When will we see an ARC F18/20

Bill
When will we see these boats? I am looking a F18 and would like more US built boats to chose from. How about an F20 to compete against the I20. You seem to like this boat for having flat decks. It's time to built one and show them on the water.
LF

Larry,
The SC20 came out in 1978. This was a 20ft by 12ft by 276ftft of sail. It had a DPN of 62 back in the early 80s. Add a spinnaker and it is 59.5.
Today there are new boats with the same sail area that are 8.5ft wide and require two big guys to hold'em down when the wind blows over 12 knots. The SC20 with its 12ft beam made it possible for two average size sailors, a guy and his girl friend, to sail competitively in 15 to 20 knots of wind. It takes a given amount of righting moment to drive 270 to 290ftft of sail area efficiently. You can get this torque with two big people on a short lever arm or with two average size people and a long lever arm. The choice is yours.
There was a light air version of this boat called the SC20TR, tall rig. It had about 325ftft of sail area with a 38ft tall mast. This boat developed a DPN of 60 without spin. Add a spin and you get a DPN of 57.5. Today the ARC22 has a DPN of 57.3. So, Larry, what's new??? Where's the new technology? Where are the breakthroughs? All I can see is that boats are lighter weight today because of improved materials properties. That is not improved boat design. Spinnakers have been added. Spinnakers have been around for 50 to 75 years or more. That is nothing new. Boats with unirigs and spinnakers are sailboats/sailplans tailored to the windward leeward race course. Go back to the triangle race course and the sloop rig with spinnaker is faster. Larry, I'm having a hard time finding any real, true, pure improved boat design. What do you want to see????

As far as an 18 footer goes: Take a SC19 and move the transom forward 1ft. This was done with much success years ago in the 18 sq class.The boat had a higher top speed than other 18sqs and it was much harder to pitchpole. If you want it, it was there 18 years ago. Where were you?
Good Sailing,
Bill

There seems to be quite a bit of nostalgia surrounding the Bill Roberts designs as of late. Are these folks looking back because nothing really astounding has come forward in the past year or two? The entire F18HT landslide of hype has resulted in some great boats, but no revolution. I-20s, N-6.0NAs, and P-19s have been around for quite a while and have proven to be fast and fun-but where is the quantum leap we have become addicted to? Have we reached the paragon or close to it without going to wingsails and asemetric hull layouts that only can go on one tack? What I am reading in these posts is sailors are looking for a challenging experience and have minds that are not going to rest when it comes to asking "what if?" If we can't beat them with computer design and carbon fiber, we will beat them with an Aqua Cat 12 and a jet engine.

The question should be...when is ARC going to reintroduce the SC 17, 19 and 20...and the answer probably is when sailors start looking for a rugged all a round performance boat that is just as at home in the ocean with the family on it as it is on a flat water lake/river/bay race course.

Now it seems many cats are bought because they are the flavor of the week, or everyone else has one, so if you want to race one design, you have to get one too.

If the catamaran comunity ever expands again to include those people that just want to have fun, then we will not need the competitive aspect driving every design decision.
At that time, designers like Bill will be recognized for designing the best boats without worrying that its a foot or two too long or too wide according to some arbitrary rule book.

The SC 17 I use to have brought me more pleasure than any boat I ever owned..the Humvee of the sea...Too bad Tom stoped building them...may be some day, some one could/would buy the molds and put them back into production...Thanks Bill! for designing awesome boats for the real world...

Bob

Well now Bill, you ask :

"So, Larry, what's new??? Where's the new technology? Where are the breakthroughs?"

Two give three examples :

Squaretop mainssails
a 20 footer weighting in a 115 kg = 254 lbs (m20)
reproductivety of hulls within 400 grams (1 lbs) or less when using prepreg materials.

May not be breakthroughs in the purest sense of the word but significant advancements just the same. You yourself just quoted the development in the Tornado class in a recent class where a wobbly boat of 450 lbs was transformed into a very stuff 375 lbs boat with a long competitive life.

That is all new and one couldn't do these tricks 20 years ago simply because the technics either didn't exist back then or were still far to expensive to be used in anything other than space flight.

Than we have the introduction of the Flyer hullshape (the original shape, not the copies) which pretty much took the A-cat class by storm. In the late 80's early 90's the a-cats went down from 100 kg's to 50 kg's overall weight. Now the min weight is fixed at 75 kg but they can be build lighter.

I can't remember but when was the prebend rig developped in the tornado class which is improved the control of the mainsail and increase the area in which the mainsail could be trimmed to it's optimal shape. I think it was done in the 80's and perfected later.

I've heard people say that ARC designs can be summarized by "stack more sailarea on it than others do and go faster". What have we seen in the last 20 years ? We've seen smaller boats with limits on sailarea go faster and faster and equalling the ARC design but innovation and advancements in catamaran design. To get more out of less is called progress, just like how modern race car are faster than their banned 80's turbo charged predecessors despite the fact they don't use turbo's anymore.

Then you indicate that :"Spinnakers have been around for 50 to 75 years or more"

Yes, but the asymmetric spis on cats are cut complete different from the symmetric spinnakers of 50 years ago. Your statement is analogue to saying that nothing new was devellopped over the last 3000 years as catamarans still use soft sails to propel them forward. In that respect a ARC is nothing more than a pre christianity polynesian proa made out of fibre glass.

I for one would like to see someone cut the transom of a SC19, put a rig of 21,15 sq. mtr. with a 80's cut (pin head) on it together with a spi that is cut like the ones of 50-75 years ago and do well against modern F18's in the F18 world cup.

I think we all know where this boat will end up and that proofs that there really has been improvements, developments and innovations over time. The may have been spread ou over a longer period of time and therefor can't be really described as breakthroughs but a modern cat is certainly not more of the same old 80's technology.

Maybe extending the transom of a SC17 to 18 foot would be a better comparison to todays F18's ; Weight and rigarea's are far more alike.

Wouter

Wouter,
These lighter weight boats are not a technical breakthrough for beach cats. Prepreg construction and the autoclave were used to make spaceship parts and airplane parts and race car parts long before they were used to make beach cat parts. As a matter of fact I have been told that Marstrom built glider parts long before he built beach cat parts. The use of prepreg materials and the autoclave in beach cat construction is not an invention. You cannot get a patent on it. It is a construction method improvement but it is not a technology breakthrough.
Square top mainsails: Nothing new! If you look in an aerodynamics text book, Aero 101, you will find a section that deals with wing spanwise efficiency. There will be a curve of wing span efficiency or effectiveness vs wing taper ratio. You will see that the wing shape that looses the most span effectiveness is the wing that comes to a point at the outboard end. As the wing tip chord approaches about 25% of the root chord, the wing spanwise effectiveness rises rapidly into the low 90% effectiveness
range and then the curve levels off with further increases in tip chord to root chord ratio. When the tip chord to root chord reaches a value of 1.0, the spanwise effectiveness begins to fall off again because of the large tip vortex caused by the wide wing tip chord. I had a mainsail on my SC20 with a 2ft wide tip chord in 1978. My first RC27 in 1983 had a square top mainsail. When was the first time you saw a square top mainsail? Did you notice that today even the Americas Cup boats are using square top mainsails? These so called "hi tech" boats are following the lead of the beach cats with higher fineness ratio hulls and high aspect ratio sailplans and keels. Today these boats require 20ft of water to keep from dragging their keels on the bottom.
Prebent Rig: Again this was a standard item on the early RC27s. As soon as I began experimenting spinnakers, 1983, I ran into the mast inverting problem. Sweeeping the spreaders aft of the mast 4 to 5 inches created two tall slendar triangles of fore and aft mast support which pushed forward on the central height of the mast and prevented mast inversion. The first spinnakers I put up showed NO improvement in boatspeed and no change in downwind sailing angle. The spinnaker filled and the mainsail became totally ineffective; no net change. It wasn't until the late 1980s that spinnakers began to work to advantage on the RC boats and that was after the purchase of several spinnakers from several different sailmakers.
On the ARC boats you and others have missed the whole point. To go faster a sailboat must have a higher sail area to weight ratio. There are two ways to get there. One is add more sail area. This is inexpensive. The other way is to reduce weight. The Tornado is an example of this. An Olympic Tornado costs almost twice as much as any other 20ft beach cat. Which way do you think the sailing public would rather go? The other very important point that goes untalked about is boat width. To be faster than other boats a superior design must have a higher righting moment to sail area ratio also. Without this parameter being superior to other designs, the higher sail area to weight ratio cannot be taken advantage of. Also the narrow boats with high sail to weight ratio area drive the competitive sailors weight to larger people. The SC and ARC products are unique here. These designs offer the 12ft beam which lets leverage do the work of generating more righting moment rather than requiring a larger weight person. Why do you think the Tornado is 10ft wide and always has been? It is not just because the designer thought it looked pretty. It has a very functional purpose. Nobody is going to build a boat faster than the Tornado until it has a higher sail area to weight ratio and a higher righting moment to sail area ratio!!!
Bill

Bill, why don't wings serve the same purpose as making the boat wider? Is it because they add too much weight?

I will take a stab at that.

Wings do and do not make the boat effectively wider. The crew weight out like on a wider boat but the weight of the hull and rigging is not. Plus you have the effect of the weight of leeward wing working against you. You also do not have the stability of a wider boat. Wings are more like, having a 2 foot taller crew than a wider boat

Don't get me wrong, I like wing boats. I think their advantage is getting your weight out in a safer and more secure way than trapping. For example, with the skipper planted securely on a wing, an 18 magnum will handle wave conditions nothing else will. A Wave with wings and that long promised Hooter would be fun too.

plus, chicks dig wings :P

(My girlfriend, once again, says that she'd find it very uncomfortable to sail on a cat with no wings)

I've been trying to calculate how high off the water I am when I'm trapping on my wing, and at a decent angle of heel. I've wanted to see how hard it would be to sail by boat without its wings, but I'm to much of a pansy to try it.

I didn't say :"lighter weight boats are a technical breakthrough for beach cats"

And how does "Prepreg construction and the autoclave were used to make spaceship parts and airplane parts and race car parts long before they were used to make beach cat parts" conflict with my statement of "simply because the technics either didn't exist back then or were still far to expensive to be used in anything other than space flight."

The fact that they can be applied now in cat design is progress and advancement.

You keep yepping on about breakthroughs, I didn't as I wrote "They may have been spread out over a longer period of time and therefor can't be really described as breakthroughs but a modern cat is certainly not more of the same old 80's technology"

Then you throw in "The use of prepreg materials and the autoclave in beach cat construction is not an invention" after I called te use of this in cat design an INNOVATION. There is a big difference between invention and innovation, Bill.

And as for "Square top mainsails: Nothing new! If you look in an aerodynamics text book" Both Arvel and Bethwaite have completely debunked the use of aircraft earodynamics to sails. It turns out that soft cloth sails behave totally different from aircraft wings and squaretops are used for different reasons than tip vortexes. And if you really want to now any aerodynamics book will name and eliptical wingtip as the perferred wingdesign when looking at vortexes alone.

This use of aircraft aerodynamics is so 80's, since the beginning of the 90's most advances in catamaran saildesign has come from low speed model gliders competition and the (renewed) study of pre- and underpowered flight experiments. These experiments focus on the seperation bubbles and reattachment zones that are simply NOT found in powered fixed wing airraft studies.

"On the ARC boats you and others have missed the whole point" Did I ? As far as I know ARC boats have not opted for the "expensive low weight tornado" route and just stacked up more sailarea and increased width and are still more expensive than common production boats like the I-20 which, as you know, gives the Tornado a good hurry up around the course. Clearly there are other things at play here too. Besides which boat do you want to trailor behind your care a 12 foot wide one or an 8 foot one ?

And "To be faster than other boats a superior design must have a higher righting moment to sail area ratio also. Without this parameter being superior to other designs, the higher sail area to weight ratio cannot be taken advantage of" is just nonsense Bill. Answer this to me.

What happens when for a given design the ratio between righting moment to sail area DECREASES LESS than the ratio for weight to overall sail area ?

Yes power is decrease by virtue of the first ration but when drag decreases even more than the given design will become faster.

How else can modern A-cats be faster than those of 10 years ago when they had shorter mast and about 25 kg's heavier platform ?

How else can a Taipan 4.9 outperform a H16 IN ALL CONDITIONS when afterall the H16 total sailarea is actually slightly more than that of the Taipan and both are of equal width ? And the Taipan has a taller mast at that. According to your reasoning the Taipan should be held back by her rig that has a worse ratio of righting to sail are than the H16.

I know why the tornado has a 10 ft wide beam and I also know that it is possible to design a faster craft WITHOUT :"a higher sail area to weight ratio and a higher righting moment to sail area ratio!!!"

Eventually it all comes down to improving the power to drag ratio and a designer can ALSO do that by making sure that the ratio of righting moment to sail area reduced less rapidly than the ratio for weight to sail area. And the logical way to do this is to reduce platform weight. Platform weight hardly contributes to the righting moment but does fully contribute to drag.

Example

-1- 150 kg crew on a 2,5 mtr, wide 150 kg's platform weights 300 kg overall and has a righting moment of 150 * 2,5 *0,5 + 150 * (2,5 + 1) = 187,5 + 525 = 712,5 where the distribution is 26 % to 74 %

-2- 150 kg crew on a 2,5 mtr, wide 100 kg's platform weights 250 kg overall and has a righting moment of 100 * 2,5 *0,5 + 150 * (2,5 + 1) = 125 + 525 = 650 where the distribution is 19 % to 81 % %


Boat two has 91 % of the righting moment of boat 2 and can therefor only carry 91 % of the sailarea with only 91 % of the power BUT is also has only 83 % of the weight of boat 1 which is directly translated in reduced drag of alot more than the 9 % of the power reduction. Ergo reduction in power coincides with an even bigger reduction in drag and thus higher speeds are achieved.

There is the counterexample of your "Nobody is going to build a boat faster than the .... (fill any boat that you want) until it has a higher sail area to weight ratio and a higher righting moment to sail area ratio!!!" statement.


Simple not ?

And how does your own statement of "It wasn't until the late 1980s that spinnakers began to work to advantage on the RC boats and that was after the purchase of several spinnakers from several different sailmakers" mix with your earlier statement of "That is not improved boat design. Spinnakers have been added. Spinnakers have been around for 50 to 75 years or more. That is nothing new"

Going by your own statements of your latest post something DID change between your first own experiments with spi in 1983 that failed to produce results and your retries of the late 80's and early 90's. Now I can tell you a whole lot changed between the early 90's worrell like spi's and the newer generation high aspect spi's of late 90 early naughties.

Now I DO share your skeptisme with respect to certain "improved designs" and indeed it is more difficult to design a faster boat than one thinks. Most designers do it wrong. As like with the M20, there the designer reduced overall weight, increased righting moment by having a much taller mast AND decreased the width from 10 to 8,5 ft. at the same time. Mastrom shouldn't have done all three things at the same time. You can do two of these and expect to have at least the same performance or better but doing the third pretty assures that you will do worse under certain conditions.

But I stand with my counter argument to your first post. There has been significant innovation and improvements in catamaran design over the last 20 years and as a result the boats have become faster. Due to the gradual improvements I don't think "breakthroughs" is the right describtion for the advancements. This does not mean however that we're witnessing more of the same 80's stuff.

it is either this or accepting that the only true breakthroughs made in multihull design were made 3000 years ago by polynesian boat builders who discovered the advantages of form stabilized designs over weight stabilized designs and discovered the vastly superior performance of Crab sails in all conditions but pure upwind sailing. After that the introduction of bermuda rigs was only a specialization to race courses that featured a dominant upwind leg.

Because in all honesty what did change since then. We still have have two floater connect together by beams, a mast with a sail made of cloth, a peice of rope to trim the sail and a rudder that is hanging from the stern to steer with.

Regards,

Wouter

Hi Mary,
Wings do add to a boats righting moment to sail area ratio as long as the sailors trapeze off the edge of the wing. Wings that sailors sit on are comfort things only. Wings make boats faster in medium and strong winds when they move the sailor's weight further outboard and away from the leeward hull which is the sailing system's fulcrum point. Higher righting moment to sail area is a powerful go fast device when the wind blows.
Who knows of a 20ft beach cat built in Florida with prepreg materials, a superlight boat, unirig with spinnaker, everyone thought it was going to be a rocketship. It was very fast in light winds, 5 knots. When the winds got up to 10 to 12 knots, other 20ft boats pulled even with it. When the winds got up in the 15 to 20 knot range, the superboat fell behind. What is wrong with this design? What was the mistake, the error, the oversight in this boat's design?
Bill

I haven't seen this much bull since the Democaratic presidential candidates.

1. The original question has been totally ignored by Bill Roberts.
Supercat, SC, ARC, Aquarius Sail has ALWAYS avoided building boats which could be raced against "normal" boats.
They use the "ultimate speed" excuse when asked why they refuse to build A Class or C Class or IF18 or IF20.
They build boats for people who want to BUY "first to finish".

2.Barjack: I don't know what "quantum leaps" you are referring to.
We reached several "Limits" many years ago. Mostly the 8.5' trailer limit.

3.Seeker: There are plenty of boats which meet your requirements from well establish companies with dealer networks and racing programs.
What is so awsome about taking an average design (Supercat 19 -dPN 69.0) and making it wider so it goes faster?
Bill constantly states that the key to "ultimate speed" is the width of the boat.
How fast would an M20 be if it were 12 feet wide?

4.Bill: "Wings do add to a boats righting moment to sail area ratio as long as the sailors trapeze off the edge of the wing. Wings that sailors sit on are comfort things only." NO DUH!! ALL wings are design to be trapped off.
Guess what else? TRAPEZES do add to a boats righting moment to sail area ratio as long as the sailors trapeze off the edge of the HULL.
TRAPEZES that sailors sit IN are comfort things only. Your boats come with trapezes don't they?
Was that comment of yours supposed to be a technical rebuttal?
Why won't you answer the man's question?
Why won't Bill Roberts design and Aquarius build a boat (IF18, F18HT, IF20) that would compete against other makers on even terms?
Why won't you prove your design?

Hello Sam-

You said:" They build boats for people who want to BUY "first to finish".

I was wondering how many ARC/SC22 owners you had personally interviewed/surveyed about why they bought their boat? I personally don't recall speaking to you. As far as racing I could care less about competing against any cat other than a 22' cat. If that means only Roberts designed ARC built boats presently that's fine with me. If you think its worth the $33k I have invested in my ARC22 to beat a slower boat, you over-estimate your importantance!

As far as why doesn't Roberts or Haberman build a particular boat; why don't you go out and buy what's available like the rest of us? Or better yet why don't you and Larry go out and design and build your own boat? Put your own time & money up as well and take the risk that what you end up with will be competitive or not as well as saleable or not to the "New"catamaran buying public.

I heard your whining scenario in the late 1960s/early 1970s when the Tornado was created and was made an Olympic class.

You say "Why won't you prove your design?" I think the question is why won't anyone else build a 22' cat to compete with the SC/ARC22? It was there before either the F18 or F20 I believe. Its been over ten years I believe. Its not like the boat hasn't been seen or heard of.

If you decide to take the risk; keep us advised as to your progress on building a proven designed boat. Include pics as well. Thats if you have the talent, genius, money and guts to do it.

thommerrill
FMS SC20 57
ARC22 2234
F25c 009

I think the "scientific" talk should be left at home. I don't think anyone has designed working airplanes, much less a widely used sailboat or rig. Until that happens, your various theories don't hold a whole lot of clout.

First of all, if you have ever sailed a boat with wings you should know that wings do help. I am not going to argue how efficently they help, but they do help control.

Second, major break throughs will not happen anymore with "beachcats". People like them simple. The vast majority of sailors will not buy new & possibly complex technology just to get a extra 2-3mph. Until you can land a tri-foiler on a beach, the majority of beachcat owners will stay with what works. Look at the H16. It isn't even that fast, but it sure is popular.

Simple + fun = sales
Complex + new = less sales
Complex + new + over $12K = almost no sales

If there were a market for "new breakthroughs" then someone would come up with something.

Mary,

Maybe I can give you a simpler (but incomplete) explanation:

The added weight of the wings is more or less offset by the reinforcements to the beam that will be necessary to widen the boat, so the wing's weight is not the big issue.

The main diference between increasing a given boat's width and adding wings to achieve the same total width lies in the contribution to righting moment from the leeward hull.

When you add wings, this contribution remains unchanged, but it grows when you increase the distance between the hulls.

The other main contribution to righting moment - crew weight times distance to centerline - remains the same in both cases.

As a consequence, the "wide" boat will have greater lateral stability then the "winged" boat - it will stay upright with more sail area or with more wind using the same sailplan.

Diagonal stability is also different, but this is another story.

Cheers,

Sam,
I'll tell you exactly why. It comes down to dollars. Would you spend $50,000 on tooling to sell 10 boats per year and make $1,000 profit on each boat. At that rate it would take 5 years just to break even. That is not smart business. All of the ARC tooling was built 20 to 25 years ago, long before there was a N6.0 or an I20 or an F18 or any of the other new boats. No effort was made to dodge todays 'normal' boats. The ARC22 came about because the SC20TR needed more pitchpole resistance. An old SC20 hull was given a nose job that stretched the front end 2ft and a quickie mold was made back in about 1990. All SC20 hardware, beams tramp,boards,rudders, mast, rigging, sails, etc fit the ARC22. This was a low cost project initially done in someone's garage. Production tooling cost big bucks. Right now the beachcat business is changing fast. What's in today is out next year. Its like the stock market; I think I'll stay out for now.
I have never heard or used the 'ultimate speed' comment. ARC products are not ultimate speed machines. The ARC 27/30 are the best family/daysailing boats going.
Barjack: When I was designing my first beach cats, the trailering width limit was 8.0ft. My first boat was 12ft wide. I talked to alot of sailors about what they wanted in a new boat in 1976 and all of the average size people were tired of being beaten every time the wind blew hard. The 8.5ft width limit came along in the mid to late 80s, about P19 time.
Seeker: Wider boats are faster as you know and weight sensitivity is less on wide boats. The average size person or team is competitive over a wider range of wind speeds on a wide boat rather than on a narrow boat.
The M20 would be awesome in a breeze at 12 to 13ft wide.
Evidently the Hobie sailors here in S Fla don't know how to use wings. I see them sitting on them all the time; never using them to trapeze from.
I have 5ft wings for my RC30.
I don't know what rebuttal you are talking about.
Here's a breakthrough for you. Ten years ago an F40 cost 1 mil+$. That boat has a demonstrated PN of 54. An RC30 has a demonstrated PN of 53.8 in 2003 and costs 1/15th of a mil and is only 75% as long. How's that for advancing "the state of the art"? An RC30 hull weighs 175 pounds rigged and painted; scale that down to 20ft and you get 52 pounds; scale it on down to 18ft and you get 38 pounds. Now, what company has the advanced technology? What company produces the lowest PN production beach catamarans in the world?

Thank you, Luiz. That makes sense. I am now visualizing a whole new concept. If we need to stick with the 8.5' width, what we need is a boat that has the capability of moving the entire mast toward the windward side of the boat and a hiking or trapezing wing or rack on the windward side, as well. And when you change tacks, you slide the mast to the other side and move or slide the wing or rack to the other side.

What do you think? And don't forget that you heard it here first.

You are asking a great development designer to bound his creations by "rules" in order to prove that he is better then other designers within those limits.

Whenever there are "rules" limiting what can be done, the design work is greatly simplified. If there is a max L.O.A., max beam and max sail area, every designer will start with those figures and a square bow and transom. You will never see a sloped bow like that of the ARC 21, for example, wich is not "rule efficient".

The final result is that artificial limits level designers of different skill level (to a certain extent).

Since this is perceived by the best designers as an unfair situation, it is only natural that some of them refrain from entering this kind of competition.

Creative designers are not challenged by working within artificial limits - they like the natural ones and set ambicious goals for themselves.

Cheers,

Mary,
What you described is a proa, so maybe I saw it somewhere else before...

Luiz,
I know it is the same basic concept as a proa, but I didn't know a proa moved the whole mast. I thought they just moved the rudder to the other end of the boat or something like that when they want to change directions.

But, of course, every time I come up with an invention, it turns out somebody has already invented it.

In your proposition, when the mast is in one of the hulls the boat should be called a proa and when it is "parked" in the middle of the beam it is a cat again.

Proas don't have "transversal travelling" masts and in fact it is not likely that anyone will develop one soon.

But what you suggested makes sense - it is like Team Philips with taller masts, using one sail in each tack. Not very practical, but still a great design.

(You know who loves proas and can tell you all about it - Chiodi)

I know I don't trapeze off my wings all the time because theres not enough wind to do so.

Ahhh, the great debate, and the often heard excuse "is not "rule efficient".

Tell me Luiz (and forgive me for contininuing with me cynical tone) how does one seperate brute force solutions from creative solutions if no limits are set ?

I mean without any limits Club Med, Playstation, Kersausons Tri geronimo and a whole lot of other boats would simply blow away all of the ARC cats right ? Would that mean that the are superior in design to the ARC designs ?

No true creativity is found in limiting rule systems like A-class, and to some extend F18 class. Here there is no easy way of the brute force methode, just the path of refinement.

The flyer A-cat design was able to to make a mark in the A-cat class under the given conditions. Spinnaker shapes development jumped in the F18 class. Anyone with a model 95 spi will be blow away by new spi designs. In open classes they would just have grown bigger not more refined.

To look more closely at your bow example. If a straight bow is better for a given maximum length of hull than when will a non straight bow be better than a straight bow ? Think about it, if it is faster for a given length than what is holding it designers back from using it in their designs. If the max length is holding it back than by the same measure the maximum lenght is ALSO holding back the straight bow.

Same applies to sloop rigs, If the jib is such a aerodynamical bad thing than why haven't both the tornado class and F18 class evolved into uni-rigs with just the mainsail of maximum size ? I mean there are not rules prevent crews from sailing with less sails than allowed ?

The only answer is that the used setups are faster. Maybe not very much faster but faster nevertheless than their round bow and uni-rig alternatives. Now some will argue that when you place the jib area into the main that you'll have a better boat. But then I answer that when I fit a jib to this new setup I will even be faster then the one without a jib.

Don't you see that this is just a theme that can be repeated indefinately when there are nor rules ? However it doesn't really change the basic conditions underlying the performance. What is better under limits will be better when scaled up or down.

Think about it.

only resently the A-cat banned hydrofoils, but this happened without any design with foils proving to be faster. Some classes still do allow hydrofoils and we'll just have to see wether foiled designs are faster in these classes.

Wouter

Wow, it is so much fun listening to all you engineer guys argue. It makes me wonder -- if they put you all on one of those Survivor Islands, do you think you would all be able to agree on how to build a shelter?

Sorry, it must be the moon phase. I am feeling very contrary today, too.

Bill,

You talking about the CFR20 versus Tornado example that has been your favorite for some time now. What they did wrong is what most do wrong; the design looked at various ratios as being independent ratios that would all lead to higher speed. While doing so they overlooked the interaction between ratios and decreased rigting related power more than they decreased the drag. In the lower wind speeds righting is not limitind power and there the boat was fast.

The fact that a design screwed up here doesn't mean that only boats with increased in both area to weight and righting to area can go faster. It is one solution that works but not the only one.

I expect the M20 to go the same way when the design stays at 2.6 mtr width.

Wouter

Bill,

You may want to look at your numbers again.

I see you are use the third order power in your following statement

"An RC30 hull weighs 175 pounds rigged and painted; scale that down to 20ft and you get 52 pounds; scale it on down to 18ft and you get 38 pounds"

When you do this than your 18 ft boat will only have 20 % of the displacement of your RC30. Now when we take 75 kg's for the 18 footer (a-cat) then your RC-30 has a mimimum displacement of 375 kg's = 827 lbs.

After subtracting 2 fully fitted hulls of 175 lbs that leaves 477 lbs for just the beams, mast sails and trampoline. A bit much don't you think ?

You can't apply your 3 order shrinking formula here as the primatic ratio of your RC 30 hull is not the same as that of the imaginairy 18 footer. You example sounds good by has no meaning in the real world as cat design formula's aren't so easy.

Wouter

Seeker,

contact Tom Haberman at Aquarius Sails (.com) ...he e-mailed me a pre-production photo of a new Arc 17, complete with spin pole...it looks way cool; although I'm admittedly biased being a big Supercat fan.

Tom had the ARC17 in the Florida panhandle back in February for some testing. I saw it then. It is a nice looking boat. It will interesting to see it compete against the I17R.

Don

Wouter,
While on the subject of whats new in beachcat technology, I was suprised you made no mention of the Ventilo Zipo (http://www.ventilo.ch)or Mattia Dynacat and all those photos on your website. These have a totally diferent rocker profile to any other cat I have seen and have flat, assymetric hull bottoms. Have you any news as to how these are performing in races, or are they still too new to have any numbers on the scorecard?
They may be fast in certain conditions and crap in others - I don't know. How about putting the url to the photos up so we can get some comments from other people including Bill Roberts.

Simon Fisher

I have often thought that a sliding trap rack could be a cool thing on a cat. [img]http://www.intcanoe.org/cnew1.html[/img] [img]http://www.intcanoe.org/c3.html[/img] [img]http://www.intcanoe.org/a5.html[/img]
Hmmm, images aren't working. Try the attached files.

'nother image attached

3rd image

I was at Moss Landing the other day, near Monterey, CA. I saw what looked like a 16' production Proa. I was out of photo film, but who needs it with the internet! Attached is a picture of the Proa and here is a link to see it. California Coastline . com

I couldn't hang with engineering so I can't address the specifics Bill & Wouter and everyone else has layed out.

I know my SC17 is an excellent sailing boat and I love it. I have also seen the photos of the new ARC 17 and spoke with one of the "test pilots" from Pensacola....apparently it is awesome....I've made some mods to mirror the ARC (sq. top main & high aspect jib), now if I can just get it dialed in.....

Can someone give more details on the new ARC17? Links to pictures? I love my SC20 but I think it would like a younger sibling!

Eric F
SC20
H16

wow. Now I would watch that! (or would I be on it?)

The way I see it it will either be a little palace or a monster of a shack that leaks everywhere.

All though Bill and I don't really have a disagreement. I mean if he builds shelters like he build cats (Big, strong and fast) than he will not get any comments from me !

The discussion between Bill and myself is pretty much a debating discussion, all in good fun. I'm sure Bill and I would grap a beer afterwards if we were doing this face to face.

Not that serious really.

Wouter

Wouter

http://www.geocities.com/f16hpclass/F16HP_boat_show_ventilo_zipo.html

To answer your questions

>>I was suprised you made no mention of the Ventilo Zipo (http://www.ventilo.ch)or Mattia Dynacat and all those photos on your website.

That is because I partly forgot about then but also because if I had remembered then I would not have used these as they have still to proof themselfs.

Up till now I haven't seen any of these being listed in a the race result of any regatta. They are quite new indeed.


>> Have you any news as to how these are performing in races, or are they still too new to have any numbers on the scorecard?

I think so. I also found that people interested in them were in doubt about wether to go for them or not. That is people that contact me about them, they eventually went for a more conventional design.


>>How about putting the url to the photos up so we can get some comments from other people including Bill Roberts.

See beginning of the post.

Bill and others have been discussing planing designs many time before however.

Wouter

"Who knows of a 20ft beach cat built in Florida with prepreg materials, a superlight boat, unirig with spinnaker, everyone thought it was going to be a rocketship. It was very fast in light winds, 5 knots. When the winds got up to 10 to 12 knots, other 20ft boats pulled even with it. When the winds got up in the 15 to 20 knot range, the superboat fell behind. What is wrong with this design? What was the mistake, the error, the oversight in this boat's design?"

Right, I`ve followed the line of argument between Wouter & Bill, and I`m intrigued as to why neither of them have seen the obvious : Take both of their ideas / theories & build a boat that conforms to both sets of ideals : Wide is good, helps lighter crews hold down more power. Light is good, helps reduce drag. Combine the two & you have the best of both worlds. Perhaps that`s why everybody compares every other boat to the Tornado : It has all the hi-tech material advantages making it stiff & light, & is also wider than other boats in the same / similar class. Seems the Supercat range of boats are heavier, so need more sail area to compensate. Due to this they are more powerful, needing a wider platform to compensate for this.
Why not take the Supecat design philosophy, reduce weight using modern construction methods (the cost has reduced over the years), and you`d have a serious monster machine.
No need for new moulds & tooling.
If width is a problem for towing, design folding / telescopic beams that are easy to dismantle & reasemble.
If the R33 can do it, so can other designers / builders.

Any takers ?

I like it, but it could use some nice, cushy padding. I can see some advantage, too, on the starting line, if you slid the thing out to leeward.

Mary,

Your post reminds me of this crazy guy who had this nervous disorder about his boat getting hit on the line. Not altogether unreasonable with me out there but what was funny is that he'd have this huge telescoping pole that he'd switch back and forth to leward while racing. It annoyed the hell outta us, but he wouldn't remove it despite our promises that we wouldn't get near his boat. He finally was forced to get rid of it halfway through the day when he poked it through someone's sail

Wouter,
Scaling hull weights by length to the third power is standard naval architectural practice. It is not something I came up with.
The RC30 hull weight of 175 pounds is a carbon hull. The three beams on the RC30 are aluminum. There are also other parts to consider like ropes and pulleys and wires and spimmaker poles and boards and rudders, etc. All up with sails the boat does weigh 900 pounds. Oh, that includes an outboard motor bracket too. Yes, the other parts of the boat do weigh more than they could but they are not made of carbon. If everything else was made of carbon as the hulls are, one could reduce the weight of the boat by at least another 100 pounds and 'double the price'. If you were the builder, which way would you go? More of these boats are used for recreation than racing. Some of them are even built with fiberglass hulls. The RC27/30 concept is not maxed-out by a long shot. All that is needed in more money.
Wouter, you speak loudly for someone who has never put a boat into production and has no record or facts to stand on. You speak out without knowing all the facts. I find that distasteful.
Bill
Bill

>Scaling hull weights by length to the third power is standard naval architectural practice.
It is not something I came up with. <

Could this be related to volume changes with the third power?

Hi All

Some of the early B-Class development cat designs had sliding seats ,-read Reg Whites books -in U K -on early C-and B class development--time frame 60s -70s ,-
PROBLEMS ARE WEIGHT -complexity and stationary for -aft location .-

One of the most interseting versions of that were on the later 80s Worrell designs in the open class -
One had a 10 ft fold up rack mounted on the outside edge of each hull on a traveler ,-
It looked a little like someone had gone wild with an erector set and put it on a Harken traveler .
--but ,-simple math is ,-put a 200 lb crew 10 ft out further 200* 10 -thats 2000 extra ft lbs of righting moment holding the sail forces ---talk about more beam !!

Another version of 10 ft fold up rack just used an alum. pole and mesh seat at the end --kind of reminded me of a giant fly swatter in appearance --
Both were very effective and fast -

Seems most everything has been attempted in one form or another ,-its refining those ideas and concepts into working form sometimes requiring connections of other ideas and invention that eventually makes them viable .--its fun stuff,-but expensive and time consuming ,-and not alaws marketable .
There are some great books on curious yachting inventions thru-out history ,-and room for more -one on cat design or multihulls would be very marketable today !!
Patten searches are a great source ,and fasinating looking at old diagrams dating as far back in the U S as the early 1800s -
Recall the ill fated giant multihull round the world racer with two masts ,-one on each hull ,-as the tri foiler has ,-You can find this pattened as applied to a square rigged ship in the early 1800 for example -many many more
The same ideas brought back in modern form and refined again and again .-eventually they work !!

Wouter,
I have never mentioned the CFR20 or M20 before on this or any forum before. One thing I am trying to point out is that boat performance can be calculated long before the boat is ever built. That's what engineers do. You seem pretty keen on these ratios now. This is the first time I have heard you mention them. The approach that I take to design a faster boat, higher sail area to weight ratio and higher righting moment to sail area ratio, does work for higher performance boats and it is the 'low cost way' to get there. This super light weight boat with all carbon parts approach is another way to get there but it is the high cost road. For example: Let's imagine a 20ft boat built in an autoclave that is made out of materials far superior to the Tornado such that another 100 pounds is removed from the boat weight. Lets's assume that the new boat has the ratios such that it is much faster than the Tornado. This new boat built out of these super materials and super construction methods will cost much more to build than a Tornado. When this new boat costs 1.5 to 2 times as much as a Tornado, how many of these new boats are you going to sell?
Here's another ratio for you, Wouter. If the pitching moment to restoring moment ratio had been calculated for Playstation when it was only on paper, the boat would have been 125ft long in the first place.
Bill

How about modified/taller elevator shoes from the '80s era?
Might be awkward getting around the tramp or beach?
Therefore, lower leg extentions could fold/pop off the lower legs.
Stilts anyone? With velcro toerails?

Or maybe heavier heads. How about wearing helmets made of lead?

I like that idea! (Although some of us have probably been accused of having fat heads to begin with. )

Yes, that is why the displacement of Bills 18 foot imaginairy hulls is so small.

Wouter

Bill,

>>Scaling hull weights by length to the third power is standard naval architectural practice. It is not something I came up with.

So is using Froude law for max hull speed but we all know that that is pretty meaningless when looking at catamarans.


>>The RC30 hull weight of 175 pounds is a carbon hull. The three beams on the RC30 are aluminum. There are also other parts to consider like ropes and pulleys and wires and spimmaker poles and boards and rudders, etc. All up with sails the boat does weigh 900 pounds. Oh, that includes an outboard motor bracket too.

Okay so I've I shrink that 30 ft platform without any changes to an 18 foot platform using the 3rd order theorema than teh 18 foot platform would only weight (18/30)^3 * 900 = 0,216 * 900 = 194 lbs = 88 kg's and that is including weight saving thingies like motor brackets and a third beams. And this 18 footer is still a double hander with jib and spi.

Doesn't this strike you as being a bit odd ? Could is be that the 3rd order rule of thumb is being misapplied here ?

Sure the 3rd order is very neat when looking at cargo ships that are limited in their overall weight (dominate by the weight of their cargo) by how much displacement (volume) they have but sports catamarans aren't cargo ships. Sport catamaran platform weight is mainly determined by strengh and stiffeness considerations.

I'm only saying that the 3rd order rule of thumb can't be applied to catamarans.


>>If you were the builder, which way would you go?

I may go your way if I was designing a fast cruising boat and my own way when designing a fast regatta boat.

I would just as luiz wrote, Go lighter, more sailarea and wider simulatiously when I could and go lighter and less sailarea when my width and length was limited.

I will never go heavier. Nor will I ever reduce width unless I'm forced to. When limited in width I will go as light as possible and adjust my rig and area to accordingly.


>>The RC27/30 concept is not maxed-out by a long shot. All that is needed in more money.

Which is exactly the direction in which we don't want to go.

>>Wouter, you speak loudly for someone who has never put a boat into production and has no record or facts to stand on. You speak out without knowing all the facts. I find that distasteful.


You sound like my old professor Bill, (and I cornered three of them in my time) he too had convinced himself that new discoveries and advancements were made by people other than young ambitious persons with no track records.

If only the Wright brothers listened to wise old men, if only Einstein had kept his weird fantasies for himself and had stuck to conventional wisdoms like 19th century contemporary physics like everybody else.

I'm not disrespecting you here Bill, I'm really not. But the fact that your 30 years ahead in life and have produced a series of boats in that time doesn't say anything about who is right and who is wrong. Mathematics and Physics don't work in that way.

So we come back at the A-cat example.

Answer please how an modern A-cat is faster than an A-cat of 10 years ago when it now has the same width, the same sailarea, a taller mast and a much lighter platform.

This example alone defies your statements. According to you is should be slower because it now has less righting moment per sailarea than before and her width was not increased when than the mast was made taller. How can it still be faster ?

Their is only one modification left that must have been more than enough to offset these negative effects and to such an extend that enough is left to make the whole setup faster and that is ....

Wouter

That's great to hear...I am glad Tom picked the SC17 to revive...Has to be the best "boardless" beach cat ever designed in the 16'-17' range...Faster, Stronger, Stiffer, Better Balanced, Points Better, Easier to Tack, Near imposible to pitch pole. All the fun of the other 16'-17' "beach" cats, with none of their inherent problems.

The SC17 made sailing fast fun, instead of work. Marketing, not the designs themselves, have (IMHO) always been the Achilles heel of the Super Cat Series. I wonder what would have happened if Hobie Cat (instead of Boston Whaler, which seemed to withdraw from the market prematurely) would have bought the designs from Bill when they were first introduced? With their beach oriented marketing machine behind his designs the SC17 might have been able to find it's true potential in the market place. The outcome of that scenario will never be known.

It is my wish that Tom has great success with the up and comming ARC 17...hope he puts some photos on his web site...don't make it a covert operation...LOL... might stur up some interest if you did a little picture story on the development of the "new ARC" from the "old SC17" Can't wait to see it...

Wouter,
Here's an example of what I am talking about,"you frequently go off half **** and don't know all the facts".

>>And as for "Square top mainsails: Nothing new! If you look in an aerodynamics text book" Both Arvel and Bethwaite have completely debunked the use of aircraft earodynamics to sails. It turns out that soft cloth sails behave totally different from aircraft wings and squaretops are used for different reasons than tip vortexes. And if you really want to now any aerodynamics book will name and eliptical wingtip as the perferred wingdesign when looking at vortexes alone.<<

I didn't say the squaretop had anything to do with wingtip vorteces. What the squaretop sail/wingtip does is prevent spanwise flow down the low pressure side of the sail that originates from the sail top where the sail is narrow, where the leech is forward relative to the sail below. On a pin head sail or pointed wing tip the air exiting the sail/wing on the pressure side near the tip turns 90 degrees at the trailing edge and flows or is pulled spanwise down the sail to an area immediately below where the pressure is lower. Air wants to run downhill just like water. The air on the pressure side of the sail near the tip is at a higher pressure level than the air on the leeward side of the sail at say 50% chord a foot or so down from the narrow leech above. The pressure side air at the leech sail dives vertically down the sail, leeward side into an area of low pressure on the leeward side. This spoils the delta P across the sail at the top and reduces the span effectiveness of the sail or wing. The square top moves the leech aft and this delays the opportunity for the air exiting the windward side leech to flow spanwise down the sail to a low pressure area immediately below. With this spanwise flow diminished/eliminated, the span of the sail/wing is more EFFECTIVE, it more closely approaches the ideal lift for a given span. You could say the square top sail or square wing tip is an aerodynamic dam that prevents a parasitic spanwise flow which reduces the effectiveness of a sail or wing. It has nothing to do with tip vorteces.
Bill

Bill,
Is there any way that you (and all these other engineers) can put all this stuff into lay terms so the rest of us can understand it? As somebody already mentioned, it kind of excludes us normal people when you guys go into all this technical jargon.

I'll bet that if I understood what you were saying about vortices and spanwise flow, I could capsulize it in a sentence that people could understand. Unfortunately, I don't understand.

I have thoroughly enjoyed this discussion except the one comment excused by someone under the influence of the moon. It is good to see passion and mathematical data liberally posted without fear of the results often experienced on the other forum. To those of you intimidated by the formulas, read them anyway, or paste them into a file you can look at later. I have pretty good sized files from both of these fellows. One day you will see what they mean, and you will get there a lot faster if you do the work to understand them. Bill and Wouter are a lot smarter than most of us, but so was Aristotle. It is perfectly obvious that heavy objects fall faster than light objects and that the earth is the center of the universe....
Einstein said that the Creator was subtle, not malicious. I believe Wouter is trying to point out that subtle design changes with an eye on all the other aero/hydrodynamics can yield dramatic improvements. And indeed they have. Many of the things Wouter has discussed can be applied to your own 'dead boat' with encouraging results.
To Wouter: The specs I have seen and a witness say that the M20 is about 9.5' beam. What is your statement that it is 8.5' beam based on? If 8.5' beam for the M20 is an error, wouldn't that substantially change your analysis of the boat?
To Bill: (relax a little, this is as upset as I have seen you) When the big cats went for the run around the world in 2001, there was a thread (old forum) where you calculated that the over 100' boats had fineness ratios that should allow speeds of over 50kts. The fastest I saw anyone goes was about 35kts. In an earlier thread you had introduced this fineness ratio as a factor in the old LWL formula. When others inquired about the 'fineness formula', you gave no reply. Am I in serious error about the top speed of the megacats? Could you explain about the fineness ratio? Also, you recently stated that the power (force, KW, hp) in the wind varied as the square of the velocity of the wind. My old DOE manual for home windmills gives a formula for wind power that has a cube on the wind speed. And that is the understanding most my landsailing buddies have. Did I misunderstand your statement?

Sincerely, and best regards to both of you.

Boeing - US Government & Wouter
Northrop - Bill Robert

The time: WWII

Things were shaky in the world and the US was looking for a new longrange bomber....
Boeing can to the table with the B17
Northrop with (model # evades me at the moment) the Northrop Flying Wing.

** No disrespect to any ones fathers or friends that servered in B17s in WWII (friend of my fathers was a tail gunner and he made it home) **

Both Aircraft were tested by the Army and by Army pilots that had never flown a flying wing. The flying wing out performed the B17 in all areas except two:
1) It was going to be dificult to mount machine guns on the flying wing with the large flat wing surface.
2) The US government was in bed with the Boeing Corp.

The result is history "the flying fortress".... So what's the point... the better plane was not the popular choice. How many of the men we lost, could have come home if they were on the flying wing.

My last point: When Boeing received the bid, the Army was ordered by the Government to distroy all Northrop Flying Wings used in Testing. So they flew them to the dessert and gathered them alltogether (landing gear up) and drove large bulldozers over them to crust them. HA HA! they didn't crush, the Flying Wings supported the weight of the bulldozers and eventually had to be cut up (try to drive a bulldozer over a B17 and see what would happen. - FYI: the Bulldozer incident was never released for public knowledge.

??? O'yes, look at the new "State-of-the-Art" Aircraft today... FLYING WINGS!!

Show me an I20 or A-Cat in 20 years that looks as good as my SC20TR today, and I will eat my hat.

THE REAL ARGUMENT BILL... The numbers on the boats - it is killing them that they spent $12K+ on a "Go Fast" only to find that a 20 year old boat timed out over them.

I guess that would be me.

What I have been trying to say, in various ways, is that all of us regular people out here think that what you guys are discussing is probably very important, and we would like to know what you are talking about, but we need an interpreter. Nobody wants you guys to stop discussing and debating and arguing in your own language. But isn't there an engineer out there who can convert some of this into lay language so the rest of us can participate, or at least understand?

I could translate it. Thats technically what my job is... to relate technical information to people who aren't technical so they can understand it.

Its quite difficult actually.

I wouldn't know where to start though... Wouter crams a lot of jargon into his blogs :P

let's split it up - you take Wouter and I'll take Bill.

Thanks guys -- and it isn't even Mother's Day.

:Technical Translation of Bill's Post:

the idea behind a square top is to reduce the air flowing downward (i.e. parallel with the mast and toward the water) from the top of the sail. As most of you already know, there are different pressures between the windward and the leeward side of the sail. The windward side is more normal to the regular air pressure around the boat but the leeward side actually creates a vacuum. This force literally sucks the boat forward.

On a pinhead sail, because the sail is so narrow and the leach is at such a forward angle near the top, it is easy for the higher pressure air on the windward side to curl around the sail to the low pressure side at the very top. When it does this, this higher pressure air tends to fall downward (i.e. gravity) in the vacuum on the lee of the sail and disturbs airflow and pressure for a significant portion of the top of the sail.

Enter the square top. The head of the sail is now horizontal and in line with the direction of air flow. At the highest point, the leech is not so close to the luff and the angle of the leach is more verticle. Furthermore, the point at which the air detatches from the back of the sail is also farther away from the draft where the largest difference in pressures reside. (The draft is generally the deepest part of the sail shape and is normally vertical and in the front 1/3 of the sail) . The result of all this is that the wind can detach from the back of the sail more cleanly without as much tendancy to curl around to the leeward side. The top of the sail can generate power more efficiently because the vacuum is not as disturbed.

So you are actually translating Bill? Or is this you? Either way, it is a major improvement.

This gets into the suck versus push thing. My father, who was the best sailor I have ever known, said it was push, not suck.

Not fair, you got the easy one :P

I gotta wait till tonight to translate.... plus I've got a mindsplitting headache and our friend Wouter tends to make them worse

I'm trying to translate Bill's text (I hope I got it right!). I had no idea that the square head was doing all this.

Hi Steve,
Relative to your question about the top speed of the big cats: The most important design characteristic of these around the world racing catamarans is safety at speed. This means that these boats have to have the capability of sailing at speeds of 35 or 40 knots with adequate safety margin. At high speeds how does a catamaran get in trouble? It pitchpoles! What makes a catamaran pitchpole at high speed? Ans. A rapidly rising hull drag characteristic. How do you delay this rapidly rising hull drag characteristic. Ans. Make the boat loooooong! Then the theoretical max boat speed is well beyond the speeds the boat will see in actual use and the probability of pitchpole is greatly reduced. Also the pitchpole resistance or restoring moment of the hull is significantly increased with longer hulls. It is a conservative approach to a situation where peoples lives could be in danger and it greatly increases thr probability of success of the whole effort.
Fineness Ratio: Hull fineness ratio is simply LWL divided by max hull width at the waterline. The equation in many books for the hull speed limit of a displacement hull is:
Vel max = 1.4 X sqrtLWL. This equation seems to work for keelboat monohulls that have a hull fineness ratio of around 4:1 or so. In this form it sure doesn't work for beach cats. What I have found is that for displacement hulls the 1.4 coefficient varies with hull fineness ratio. For beach cats this coefficient varies between 4 and 5 depending on hull design. This says that a 20ft Tornado will have a max top speed of ( Vmax = 5 X 20**.5) or
22 knots. This relationship has served me well in analytical studies.
As far as the width of the M20 goes, the 9.5 or 9.7ft width is correct. It is disassembled to trailer. The boat has a 34ft tall mast and all the sail area in the mainsail so the center of effort is much higher than in the Tornado sail plan. The boat is 130 pounds lighter than a Tornado so the platform righting moment is well down from the Tornado, like 40% less. Add to this that the M20 crew lever arm is shorter than the Tornado and one can quickly come to the realization that the the M20 system is much overpowered (overturning moment/righting moment ratio) relative to the Tornado. If the boat had more righting moment, the crew could drive the sails harder and develope more sail thrust and make the boat go faster. It is that simple, f = ma.
Wind Force and Wind Power:
Wind force is a function of velocity**2 and has the units of pounds force.
Wind power is wind force times velocity and has the units of ftlbs per second. Wind power is a vel**3 function.
Sometimes people use these terms interchangeably but in the context of what they are saying you can usually understand what they mean.
Bill

Anyone got a sc20tr for sale?

Hello Bill-

Along time ago [20 years approx] we had a conversation about you cutting the nose of a SC20 and then stretching it out about 4 feet. You then took it out and tried it on both tacks with a noticeable difference. I am really curious as to where the theory and practical experience merge into the final design. I would think the R/D would progress until max velocity/stability is reached. Of course I know back then we didn't have computers at home. I believe there was a RC24 then the SC22. Was the RC27 part of this development from that experiment?

thom

Thom,
I did stretch a SC20 hull to 23ft once as part of a hull fineness ratio study/test. I put the boat together with a standard 20 hull on the other side. I ran speed tests on this system with speedos many times. I remember that when the boat would go 20 on one tack; I could come about and load the longer hull and the boat would go 24 or 20% faster.
The ARC22 has the bows from the 23ft test hull, finer entry and reduced bow wedge angle. The 22ft length was chosen because by moving the transom forward 2ft one could have a 20ft hull with lower drag the 22 bows all designed for ocean sailing. That boat could be built today out of the 22 molds.
Bill

Like this thread offshoot better ,-

Ya ,-think the whole disco era is responcible for numerous problems today ! Maybe the conformity and ready acceptance of regulation and incompetent govn controls begane there -
{joking too }

dance till your stupid ,--kind of sums up that era .
big heads big hair platform shoes and obnoxious music -

do like some of the "current music out ,--Big Yellow Taxi ,-some things have integrity and a timeless quality -art music theatre , invention etc,-
this is born of creative human freedom at work ,
We see it in excellent cat design too.

As Solzhenitzyn said in 78 --"This ascension will be similar to climbing onto the next anthropologic stage. No one on earth has any other way left but -- upward. "

Hope it continues ,its up to us !-
Carl

World Split Apart -Harvard Commencement speach 78 -

http://www.columbia.edu/cu/augustine/arch/solzhenitsyn/harvard1978.html

Gosh, Carl, and I thought the engineers were hard to understand. Guess I need an interpreter for you, too.

Don't forget the dictionary...

thom

Yeha Carl, anything you said was over my head there.

Do I need to continue with the 70's theme and be high on some kind of drug to understand it?

I was only half following the engineer-speak, but the disco/Solzhenitsyn post seemed perfectly clear

This is one of the coolest threads we've had here in a while.

Also it's good to have Bill Roberts back. He's been conspicuous by his absence(sp?).

David Ho
TheMightyHobie18 1067

OK - so who's translating for Carl?

I don't have the time to continue this further.

Tip vortex, flow from high pressure side to low pressure side, Leech vortexes and the shape of the top of the mainsail are all linked to the same processes at the end (tip) of a lift creating section.

A sqauretop main may reduce leech vortexes but will increase the magnitude of tip vortexes. They are all linked.

But the main point still remains that squaretops mains of equal size than pinhead sails aren't that much faster in top speed, they mainly behave better and quicker in gusts and lulls. And yes, this is the outcome of real life tests using identical platforms and well known sailors. Of course with a squaretop main you can put more area in the main but that is that brute force approach again which is skewing the picture.

Now, I much give up my participation in this debate for reasons of time. Till the next time Bill.


Wouter

>>To Wouter: The specs I have seen and a witness say that the M20 is about 9.5' beam. What is your statement that it is 8.5' beam based on? If 8.5' beam for the M20 is an error, wouldn't that substantially change your analysis of the boat?

I confirm that 9,5 feet is the right number and not 8,5 mtr. I have seen quotes from 2,6 = 8,5" to 3,0 mtr = 10" in the past but Texel just remeasured the M20 and it found 9,5". (I know it is not used in the system, but it is measured anyway)

Does this change the analysis. In relation to 8,5 mtr. boats "may do so, yes", I relation to the 10" wide Tornado, no.

This dependent on which reference we agree upon.

My argument was based on choosing a reference platform and modifying it. Than to make conclusions on what to expect as the result of the mods.

Take a tornado and lets make it lighter en less wide. This will lead to a boat likely to preform worse in trap condition. If the Tornado is made lighter but keeps the same width than it is has a good change of performing better.

However all is determined by the magnitude of the changes. 1 inch width reduction and 100 lbs weight reduction will have a different outcome than say 2 feet width reduction and 1 lbs weight reduction.

And here is where the main point of my argument is to be found. All of these aspects are linked ; the net effect of a certain reduction here is partly determined by a reduction (or increase) somewhere else. So when modifying important ratio than the ratio between the ratio itself is also important.

In this sense the statements made by Bill about width and weight are a subset of the more general case that I expressed. Bills way of improving speed is correct but it is not the only way of improving it. And there is the casue that started the debate between him and me.

In simplere analogue terms.

Bill argument is analgue to claiming that to go faster in a car you must use a bigger engine and preferable place it further back to put more weight in the driven wheel to avoid slipping.

My argument said that you could go faster with an even a smaller engine than before and also keep it in the same place as it was when you are succesful at sufficiently reducing forms of drag or resistance to acceleration. Examples of this are lighter wheels and a lighter flywheel in the driving system (not a lighter car ! mind you) or even reduced frontal area to reduce aerodynamic drag which reduces the amount of power available for accelerations/speed.


In the first example you increase the important factor that caused speed or accelleration. (Brute force methode)

In the latter example you analyse and try to optimize the ratio between important factor in such a way that the overall governing ratio is improv ed. Of course the first example implicitely does the same trick but without explicitely refering to it or even knowing about it.

On the starement of :

>>recently stated that the power (force, KW, hp) in the wind varied as the square of the velocity of the wind. My old DOE manual for home windmills gives a formula for wind power that has a cube on the wind speed. And that is the understanding most my landsailing buddies have. Did I misunderstand your statement?


The energy contained in a GIVEN (and constant) volume of fluidum is relative to the windspeed squared.

The energy contained in a volume of fluidum flowing through a given (and constant) stationary area is relative the windspeed to the 3rd order or cube.

Of course both windmills and sails are more closely described by the second case. When the wind blows harder than a bigger volume of fluidum is blow past the energy harvester which are sails and windmill wings. This volume increases lineairy with windspeed and it constant volume enery containment has increased with the sqaure. Together they from a 3rd power. as X time X squared is = X to the 3 rd power.

I hope this explains things

Wouter

>>Fineness Ratio: Hull fineness ratio is simply LWL divided by max hull width at the waterline. The equation in many books for the hull speed limit of a displacement hull is:
Vel max = 1.4 X sqrtLWL. This equation seems to work for keelboat monohulls that have a hull fineness ratio of around 4:1 or so. In this form it sure doesn't work for beach cats. What I have found is that for displacement hulls the 1.4 coefficient varies with hull fineness ratio. For beach cats this coefficient varies between 4 and 5 depending on hull design.

This formula of Vel max = 1.4 X sqrtLWL is directly derived from the Froude law and make a link between the wave length of the created (bow - stern) wave system and the waterline length of a given hull.

This formula givens the speed at which a given length hull needs to travell throught the water in order to have a single wave spanned along it hulls. With a crest at its bow and a crest at it stern.

In heavy vessels this wave system is a huge boundery as drag suddenly increases rapid at this speed and hardly any engine and no sailing rig is powerfull enough to overcome this rapid increase in drag.

Please note here that the factor of 1.4 (in this form of the formula) is a constant determined by the way waves on a water surface behaves. It has a very clear physical interpretation, A free wave travelling at the given speed has the same wavelength as the hull waterline length. The adjusted factor of 4 to 5 HAS NOT. This adjusted factor is nothing more than an imaginairy factor that someone dreamed up to make the froudes law useable for situations where it really doesn't apply. Such a case are catamarans. What has been done is that the end result has been determined and a factor is calculated from that that gives this end result at a given speed. This is a circular reasoning.

In catamaran design the situation that Froudes law describes (wavelength of bow-stern wave = waterlinelength) is found at the speed which the formula Vel max = 1.4 X sqrtLWL gives. However because of the special qualities of the catamaran design (maily very light weight) this wave system is much much much less significant from a overall drag point of view. In fact the drag is there (make no mistake about that) but it's magnitude so small in comparison to the other forms of drag on a catamaran design that its effects are not noticed on cats. Cats simply power through into the force mode state and continue to accellerate much longer till they reach much higher speeds where the other forms drag have grown to such a magnitude that they are big enough to stop further acceleration.

Simply put adjusting froudes law to cats is useless. Froudes law works very well in heavy displacement vessel (Heavy crusing cat design MAY be included here) but in general it is misapplied in light weight vessels like sport cats and some navy ships. Continiously adjusting the factor to make the formula work is fooling oneself.

Bills eaxmple is correct with the excepting that bill doesn't account for the reduction in overall drag due to the same reduction in weight.

The following statement

>> The boat is 130 pounds lighter than a Tornado so the platform righting moment is well down from the Tornado, like 40% less.

is simply misleading.

It the combination of Platform and CREW that is important here and not the platfrom alone. When looking at this combo the righting moment has only been reduced by 13 % and not 40 %.

See the math (in SI units) ; assumption centre of effort of the crew id 1 mtr (3 ft) up from their feet.

Tornado + 150 kg crew : 170 kg's * 1/2 * 3.0 mtr. + 150 kg * (3 + 1) mtr = 855
Lightweight Tornado + 150 kg crew 170 - 60) kg's * 1/2 * 2,9 mtr. + 150 * ( 2,9 + 1) = 744,5

744,5 / 855 = 87, 1 %

Wouter

>>I wouldn't know where to start though... Wouter crams a lot of jargon into his blogs :

Sorry,

I will try to do less of that in the future.

Wouter

Ohh, I'm quite exited to see how you will do it Maugan.

I'll be watching this thread closely over the next couple of days.

Wouter

Sorry ,-
typical designer ,-off on a different tangent -as usual

Really enjoy cat design posts --own a Supercat so am a big fan of Bill Roberts ,--also the same last name as mine ,-so in the past I,ve recieved questions from others that confuse us ,--that I refer to Bill on specifics of cat design .He has a tremendous working knowledge and readily available applied engineering formulas . --great stuff and really appreciate his posts .

Wout has done a very good job along with others input on the F-16 .

interpretation -
responded to earlier posts on sliding seats and their history applied to cat design .
The post commented on sliding seats and earlier W-1000 innovations of 10 ft racks mounted on travelers .also commented on patten searches and concepts and ideas over time ,--

Sail 7 seas responded with a comment on platform shoes etc of the era -
the return post was an attempt at a humorous responce on the era also with some added philosophical comment ,off on a different tangent -thanks Mary

Kev ,-thanks we are the same age so share similar experience and thoughts on numerous subjects -

Dav Ho --always good to read your posts --
It IS one of the best threads in a while
each have their own experience and perspective ,
Not sure if its a cultural thing but Wout often comes off as Bill noted as being "distastfull" in opinions offered .
needs to work on that as I do ,--thats why its recognized.
MAHALO
from a former Kaneoe beach cat sailor ,

Thom ,-- thanks ,-can;t see or spell worth a %$#@@#)%

.-Mg H-17 --It helps --but not recommended .

Been attending graduation cerimonies --so thought the Harvard speach from 78 that I ran across in other articles was timely and an interesting look back at the era --
then of big shoes --big hair -etc as sail 7 seas noted -
read it if you get a chance --link on the post
its fasinating -

"we have no where else to go ,---but upard on the evolutionary scale ,--

whew ,--

conversely also liked this web site -
http://stupidity.ca/

have fun
Carl




-

Mary,

It may probably be best if you named the individual parts you find yourself struggling to understand. Otherwise there will be to much to write.

vortices :

really something common. That funnel that you see when you empty your washbasin is a vortex. A tornado is a very large vertical vortex. Vortexes on the tip of wing (or any object that has a high and low pressure side) are just invisible horizontal spinning (around centreline) volumes of fuidum (air) and are called Tip vortices. However similar spinning volumes can be found on leading and leech edges as well depending on the design of the object. They can also be found behing chimnees and buildings. A vortex is a special type of turbulences. In general it is turbulence with a highly predictable and uniform shape. General turbulence moves all over the place while vortices can be very clearly defined. Dependent on their rotational speed these vortices can sap alot of energy from the pressure difference that is causing then. Of course energy is the final baseline of all processes. The sail develops power by milking energy from a energy rich medium.


spanwise flow : Just what is, says flow along the span of a wing.


Mary, you said that your father indicated that sails are pushed along.

How strange it may seem but many tests have shown that a wing section experiences much greater low pressures on the leeward side than high pressures on the windward one. So there is indeed a push component on the sails but a far bigger of the portion is the sailpower is developped by an underpressure (low pressure) on the leeward side.

Mary, the hard part is that fuidum mechanics and fluidum dynamics is a very strange world and often it is just a little different form what you would expect. Our dear God had a really jolly mood when he worked on this area.

One example is that a flow through a pipe at the part where the pipe narrow and then widens again will first drop in pressure and than rise back to normal pressure instead of the other way around. This is called the Venturi effect. Normal people will just expect the very opposite.

Anyway, what else do you want explained ?

Wouter

You may be above my head... I've got to sit down and think of laymans terms to put all this stuff in.

Write a book :P

Most of this thread has been about individuals arguing engineering theories applied to boat design. They are called theories for a good reason. In reality there is very little engineering fact when it is applied to the real world. Things are far too complex. Engineers use the theory to guide them toward a design. Bill Roberts designs good cats, it doesn’t matter if you don’t believe in the theories he has used to reach that design. The proof is in the pudding.

A good example of this is Mary’s proposed sliding mast design, in reality it will not give a larger righting moment see http://www.wingo.com/proa/rig_placement.html ( I think that is what she was getting at, forgive me if I am wrong). But if she went and built it she would probably find it does give more power for a number of other reasons, so building something based on the wrong theory is not necessarily a bad thing. The important thing is to try things out.

Mary, if you or any other non engineers want to understand engineering better I would recommend the book “Structures or why things don’t fall down” by J.E. Gordon its available in paperback about $12 on amazon.

In boat design, because conditions change every time you sail, then its nigh on impossible to say you have a better boat than the next man. Using a system of rules narrows the field down and allows a little more comparison, which appeals to many people (not me). I believe the ultimate measure of a boats performance is the size of your smile. If you hadn’t guessed I am a design engineer (engines) and amateur boat designer/builder and my interpretation of the theories are very strange indeed.

Gareth Roberts (no relation to Bill or Carl)

A friend of mine just finished building one of these (CLC Proa Mbuli). We'll be launching it next week. Hopefully I'll have photos to post. (sistership shown below) Believe it or not, you can actually go below decks into that coffin-like cabin

Grob,
It was not really my idea -- just a visual interpretation conjured up in my mind based upon Luiz's explanation about righting moment. The book sounds interesting, but I certainly would not want to limit my creativity by learning too much about the laws of physics.

Ok, moderatly long winded but hear me out. I'm gonna bill this as a blend of Bill and Wouters statements.

My favorite comedian is George Carlin. He does a bit about license plates and the things that the states put on them for slogans. One of the states that he mentions has “Live free or die!” on it while another has, “Famous potatoes”. He comments on the absurdity of these two and states that the truth of the world probably lies somewhere in between.

I think this whole discussion is in the same ballpark as George’s bit. The real answerer is some where between Bill’s brute force method and Wouter’s extreme finesse.

The construction techniques available to us today are much more advanced at a more reasonable/reachable price than in the past. Carbon is still exotic, however much more becoming the norm for many components. We can decrease weight, increase strength and produce a mast which will bend anyway we want just by adding a little carbon here, removing some there. Producing not only a lighter stronger mast, but one that is possibly more effective across a wider range.

The laws of fluid dynamics have not changed, but our understanding of them has improved. Not only our understanding, but also our ability to more accurately model the flow of fluids across sails, hulls and other appendages. When I was in ChE class, our professors would have us do more work on a problem than was specified in the book. When we asked why, he replied, “Your books were written in the 50’s, since then computers have come a long way. Since you do all of your work in MathCAD, you can more easily do the complicated calculations that are required.”

Older hull and sail shapes designed by paper, spreadsheet and slide rule would take drastically longer to design than newer ones done with the current crop of software. The older shapes would most likely be less efficient than their new counterparts. By “hand” we can only calculate a certain number of intervals along the hull to judge the effectiveness of the design. While the software packages can do extraordinarily finite calculations across the entire surface to produce a more accurate picture of what is going on with the hull and sails. Some of the software (I think I saw it somewhere) is not only looking at the hull through water, but the hull and sails as a complete package with wind and waves. This provides more information than was ever imaginable before to determine the optimum direction to take the hull design in.

The best designs are the ones that not only provide for a great deal of power, but also incorporate it in the most efficient package possible while staying manageable across a wider range. I think the true art of design is knowing how to find the optimum middle ground…not only power, but efficiency also. Realizing that not only power and efficiency are needed, but look at things like momentum. The HT was on the efficient end of the spectrum, but look how it does in waves….or doesn’t when the wind is light. A down fall of that particular design.

Wouter and Bill are both coming at the same problem in two different directions. Wouter has probably spent more time behind a keyboard while Bill more time at a drafting board. I can’t give an edge to either design method because there is much to be said for both experience and computational ability.

I think I read the statement earlier in this post about formula rules limiting creativity (or something like that). I think it is completely to the contrary. If given a set of design guidelines I would expect it to take much more creativity and ability to produce a winning design. Since the major parameters have been established (LOA, SA, beam, mass) your brute force (SA/mass ratio) has already been determined. To create a more flexible and effective platform within those guides would require more resourcefulness to get the most out of the available power.

Look at two similar designs, the I-20 and the N-6.0.


These numbers straight from the Performance web page
I-20 US 390 lbs 246 ft^2 SA/wt=0.6308
N-6.0 NA 420 lbs 264 ft^2 SA/wt=0.6286

The sail area to weight ratios are VERY similar, however the I-20 beats the 6.0 upwind. (I only mention upwind because with today’s Bermudan rigs, they are mostly optimized for upwind.) Why is that? More efficient platform I suspect (hull shape, square head, aspect ratio of foils and sails). I would also suspect that the I-20 has also had more time put into its sail plan optimizing it for upwind (since it was designed for a spi).

I’m no expert, but I think your both a little crazy/fanatical (did have some psych in college….)! You both believe deeply in your design philosophies. Like I said before, I think that anyone can make a boat faster by adding some sail or by improving it’s efficiency, however if both are not considered together the end result will be less than equal to it’s full potential.


Will R

Will,
I agree with you that it takes more creativity to design within a formula. It's sort of like poetry -- it is easy to write free verse but takes much more discipline and creativity to write within specific parameters of rhyme and meter.

exactly -
a wonderfull syncronisity exists connecting many things -

An interesting series on the history channel by Berk showed inventions of very different sorts over centuries -the successes and failures ,-most importantly how these discoveries and inventions effected one another in development ,-and how interconnected it all is as one could not have been created without other related earlier attempts ,---one builds on the knowledge of another and another creative result of engineering and design often through trial and error process .

really like Gareth's {grobs} 4 hull design -
http://www.caemodel.co.uk/boat.htm

think it would also be great without a sail -
just as a fold up -cartop paddle-boat with added seat and maybe peddle driven prop and rudder ,--ideal lightweight stable fishing platform or just recreational watercraft as well as alternate sailing craft ,-

He most likely has already thought of the many other applications ---fun stuff

check it out --congrates Gareth !!

http://www.caemodel.co.uk/boat.htm

Well hello everybody,
I'm glad to see the title change. An engineer is the person who takes all this theory stuff and makes it work in practice.
In 1981 I went over to Brest France to the World Championship Speed Trials for Sailboats. There were mostly sailboards and beach cats there. I was obvisously interested in the beach cats. There were boats there of all sizes, 14ft to 20ft, and descriptions, all the popular classes plus sone one of a kind boats. There were three days of speed runs and every boat was allowed to make as many runs as they wanted to until the clock ran out. The results were calculated by computer and printouts were available every night of every run on every boat that tested that day. I brought those results home with me and studied them and tried to figure out why some boats were faster than others. I knew the old formula, Vmax = 1.4 sqrt LWL. The 1.4 coefficient is called the speed to length ratio. I solved for the speed to length ratios for the fastest boat of each size and then tried to figure out what could be making these ratios or coefficients vary between 4 and 5. I considered hull loading, displacement/length **3, bow wedge angle, work and power of pushing the water aside and many other parameters were considered. What I finally realized was that when I plotted speed to length ratio vs hull fineness ratio the data defined a line that was almost straight. Then I connected it to the 1.4 value for monohulls at a hull fineness ratio of 4 and it too fell on the line. Well now, how about this, we now have a Simple Simon way to estimate beach cat max speed based on boat length and hull fineness ratio for boats in the 14ft to 20 ft length. This I have used in my boat design calculations and it has served me well. I have predicted the Portsmouth Number of the boats I have designed using this equation and many other parameters and ratios and hit the PN of these boats right on the money every time. And for Wouter: This system is not the first law of catamaran boat speed but it is a system that I have come up with and it works very well for me.
Here's another Wouter point that I should respond to. Wouter is bringing forward the position that as boats are built lighter in weight with higher sail area to total sailing weight ratios they can go faster even though they have lower righting moment to sail area ratios. I have a hard time going along with that. I know of no example where that is true. Wouter pointed to the A class cat as an example of success here but I don't go along with that because the A class cat is a development class and many things are improving about that boat as well as the weight going down. I am not willing to give weight reduction total credit for the performance improvement in the A class catamaran. Wouter also pointed out that the Tiapan4.9 was lighter and faster tham the H16 and the Tiapan is the same width and length. Not a fair comparison, Wouter. I think the Tiapan has daggerboards and you can't compare beach boats to board boats on performance. The board boat is faster every time. We do have this comparison: A year or two back they held a trials in Europe to consider a catamaran to replace the Tornado in the Olympics. All the new hot 20 footers took on the Tornado. The Tornado won every heat. WHY??? The Tornado has a higher sail area to weight ratio and it has a higher righting moment to sail area ratio than any of the other boats in the race. Well done basics, fundamentals, will win every time.
Bill

This thread has brought forth many different opinions and ideas relating to catamaran design...always interesting to hear different perspectives.

However, when it is all said and done, to the best of my knowledge, no one who has responded to this thread has the "proven track record" (encompasing both race winning sailing and design expertise) that Bill Roberts has exhibited over the course of his life time.

It is one thing to theorize about what may or may not work based on opinion, or a computer model, it is a different story to have a solid history to back up your position. We have to remind ourselves that while computers make many things easier to calculate, it still is in essence a tool. It is only as good as what you put into it...

It is amazing how bold we can be when sitting behind a key board...basicly challenging a successful and inovative aeronautical engineer/catamaran designers whole carrier based on our elementary understanding of sailing and boat design (in most cases)...Or at very least without the benefit of his years of practical experience and experimentation.

It is a real blessing that Bill comes on this forum and take the time and energy to respond to questions with detailed technical explanations. Blending engineering skills and practical experience, he is uniquely qualified to help us all...Let's make sure we continue to give him the level of respect he has earned.

Bob

The ISAF trial occured in March of 2000 in Quiberon France. The Marstrom 20 hit an underwater cable early in the week and was not able to sail (due to broken daggers) till the last day. An exert from an article, "The Marstrom 20 finally got out on the water. It had hit an underwater steel cable early in the week and was out of action pending repairs. In the only race it sailed, it walked away from the fleet."

The whole article can be found here: http://old.cruisingworld.com/2000/03/isaf5.html

I have a spreadsheet at work with a lot of the current popular US boats on it. Their weights, SA's, LWL, beam and DPN. I had Excel calculate the SA/wt for each of them. The M20 had something on the order of 1.1 ft^2/lb, more than anyother boat on the list.

M20 54.0 [58.0] (55.8) (54.0) [52.5]
TORN 58.8 63.0 60.9 58.5 55.5
RC-30 53.9 56.0 54.5 (52.8) 50.7
NI20 59.2 62.8 60.2 58.6 57.1

Interisting thing I see here is how similar the T is to the I-20. However what is more interisting is how much faster the RC-30 isn't vs the M-20. 100k??? dollars vs. ~17k, 30 ft full carbon monster (brute force) vs. a 20' modern "balanced approach" design. The boat is light, wide and carries plenty of sail.

I think it is undeniable that PROPERLY applied technology will always win over an older design, no matter how good.

I stopped believing in wise old men quite a while ago when I found that in some classes taught by long time professors I had to make deliberate errors in my exams to get a passing grade. And I was not the only one, the whole class did it and knew it. We tried to explain it to the professor but his only reply was :"Why do you as a young student think that your answer is better than mine, being an professor in this field for many years now". As if the universe and law of physics (aged 5 biljoen years) give a damn about some misguided professor who was able to reach the age of 55.

The 5 of us got sick of this self glorifying answer tactic and left it at that. The next exam we ignored all constants like 1/2, 1/3, 1/4, ... and so on and wrote down answers that were always a factor 2, 3, 4, 5, .... wrong and we passed the test. I must say a really saddening experience.

In hinsight this was one of the most instructive episodes of my university years. Now I look only at the math and derivations made by people and never to the age or the background of the person who has made them. Afterall 1 + 1 = 2 even when a 90 years old professor with 10 nobelprizes for mathematics says 1 + 1 = 3.

Wouter

But you were right Mary !

Moving the rig to the windward hull DOES increase RIGHTING MOMENT

It does not however increase HEELING MOMENT in that sense mr Speers article is correct.

Grob misinterpreted RIGHTING MOMENT for HEELING MOMENT.

The two are closely linked but they are not the same

Wouter

>>but I think your both a little crazy/fanatical (did have some psych in college&#8230;.)!

Indeed, I admit to that.

I totally agree with you and I wish to underline the following.

I'm not saying Bill is wrong (apart from his application of the Froude law) but that his way is the only way to go faster is wrong.

I'm trying to show that there is another way to go faster that is not described by Bills statement ;

"Nobody is going to build a boat faster than the Tornado until it has a higher sail area to weight ratio AND a higher righting moment to sail area ratio!!"


I never said his way would not produce faster boats ! That is how some of you have interpreted my statements as Bill has too.

Wouter

As an odd coincidence, I was reading about Johannes Kepler on one screen and Wouter's comments on another. Kepler was one of the greatest mathmatician/astronomers. Here is a brief bio on Kepler (or is this Wouter?).

Wouter, I hope you take this as high praise from a 50+ year-old chem professor. As a tourguide for youthful intellect, I embrace your unbridled enthusiasm!
_______________________



The new teacher for Mathematics of the Province arrived in Gratz in April 1594, at the age of 23. He thought himself a poor pedagogue because, as he explains in his self-analysis, whenever he got excited, which was most of the time, he 'burst into speech without having the time to weigh whether he was saying the right thing'. His 'enthusiasm and eagerness is harmful, and an obstacle to him, because it continually leads him into digressions, because he always thinks of new words and new subjects, new ways of expressing or proving his point, or even of altering the plan of his lecture or holding back what he intended to say. On these grounds his lectures are tiring, or at any rate perplexing and not intelligible.' The fault, he explains, lies in his peculiar kind of memory which makes him promptly forget everything he is not interested in, but which is quite wonderful in relating one idea to another.

http://www.mathstat.uottawa.ca/Profs/Rossmann/Kepler_1.htm

Hi Wout

Hope your not judging all people by age alone !

The "wise old prof. " and others did {though sometimes inadvertantly } get you to think ---and think for yourself to seek truth .
the best thing any teacher can hope to accomplish .

The implication of relating this prof story into an engineering design discussion is not directly relavent to
S C designs and Bill,s accomplishments however .
Interesting story though ,
Seems people often reach a position of authority in gov structured organizations and societies that they have not earned and could not in the real world or open free marketplace where people are free to choose another option.
Sighting age is not the cause ,--maybe socialistic ideals ,-shades or grey or otherforms are more the base cause .
People of all ages continue to be inventive and have creative minds throughout their lives .Examples are numerous in all forms of human endeavor .

Nice that so many good people take time to respond to sailing posts ,--we worry about each other .-each others ideas and opinion ,-try to point to the short explaination and perspective of each ,--

S C and Arc designs have been reasonabley successfull in the marketplace and continue to be -

Bill mentioned earlier that any could take the Arc 21 design ,build a 20 ft--8.5 beam version - take a 1-ft 3 in . off the stern and have an excellent F-20 type cat design . add a C F mast and similar sail plan and it is a speed machine equal or better than most when sailed to its potential .
There is no doubt in my mind that this would be a superior performing 20 particularly for distance ocean racing in seas in races like the Worrell or Tybee 500 .-
Comparabley the current "fastest 2o"-The Inter 20 has large bow sections ,-nearly 16 in in width with very flat underwater profile which slaps and sometimes pounds in waves . It is also skidish and does not track like a deeper narrower hull section design ,-helming is a factor also,particularly in distance racing .

As a Formula racing advocate you must realize the value of this and others options . The underlying reasons why existing design is valued and new innovation and refinement from them is vital for the sport and its future.
Like everything when it becomes stagnant it begins to decline and die .

We will see the S C and Arc designs as well as many design features Bill incorperated into them subsequently applied by other designers that have influenced them greatly and will continue to ,-around for a long -long time .-

-

Wouter,

I didn't misinterpret righting moment and healing moment I deliberatly swapped one for the other. My understanding of these two is that while they have different meanings they are equal and opposite so one can't increase while the other stays the same.

I may have confused what Mary was saying and that is why I apologised to her in advance in the same posting.

Can you explain how RM and HM can be different.

All the best

Gareth

Meek, nerdy student cowering in back of classroom slightly raises his skinny hand, raises his shaky, wimpy voice and states:

Righting Moment (RM) is the force that tends to keep the boat upright. Heeling Moment (HM) is the force that tends to knock the boat over. Shifting the rig to weather will increase RM the same way shifting crew to weather does: The lever arm for the mass of the rig is increased. HM stays the same, because a rig of X height, having a center of effort Y feet above the deck, will ALWAYS have the same HM. Of course, as the weather hull flies, the HM increases faster than it does when the rig is centrally located, as it rises above the water (and the leeward hull) faster.

sail fast

Bill-I mean absolutly no disrespect-I have old magizines describing your transition from FD's to Contenders and I would love to sit down with you with a beer, but why not put out a 20' 8'6" cat?

A few years ago when the CFR 20 was still in development, the Chief designer put a few posts about it on the old forum. I think his name was Preston Carter or Carter Preston or Preston Tucker, or something like that. I told him he should go to a wider beam either 10 ft. or 12 ft. He replied that the 8.5 ft. beam was neccesary because he wanted to stick to a "KISS" design phlosophy. I told him why not make his 8.5 ft version and call the 12 ft. version the CFR 20 XL. I also told him when it blows, I'd beat the 8.5 version every time with an XL. The thing to do is get the CFR 20 hulls, boards an rig and get some 12 ft crossbars. By hot-rodding the CFR 20, you can make your own CFR 20 XL. Then you can have light weight and more righting moment.

David Ho
TheMightyHobie18 1067

Preston Blake was the chief producer of the CFR-20, with design input from Morelli and Melvin. This potentially fine racing instrument saw superb performance early on in light airs with/after tuning by Randy Smyth, then has, sadly, disappeared from public view. This featherweight and still pristine prototype lives quietly in a shed somewhere in Gainesville, Florida, perhaps at the former Ghostdance Marine manufacturing location. It has been carefully kept dry and out of the sunlight at our local Lake Santa Fe. The CFR-20 has been invisible for the past 2 years or so, as has Dr. Blake.

An ARC21 can be ordered in a 20' length 8'6" width. Basically the same boat but with 1' off the stern. Contact Aquarius for specifics.

thom

I know I am in way over my head here, but I have questions, and I can't help it.

Grob says:
I didn't misinterpret righting moment and healing moment I deliberately swapped one for the other. My understanding of these two is that while they have different meanings they are equal and opposite so one can't increase while the other stays the same.
Can you explain how RM and HM can be different.

And Andrew says:
Righting Moment (RM) is the force that tends to keep the boat upright. Heeling Moment (HM) is the force that tends to knock the boat over. Shifting the rig to weather will increase RM the same way shifting crew to weather does: The lever arm for the mass of the rig is increased. HM stays the same, because a rig of X height, having a center of effort Y feet above the deck, will ALWAYS have the same HM. Of course, as the weather hull flies, the HM increases faster than it does when the rig is centrally located, as it rises above the water (and the leeward hull) faster.

And Mary (that's me) cannot understand physics concepts unless she carries them to their ridiculous extremes. So she interprets Andrew as saying that it doesn't matter whether the mast is on the leeward hull, in the middle of the boat or on the windward hull -- that the heeling moment will remain the same (except that heeling moment will increase faster if the mast is more to the windward side of the boat.

Did I understand Andrew correctly -- and is he correct? If so, it challenges my limited store of common sense.

mary, I think you're interpreting them correctly.

My thought on the matter is this: Our cats are faster when it's just beginning to fly a hull because of a combination of maintaing the righting moment and reducing wetted surface area. The problem is that as we fly a hull, the mast and sails start to lean toward the water producing an increasing downward component to the power provided by the sails. The farther you heel the boat, the greater this downward component becomes. If you were to lean the mast to windward so that if you fly a hull the mast remains perpendicular to the water and you reduce wetted surface area how can this not be faster?

BTW...I'm pretty certain that the open 60 tris have windward tilting rigs.

What I believe he's trying to suggest is that the heeling moment stays the same, because it's dependent on rig size/height/etc;

When one moves the rig around, you are making changes in righting moment.

Do I understand you correctly, Andrew?

I ain't gonna comment on the correctness of the statement, but here's a link for a GREAT article by James Wharram, he's been designing cats since God was a baby:
http://www.wharram.com/catamaran_stability.shtml

When I getaminit, I'll read Wharram's article...

sea ya
tami

As you heel, your are decreasing the cross sectional area of the sail to the wind, but increasing things like your tramp area to the wind (hence mesh tramps). You are also decreasing the amount of weight that you have that is put towards righting the boat. Since your weight stays normal to the ground line as you heel, instead of trying to right the boat, you are now just pushing down (varys with angle of heel) on it. The more you heel, the less you are doing towards righting the boat.

wouter

Gareth,

>>I didn't misinterpret righting moment and healing moment I deliberatly swapped one for the other. My understanding of these two is that while they have different meanings they are equal and opposite so one can't increase while the other stays the same.

This is a deceiving way of putting it. While your statement is correct is suggests something that is not correct.

By virtue of this relatio you conclude that while the heeling moment is unaltered by move the mast to the windward hull that the righting moment isn't changed either. BUT the maximum ACHIEVABLE righting moment is changes; this is increase to a crew is forced to depowered at a higher windspeed.

So yes there is always equilabrium but the windspeed at which extra effort needs to be taken (depowering the rig) is affected which in turn means that the overall speed of the platform is affected in depower conditions.

In the example the modified boat can sail faster in depower conditions because as a result of the increased MAXIMUM righting moment it needs to depower less to maintain equilibrium. Less depowering means more power in the sail and means faster sailing.

The analogy to trapezing or not trapezing is quite good. Also here the heeling moment is not directly changed but still teh boat with the trapezes is faster in depowering conditions than the one without.

>>Can you explain how RM and HM can be different.

It comes down to the fact that the relation to HM and RM is one of equality. It is more a master-slave relationship with two distinct windspeed ratios.

Light winds to fully powered up. : RM follows HM
Fully powered up to strong winds : HM follows RM

All the best

Wouter

Mary, Let me attempt to clear up the confusion I have caused.

First thing to remember is a moment is a force times a distance.

The righting moment (RM) is the total weight of the boat and crew multiplied by the distance between the centre of buoyancy (CoB) and centre of gravity (CoG) in the horizontal direction.

The heeling moment (HM) is the Force of the wind on the boat (mainly in the sail though) multiplied by the distance between the CoB and the centre of effort (CoE) of the wind in the vertical direction.

As with most things in engineering these two forces have to be opposite and equal otherwise the boat falls over.

With the HM the distance is more or less constant but as the wind changes the force increases and so the HM increases.

With the RM the weight is more or less constant but the distance increases as the crew moves to windward (CoG changes) and/or the boat heels (as the boat heels the CoB moves toward the leeward side).

One thing to remember here is that these two things change constantly but what we are interested in is the maximum HM or RM. With the HM there is no maximum, the wind can blow very hard, but there is a maximum RM the crew can only move so far to windward! That may be why most people talk about RM not HM.

So when there is no wind the HM force is 0 and so the crew sits on top of the boats CoB so the RM distance is also 0. As the wind starts to blow the HM force increases and so the boat heels and/or the crew move to windward just enough so that the HM and RM are again equal.

Lets say the Heeling moment distance is 4 and the RM weight is 200.
HM RM
Force x distance Force x distance
Stationary boat 0 x 4 = 200 x 0
Windy boat 100 x 4 = 200 x 2

Everything nice and equal.

This is a dynamic thing and both are constantly changing with the crew moving and reacting to each change in the wind, but over any period of time the two have to be equal and opposite and cannot exceed a maximum governed by the weight and width of the boat.

Some people think that by moving the mast to windward you are lengthening the HM distance as you are moving the CofE further away from the CofB.

And that is what I thought Mary thought and that was dumb dumb dumb as I have no Idea what Mary thought.

However moving the mast does not alter the HM because the heeling moment only takes into account distance in the vertical direction.

I think Wouter and others are saying it does increase RM because among other things it moves the CofG slightly further to windward.

I did not understand Wouters statement because I knew that HM and RM have to be equal and opposite and Wouter was implying they could be different. I don’t think that is what he really meant. What he meant to say was that maximum RM does increase. It’s a bit of a chicken and egg thing because then the HM also has to increase to be equal and opposite.

It’s a case of both of us not being clear enough. And that is partly why engineers argue all the time!

Is that Clear enough?

I have no idea what anybody is talking about because some people seem to think I was talking about tilting the mast one way or the other. I was not talking about that at all. I was just talking about moving the entire mast -- vertically, 90 degrees angle to the main beam -- moving the entire rig to windward. Grob seemed to originally say that doing this would increase righting moment and would also decrease heeling moment because the leeward hull would be able to help more with the mast farther away, just as with a wider boat.

Here's a drawing to go with this technical description by grob. This is one scenario where the windward hull just begins to become airborn. If I get a chance, I'll draw one with a tilting rig. The formulas for this (simplistic and 2 dimensional - it's not quite right because it doesn't take into effect the vectors of these forces - more on that later) are as follows.

RM = CoG X D2
HM = WF X D1

If the boat is stable sailing like this (hull not going up or down) then RM=HM. If the hull is rising higher and higher then HM > RM (is greater than). If the hull is falling back towards the water (pointy side still up) RM > HM.

I was thinking in the same line you were, Mary. All I'm saying is that if you move a, say, 50-lb rig, from the center of the boat to the windward hull, you have accomplished the same thing as having a child crew moving the same way. Righting Moment is increased: clearly it will now take more force from the sails to fly that windward hull, because you now have the weight of the rig to lift. On the other hand, Heeling Moment, ALL ELSE EQUAL, is the same. For a given wind strength and angle, a given rig will always produce the same heeling moment and the same amount of drive (assuming everything else is the same of course.) In the same conditions in which the boat was just flying a hull, with the rig in the middle, it no longer is. Now, the equilibrium Heeling Moment, when the hull begins to fly, must be exactly the same as Righting Moment, but both forces will be greater than they were when the rig was in the center of the boat. Of course, don't try to tack!
hope this helps

No, it doesn't help.
Are you saying that if you have a 50-pound bag of sand in the middle of the boat, and you move that bag 4 feet to windward, it will increase the righting moment but it will not decrease the heeling moment?

Moving the bag, or moving the mast, increases the potential maximum RM, the RM and HM are always equal and opposite. Without the wind in the sails the boat simply heels until the centre of Gravity and Centre of Bouyancy line up agian.

Try this series of articles, http://woodsdesignssailingcatamarans.com/indexstart.html

It talks about HM and RM and why Hobie Cats can fly a hull safely yet narrow cruising catamarans cannot.

Should have added

Go down to the bottom of the page and click on the technical article "stability 1"

Mary, I hope you don't think that I was calling you dumb when I said "And that is what I thought Mary thought and that was dumb dumb dumb as I have no Idea what Mary thought.".

I was calling myself dumb for thinking that I knew what you were thinking.

No, Grob, I was basically saying that what you were saying made sense and that what Andrew was saying did not (at least to me).

Well, actually, I don't know anymore who said what except that I agreed with Luiz originally, and what HE said made sense -- that righting moment and heeling moment are essentially equal and opposite.

Hi Mary,
Moving the mast to windward, say 4ft, does increase the righting moment. Say the mast and rig and sails weigh 100 pounds. In the center of the boat they generate 400ftlbs of righting moment. Move them 4ft to windward of center and they generate 800ftlbs of righting moment. The people righting moment on this boat would be something like 11ft X 325lbs = 3575ftlbs. Moving the mast to windward would increase the righting moment roughly 400 ftlbs out of about 4000ft lbs or 10%. This sounds a somewhat interesting until we look at the included angle between the mast and the windward shroud. It the mast is stepped 8ft away from the leeward hull on an 8.5ft wide boat, what is our windward shroud angle relative to the mast?? Ans. 1.4degrees. I don't think that is enough to hold the mast up, Mary.
Bill

Wouter,
You abused what I said here and misused the information I supplied and I do not appreciate it.
I addressed hull weight only and scaled hull weight only with the LWL**3 relationship. My objective was to show interested sailors that the manufacturing method/process of the RC30 hull is outstandingly low in weight and by scaling a finished RC30 hull weight at 30ft down to 20ft and 18ft you arrive at hull weights equal to or better that anything else available anywhere in the world.
The rest of the RC30/27 parts like, beams, tramps, rigging wires, rudderheads, ropes, blocks, etc. are not outstanding in minimum weight because they are plain old aluminum and dacrom and 316 stainless and plastic etc. so they are not superlight as the hulls are. That is why these parts are not outstandingly low in weight. Well, 'why not', you might ask? COST!!! I still have appreciation for the customer. I'm sure at least 100 pounds could be taken out of the weight of a RC27/30. And guess what? IT WOULD DOUBLE THE PRICE OF THE BOAT!!! Tom Haberman and I don't think it is the thing to do. It is the same situation on the ARC22. It could be lighter also. The ARC27/30 and 22 hull weights are outstanding in construction method and weight; today's technology. The rest of the boat is 1960's technology as far as construction method and weights go. This is why what you did with the total boat weight scaling is misleading to other readers. You mixed apples and oranges and you didn't know you were doing that; but you did know that you wanted to make the RC hull weight numbers look highly questionable if not unbelieveable, "a bit much don't you think'?
Bill

**** and bull ramblings, but you should so more respect where it is due.

The SC 22 (ACR22) carbon hulls are a work of art. They are beautifully finished, amazingly stiff/strong, and very light. Bill has designed and built a least six designs, that I am aware of. How many have you brought to the water? I suggest that until you establish yourself as an authority, that you show more respect for Mr. Roberts.

If you want to talk about your comparative sailing skills.....well, I definately would not go there!

Wouter, until you prove yourself as a sailor, designer, or anything else dealing with catamarans, you should pick your fights a little better.

Bill, I would not dignify Wouter with response.

Regards,

W.F.
Bill Roberts Fan

Bill,

I didn't misuse your information Bill, I just pointed out that you can't use the 3rd order approach to proof that the RC30 hulls are indeed light for their size.

In simple terms teh RC30 hull are not at all similar to a 18 foot platform that is scaled up by a factor of 1,66 in all directions.

The RC30 hull maybe be 1,66 the length of an 18 foot hull but it is more likely to be only 1.3 times the width and depth.

By assuming it is nothing more than a scaled up 18 foot hull with the same factor for all dimension you made it look like a comparable 18 foot hull would have to be lighter than what anybody else is producing at this time. Including A-cat hulls.

If we would continue the 3rd order approach to 16 foot cats than a Taipan hull of 22 kg's has to be only 12 kilograms to be equivalent to your RC30 hull.

That is why I made the calcs that compared displacement of both boats. You will find that displacement doesn't follow a 3rd order trend either so why would hull contruction be accurately described by it. Afterall displacement is the most important design parameter when designing a cat hull.

Bill, I truelly respect your vast amount of experience, standing and the cats designed by you but when it comes down to applying formula's I've found myself to be in strong disagreement with you.

And may post are just that; disagreements on how formulas like Froudes law are used and applied. Nothing more,

Wouter

Why exactly would it cost so much to lighten the boat up if the hulls are already, as you say, relatively low in weight in the first place?

Doing the things to really lighten the boat would include things like:
Dynaform wire or carbon standing rigging
carbon beams
carbon rudder castings
carbon mast
carbon boom
(seems like a lot of carbon hu?)
Ti bolts and metal fittings

the cost/lb is MUCH higher for the carbon parts. I was told what a set of carbon standing rigging for the M20 costs (have forgotten it now), but I amazed by it's cost. As a comparison, the I-20 mast costs something around 3500 dollars (if I remember right), the 6.0 mast is like 1600 i think (don't quote me). I'm sure that Bill's 27/30 mast is not cheap in AL and the cost of a mast goes up exponentially with it's length (last I heard an ACC mast ran something like 1/2 million...don't quote me again...just working from little bits of memory)

Things like beams and castings made of carbon are also substantially more expensive than their AL counterparts. You hit what we called in engineering class a point of diminishing returns. You can keep dumping money in, but the weight you save/dollar keeps going down.

Bill saves the big pounds where it is easy (in the hulls). By building in carbon, not only does it save weight, but it also increases the life of the product. I have to admit that I don't really agree with the way that either Bill or Wouter are trying to scale hulls and boats up or down in weight. Bill is building in carbon while most boats are glass (apples and oranges). I think to properly compare the two, you must use the same build process.

There are also some other weight factors that will not change as much with size as some things do. No matter the size of the boat, there will be a minimum attainable weight in rigging. As the boat goes up in size, the rigging does not change as drastically in weight as does say the hull weight (just an example, there are several other things that would follow the same principle).

The only reason I participated in this conversation was to try and add another view, learn some and hopefully get some feed back on my thoughts. It's been fun, hope this doesn't turn into a name calling contest.

Will

p.s. this has got to be some sort of record setting post

Come to think of it.

Wouldn't the ratio of hullweight / displacement be a more appropriet measure ?

Wouter

Bill,
Why would anyone want to have a mast that slides back and forth on the beam? That's ridiculous.

This all started with the question as to whether wings will have essentially the same effect, as far as righting moment, as having a wider boat.

Luiz said, I believe, that it will increase the righting moment but it will be offset some by the wing on the opposite side. He added that the real benefit of a wider boat is that the leeward hull (being farther away from the mast) plays a greater role in reducing heeling moment than it does on a narrower boat.

So I conjectured in a totally non-serious way, that the only way to make a narrow cat act more like a wider cat is to have a hiking rack only on the windward side to increase the righting moment and also slide the whole mast to windward, so the leeward hull could help to reduce heeling moment.

For instance, the difference in width between a trailerable boat and a Tornado is 1.5 feet. So if you slide the mast to windward 9 inches, you would have, in effect, a 10-foot wide boat on the leeward side because of the increased distance from mast to leeward hull, and (at least)a 10-foot wide boat on the windward side, as well, because of the ability to get crew weight out farther.

And all this is assuming that you are sailing in enough wind that you NEED to increase righting moment and reduce heeling moment.

I haven't yet asked the question as to whether wider boats have an advantage in light air where all these "moment" things are not an issue.

Hello MauganH17,
The answer to your question is tooling costs. One can use the same hull mold to build fiberglass or carbon composite parts. To build any composite part, a mold is required. So to build all of the parts that are metal now, tubes and brackets etc, require molds, molds that do not exist now.
Bill

Hi Mary,
On a 10ft wide boat the center of gravity of the boat platform is 5ft from the leeward hull center of bouyancy. This is 9 inches further to windward from the leeward hull than on an 8.5ft wide boat as you said. Moving the mast 9 inches to windward won't quite compensate for the 8.5ft vs 10ft wide boat difference because you are moving only the mast and not the center of gravity of the whole boat. In the case of the Tornado, for example, you are moving only 60 pounds of mast and sails and rigging weight to windward 9 inches. The boat weighs 375 pounds, so you need to move 375 pounds to windward 9 inches to make an 8.5ft wide platform have the same platform righting moment as a 10ft wide boat. Now on top of this we have the trapezing righting moment difference between an 8.5ft and a 10ft wide boat to make up for. This can be done with wings. The windward and leeward wings do not offset each other in righting moment. The windward wing has the full width of the boat, i.e. 8.5ft as its lever arm to hike with and the leeward wing has only the width of the wing, i.e. 18 inches to generate negative righting moment with.
Wide boats have no advantage in light winds. If anything there is a disadvantage because the wide boat is heavier. The wide boat also has to be built stronger than a narrow boat because the forces are greater on a wide boat. That is what makes the wide boat go faster in the first place. It gets more push out of the sails but only when the wind blows hard. I hope this helps.
Bill

Yes, that helps a lot. Thanks, Bill. I had been thinking that the crew weight to windward figured into changing the boat's center of gravity and, therefore, also figured into reducing heeling moment. I still don't understand why righting moment and heeling moment are not equal and opposite, but that's okay. I'll just take your word for it and have faith that it is so.

Somebody mentioned something about this thread being so incredibly long. I think it is because debates and explanations about engineering questions are like debates about sailing rules -- never ending. There's always another "but what if".

Since we're going for the record longest post anyway, let me ask what my (engineer) crew keeps asking me: Why not use titanium?
I'm assuming the answer is cost, so how much more expensive is titanium than carbon? or is there some other factor?
Al

I own two Ti road bikes [Litespeed Ultimate, Fuji/Sandvik metal works] both have carbon forks [Look] and one has Graphite Paul Lew 4quad wheels. The characteristic of both frames is the expense [L=$2400, F=$1750] as well as welding them in Argon gas environment plus they adsorb road shock. Weight wise you may save 15% or less depending on the stress loads placed on the beams/mast. The Russians have a machine makes huge wing sections for their C5A bus. They offered ti to a couple of suppliers a few years ago. They maybe approachable today if you can handle their minimum qualties.

thom

Actually I enjoy Bill's responses to the questions of those that want to know [me included] as well as those that may or may not want to debate. I hate to be a pest about asking novice questions but sometimes I fall into the its going great and I don't care why... So I look forward to when Bill takes someone to class. We all get to learn something from someone with demonstrated first hand knowledge and experience.

thom

example, headboard shackles (4000 lb working load)

steel - $20
Aluminum- $38
Titanium - $120
Carbon+ - $190

This does not really apply to cats but, it gives you relative prices.

I have used titanium on cats. I bought some and built some to replace aluminum and SS parts. The only place it showed a clear advantage over carbon or ss was sister clips or where it needed to act as a spring, it makes great sister clips.