You could try it. But it would act like a brake if the rudders kicked up.

Lifting foils ("T" shaped, reverse canted daggers, etc.) are not class legal in F18.

Think about the mechanics of rudder-mounted horizontal foils off the wind: Do you want to lift the sterns= keep the bows low (maybe promoting pitchpoling?). OR do you want to lift the bows= keep the sterns low (draggy & maybe avoiding pitchpoling)? But if your boat slowed down suddenly after speeding over a wave and sticking both bows into a large wave, the rudder foils will be rapidly lifted up and OUT of the water! I think there would be short-lived contribution to anti-pitchpole forces during this process. If there is still a 30k blast on your sail, the boat (A-cat) has pretty-much stopped and is going over frontwards anyway. I have seen this close up twice recently (sorry to finger Charlie Johnson for them, but he says the situation under which he left the boat was "Flicked like a booger".)

I think that what I am trying to say is to somewhat repeat what is written about the foils at the stealth web site. (http://www.stealthmarine.co.uk/)

They use the foils as neither a lifting nor a sinking device. It is used as a device to keep the bow from either pitching up or down, by keeping it neutral.

By keeping the boat from pitching up or down they claim the boat to be less affected by that constant pitching moment induced drag. Ultimately the only way to determine if it is true is to try their rudders. (or try to make your own)

I have no way to determine if what they clain is accurate.

I suspect that travelling over large rollers as opposed to smaller lake sailing will affect whether this idea has merit... They claim that it's like having a 2 foot longer boat.

Ultimately, if you are about to be "flicked like a bougger" (is that how you spell it?) ain't notting gonna 'elp ye!

The size of your boat relative to the rollers you are sailing in will inevitably be a factor as well as lots of other factors.

Has anyone tried this idea?

They use "T" foils on the rudders of the international 14 (skiffs) to quite amazing performance improvement over boats without them. They are able to change the angle of attack simply by either "tilting" the entire rudder or having the foils "tiltable" independent of the rudder rake. They can lift the bow (or depress it) upwind or down and it has made the boats so much more controlable and faster that I don't think they would be without them ever again.Anyway, they are illegal in the F18's at present.
Darryl J Barrett.

Thanks Darryl!
That's what I was looking for.

I found a link.. http://www.i14.org/boat/articles/bieker-rudder.html that briefly tells the story of one sailor.

I would be inetersted in knowing if there are others or manufacturers out there making these.

PS, I don't race as there is narry a cat for about 900 Km's.

Fastacraft in Australia are also specialist foil makers. Hydrofoils a specialty.
Attached picture is a rudder for a 12ft skiff, symetrical wing with an adjustable flap.
web page

In a move that I'm not altogether suprised with, the Reynolds guys (R33 folks) have started a foiler version.

Any other information about it?
Thanks,
Luiz

no, they just made mention of it on their website.


http://www.reynolds33.com/en/update/index.asp

Looks like the foiler market is going to get interesting.


W00t found more!!

It's interesting that they have designed this rig with J-foils. Sam Bradfield built a 20 foot J-foiler in the 1980s before carbon fiber, but it was a bit heavy and the solid wing was apparently a nuisance: Sam then changed to T-foils.

Spectacular. Looks like a smaller Hydroptere but for the L foils and bow sensors. I hope the structure and stability problems of the "big brother" won't be repeated.

Luiz: Most of us never heard the details about Hydroptere' and stability issues. I heard that they broke several main lifting foils. Anything you could add would be useful. Hydrotere' did look WAY high out of the water when I saw pix of it foiling.
Alex Shafer and Nigel Pitt are sailing a Reynolds 33 on the west coast last weekend? The one with foils?

I don't know a lot, but it is of public knowlege that Hydroptere uses a computer to control the main foils, in part to cope with stability problems.

The comment that hydrofoils stability with waves is no small issue comes from Aldis Eglajs, designer of the Catris. Each time I send him a photo of Hydroptere he writes "note that all those pictures are taken with flat seas".

My inexpert analysis/opinion follows:

Water movement within a wave ciclicaly modifies the foil's angle of attack (plus each wave is different). An active sensor helps cope with that, but it will necessarily be placed in one fixed position, so for this purpose it is necessarily optimized for one certain wave amplitude in each boat speed.

If this reasoning is correct, then a bow sensor like in the Trifoiler is optimized for higher speeds-larger amplitude waves, while the Rave's lateral sensors would be optimized for slower speeds-smaller amplitude waves.

Adding to the seas influence in angle of attack, the required angle of attack is also changing due to the secondary effects of the waves: zigzag of the boat over the water, pitch, roll, inconstant wind, etc.

Passing the sensor's information through a computer probably helps optimize the work of the angle of attack actuator, but the programming is not exactly easy.

Does all this coincide with your experience or at least make sense??

Cheers,
Luiz

Luiz, this could help explain why the "J" (or "L") shapped foils would be an advantage. The lifting portion of the foil will be located deeper below the cycling flow of the wave. I remember that Hydroptere has angled lifting foils that lift from their length to the surface of the water. I would think this angled foil would be much more suceptible to wave flow influences than a deeper J or T shapped foil.

This cycling in ocean waves might be particularly a problem with very large tapered Surface-piercing foils like on Hydroptere'. The lifting capability is very high at the top of the foil. When this part passes through a wave, there will unavoidably be a severe lifting force exerted. I think this motion would be hard to dampen with even a large flap.

It is likely that this is part of the rationale for using submersed foils instead of surface piercing foils - inverted T or L fois should be more effective to avoid the effect of smaller waves. The other reason I know is ventilation.

However, no foil can avoid the effects of big waves and an offshore foiler requires a solution that doesn't depend on avoiding waves or their effects. It has to keep working with them. A big challenge.

Agreed, but I thought Hydroptére's foils are narrower in the tip instead of larger in the top...

Sounds like a joke, but maybe it isn't. Since that boat is so powerfull, it needs proportionally less foil area in the tips after takeoff then others.

Or could it be that it needs a larger top because they want to take off in lower speeds (otherwise it'd be a dog in light conditions)?

Yes, angled tapered foils like Hydroptere' have wide chord at the top and narrow chord at the apex (bottom tip). Constant chord surface-piercing ladder foils try to get around this by climbing up onto the bottom lifting foil at speed while the other lifters are out of the water.

A constant chord surface piercing foil (rectangular) would also have more submersed area in low speed and less in high speed - a usefull feature.

I'd say that the tapered foil is due to Hydroptére needing a wider range of lift force then that provided by a constant chord foil.