Velocity prediction?

hello!

I have been reading some texts on naval architecture, and there is reference to Velocity Prediction programs. But, I find very few sources to explain how these programs work, or how they are used in much detail.

Are there some good references that are good survey papers or describe the mathematical models, uses and limitations of VPP techniques.

Thanks for any tips.

Mohan

 

There are a few comments on VPPs on this forum, mostly from myself and Nico.

Notably:

http://www.boatdesign.net/forums/showthread.php?t=10383&highlight=VPP

a VPP really does nothing more than solving (by iteration) for resistance and propulsion forces. Thus it is really fairly simple to use any resistance and any powering formula. Typically, though one would use the delft systematic yacht series and Hazen's aerodynamic model.

You can please yourself if you work out trim, heel and leeway. My VPP does, others don't. The most important thing to remember is that a VPP is NOT an assurance of real-world performance. It is a representation. Therefore, if you are going to compare a number of boats, do it on the same version of the same software.

Tim B.

 

Velocity Prediction Program

Mohan
I have a little Excel program that has a goal seek macro for balancing the thrust and drag for given propeller rpm.

The drag calculation uses Michlet for the hull plus wind loading based on estimated Cd for the particular deck line. I use high aspect foils for propellers at low power so the propeller efficiency is based on the foil lift and drag coeeficient for the Re# at each iteration.

This method has proven to give power demand within a few percent for long slender hulls in calm conditions.

Rick W.