finding boat's resistance

[plain_sailing]

A friend of mine is aiming to build a 10 m motorboat and he asked me if I could calculate the effective horsepower of the boat in order to choose the appropriate engine.
Does anybody know which is the best method to find boat's resistance knowing only the main dimensions, the lines and the service speed.
I don't have time to make a model and test it.

Thank u in advance.

[Stephen Ditmore]

One method is to find a book that has a plot of HP per pound on one axis and velocity on the other - but it must be for a hullform similar to yours, pref with similar drive, propeller, and weight distribution.

A more sophisticated way is to use software like that available from Hydrocomp.

There might be related information in "The Propeller Handbook" by Dave Gerr.

[fireball]

There are many different regression equations for calculating the resistance of a vessel. Most of these regression equations have been generated using non-dimensionalised ratios of hull parameters for a particular hull type.

Is this a monohull or catamaran? Does this speed correspond to a displacement, semi-displacement, or planing hull? It is possible to use a software to determine the resistance, however most of these softwares require you to select which of the methods you wish to use unless it is CFD.

If you provide this information it is possible for me to help you. It is important to remember that any value of resistance you obtain for the service speed must take into account losses for a sea margin to account for added resistance in waves, and shafting and propeller losses.

[plain_sailing]

Stephen and fireball thanx a lot for your help.
The boat is monohull & displacement hull.
The main dimensions are listed below :
L (wl) = 10 m
B (wl) = 3,1 m
T (full load) = 1,08 m
speed = 11,5 knots
Displacement = 10,6 metric tons
transom stern
round bottom
no bilge keels
8m center keel
longitudinal center of buoyancy = slightly fore midship