Which one is more hydro dynamically efficient at moderate speeds up to 20-30 knots for moderate light vessel?
Planing or Hydrofoil ?
I am considering to upgrade my power catamaran with hydrofoils similar to moth foils.
It will be very interesting to find out what is minimal HP required to lift such boat
almost 5 meters long 110 kg boat + 150 kg crew + 30 kg motor = 290 kg
Above the water on hydrofoils or get planing (on specifically designed planing surface)
I have 3 motors available for tests:
- 6 HP Suzuki
-Tohatsu 18 HP
- Electric 2 x 1.1 KW 24 V
Apparently for windsurfing at moderate speed there is no obvious advantage to have hydrofoils.
Here is some test done by amateur Frenchman some times ago:
gerard.delerm.free.fr/clair/b_page2a.htm
Go the hydrofoil!!!!
And video or it didn't happen 
However seriously, you will need enough power to get your boat planing before the hydrofoils will generate enough lift to get her out of the water.
Hydrofoiling is based on area and speed so you don't need big speed to get airborne, when you double the speed, the lift quadruples so a small increase in area and speed can make all the difference.
Hydrofoils are smoother, quieter and just way cool to ride.
High aspect foils like on the Moths are highly efficient but lower aspect foils give a more stable ride.
I hope to learn something and avoid too many mistake on somebody elso expertise :
www.amazon.com/Hydrofoils-Design-Build-Ray-Vellinga/dp/0982236115/ref=sr_1_12?ie=UTF8&qid=1367297750&sr=8-12&keywords=hydrofoil
mate you seem to be keen to reinvent the wheel at every turn.
Hydrofoils so not practical on so many levels not the least of which will be transport and draught of boat.
Add countless manhours of tuning and reinventing wheel and you will still be behind.
How many hydrofil passenger ferries do you see around anymore ? none. thats because of real practical reasons. they were everywhere in the 60's. Now they are all cats. .
it's actually very hard to beat a displacement cat (what you have) for efficiency. Modern designers like shionning, crowther etc make fast displacement powered catamarans that are very easily driven. there are even some solar electric ones, but they are of course, pox....
Hey macro i have a moth on the gold coast I'm selling, it's full carbon with machII main foil. Message me if you want some more info. Maybe ditch the cat idea and run a mono with electronic stabilisation on foils
I've actually been thinking outside the box and have come to the conclusion y\that you are aiming a bit too low. Foils.... hmmmph, been there done that, as someone said in post 3, even some dude in a windsurfer at 8kn can do that. I think you need to look at the bigger picture, I'm thinking more along the lines of, your cat with a solid wing tramp and a couple of sponsons that are more wing than sponson and you're away like these bad boys.
