16-17' Fixed Keel Self-Righting Foiler

Why do you think the crew can move aft upwind with the rudder foil? It's because they are using the rudder foil to lift! No question about this being a successful application of foil assist. I think I remember a Bieker article where he uses the term-I'll try to find it and post it.
It is using hydrofoil lift to improve boat speed without fully flying-the definition of "foil assist"! The lift from the foil provides enough lift to overcome its own drag and improve boat speed as a result-a classic application.
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My application is just slightly different using two foils upwind to improve boatspeed-making the foils "pay" for themselves upwind while the doubling of power offwind allows the boat to fully fly.
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Bieker link is dead but I think he referenced a lift of 80 lb upwind on the 14 foil. At any rate it works just like any other hydrofoil upwind:it lifts.....
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From Paul Bieker:
nominal upwind configuration of I-14-
1) Lift from buoyancy= 496 lb
2) load-crew+boat(aft of CB)=585lb
3) Lift from foil=89lb.
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Lift from buoyancy+Lift from Foil=585lb.

[bistros]

Originally Posted by Doug Lord

Why do you think the crew can move aft upwind with the rudder foil? It's because they are using the rudder foil to lift! No question about this being a successful application of foil assist.

I'll try to break out the crayons and use little words:

The T-foil rudder on an I-14 is certainly generating lift, on that I agree. The purpose of this lift is to reduce drag from the stern being weighed down and the front 1/3 of the boat being OUT of the water. The T-Foil rudder is being used to INCREASE wetted surface by forcing the bow DOWN - completely different from a foiler trying to lift both ends up in balance. This applies going upwind only.

This is nowhere near the typical use of hydrofoils in a foiling boat application. This isn't foil-assist in the same sense as offshore racing boats, true foilers or any variation on those themes. There is absolutely, positively no attempt to partially sorta "fly" the boat going on - just the opposite - driving the boat down to level sailing.

Doug, go out and SAIL on a performance boat instead of trying to "reason" it out from behind a computer screen.

Originally Posted by Doug Lord

My application is just slightly different using two foils upwind to improve boatspeed-making the foils "pay" for themselves upwind while the doubling of power offwind allows the boat to fully fly.

Your application is COMPLETELY different, providing lift on both ends of the boat to reduce wetted surface area and drag.

As always, numbers and calculations without understanding the issues is pointless.

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Bill

Originally Posted by bistros

I'll try to break out the crayons and use little words:

--
Bill

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Lift generated on the I-14 is equal to 15%(at 9 knots boatspeed) of the all up boat+ crew weight. That is "foil assist" period. The hydrofoil is lifting the boat just like a Moth hydrofoil or any other hydrofoil(.38 Cl @ 9knots). The lift from the rudder foil upwind on a 14 allows the crew to move aft without the stern sinking because the hydrofoil is lifting the crew+ the boat. There is an extra boost with the Bieker foil because of its placement in respect to the stern wave.
"Foil assist" can work with the foils lifting widely different percentages of the all up boat weight: on ORMA Tris the foil lifts about 70% of the weight of the boat. On my boat they will lift about 15-30% of the boat upwind.
The 14 ,thanks to the Bieker foil, has pioneered "foil assist" in dinghy design.
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The 14 rules allow .14 square meters of lifting area(1.5sq.ft.)-the Bieker foil is about 1 sq.ft.. There are a lot of reasons for having the foil aft:reduced drag through interaction with the stern wave, reduced upwind and downwind pitching, maximization of the lift available within the framework of the rule,improvement of upwind hull shape and more. Biekers design is brilliant and instructive to any contemplation of upwind foil assist coupled with downwind flying unrestricted by any rule.

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Illustration by Paul Bieker: