# Peters on fast boats

Discussion in 'Powerboats' started by Mikthestik, Mar 22, 2016.

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### MikthestikJunior Member

I haven't had much to contribute for a while. High speed power boats I find interesting but I think that unless you are designing a high speed rescue launch. sport fisherman, racing machine or MTB they are more fun than practical.
I used to be obsessed with speed power calculations until I decided on Kieth's formula for boats up to SL2. For boats => SL3 crouches formula was the way to go. Now if there is a problem with his formula it is this you have to guess the constant which ranges from 150 to 220 depending on the type of boat.
While searching for an alternative I came across two PDF documents with the above title. I could not attach them because they are to big. In this PDF there are some examples of modern racing cats with C values >300.
The range of coefficients for this formula is K = 2 to 2.5
K for the racing cats can be under 2. This formula is surprisingly accurate. I like it because with such a narrow range it should be easier to be accurate.

Kts = K(4.64 x BHP/disp in long tons)^0.5 The PDF said 46.4 an obvious misprint.
Google Peters on fast boats to get the PDF docs.

Last edited: Mar 22, 2016
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### AlikSenior Member

Crouch and Keith formulas are both just rules of thumb, designer can't take them seriously. They do not take into account many factors.

Talking about use of formulas and values of coefficients, those coefficients should be only defined using similar prototype boat, i.e. same bottom loading, deadrise, CG, appendages, propulsion system, also boat size.

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### Ad HocNaval Architect

What he said

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