Foiler Design

Doug Lord said:

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Paul, do you think it might be diagonally unstable? Or wouldn't it matter?

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With only an incline surface up front, you do get into issues. With a 45 degree foil operating angle, for example your side force would end up being very close to the same a the lift provided.

The above is why I indicate a need for a vertical portion that would be able to handle the side loading with little or no help from the side loading of the inclined portion.

The big difference in foil side loading has traditionally be the much lower loading for downwind runs. However, side loading for the new fast foilers can not be that low given that they are flying a hull. This would seem to indicate that for my proposed "what if" situation, there should be more side force needed from the foils than you get from the inclined portion of the foil. As long as this situation holds, the side forces from the two portions of the foil are never in opposite directions. Having different foils surfaces producing forces in opposite directions is where you get lots of wasteful induced drag and is one big reason for poor V foil efficiency.

One objective of the above would be to have all surfaces of the main foil producing nothing but lift forces that are needed for either vertical lift or for leeway control.

P Flados said:

...Consider a foiler similar to Hydroptere, but designed to have only the leeward dagger foil and the T foil rudder in the water. The vertical extension of foil at the bottom could be sized for providing all require horizontal force with acceptable leeway. The inclined portion can be then angled such that the foil only stays submerged to the extend that the angled portion supports the entire weight of the boat. It does this while operating at an AOA that provides a good L/D. ...

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As the speed increases and boat rises, the horizontal span will be shrinking. This can raise the induced drag considerably if the foil operates at a constant section lift coefficient. The induced drag can actually increase with speed, which eliminates the whole reason for using foils in the first place. This can be ameliorated by changing the pitch attitude to reduce the lift coefficient and operate a more of a constant depth.

There will be some relief from leeway, too, because as the boat goes faster the leeway angle will decrease and this will reduce the angle of attack (measured normal to the panel's axis) of the inclined panel.

Bear in mind that induced drag is doubled at the surface compared to deeply submerged. So the reduction in wetted area of a surface piercing foil has to overcome the fact that as the boat rises more of the lift is concentrated near the surface when the wetted area is reduced.

As the speed increases and boat rises, the horizontal span will be shrinking. This can raise the induced drag considerably if the foil operates at a constant section lift coefficient. The induced drag can actually increase with speed, which eliminates the whole reason for using foils in the first place. This can be ameliorated by changing the pitch attitude to reduce the lift coefficient and operate a more of a constant depth.

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Which leads a layman to ask why is the Banque Populaire foil assist solution not the way to go?

I realize that Banque Populaire is a much bigger boat than the ac 72s ,so it is not a fair comparison. Its top speed is about the same ,45 knots or so, and its around the world average speed was a lot faster than the ac 72s around the cans. I know again not fair , a down wind race. But 26.5 knots around the world?

J foils

The inward pointing J foils on many multihulls. Why are so many operated so close to the surface as to almost continuously breach the tips?
Is it poor trimming/trim ability?
Or is leeway induced incidence angle on the horizontal foil in fact a completely inadequate stability mechanism so that loss of lift due to surface proximity must take the job?

Some of them have little wingtips (10% of span?) pointing upwards, breaching even sooner one would think. What is the reason for those?

UptiP foils

In "Sailing Foiler Design" in the aero-hydro forum here Tom Speer said it was draggy for an UptiP* foil to be sailed with the inboard tip breaching the surface.
A couple other designers have said that the breaching of the inboard tip is a back-up altitude control.
In the real world the GC32(designed by Martin Fischer), Flying Phantom, NACRA 20 FCS, Gunboat G4, Gitana(now Maserati) modified MOD 70 and others sail on a regular basis with the lee uptip foil inboard tip breaching the surface.

* Note that also in Sailing Foiler Design the designers of the first UptiP foil call the foils(TNZ with Morrelli and Melvin), not "L" foils, not "J" foils, not "V" foils but "up-tip" foils.

http://www.boatdesign.net/forums/hy...ler-design-foil-assist-full-flying-40894.html
See posts 40, 49-Tom Speer correcting post 40, 42-Morrelli and Melvin on "up-tip" foils(read Part 1 and Part 2), 59-a bit from Dario Valenza, 62 &72 Tom Speer.

PIctures,L to R-1) Flying Phantom, 2) GC32 on record speed run, 3) Gitana MOD70, 4) NACRA FCS(click to see foil tip), 5) AC45-you can see disturbance caused by foil tip but no tip, 6& 7) Fire Arrow Test model- UptiP ama foils--tip rarely breached the surface in first successful tests:

Sigurd - the reason is lift control. The V or J foil breaking the surface is used to automatically control the area of the foil so its lift gets balanced with the weight of the vessel and the applied loads from the sail. Otherwise the foil has top be trimmed in real time with a wand or sensor to reduce lift as the boat increases speed. Peter

Thanks Doug, very informative pics. Great thread you made. Thanks petereng.

I guess in practice, the leeway/heave couple is not usually strong enough to rely on it, so they fly higher to use their 'backup stability 1', surface proximity, 100% of the time, and then most of them use 'backup stability 2' (tip breaching) very much too.
With that in mind maybe 2/3 V is the better moniker, them being used like V's most of the time.

Seems to me maybe a greater change in leeway per ride height would be nice, a sort of lift distribution taper off towards the bottom would do that.
So do they twist or change camber close to the bottom of the strut to lose side lift there?

Do any of them ride deep enough to rely on the leeway-heave couple alone?

You're welcome-but Tom Speer started this thread. AC 45's don't always have an exposed lee tip.....

PS- in my opinion, they should be called "uptip foils" in honor of the name given them by the inventors.

I was referring to the thread you linked: Sailing Foiler Design: Foil Assist and Full Flying.

I don't have specific examples but my interest in foils go back a few decades and I've never heard them referred to as anything else than J or L, that I can recall, before now. Just keeping to the ASCII nomenclature I was taught as a kid.

You Americans of all people should understand, your measurement system is completely baroque. Using snails and human limbs as reference - absolutely odd.
'Two slugs of butter please?'
'Just a moment. Ofelia, will you be so kind as to go and fetch two slugs from the garden? Look in the turnip rows, please - it's for Dr. Henderson.'

UptiP foils

The problem is that the UptiP foil is a whole new kind of foil and it seems to me that it ought to be called by the name it's inventors gave it? It's not an "L" or "V" foil and there is surely a lot of confusion about them and almost a whole alphabet of made up names for them. Dario called them "L/V" foils! Anything but their actual name......
Oh, well.

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Link to Part 1 and Part 2: http://www.cupinfo.com/en/featuresindex.php

Quote from the article,Part 1:

When we were working on the rule, we knew you wanted to get as much lift as possible when you were going fast downwind,” Melvin says. "For instance, in the 2010 America’s Cup, sailed on giant multihulls, the maximum amount of lift we thought we could get was about 50% of the weight of the boat. At that time, we were still relying on the hull to provide pitch control, so what’s come out of this is the boats all now have elevators (the horizontal foils on the rudders).

“At Team New Zealand, we developed a new type of foil that allows you to keep your height above the water more or less steady. No one had been able to do that before, at least not on a course-racing boat that was not going downwind. We developed that mostly on our SL33 test boats -- they came with the stock constant curvature “C” foils and with those kinds of foils, you can generate 50% boat weight lift before they get unstable. But we noticed that when we could get one boat up fully foiling for a few seconds it would really accelerate away from the other boat – and that got the wheels turning. How, with such a huge potential benefit, can we achieve stable flight downwind? So our design team came up with the “up-tip” type of boards. We refined those on the 33s and our 72 is designed to do that and fortunately it worked right of the box.”

The siurface pierching V foil is not really "new" its been in use for decades on ferries, naval ships and other boats . TNZ however did cantilever it vs attaching it both sides. This was possible due to materials ie changing from aluminum to carbon fibre and the drive for innovation that the AC is? Peter

Peter, depending on the design an UptiP foil can maintain altitude with little to no change whereas any surface piercing foil changes altitude with speed. AC boats make small adjustments to rake to change altitude for the conditions but the foil is pretty good at maintaining altitude with no intervention.

Peter,if you go here: http://www.boatdesign.net/forums/mu...f-righting-trimaran-test-model-36058-157.html post 2342 pictures "A" and "B" you can see the uptip ama foil on my large test model maintain the same altitude with a big change in speed and load.