New High Performance Monofoilers

Gulari here:

Gulari on DA:

The case is closed on this question-or shall we say ,statement(s).The pictures in the previous post irrefutably prove that a twin strut bifoiler CAN be veel heeled.


As to this:

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The only discussion of a twin strut foiler so far in this thread revolved around Gulari's statement here and on DA that a twin strut foiler could not be sailed with veal heel-and my contention that it could be sailed with veal heel- the discussion was never about performance. Both here and on DA I've said that I think a single strut is better than twin struts but that is mainly conjecture at this point. Though it is backed up by an analysis of the sketch I did above(and below) that clearly shows that the wetted surface gain of a twin strut foiler is easily over twice that of a single strut foiler when veal heeled. That gain can actually be measured from the sketch should you choose to do so. I do not think a twin strut foiler can be as fast upwind or offwind as a single strut(for the main foils) foiler can. But speed is not everything and there may be advantages in some cases to the twin struts. Take Bethwaites foiling 49er,for instance: that boat is still sailed as a competitive 49er w/o foils and so the twin strut arrangement allows foils to be fitted w/o any surgery to the boat.
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Further, a number of people including me, think that the most significant gain from veal heel is the gain in RM which can be up to 20%. Only bi-foilers(or bi-foilers with power foils) can increase RM with windward heel: that is the significance of the term "veal heel". The term does not just describe windward heel-it describes windward heel with a gain in RM that can only happen on a bi-foiler. You ignore this in your comments and it is critical to a bi-foilers' upwind performance.
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beg to differ: see posts 266 and 267 of this thread!
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Use the centerline of the sketch below to visualize(or measure) the wetted surface gain of a twin strut foiler with veal heel vs a single strut foiler with veal heel:

 

it is so funny that you know so little about sailing foilers. The 49er has a major issue that is plainly obvious in the picture to me but your expert eyes must not be able to see.

 

High Performance Monofoilers

Well, as I've said NUMEROUS times to you: if I'm missing something I'd sure like to know what it is. Please explain. Thanks.

 

not until you go sailing

 

I've just been sailing. Please explain what I'm missing. Thanks.

 

Doug:

Rather than ask someone else to do my thinking for me, I'll propose a couple theories which will expose either sound thinking (or likely poor judgment) on my part. I'll take a swing at explaining what I theorize Bora may be talking about from the 49er pictures:

1) There is a dramatic difference between the amount of lift and drag generated at the two opposing vertical foil struts. This difference appears to be seriously affecting the boat's ability to be directionally balanced. These horizontally separated foils have to travel different distances in all turning maneuvers, and water flow speed is different on each vertical surface unless the boat is moving straight and level.

2) The boat appears to be experiencing serious lee helm, given the tiller position and subsequent added drag on the canard to compensate. Windward heel definitely increases lee helm conditions on most boats, much as leeward heel increases weather helm. Windward heel is also affecting the side to side location of the CLR in this boat much more than a Moth style boat.

3) Optimizing the foil depth to keep wetted surface area reasonable renders high angles of windward heel impossible without bringing the leeward side of the horizontal foil too close to the surface and causing ventilation and loss of lift over the whole foil. Deeper foils to mitigate this would increase wetted surface area and foiling drag to the point where it may not foil.

4) There is one hell of a lot of vertically disturbed water behind the boat, that does not look typical compared to a minimal wake foiling Moth. Turbulence equals drag.

Just speculation, but rather than ask someone else to spoon feed me I'm willing to take a swing and think for myself.

--
Bill

 

Kutta 2:nd order vortices enjoyed

Hi!
I agree with bistros. Anyway, nice to see the canting-keel man back in good shape. Bgulari, seems that the guy has really been out sailing and enjoyed those 2:nd order Kutta vortices.
Regards,
Booster

 

New Monofoiler

"analysis" from DA by Phil S:
"16ft long, about 2.7m wide, 12 sq m of sail, all carbon, very light, converted Ilett moth foil, about 5 years in development, beautifully built by a professional boatbuilder as his pet project. Bruce Gault has also spent many hours learning to sail it and its prototype predecessor before foils were added.

He now sails it with considerable skill. But its still a big handful and although he shows remarkable downwind speed sometimes, he swims too often and he only beat the moths in the very light last race of the weekend where sail area and LWL counted most. The rest of the time he was pacing me at the back of the fleet, many minutes behind the fit young guys with the fully developed, and properly tuned moths. (I admit my new moth at this stage of early development is way off the pace and my early season fitness is also well below standard.) (But we did enjoy some good competitions and close finishes.)

Please take note Wind apparent and other exponents of big foilers, big does not necessarilly mean easier or faster. "

Right, but ah, it also doesn't mean it won't be faster or easier to sail.
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Just a note: The RS600FF(see earlier in this thread) monofoiler has beaten the Moth even though it weighs 2.5 times as much. It is larger(with much more SA) and is a trapeze boat. Some people consider that the trapeze would make the 600FF harder to sail than a Moth, others say thats not true.....

Pix from DA

 

Following Bistros’s admirable example, I too have been trying to think for myself:



Regarding weather heel, I remain unconvinced of it’s advantages for a foiler sailing close to the wind, although for a sail boarder I can see that the situation might be different.

1) any heel will move the apparent wind angle forward, though the effect will be small unless the heel angle is extreme.
2) the sail’s lift reduces foil loading but the foil also heels so foil drag is not reduced.
3) one foil tip is brought closer to the surface with increased risk of cavitation or even ventilation.

On the other hand, with weather heel the foil lift has a windward component that reduces lateral force on the strut (struts, daggerboard, whatever) that should reduce strut drag and potential for ventilation. Is it sufficient to offset 1) and 3) above? Good question!

The only other reason for intentionally sailing with heel that I know at my present level of understanding is reduction of wetted area, applicable mainly to skiffs and garveys.



On the double strut question, I cannot see what it has to do with the ability to heel if the foil width is the same.

A) It may have a slight structural advantage since a uniformly-loaded member has 33% less bending moment when supported at its ends (assumes infinitely stiff struts).
B) flexing of the struts and foil is minimized placing the struts at 20.7% of the overall span, in theory. A bit more in practice due to tip vortices.
C) there is more vertical area and hence drag.



Not all of the above is new of course but I am trying to get (and give) an overall picture. I may be wrong here or there but I’m always happy to learn. The double strut configuration is of interest to me as it has potential in a retrofit foiler design I am working on and I normally work in wood which is weaker than carbon composite.

 

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Well, following good examples is always, sometimes, maybe advantageous.
1) Veal heel is proven for years in the Moth class-if you can't/don't do it upwind-you lose.
2) Major advantage you may have missed: many boats heel to windward but only a foiler gains up to 20% RM for "free".

pix from Bill Beavers paper on the Moth: (note righting arm is the distance from a vertical line thru the center of lift of the foils to the CG of the boat/crew combination-not just to the cg of the crew as shown)

 

That's a really cool idea, Doug, but it's not free.

 

Bill nailed it.

I dont respond to anything doug aims at me.

 

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Bistros may have nailed "IT"(whatever that is) but you never answered my question about why you made the comment above:
1) The KissKut foiler has the twin struts forward-not aft like on the foiling 49er.
2) The sketch I did at your suggestion clearly shows that there can be performance problems with a twin strut arrangement(which I've said from the begining) but just as clearly shows that there is no reason a twin strut foiler can't be veal heeled-not "no weather heel sailing" as you put it. You were talking about the KissKut ,afterall....
3) So, ah, why did you make that statement? Just curious.

 

Doug:

Bora clearly was discussing the Bethwaite twin strut foiler when he asked YOU what the visible problems were in post 222 above by analyzing the modded 49er pictures. You did not answer his question, and have repeatedly asked for explanations. I tried to help.

If Bora Gulari, an accredited aeronautical engineer, experienced and successful composite fabricator, foiling expert, World Champion in the Moth class makes a prediction about performance in a design, I think you may find it worth considering.

Most if not all of the points I proposed as potential issues with the Bethwaite design may also apply to the Swiss design.

--
Bill

 

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bistros: the above is post 222-what are you talking about? Why don't you let Bora answer the question? Are you trying to run "cover" for him? The question was not about performance but was whether or not the KissKut foiler could potentially be sailed with veal heel. Simple.
The discussion started in post 261 when I posted the first post about the KissKut foiler. The very next post was Gulari saying "no weather heel sailing"-he was clearly, unambiguously referring to the KissKut foiler! I was curious then and am still curious as to why he made that comment. Just curious.....