# frictional resistance Froude's formula

Discussion in 'Boat Design' started by Et', Nov 5, 2006.

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### Et'New Member

Hi!
could anyone define γ in the Froude's formula:
Rfriction = (λγ/1000) . WSA . V^1.825 where: λ=0.1392+[0.258/(Lwl+2.68)]
kind regards. thank you

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### marshmatSenior Member

Usually when I see a gamma (is that the letter you're referring to?) in a formula, I think 1/sqrt(1-v^2/c^2). Since sailboats do not travel at a significant fraction of the speed of light, I presume that's not the one you're after?

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### french44Junior Member

hi,
I read your formulation and i think you lose a piece of . I use to froude methode and the right name is froude le besnerais and the formulation is:
Rf/D=(1+0.0043*(15-t))*(S*Lwl/VO)*(0.1392+(0.258/(2.68+Lwl))*(Lwl^-0.0875)*(V/(Lwl^0.5))^1.825
D metric ton
t water temperature in degree
V m/s
Lwl m
S m²
V0 cubic meter

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### naval arkMember

Gamma is the specific weight of the water you're testing in, close enough to 1000 kg/m^3 if fresh water, so it's just there to account for other densities.

As touched on, the formula is only technically correct for water of 15 degrees C, and the (1+0.0043*(15-t)) term handles the temperature differences. If you wish to use a different temp, just put this term in the numerator.

And don't forget that the Rf is given in kgf - not N!

Good luck...

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### marshmatSenior Member

"And don't forget that the Rf is given in kgf - not N!"..... Empirical formulae drive us physics types nuts! It ain't hard to make an equation dimensionally consistent....

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