Total Resistance Formulation of Hydrofoil Craft

Discussion in 'Boat Design' started by leviathan, May 30, 2012.

  1. leviathan
    Joined: Oct 2011
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    leviathan New Member

    Hi all, I'm a naval architect undergraduate student, and recently I'm doing my final assignment about hydrofoil craft.
    I have done a towing tank test and obtain the total resistance, but I need the formulation to calculate it numerically for validation.

    Can anyone give me any advice or suggestions about the formula , please?

    thanks and regards
     
  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Depending whether you hydrofoil is a surface piercing or fully submerged, the forces are given by:

    hydrofil forces.jpg

    You have to work out the lift and drag of each foil, so i the figure above the total drag shall be = Drag (aft ) + Drag (fwd) + Drag (aero)

    where:-
    Drag(aft) = drag of the aft foil
    Drag(fwd) = drag of fwd foil
    Drag(area) = the aerodynamic drag of the hull once foil borne.

    There is a very good section in the book "Mechanics of Marine Vehicles" by Clayton & Bishop
     
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  3. Dingo
    Joined: Dec 2003
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    Dingo Junior Member

    Method to work out resistance of hydrofoil boat

    Let e = Rt/displ where Rt is total resistance and displ is displacement
    Also, for the model, we have e_model = Rt_model/displ_model

    e = k.e_model where k is a correlation factor and is given by:-

    k = 1 - (Cfh_model - Cfh)/Ct_model - [(Cff_model - Cff)/Ct_model][Sf/Sh] - [(Cfst_model - Cfst)/Ct_model][Sst/Sh]

    Sf is surface area of foil of boat
    Sh is surface area of hull of boat
    Sst is surface area of strut of boat
    Cfh is hull friction coefficient after ITTC 57 line
    Cff is foil friction coefficient after ITTC 57 line
    Cfst is strut friction coefficient after ITTC 57 line
    For the model, use Kirkman's method "Scaling Problem of Model Appendages" or as reproduce in Principles of Naval Architecture to determine Cff_model and Cfst_model for a given Re
    Ct_model = Rt_model/(0.5 rho_model V_model^2 Sh_model) which is based on the wetted area of the hull alone. Rt_model is what you measured in your model test.

    Hope this helps.
     
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  4. tspeer
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    tspeer Senior Member

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