe even longer…how long has the formula boat classes been out? F-16?…F18?….F18HT?…F20?…(I think the Formula idea is great, just don’t accuse an established boat of being elusive of competition)

Why did everyone hop over the 17’ boats (SC 17, Hobie 17, Inter 17) and start new classes? Instead of making a F-17 class?…With all due respect, the SC 17 was in production when some of its current critics were in grade school or maybe even in diapers…

It was a great boat when it was conceived, and 23-24 years latter it is still the benchmark for board less beach cats. If it’s not… then why is everyone (except it’s owners) complaining that the boat is so much faster than it’s assigned PN…

In fact that seems to be the same complaint about the SC 20 Bill raced a few weeks ago…Make up your mind…either the SC/ARC designs are unfairly fast, or Mr. Roberts design concepts are “smoke and mirrors”…you can’t have it both ways!

Bob

I found the SC17 to be a lousy beginners boat. Nothing for the crew to hold on to on deck. sharply rounded decks very uncomfortable to sit on. The only time i had a crew get hurt badly was on one in a lake. the boat dived the bows under sharply and quickly and came to a sudden halt when the massively draggy main beam hit the water. With nothing to hold on to the crew injured her knee after being flung forward.
My friends wife also hurt her back when they tipped over. nothing for her to hold on to.
I theorize that the forward canting rudders have something to do with the bows of the supercats wanting to dive all the time.
Also the 17 was meant to be a 2 up boat when first sold. that's why they made a 15 for 1 person. There are boardless boats from many builders that can be sailed by 1 that were originally designed for 2.
My memory of the symetrical boardless cat evolution of the 70s-80s is as follows.(not including the kind with fins-dart type)
Sizzler-aluminum hulls
G-cats
Supercats
Trac 16
The Trac 16 was an improvement over the Supercat IMHO.
There was nothing faster than a G5.7 off the wind in the days before the assy. We worked our way up to top 3 once at Texel on the downwind after a mediocre start.

The whole point comes down to the fact wether the ARC products are fast because of efficiency or because of the huge rigs they feature. The problem here is that without having a really comparable design using the "normal setup", it's hard (if not impossible?) to tell wether any speed increase is the result of superior efficiency or just the result of having a bigger engine.

Last year the Dynacat F18 (with planing underside, hard chines, and step) was launched; it didn't make an impression in the F18 class and wasn't seen to beat the "normal" F18 designs. Therefor the conclusion is simple. Now assume that the builder Mattia had put 20 % more sailarea on it, reduced the weight and made it wider as well all resulting in a boat that was a somewhat faster than a standard F18. But how much of the increase in speed was the result of the sailarea, etc and how much of the planing hull ? It is very possible that the planing surface made the hull less efficient and therefor slower while the increase in sailarea, etc was still enough enough to still make the overal design faster. We would never know without a proper reference boat. And the ARC product line is so off in specifications that there is simply no reference boat for any of them.

It appears that all ARC's are underrated in PN despite any outcome of the question above. Bill claims the designs are surprisingly fast in various posts as others, like you, do as well. The SC's are so much more efficient and fast ? Than why is Prindle 18 = 74.5 ; when SC-17 with 13 % more sailarea on taller rig = 73 = 2 % faster. Note also how the SC-17 = 73 = only 4 % faster than a H16 = 76.1 while the SC has no less than 15 % more sailarea than the H16. If anything; the ratings of the SC-17 are remarkably unimpressive considering the rig that sits on it.

Note that the sailarea's of the H16 and P18 are as good as identical. The weigths of both boats are relatively close as well. Increases in waterline therefor can only account for some 2 % speed increase. Please also note that the OLD SC-17 has more sailarea than the F18 = 63.5 as well. So somewhere a significant portion of all that power is lost in order to arrive to ratings that are 11% (spi) to 15 % (no spi) apart. This actually signals inefficiency !


So what is it ? You can't be more efficient and alot slower at the same time. Are the ratings correct and is the setup less efficient because the SC setup only achieves respectively 2 % and 4 % increases in speed for 13 % and 15 %increases in power ? Or is the setup more efficient in addition to having more sailarea and are the PN's are way off ?


The contradiction is not in the complaints but in the claims !

Therefor we can definately "have it both ways".

The refusal to adres this glaring contradiction and camouflage it with lenghty explanations using unprovable claims is the part I named :"smoke and mirrors"

The diaper comments fall fully under the smoke and mirrors description. Or else we must claim that Ellen McArthur can never win a race because she was still in diapers when all other Vendee Globe and mini sat sailors were already winning their first opti races.


Wouter

Your comments lead me to question if you ever stepped foot on a SC. I use to take my eight-year-old daughter, and 5-year-old son with me all the time on my SC 17. Never once did I lose either of them overboard, and they never lacked for something to hold on to. I never experienced “the boat dived the bows under sharply and quickly and came to a sudden halt when the massively draggy main beam hit the water.” My sailing was predominantly in the Atlantic Ocean out the Ft. Pierce, Inlet and along the beach. We are talking waves here… with heavy chop on top of the swells…the boat absolutely loved rough water.

The actions you described were quite common occurances for me when I sailed a Hobie 14…but I never experienced them on the SC17.

Bob

Wouter…my friend…I did not mean to be offensive in my diaper comment…only use it for dramatic effect in stating that it is ludicrous to say that a 23-24 year old boat is avoiding competition when it was designed, and in production just short of two decades before these new classes with their self determined rules even existed. It would be easier to argue that the new classes should have been built within the 17’ format ( SC 17/Hobie 17/Inter 17/Nacra 5.2).

Surly, you must know that a boat is designed around a whole group of variables…and only becomes a superior design when all are working in harmony for the intended purpose along the chosen design path…why then does every one keep insisting Bill Roberts take his well balance designs and bastardize them to fit into the latest manifestation of catamaran rules? If one of the designs were changed to fit the current trend and it suffered a performance loss, what would that prove? Nothing!…The boat was designed to work a certain way, in certain conditions, within certain physical perimeters.

If you reduced the sail area or beam to match that of another hull design that cannot carry as much sail because of pitch poll problems, have you proved anything? All you have done is limit a design, which has superior pitch poll resistance. And in effect excused the poor design on the new boat. Is this progress?

I would say the SC series has been kind of a reality check for those who have fooled themselves into thinking that catamaran design has made progress in "leaps and bounds" within the last 20 year time frame. It really takes the pizzazz out of marketing High Tech and/or High Performance classes when those pesky 20+ year old SC’s keep coming back from the grave with a few sail tweaks to beat the latest and greatest high tech wonders….

Why can't we have room for both...designs which are free from artifical restraints on length, beam, weight, sail area, and the "effeciency" design aproach within constrictive perimiters you are so fond of? Because when you look at the big picture, and the time line of catamaran design, it looks as if the F16, F18, F18HT, F20 classes are the new guys on the block crashing the party...not the other way around.

Bob

I think Wouter's comments were more along the lines of; if you really want to prove superior design elements, then design it within the arena of other existing designs. For example, if I build a go-kart that's twice as wide and has three times the engine against a standard, more conventional, go-kart and win - what have I proven? If I want to prove that my go-karts designs are faster, then I should build my go-kart within the current popular parameters. By all means, we should build the wide one if it will sell, but we can't really get excited about having superior design elements based on the fact that we're beating more conventional ones. To say that these boats should be a "reality check" to boats that are designed within different constraints is a bit of a stretch. If you took the SC20TR, lopped 4 feet off it's beam and 6' from it's mast such that it falls in the same category as the boats we seem to be claiming superiority over, things could look a bit differently. Where do you think an SC20TR would place racing boat for boat with a carbon Marstrom 20 (even though the Marstrom is still not as wide and doesn't carry as much sail area)?

Bill himself has indicated that the rating on the ARC17 is a bit soft and it's public knowledge that the rating on the SC20 is not very accurate (A Nacra 6.0NA owes a SC20TR, who's mast is nearly 6' taller and beam is 4' wider, time). The SC / ARC boats are more powerfull and faster than their ratings. So we can't really point to race results to say that one is better than the other. The standard for comparison is known to be faulty.

Don't get me wrong; I like the SC20 and the ARC series, I like the idea of a 12' wide boat, or experimenting with the boundaries of the shared lift concept, or adding more sail area to make it faster - but if these concepts are so revolutionary and successful, why don't we see a boat in the highly competative classes and formulas with these features? If it's really because all the other manufacturers are dumb, why don't we see an ARC conform to one of said classes to prove it? I guarantee that if a 'shared lift' ARC F18 was capable of outruning most other F18s it would sell like there is no tomorrow - ARC wouldn't be able to build them fast enough.

Why not constrain what really matters rather than putting artificial constraints on sail area or length? If you ask the wrong question you are unlikely to get the right answer.

1) Cost. The average annual cost over the lifetime of the boat is really important to many of us. Do I need to buy new sails every 2 years? What else do I have to replace on an annual basis? Will the hulls go soft after 10 years of hard sailing? Do I really need to pay an extra $2000 for carbon pre-preg hulls or can I spend $200 on a larger sail plan and go just as fast?

2) Real Performance. Is the boat still fun to sail through powerboat slop when the wind is gusting to 11 knots true? Can I make it home in one piece when the wind cranks up to 30? How wide is the range of conditions that the boat is fun to sail? Some of us have to plan our sailing days long before the weather forecast is reliable.

3) Setup. Can the boat be set up (from the trailer or cartop) by the number of people who will sail it - assuming one of them knows how to assemble it? Can this be done quickly enough to sail after work? If it is a singlehander - can you put it away alone in the dark?

4) Reliability and reparability. What is the mean time between failures that waste a good sailing day? If the boat gets holed by a floating log can I repair it myself?

5) Safety. Could the intended sailor be injured seriously as a result of the boat's design? Sure - some degree of risk may be accepted by the sailor. I would not want anyone to alter something that cripples to the performance of the boat just to make it safer, but don't build in booby traps.

6)Maintenance time to sailing time ratio. How many quality hours do I spend working on the boat versus sailing it?

7)Versatility. If the boat is designed for 2 can I still cruise with 3? Can I still sail it alone? Can the boat go racing one weekend and cruising with the kids and dog the next?

I want the fastest boat that is designed around these constraints, not some arbitrary number intended to limit performance but not cost.

colin pitts

I guarantee that if a 'shared lift' ARC F18 was capable of outruning most other F18s it would sell like there is no tomorrow - ARC wouldn't be able to build them fast enough.

Jake, you bring up great points...
Bill, it sounds to me like the gauntlet is out, fear not the challenge! Respect the outcome....

Hi Sam,
We are communicating better but still not totally.
It is no bull that the ARC17 has options of unirig or unirig plus jib or uni rig plus jib plus spinnaker. When you get to the order boat form, the orderer checks off the options they want even down to the color of the spinnaker.
Here is an example of our communications problem. When I talk about beach cats, I am talking about a small catamaran WITHOUT dagger boards; a boat you sail on and off the beach. To the beginning sailor dagger boards can be a real problem. Try coming in through even small surf with boards down. New sailors sometimes forget about the boards. I've seen it happen and sometimes it is not pretty. The ARC17 is a "keep it simple" boat. If you could see how it is rigged, I'm sure you would agree. Comparing it to a board boat is a non contest. The 17 is a boardless boat a with low aspect ratio sail plan. It is not intended/designed to be fast to windward. The 17 always has always been fast on a reach and downwind. This is the way beginning sailors like to sail. If they want to race at all, they want to drag race on a reach. The ARC 17 is not a racing boat, it is a beginners boat, a boat for people to learn how to sail on. Don't compare it to a racing boat because it is not a designed as a racing boat.
I took the ARC17 to the Tradewinds race for people to SEE IT. The boat has no US Sailing PN. It is a new boat. The best shot at a PN for the Tradewinds Race only was to use the SC17 PN and make adjustments for the things that are different between the SC17 and ARC17, boat width and sail plan. For the next race it sails in, I think a better number would be to take the last four heats of the Tradewinds and reverse engineer a PN for the ARC17 and calculate what the PN needed to be to make the ARC17 tie on corrected time with each one of the other boats in these heats. Then throw out the odviously high numbers, if there are any, and average the best of the low numbers. This should be a more correct PN number for the boat. This is how you get a correct PN for a new boat. This is the process in action.
You are right, Sam, there is no ARC17 class at this time. There are two boats in the whole world. You have to start a new class somewhere. When the class grows to ten boats or so, an association will be formed.
There is an ARC22 class organization with officers and race schedule and class rules etc. Every 22 that has been sold came with a book of class rules to keep the boat/sails etc class legal. A US National Championship Regatta is scheduled for this year. All SC and ARC boats are welcome.
The class has a web site with forums, etc.
All ARC products have class rules for platform geometry, rigging geometry, max sail sizes, etc.
I hope you are feeling better real soon, Sam.
Bill

Steve,
What I find really interesting is the "cultural" difference between sailing cultures on the various continent..

(My opinion)..
We in Au have been unfortunately been invaded by the heavy plastic under powered under achieving "international" classes..

My father learnt to sail as bailer boy on 6, 8, 10 and 32 foot skiffs.. If you can have a look at the sail areas they used to put up..Then graduated to skippering a home built 6 footer.. (at 13).. My first was a VJ.. 11'6 (just under 3.5 meters) sharpie planing hull.. Sort-of like a pointed bowed hard chined scow, 3'6 wide at the gunwales, and to keep her upright twin planks (the class was designed before trapezes were invented).. 45kg weight limit.. 120? sq feet working sail area with a assymetric kite.. chine to gunwale height 200 mm.. The races started at 1:30 pm.. My local pond has a summer breeze of 22 knots average so many days we started in conditions where foam was blowing off the chop.. On those days I just wore 6 wool jumpers rather than the normal 3.. I was 13 weighed 5 1/2 stone (35kg) I still remember the day we put the kite up and sailed over the Australian 14 skiff champ on a shy reach.. To be honest it was in the days before a wind upper restriction applied.. The hull was out from just behind the centreplate and only 1/3 of the width of the hull.. Scary yes but exhilerating.. I was hooked!!!
A few years ago I unfortunately took my son down to his first sailing experience.. So he went out on an opti... and came back bored.. Now getting him near a boat is difficult as he considers sailing is boring.. When my arm is ok I hope to take him out on the F16 and show him it can make his young heart skip (he is 10).. The first impression is important and takes a lot of good experiences to overcome the first..

My point after the ramble.. Wish I had taken my son out on an higher preformanced boat like an ARC17 (not that I have seen one) rather than let him see an opti..

Weren't the first classes open boxed classes?... A, B, C and D..

Just wondering which new class is "High Tech"?
Nomex honeycomb carbon epoxy was used to build boats in the 80s.. So its now what 20 years old as a technology..

Hi Stewart

I agree with you…the building materials/method of construction is twenty years old…yet they market it as something new and improved…you will notice in my earlier post I said some of the new boats/classes are marketed as High Tech/High Performance…I didn’t say whether they “were” actually High Tech/High Performance…:) that remains to be seen...and when a 20 + year old boardless beach cat design comes out of mothballs with a new sail plan and sails that well against current racing cats it calls a lot of things into question beyond just the PN of the ARC 17...

Bob

This thread was originally a question about planing hull cats vs. displacement hull cats with spinakkers, but was quickly hijacked to become an advert for Bill`s new boat, while at the same time gave Bill an opportunity to discredit designers of other boats :Quote from Bill Roberts, after hijacking this thread to turn it into an advert for his products :'"All boats that fly spinnakers have lee helm". Only boat designs that place the daggerboard in the classical position, approximately at the shroud chainplate, have lee helm with the spinnaker up. This is a system design that has ignored the spinnaker during the design phase of the boat development and the designer/manufacturer expects the sailing public to put up with it. There is a sail/boat design system that does take this CE migration into account. The design system is called "shared lift" and it is incorporated into ARC products. It has to do with shifting the board location forward so that the CE with spin up cannot get in front of the board. Then down sizing the board and up sizing the rudder so that the shared lift between the board and rudder is in the correct effective location for sailing the boat as sloop.'
That`s wonderful news. He then goes on to tell us how any beach cat that was designed by anyone else has terrible tendencies to kill, maim & frighten the hell out of anyone, while his boats are built with only SAFETY in mind. I hope he has good legal counsel, from what I understand you can get sued in the US for looking at someone funny, never mind calling them an irresponsible yacht designer : "I see nothing but praise for the H16 on this forum. In West Palm Beach, Florida two sailors have lost their lives because of the unsafe characteristics, easy pitchpole tendency, of the H16 design. It is the same for everyone sailing a H16 so, what the heck." Bill, I suggest you write to some US sailing magazines & ask them if they`ll publish that for you, then wait for Hobie`s lawyers to start calling you. It must have been a HUGE pitchpole, if that was the official cause of death. Personally I`d rather be caught out on a H16 in a storm than a 17ft boat with more sail area than it can cope with.

Yes, there are more than one way to make a cat fast - one method is to improve on construction methods to make the boat stronger & lighter, and put on a reasonable sailplan that is manageable in up to 25knots of wind, probably the upper design limit for most beach cats (oh, except for the SC range of course). The other method is to use cheap construction methods, overbuild them to make sure they`re strong, don`t worry about the weight too much, you can always load up the sail area & widen the boat to compensate.
Just don`t ask me for help dragging it up the beach.

I still can`t figure out how some people believe that a 17ft boat with more sail area than a F18 can be regarded as a beginner`s boat. I`m really impressed with the idea that someone actually built the thing, it seems horribly overpowered to me. The only SC boat I`ve seen is a Supercat 20, took the guys 2 days to rig it, was heavy as a speedboat, and once capsized it had a complicated stay-lengthening device to help right it.It took so long to manipulate that they went turtle, and needed a rescue boat`s assistance. It never beat a Tornado over the line at our club, old Tornado with old rig, one trapeze and heavy by today`s standards. Perhaps the owners never read the manual.
I also understand that the "new" 17ft design is not a re-hash of the old SC17 hull shape, but is in fact a new design, which is what lead me to ask why design something new which doesn`t fit into any of the formula classes - If this was done it would go a long way to getting more growth in the formula classes in the US, which would benefit everyone. I`m absolutely amazed that anyone would buy a NEW boat that doesn`t offer the ability of inclusion in one of the Formula classes. I know that the Formula classes are not huge in the US, but then if the US designers are purposefully avoiding them it`s no wonder.
I believe that Wouter has made the only sensible comments on the original question in this thread, and summed things up quite nicely with this :
The whole point comes down to the fact wether the ARC products are fast because of efficiency or because of the huge rigs they feature. The problem here is that without having a really comparable design using the "normal setup", it's hard (if not impossible?) to tell wether any speed increase is the result of superior efficiency or just the result of having a bigger engine.

I`ts good that Bill designs boats that are different, challenge the "norm" and don`t conform to formula rules. As he says, they aren`t intended for racing, except against themselves. Sounds like his ideals are not so different from those he criticizes the most.

Cheers
Steve

BRAVO!

Hi Eric,
All it takes is money. The tooling that Aquarius has was built back in the 1980s and that is all there is. You guys stand around and say "build a new boat of this or that size and the world will beat a path to your door". Been there and done that and it doesn't work. The telescoping SC20 won the OAK Regatta in 1981 by a wide margin over all the California hot dogs. The SC20 had a demonstrated and substantiated PN of 62 and the Tornado had a PN of 64 in the early and mid 1980s. The tall rig 20 was 60.I gave the sailing public what they "said" they wanted (a boat faster than the Tornado) and I built it and then they didn't want it afterall. A couple of hunderd boats were sold over ten years; not enough to keep a boat company in business. I lost a nice retirement building the SC product line. The SC 17 is the only boat I designed that made any money/profit. I have some sensitive scar tissue, Eric. Understand now why there is an ARC17 effort?
Good Sailing,
Bill
Good Sailing,
Bill

Hi Jake,
All of the SC design work and tooling building was done back in the late 1970s and early 1980s. This is long before there were any box rule design design classes.
When I was doing my bech cat design work, the contest was about speed not efficiency.
But speaking of efficiency: The RC30 has a PN of 54, same as a Formula 40. The RC30 is 30ft long vs 40ft for the F40. A new carbon RC30 with trailer, beach wheels, an extra siut of sails, spare battens, outboard motor, life jackets, trapeze belts, gloves, tool box and hand tools, anchor and line, lights and navigation charts, everything one could possibly need for the boat costs less than $100,000. A new F40 costs over a million dollars. Now, how's that for efficiency, Jake?
Bill
PS You Applaud the M20. I do too. The unique thing about the M20 is its weight, 150 pounds less than a Tornado or 200 pounds less than an I20 or N6.0 and you do not mention that. Why not? Do you have any idea what it would cost to take 200 pounds off the weight of an I20 or N6.0?

Hi Wouter,
I appreciate your compliments and good wishes. This is quite a change. I can't help but think you have had something special to eat or drink just before you wrote the above letter. Your mom must have fixed you your favorite dinner.
Good luck with the F16 class.
Bill

I understand, Bill. I just wonder, as others do, why you have not focused your efforts and resources to build a boat to compete against a more popular design. Using the same box or "formula" would for sure highlight your design innovations. Don't get me wrong, I think the ARC 17 is an excellent design, innovative in design of the controls and now I have seen that is very fast in moderate winds.There is just no boat to compare to to ferret out the strenghts and weaknesses. If I had the cash I would look at the Arc 21 0r 22 in a heartbeat, again, great innovations and simplicity.
I appreciate the fact that you have devoted your time, talent and treasure in the pursuit of your interests, not many people can say they had the balls to do it.
NOTE: Another poster threw down the gauntlet, I just stirred the pot.

Ahh Bill,

Not much has changed. I'm really not hung up on the ARC-17. I expect it to be a great boat and would love to see more of them on the water. I'm still comfortable with you as well; next time I see any of the SC in NL again I will again take their picture and send it to you (like I did a Texel) and convey the regards of their crews.

The thing that got me going was the "story" around the ARC-17 design and its quite implied dissing of several other designers and related designs.

Really you are not the only designer who has experimented on cats or taken measurements. Nor are you the only one confronted with the issues around a spinnaker. You solved it in your way the others in their way. The real life results are different from what was stated as undeniable truth. Therefor the theoretical model you used was not describing the reality accurately. It is by all means a "feels right" model but inaccurate none the less.

Without hard proof the views expressed become dogmatic. Hence the gauntlet thing.

Now on my my part I haven't quite worked out why it behaves differently but that is mostly because of lack of effort. When something is not a problem than I'm less willing to explain why it is not a problem. I tend to accept it and move on.

Factors that may result in the different behaviour :

-1- Spi is fitted asymmetrically to the boat. The normal rig pushed the boat along almost along the centreline. The Spinaker is to the lee of this and thus its lift factor will induce a weatherhelm effect as well.

-2- The conponent of the total lift force that lies along the centreline may be several times greater than the component perpendicular to the centreline. It may be that

Leehelm component - weather helm component = lever 1 * force perpendicular to centreline - lever 2 * force along centreline = close to 0 or very small.

To give another example. Yachts without a spi have greater weatherhelm on deep downwind sailing legs than on upwind legs. With spinnaker they balance out again. A different setup I agree but it shows that there is more to the system than the simplied model that was used in this thread.

This is my last post in this thread.

Now, indeed Fair winds to you and I'm looking forward to more race results. If anything it helps to improve on the understanding we both have on the subject.

Wouter

Hi Wout -Bill -John and all ,-great thread ,-just sat back and read others on this one though very interested ,
like John P posts and Bill,s as active designers of existing cats in the marketplace .

Wout your perspective is from a main objective and goal of building a Formula class {worthy endeavor } but in discussions it often makes you {talk past another} as they say .

An interesting project > I have a SC 15 that I,d like to modify w spin {experimented a little already with one on the sc } and have it comply with F-16 rules for future racing ,--I,m not sure if I,ll add boards or a smaller molded in skeg or just use more rake and load up the large rudders more on this non boarded design .

I may add a little foam expoxy v shaped {for rudder movement} fairing plate off the stern to make it a full 16 ft .

The problem earlier on migrating CE forward with the spin up is the problem I,ll face in adding the spin .

In looking at a side view diagram of any cat -
http://www.parlier.org/site02/images/vue-face.jpg

The CLR -{area of underwater profile inc boards & rudders}
has been designed in older non spin cats without consideration of the spin area which when raised moves the CE way forward .
Most racing sailors have found that when you rake the mast aft more under spin the better your speed and handling characteristics. In effect moving the total CE back -
but how much ?
The spin pole is a certain distance from the bows per rules ,-the mast base in located the same ,-an extreme amount of added or extreme mast rake may be a meter or little more ,--thats all .
Draw this out on a particular design with accurate sail area mast height and general specifications in the normal position {without spin} and with extreme mast rake and spin area in calculation of CE to CLR .
Spin are av equal to or larger than the main &jib area
spin tacked out forward on the spin pole.

The CE evan with extreme rake is still way ahead of the CLR , tHIS NECCESITATES the moving of the board forward ,near or at front crossbeam location as noted , for spin boats .

One other interesting option would be an evan more forward located smaller angled lifting foil or skeg to change the CLR to CE .
for other readers -
CLR is Center of Lateral Resistance =side view underwater profile under sail and center of area inc boards foils and rudders .
C E is the Center of Effort = center of areas of the sail plan -main -main jib -or main jib spin combinations .

Generally the CLR leads the CE by a small percent ,-allowing for mast effects and wanting some weather helm designed in or nearly nuetral helm .

The forward lifting canted foil nearer the bow to balance the spin CE would create added drag , offset by its ability to lift at higher speed and balance the helm under spin.
In upwind mode this would load the rudders evan more ,
requiring a smaller aft board as well ,-this type of for and aft board configuration is very versitile under many different sail combinations ,--thinking of larger cats -reefing jibs and mains ,-stormjibsails,-and cats with adjustable rigs ,- etc .

An ideal cat design would have an ajustable mast rake ability under sail ,-forward position in normal windstrengths upwind ,--then raked back to an extreme downwind .
The 60 tris have adjustable rigs ,-the first I saw it on beach cats was the 87 Worrell 1000 ,-It was Reg Whites son on a 12 beam Hurricane that had attached a 3 to one block system and cleat at the base of all stays with about 6 ft of adjustment ,-it could be raked back ,--and also to windward a little if desired .

Small inward canted forward lifting foils particularly for 16 ft cats that counteract forward forces -used on the 60 tris so well to carry their huge sail plans ,may be the ideal development for them allowing them to be pressed much harder in high wind speed conditions .

fun to theoretically go through design options and potential variation to explore .
good winds

Seeker San,
So what do your kids hold on to on the 17? Shroud, or hiking straps? Most people think a begginner boat would be like a hobie wave or something with a lip that you can grab on to.
There really aren't any cats that don't dive the bows when pushed hard enough. I just think supercats sail bow down when powered up. Many factors contribute to this. Even if they are hard to pictchpole it still isn't very fast to have the whole hull under water. In the picture that i posted before, the supercat is working very hard to keep the bows up while we are leaning forward. We started at the same time as i recall and we are on the same downwind leg of the race. pretty shure that is Bill at the helm of the SC.
I personally like to sail a boat bows up or flat, not bows down. Wouldn't feel comfortable at high speed reaching with the bows down to get shared lift. Also i take offense will Bill's comment that v in the tail is improper design. So what if it makes a boat harder to tack. Even Tornados only make 1 tack to the A mark if possible. V in the tail and bows up are good in the waves.
In answer to your question about me sailing a SC17, actually, i worked at Boston Whaler SuperCat untill i was fired for not working on Saturday in spite of the fact that they had paid my expenses to race in Miami that weekend. Corp. b.s. -one hand didn't know what the other was doing. 1980 or 81...
Bill's best design was the captive mast step-cudos there, the boats themselves don't do it for me. The round top just funnels the spray into your face and isn't worth it.
The big Trimaran guys seem to use a similar hull for the ammas though.
In any case it's a good thing that you get your kids out there cat sailing in the ocean.
PS. there could be some errors here because the 80's were a while ago.

Hi Eric,
The reason the SC17 was revisited/reinvented/put back into production is because it sold well once and it took no big bucks, no new tooling to bring it out again. The SC17 was designed 25 years ago. All that was done last year was to put new sails on the same rigging and spar and add a spinnaker as an option. This brought the 17 up to the same technology level as the other ARC products.
You asked about something to compare the ARC 17 to, Eric; here are some thoughts.
So, what is the correct PN for the new ARC17? Let's go to the Tradewinds Race results, 2004, and see what we can learn. I suggest we use the last four heats because in the first four heats boats were going around the wrong race course and the 17 used the spinnaker in three out of the first four so things are sort of scrambled. The last four heats are cleaner data and the 17 did not use the spinnaker.
Fifth heat analysis: Using a PN of 70.1 and not using the spinnaker, the ARC 17 finished second on corrected tine. That is 44 seconds behind the D18 and 2min and 27 seconds
in front of the T4.9.
Sixth heat: The ARC17 finished first on corrected time but only by a whisker. The 17 was 22 seconds ahead of the D18 and 1 min and 14 seconds ahead of the H20.
Seventh heat: The ARC 17 finished first again on corrected time. This time it was 50 seconds ahead of the D18 and 1 minute and 55 seconds ahead of the H20.
Eighth race: The ARC17 finished second on corrected time. This time it was 14 seconds behind the T4.9 and 30 seconds ahead of the D18. Tight race!
We could also use the fourth heat: Here the ARC17 finished second on corrected time in between the two T4.9s. The 17 finished 6 seconds behind the first T4.9 and 8 seconds in front of the second T4.9. Tight race again.
Summary: Assuming this crowd of sailors sailed their boats to their respective PNs, it looks to me like a PN of 70 for the ARC17 without spinnaker is a better number than 70.1 with spinnaker. This would make the PN for the ARC17 with spinnaker equal to 67.2.
Here is some more interesting information comparing PNs of boardless beach cats of similiar size.

H16, actual length 16ft and 6ins. PN = 76.1
P16, 16ft PN = 77.5
P18, 18ft PN = 74.5
SC17, 1980 intro. 17ft PN = 73.0
ARC17, 2004 intro. 17ft PN* = 70.0 sloop, new
sail plan
ARC17, 2004 intro. 17ft PN* = 67.2 with spinnaker

The 2004 ARC17 is the same boat as the 1980 SC17 with new sails and spinnaker.
Conclusion: The SC17 always has been outstandingly fast beach cat for its size. History tells us that. The new ARC 17 appears to be even faster.
* PNs calculated based on one,(1), regatta and subject to change as more data is accumulated.
Good Sailing, Eric
Bill
PS In the future, Eric, I am going to respond to questions on Aquarius products on the owners.aquarius-sail.com web site. When I talk about these products here, I get pounded with questions via e-mail from individual SC/ARC owners and I end up answering the same question at least 10 times. It is wearing me out.

Hi Carl,
I want to help you out a little with this SC15. The 15 plug was made from the 17 plug. Two feet was cut off the back end of the 17 plug and then the keel rocker in the aft end was increased, rolled up to a new transom at 15ft to add displacement in the aft end of the hull. The important thing for this discussion is that the front end of the hull was not changed. This means that the 15 like the 17 has the hull lifting surface, deep vee hull shape, in the front 6ft or so of the hull. The middle 5ft is transition shape from deep vee to round and the aft 4ft is a round hull bottom shape, therefore no lift here. Same 2x size rudder is on 15 and 17. This was all done in 1979/1980 to produce a boardless beach cat that would TACK. The aft end of any hull has to be free to slide sideways for a boat to tack quickly and easily. The no lift aft hull end automatically puts the lift burden on the rudder which is a high aspect ratio foil, therefore low induced drag. The rudder is like a steering daggerboard. This boat design is another example of shared lift done in 1979/1980 to make a boardless beach cat tack well.
Now here we are in 2004 and we want to put a spinnaker on this boat. Well how about that; aren't we lucky. This boat already has the hull CLR well forward, like 3 to 4ft back from the bow so adding the spin is "no problem". This boat will exhibit no lee helm with spin up because the sail plan CE will always be behind the hull CLR.
The motto of the best SC15 an 17 sailors is "drive those bows". By that they mean trim the boat out with the waterline halfway up the stem. Always keep the waterline tape underwater at the bow.
This hull design scheme has also led to an increased boat speed hull shape sailing to windward for boardless beach cats. The normal boardless beach hull shape has its lifting hull shape for the full length of the hull. The underwater aspect ratio for this hull shape is the average depth divided by the waterline length. These are numbers like .75ft deep by 16ft long. The induced drag due to generating lift is inversely proportional to this number. This number in this example has a value of 21.3 and it is a multiplier in the induced hull drag calculation. In the case of the SC15 and 17 this multiplier is made up of two parts. One is the hull induced drag and the other part is the rudder induced drag with each lifting body carrying half the total lift force. For the SC15 and 17 the hull induced drag aspect ratio is something like .75ft deep by 7ft long which leeds to a induced drag multiplier like 9.3. The rudder aspect ratio is like 2ft deep by .75 ft wide which leads to an induced drag multiplier like 0.375 acting on 50% of the lift force. So the induced drag coefficient for the hull plus rudder generating lift on a SC15 or 17 is equal to 0.5 x 9.3 plus 0.5 x 0.375 or a total of 4.84. This compares to 21.3 for a normal beach cat hull design. Needless to say, the hull drag on the SC15 and 17 is significantly less than the other beach cats. This shows up when comparing PNs between boats of similiar size. The SC17, which has a PN base, its PN is 4 to 5% lower than other beach cats of similiar size. The hull induced drag makes the difference.
I want you to understand what you have got, Carl, and why it sails like it does.
Good Sailing,
Bill