Unlimited C Class Sailboat Racing Rule (UCCSRR?)

I sincerely doubt you are going to get a response from Steve - he's too busy building the obvious answer to your question right now.

There is much more to sailing fast around a race course than just being fast in a straight line under optimal conditions. Speed of maneuvers, skill level required, fun while doing so are all factors in creating a race-able boat. I for one would not want to have to run 30' or so on every tack or gybe just to enable a wide beam that could supply righting moment for an overpowered rig.

Fredo explored (and put real money into) the foiling C Class concept quite thoroughly - and reached the conclusion a normal cat was faster AROUND THE RACE COURSE. Given Fredo's resources and the capabilities of the folks around him, I expect they did discuss, explore and dismiss the idea of a "monofoiler" arrangement for their foiling C Cat. These guys aren't dumb, they aren't hunting for funding and they certainly meant business when they challenged Steve Clark and Cogito.

Steve's response above is the same as it was a year ago - build something and he'll happily meet you on the water. He's a doer, not a talker.

 

Numbers: THE ANSWER!

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Mirabaud 26'
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Foils- two fully submerged foils, one on daggerboard ,one on rudder:
a. mainfoil area= 3.77 sq.ft.
b. rudder foil area= 3.77 sq.ft.
c. mainfoil loading*@ 80% of sailing weight= 191.4lb./sq.ft.
d. rudder foil loading* @20% of sailing weight= 47.85lb./sq.ft.
* rudder foil loading changes in sailing
e. SA/ws on foils including immersed part of struts: 19.1/1
f. W/SA= 2.54
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Rocker 27'
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a. mainfoil area=3.34 sq.ft.(two foils at 1.67 sq.ft. each)
b. rudder foil area= 2.6 sq.ft. (two foils @ 1.3 sq.ft each)
c. mainfoil loading*@ 80% of sailing weight= 183.23lb./sq.ft.
d. rudder foil loading* @ 20% of sailing weight= 58.84lb./sq.ft.
e. SA/ws on foils including immersed part of struts: 23.18/1
f. W/SA= 2.55
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This is the first time I have compared the nearly equal Mirabaud MONOFOILER
with Rocker-the C Class MULTIFOILER and the results are startling.
The two boats are virtually equal in foil loading and SA/ws on foils; both are
better than the Moth in these respects. In racing that has been done in Switzerland we know that the Moth and Mirabaud were virtually equal in speed last year. We know that the top speed of the moth is 30+ knots and that the top speed of a C class cat is 23 knots and that Rocker was generally slower than the top non foiling C Class.
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Why? When I was first getting in to hydrofoil design I read and was told by Dr. Bradfield that surface piercing drag was a large drag consideration for any foiler. And almost everyone soon learns that the tips of hydrofoils can be a large source of induced drag when the boat is on foils.
Look at this while keeping in mind that the other technical details of Rocker and Mirabaud are nearly the same:

Rocker-
a. number of foil tips= 8
b. number of surface piercing struts= 4
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Mirabaud-(and any other bi-foiler!)
a. number of foil tips= 4
b. number of surface piercing struts = 2

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This is not a 1.3% difference-this is a 200% difference-Rocker has TWICE these drag producing elements with the other statisics very nearly equal! Very likely a large part of the reason a four foil catamaran is slow......
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Thanks to Thomas Jundt for the Mirabaud numbers and to Steve Killing for the Rocker numbers that made this analysis possible.

 

Rocker flew too high, had too many foils. therefore had too much drag to be competitive with the pure C Class cat. That was pointed out last year by me and others by just looking at the photographs. Still thinking a flying trimaran configuration with 2 foils immersed, one rudder, one to leeward foil is the fastest and most stable configuration. Mirabaud and the Moths are not stable enough, hair trigger tripping and nose burying. I know the direction to go but don't expect me to build it. Well, give me multi thousands and I'll reconsider.

 

Monohull foiler vs multihull

I wonder if the analysis above would have any application to larger boats-say 90 waterline boats? Or this,perhaps? http://www.boatdesign.net/forums/sa...acing-monofoiler-design-discussion-15143.html

 

Doug, to calculate induced drag you would like to know load and span for each foil. If you cut the load in half and scale the dimensions to have the same foil loading and the same aspect ratio, you will also cut the induced drag by half. So there is no reason for the cat induced drag has to be higher. Certainly the spray drag would be though.

I have another bright idea. Bertarelli talked about the importance - realized too late - of drag vs power. The C-class foiler used, I'm pretty sure, the standard setup for the foils that provides down force at the windward hull when needed. That allows more power from the sail, but increases drag. Also, there is at least the potential that a design to provide force in both directions is not optimized for either.

How about only allowing lift from the windward foil. Then at speed the windward foil would lift out. Instead of flying a hull, you'd be flying a foil. Then, you have the same righting moment you do now, but 1/2 the foil area. The wing can be depowered to a lower drag configuration too. Less foil area, so better lift-to-drag at speed. Lower lift coefficient from the sail, so potentially better lift-to-drag there too.

This would also give you a different optimization of foil sizes. Maybe a little larger on the foil sizes, since 1/2 will be out of water at speed and the larger size will give a little lower lift-off speed.

Flying with the windward foil out of the water will probably require a little more heel. You might want to cant the t-foils out a little, so they are level with one out of the water. This would hurt you a little at lift-off, so there is an optimum someplace. Having the lifting foils producing a component to leeward and adding to the lateral lift required from the struts would hurt.

Peter Raymond

 

One more pitch for complexity: If you can lift and lower the windward DB and lock it in position, you could fly level on the leeward foils alone.

Peter Raymond

 

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I think that there is not much doubt that a boat(multi or mono) using just two foils for lift and able to use veal heel(by being specifically designed for it)
would be a very ,very fast boat in light to moderate air, and coupled with retractable "power foils"(very small foils designed to pull down in high moderate to heavy air and optimized for that specific job) would be a threat in any condition.
That's the point of this thread and the raison d'etre for the proposed rule.

 

Peter, what you're saying is pretty much what I have on Groucho Marx - but instead of angling the foils to accommodate heel, I've placed inverted V's. These work fine, no ventilation and no crashing whereas my angled surface piercers of before had a tendency to do that occasionally. However the inverted V foils are fixed, at 3 degrees attack, but because the platform has dihedral, the windward foil flies clear of the water. presenting no drag, aside from air that is. But the faster the boat goes on downwind courses, the leeward foil starts providing so much lift that the leeward ama lifts and sets up a rocking motion, then the windward one touches, begins foil lifting and rocks you back again - which is slightly annoying but you can live with it. This is really a case to have water ballast to leeward. On the wind of course, no such rocking occurs, the foil just keeps the float kissing the surface, no matter what the wind strength.

 

Doug,

With all due respect, we seem to have gone backwards in the discussion to, once again, "not having much doubt" about the efficacy of a non-existent boat design.

It's still just speculation until you build one, sail it as advertised and prove, without doubt, that it can be a stable boat that has speed realities beyond that which exist today from far lower levels of operational complexity and cost. The rub is now and shall remain, that there are no previous examples of this system in use from which to draw parallels as to function or performance.

Doubt, therefore, remains. It is still on the table for someone to prove. That process would do wonders regarding the erasing of the doubt.

 

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The princibles by which such a boat would operate are well proven albeit on different types of boats. That puts the applicable technology and a resulting design in a wholly different category than one just fantasized about off a clean sheet of paper. You may have doubt for whatever reason but there are many who don't and who are actively proceding with developing a test boat(or boats), including me.
This thread is about a rule that would facillitate and encourage the developing, testing and racing of boats like I have described with the best that there is from other technologies. It is thru participation in a rule such as proposed in the first post that the technology can be proven-or disproven.
Unless, of course, it is proven somewhere else on much larger or smaller boats first. Exciting times!

 

So in comparison between the two boats it seems clear to me that the induced drag for the cat is close to twice that for the monofoiler. As is surface piercing drag and spray drag as you suggest.

The foil loading does not give you the induced drag. You can have a huge range in values for induced drag with the same loading. If a cat and mono-foiler both support the same total weight on their main foils, but the cat has two foils that are identical to the mono-foiler, except that span, cord and thickness are all divided by the square root of 2, then the total area will be the same and the induced drag will be the same.
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All three were extremely fast in stronger winds and suffered in lighter air. Rocker experimented with neutralizing the windward wand to no appreciable benefit. No "conventional" multifoiler can take advantage of veal heel which is a major speed producing factor and helps in a number of areas not the least of which is up to 20% "free" RM.

They were fast in strong winds becase they were heavy and the foils were on the small side. At high speeds the drag comes from profile drag, so the weight doesn't matter.
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It sure would hurt-just the opposite of "veal heel"! But I'm not sure I get your idea-you can't mean this, can you? You mean lift just from the leeward foil, leaving the windward foil out of the water, right? The Rocker guys tried this ,I believe, without much success. Read Killings article under the "multihulls" forum.

Maybe the Rocker guys were trying it with a boat that wasn't designed for flying on the leeward foils only. Maybe their foils were optimized to give lift in both directions, the t was not canted to keep the foil level in the heeled position and their struts were not designed to allow the windward foil to be lifted to allow the boat to fly flat.

++++++++++++++++++++++++++++++++++

I think that there is not much doubt that a boat(multi or mono) using just two foils for lift and able to use veal heel(by being specifically designed for it)
would be a very ,very fast boat in light to moderate air, and coupled with retractable "power foils"(very small foils designed to pull down in high moderate to heavy air and optimized for that specific job) would be a threat in any condition.
That's the point of this thread and the raison d'etre for the proposed rule.

Yes, that boat would be fast, but maybe not the fastest. Veel heel gives RM to a monhull, but the width of a cat gives more. Although, Veel heel might also help in that the lift from the main foil has a component to windward and that may be a significant benefit.

A monohull is potentially lighter and nominally has less windage. These boats are fast enough that windage is probably significant. The goal is maximum system lift to drag, so I'm not sure how much the power foils help on a very low drag design. On most boats more power is good, even if it raises the sails induced drag, but that was not the case, upwind or down, in the latest AC, and may not be for C-class either.

 

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Peter, as you understand it, does the doubling of the wing tips for the cat have any effect on drag as compared to the monofoiler?

 

If you cut off the end square, well yes I think you could say that more tips means more drag. The foils being made now though have carefully shaped tips, so I don't think you would have drag from disturbed flow around the tip. It may be that we are talking about tip loss, which would be different way of talking about induced drag.

Some comments on this would be nice, but this is my understanding:
In reports and discussions of 3D CFD analysis, you don't see mention of optimizing "tip drag", but you do see profile drag, friction drag and induced drag. Hoerner, in Fluid-Dynamic Drag, talks about which tip shape works best for airplane wings, but in terms of minimizing induced drag.

There is not too much of a penalty for a straight tapered foil with 40% cord at the tip, so if I was experimenting and I wanted to do quick turnarounds, that's what I'd use.

This points out a further problem with removable tips. Maybe not a huge deal, but you can't have the best plan form both with and without the tips. With the tips off you would have shorter span, lower aspect ratio and the wrong plan form. Every one of these makes it hard to lift off, so taking off the tips would shift the wind speed range, but also narrow it. Induced drag is proportional to the square of span, so you can't reduce that too much without a big penalty, so your removable tips would probably end up pretty short and not extend the top end much.

Reducing the span and area after you are up to speed is theoretically more acceptable, if you can do it after you have reached a high enough speed that profile drag dominates over induced drag. Really, a VP program is the way to look at the trade-offs, because the foil performance and the sail performance are changing at the same time.

On a Moth, if it were legal, it might make sense to find some way to store a spare main foil on the boat. In situations where you couldn't just sail over to the beach between races you could capsize the boat (not hard to do I've heard) and swap foils. How much is this worth? You still don't want to cut the span much because of the squared effect on induced drag, but you do want to reduce profile drag as much as you can.

 

The design of the removable tips would be important. I see them as being used to enhance low windspeed takeoff especially on boats like a Peoples Foiler where foiling would be important in winds from 4-5 knots up. There are so many light air venues in the US I think it is critical to design for very early takeoff in this application. Top end speed is not as important....
For racing applications the design would include a low drag tip that is removed and an extension with a low drag tip put in its place. The problem then could be partial span flap drag. Every innovation has its price-the key is designing a system that offers more benefits than it costs in every way.

 

Gary,

I should have probably known, but I hadn't seen your boat before. It looks incredibly cool. Is there a web page?

I find myself wishing I lived on the other side of the world: Both East to West and North to South. I have heard that we do have some A-class cats in Colorado-USA, actually sailing near my house. Otherwise most of the interesting boats in the world are at least half way around the world, your boat included.

It might be that with a tunable t-foil on the rudder you could trim the angle of attack on the foil on the ama and keep it from lifting too much when you are off the wind. Might not make the boat faster, but it might feel better.