Hydrofoil calculations

Discussion in 'Hydrodynamics and Aerodynamics' started by TrulsT, Oct 13, 2017.

  1. TrulsT
    Joined: Oct 2017
    Posts: 1
    Likes: 0, Points: 1
    Location: Oslo

    TrulsT New Member

    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.
     
  2. Doug Lord
    Joined: May 2009
    Posts: 16,597
    Likes: 300, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    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....
     
  3. sigurd
    Joined: Jun 2004
    Posts: 827
    Likes: 8, Points: 18, Legacy Rep: 65
    Location: norway

    sigurd Pompuous Pangolin

    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.
     
    Last edited: Nov 13, 2017
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