Hydrofoils, how fast do you have to go to get it out of the water?

First, this isen't my idea, really. My brother wants to build one. I tried to tell him that even on a small boat it would be rather complex. The stresses on the foils would exceed the materials he could afford. The draft would be relitivly deep (there arn't a lot of deep lakes 10' or more near here).
The drag the foils would make the boat impractical when the entire hull is in the water. Not to mention, and this is the one that I used to finally talk him out of it, you couldent get the boat out of the water at a boat ramp, you would have to lift it out of the water at a dock.

So does anyone have any practical info on what a 'cheap' hydrofoil costs, and how fast you would have to go in order to get it out of the water?

Just in case he comes back to me with this idea.....

Thanks

 

hydrofoils

Powerboat or sailboat?

 

I think he was thinking he could do it with a sailboat.....

 

foilers

Well, he can after a lot of research. See www.foils.org & see the "Foiler Design" thread under "Sailboats" on this forum. You might also check the "Moth on Foils" thread under Sailboats.
There are multihull foilers and monohull foilers; foilers with 2,3 or 4(and more)foils.
A lot of research needs to be done to fully understand what your options are....
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Here is the Australian International Moth Class forum. The Moth is the only sailboat class that regularly races on full flying hydrofoils. There are some detailed discussions about foils under "hydrofoils":
Australian Moth Class Association :: Index
Address:http://www.moth.asn.au/forum/index.php?sid=b2984b019982eb0292321c902664a9d2
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You might google International Moth Class and look at some of the video's and stills on the Aussie and UK sites. You can also look up "Rave" and "Hobie Trifoiler" to get an idea of what multihull sailing foilers look like.

 

Ok heres one for the forum..has anyone got any thoughts on how to develop H/foils for an ocean racing kayak (21ft/14Kg). If you google 'flyak' you will find it has been done on flat water...suffice to say with alot of energy expended..I am interested in how to take the advances and apply to an ocean racing kayak to increase performance in wind chop and down wind paddling...with as little drag as possible and without impacting manouevourability....

 

oceanfoilyak

Contact John Ilett at: john@fastacraft.com and/or
Eric Sponberg at : www.sponbergyachtdesign.com

 

Thanks Doug will do...