Effect op appendages on friction/fuel

[rnuyts]

Hello,
Does anyone know more specific details about the effect of appendages like anodes on the hull and the effect on fuel and increased friction? Is there some kind of percentage that I can use and is reliable to calculate the Horse power maybe?

Thanks a lot,

best regards
Rik Nuyts

[danielc]

For quick calculations in our small craft design course we always used the approximation that a 2% reduction in drag results in a 1% increase in speed. Likewise, a 2% increase in drag results in a 1% decrease in speed.

This ratio was given to us by our Prof who has extensive model testing experience at very high levels of design....but I really do not myself know how accurate this is!

So you could just calculate the added drag of the appendages and go from there...depending on the appendage you could use wetted surface area or frontal area to calculate drag....but you need drag coefficients for the appendage shapes. Then just use 1/2*Cd*rho*A*V^2...pretty quick and simple, but of course neglects separation effects and hull/appendage interaction. You also need to know the original resistance before adding/subtracting the appendage.

The relationship is useful for any increase/reduction in drag from appendages, sails, rigging....

hope this helps.