Talador wrote:

"It is important that this be foil assist and not actually designed to lift the boat out of the water. It should be designed to take most of the load of the boat at  20 knots or so.  This foiling design is unstable if the hull actually comes out of the water, especially if the foils come out of the water."

Firstly you can't make the claim that 'this' foiling design is unstable.  You have specified a foil, but not a configuration.  What configuration are you referring to? E, V, T, Y, L, U, O, C, J, L, S, or inverted (ladder) Pi?  Until you specify this (for all foils in the configuration), you cannot claim that that a particular design is pitch, heave and yaw unstable.

For examples of this sort of stability see C-fly and Tom Speer's Basiliscus discussion paper:

C-FLY | Offshore Hydrofoil Sailing

			C-FLY | Offshore Hydrofoil Sailing C-FLY is a unique sailing craft, with innovative wave piercing hydrofoils that deliver incredible speed and stability in all sea-states.
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index

			index The Basiliscus Page Welcome. This page is a living design case history on the development of my sailing hydrofoil, Basiliscus.
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http://www.basiliscus.com/CSYSpaper.pdf

Talador wrote:

"There is another thing to consider. A long slender hull is already pretty good at reducing wave drag and the benefit of foils will not be as significant for that hull shape.  In other words if the Proa can already go 15 knots adding foils is going to reduce light air performance and only add a few knots at the top end, but it will make it a lot easier to get to the top end too."

For these reasons the proa I'm building is round bilged, low wetted surface, in order to assist light wind performance.  You've probably noticed that the emphasis at HP is on beam mounted, retractable, kick up foils that enable reduction in wetted surface and foreign object impact protection.  Hence, lifting foils can be retracted in light winds.

I'm interested in full foiling, not merely foil assist.  Surface piercing seems to be the way to go in order to generate pitch  and heave stability.  T foils are more efficient within a prescribed design speed range, but require progressive depowering as speed increases.  Surface piercing does this thru reduced wetted surface.  Yes there are drag penalties.  The challenge is to design an efficient system for the proa.  I'm not going to discuss my design thoughts at this stage - I've got plenty on my plate as it is.  All in good time.

We've already covered ground that's been covered before:

Harryproa

			Harryproa Harryproa discussion group is for everyone interested in the Rob Denney conceived proa series. If you have found your way here you probably already kn...
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I should have made a point of commenting here but haven't been prepared to set aside the time:

Can a Pacific Proa Benefit From Lifting Foils ? - Boat Design Forums

			Can a Pacific Proa Benefit From Lifting Foils ? - Boat D... Can lifting foils benefit a pacific proa's pitch stability and lift its displacement out of the water ? The pacific proa usually has three foils: a
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