Hydrofoil calculations

Hi

I am trying to design a 25 ft tandem hydrofoil boat(4 T foils), but I need a little help with the calculations when the boat will take off, the Vmax, and the drag. The boat has a v shaped hull and is electric powerd and going to weight around 2.2-2.5 tons.

 

Get the book: "Hydrofoils Design Build Fly" by Ray Vellinga. It has all the calculations required to design and build a foiler done in an easy to understand manner by a master of hydrofoils. Probably still at Amazon....

 

You need an outrageous amount of area to lift a 25 foot displacement boat of 2.5 ton at displacement speed (<7 knots).
You must provide some data in order for anyone to answer your questions. How much power? Is there rocker, is it a deep V, how wide are the hulls, what does the aft end of the bottom look like, how wide is the stern?

Without a really big engine I believe this is a dead end. Here is the formula for lift in kg.
L = 0.5 * rho * S * CL * V^2 / 9.8

rho: Water density - a bit over 1000 kg/m^3
S: foil (projected) area in m^2
CL: Coefficient of lift - it could go as high as.. eh 1? 1.2?
V: velocity in meter per second (m/s) = knots * 1850 / 3600 or about knots/2

That's at least three (3) square meters for takeoff at 7 knots. At 12 knots it is still over 1 m^2 and I have no idea how you would get a 2.2 ton 25ft boat to that speed.
Maybe look into rungs / ladder foils. They will unsubmerge one after the other, and can even be made passively balanced. www.tspeer.com look for 'basiliscus' - a ladder foil trimaran project.