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#28157 - 01/28/04 07:42 PM Re: Spi + planing hull = ? [Re: Thomm225]  
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Hey Bruce,

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

Tom

-- Have You Seen This? --
#28158 - 01/28/04 07:46 PM Re: Spi + planing hull = ? [Re: Thomm225]  
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Bruce,

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

Tom

#28159 - 01/28/04 08:06 PM Re: Spi + planing hull = ? [Re: Thomm225]  
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Tom and Les,

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

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

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

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

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

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

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

regards,

Bruce
St. Croix



#28160 - 01/28/04 11:45 PM Re: Spi + planing hull = ? [Re: brobru]  
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BRoberts Offline
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S. Florida
Hi Bruce,
The ARC 17 is a beginner's boat, no boards, a true beach cat. It does have "shared lift" between the forward half of the hull and an oversize rudder which in actual practice could be called a steering daggerboard. The objective of this hull design was to have a "beach cat" with a better underwater lift to drag than other boardless beach cats so it would go faster and a boat that would tack easily and quickly. These goals were acheived. The underwater part of the ARC 17 hull is a deep Vee hull shape forward which transitions into a round bottom shape at the transom. The deep Vee forward acts like a low aspect ratio daggerboard and provides 50% of the sideways lift force while sailing to windward. The other 50% of the sideways lift force comes from an oversized high aspect ratio rudder. The result is a much higher effective underwater aspect ratio lifting body and less induced drag due to generating side force than the full length assymetrical hull shapes. The other benefit of this hull design concept is that since the hull shape near the transom is round, it can slide across the water sideways with ease. When the rudder exerts a sideways force on the transom, the hull spins right around. On a beach cat hull shape that carries the hard corner and assymetrical hull shape right into the transom, when the rudder exerts a side force to turn the boat, the rudder and hull near the transom get in a fight. The rudder is pushing the aft end of the hull sideways and the hull is saying, "no, I am designed not to go sideways" and there is a large hull drag increase and the boat comes to a stop about half way through the tack. Now the jib must be backed to complete the tack and the boat backs up and this causes the rudders to have to be reversed as the boat backs up and finishes the turn. Now with no forward speed coming out of the tack, if the mainsheet hasn't been let out, the rudders stall and the boat goes into irons. What a complicated mess it is when tacking can be so simple with proper design.
Relative to the spinnaker:
With the effective sideways lifting part of the hull being in the front half of the hull, the ARC 17 handles a spinnaker very nicely, no lee helm. The 17 was my very first "shared lift hull design". The ARC 17 is the only boardless beach cat that will carry a spinnaker without lee helm for the above reasons.
Good Sailing,
Bill

#28161 - 01/29/04 01:07 AM Re: Spi + planing hull = ? [Re: brobru]  
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Hi Bruce,

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

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

Jerry

#28162 - 01/29/04 01:12 AM Re: Spi + planing hull = ? [Re: Thomm225]  
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rbj Offline
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Thanks, Tom.

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

Jerry

#28163 - 01/29/04 05:11 AM Re: Spi + planing hull = ? [Re: rbj]  
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Jerry

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

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

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

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


John Pierce

[email]stealthmarine@btinternet.com
/email]
#28164 - 01/29/04 07:55 AM Re: Spi + planing hull = ? [Re: rbj]  
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Jerry,

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


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

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

Tom

#28165 - 01/29/04 08:21 AM Re: Spi + planing hull = ? [Re: Thomm225]  
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To continue, because of all that is going on with the spinnaker up, most of us have move our mast rotator line cam cleats back aft of the boards. Also, we have added a cam cleat for the spinnaker. While distance racing in " safe " conditions ( inside, not out in the gulf ) we lock in our spinnaker sheet, move to the back of the boat and trap out. We then control the boat with the main traveler/sheet only (mainly traveler). If the wind is up, the boat will simply fly!!! And the spinnaker will make this moaning sound.......on my boat anyway. It's great. Other guys have customized their boats in other ways. That's what makes the I17R so much fun. You sit around and try to figure out how to make things easier for yourself with so much going on.

Tom

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

Tom

#28166 - 01/29/04 09:04 AM Re: Spi + planing hull = ? [Re: john p]  
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Hi John,
I just returned from sailing in the Tradewinds Regatta in thr Florida Keys. I saw many different types of boats with spinnakers. Most boats have poles that are too short. When the spinnaker fills, the bows dig and the skipper and crew head for the back of the boat. I think that the reason for the short pole is that the longer pole pushes the CE further forward and requires even more mast rake than we see today to get rid of lee helm with spinnaker. Now take the spinnaker down and the sloop rig CE is so far aft that it stalls the rudders. So what do you do??? Go with a short pole and small spinnaker and less mast rake and live with it. You can "get by".
A better solution is go with the long spinnaker pole that lifts the bows and move the centerboard trunk forward a couple of feet to trim the boat out with spinnaker. Now without spinnaker, this will automatically reduce the side load on the forward located centerboard and increase the side load on the rudder. Therefore downsize the centerboard until it is carrying the boat's original design point lift per square foot of board area and upsize the rudder until it is carrying the boat's original design point lift per square foot of rudder area. This puts the centerboard and rudder back to operating at their respective design point loadings which results in the these foils operating at their highest level of lift to drag ratio while the boat is sailing to windward.
The other scheme of raking the mast back and balancing the rudders and "live with it" is a second level of performance compromise, a slower boat to windward.
Bill

#28167 - 01/29/04 09:35 AM Re: Spi + planing hull = ? [Re: BRoberts]  
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Bill

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

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

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


John Pierce

[email]stealthmarine@btinternet.com
/email]
#28168 - 01/29/04 10:30 AM Re: Spi + planing hull = ? [Re: BRoberts]  
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Jake Offline
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Bill,

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

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


Jake Kohl
#28169 - 01/29/04 01:10 PM Re: Spi + planing hull = ? [Re: Jake]  
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Jake

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

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

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


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

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


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

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


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

#28170 - 01/29/04 02:30 PM Re: Spi + planing hull = ? [Re: carlbohannon]  
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Quote
I would open it up and keep my camera handy for the guy who tries to use his spare mast as a spin pole.


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

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

#28171 - 01/29/04 03:04 PM This is just nonsense ; read the F16 rules again ! [Re: carlbohannon]  
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Wouter Offline
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>>In simple terms, Tornado's and 6.0's have long bows so spec'ing the pole 80 cm in front of the bow gives you a long pole. F16 have a 4 ft shorter bows so you end up with a shorter pole.


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

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

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

THAT is cherry picking boatdesign.


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

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


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

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


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


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


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


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

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


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

And you would also by one of these boats ?

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

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

Really !


Wouter




Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#28172 - 01/29/04 03:33 PM Sorry; I would like to add this [Re: john p]  
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Wouter Offline
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I'm afraid we are flying alright where we should be standing with both feet on the ground.

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

Formula 16 does not.

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


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


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

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


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


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

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

Wouter



Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#28173 - 01/29/04 04:43 PM Re: Spi + planing hull = ? [Re: BRoberts]  
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rbj Offline
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Hi Bill,

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

Jerry

#28174 - 01/29/04 07:32 PM Re: Check MauganH17's post [Re: rbj]  
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Hey Bill, John, and you other engineer types,

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

Tom

#28175 - 01/29/04 09:05 PM Re: Spi + planing hull = ? [Re: BRoberts]  
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brobru Offline
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Bill,
thanks for the info on your new ARC17,......I went back to your site and looked at it alot closer......

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

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


regards,

Bruce
St. Croix

#28176 - 01/29/04 09:48 PM Re: Spi + planing hull = ? [Re: rbj]  
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BRoberts Offline
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BRoberts  Offline
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S. Florida
Jerry,
You are not with me yet. The spinnaker up causes a CE migration, we all agree. With spinnaker up lean the mast back to get the CE at or behind the centerboard to balance the boat, no lee helm. This is what is done today, we all agree. Now take the spinnaker down and the CE of the sloop rig is well behind the centerboard much closer to the rudder. Now the rudder is overloaded and prone to stall. This is what we put up with today.
Here's another way to solve this problem: With the spinnaker up and the CE moved forward, move the centerboard forward to bring the boat in proper balance. Don't rake the mast back. Now we are in good shape with spinnaker up. Now let's take the spinnaker down. The CE moves aft a couple of feet from where it was with spinnaker up. This loads up the rudder and unloads the forward located centerboard. Now, reduce the centerboard area the same percentage that the load on the centerboard has been reduced because of its forward location. This is going to be a number like 10 to 20%. The reduced load on the centerboard now falls on the rudder as an increase in load. Therefore increase the rudder area, rudder balanced, in direct proportion to the increased load it now carries. Now the centerboard is happy and so is the rudder and lee helm with the spinnaker up has been solved. The CE migration dragon has been captured and put in a cage under our control. This will place the centerboard immediately behind the main beam or if you feel bold and run a long spin pole and put the centerboard just in front of the main beam. As the centerboard is located further forward, it is becoming smaller in area and the rudder is becoming larger in area and the system is kept in balance on all points of sail. No more radical mast rake required and no more overloaded rudders with a hair trigger ready to stall sailing to windward.
Bill

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