horsepower for hull calculations

[ifishcq1]

I have read on different sites about crouches speed calculator and sorensons guide to power boats does anyone have a tried and true formula that is within the ballpark for working out the best allround hp for a hull without trial and error
thankyou

[Wahoo]

Scott, ( fnq ) where are you, im sure you could answer this, i would be keen to know also


Daz

[Chimo]

There were threads on this site on this some time ago . Suggest you do a search.

Also the manufacturers plate should give you an upper limit that is worth considering esp from an insurance and liability point of view. Writeups also often give optimum HP based on their tests too.

Cheers
Chimo

[cbs]

If you are looking at determining the maximum HP that should be fitted to your transom, ie what is shown on the builders plate, then AS 1799 has the details for determining that. Also note, that these numbers are not binding to any specific manufacturer, as they can advise whatever they would like to. (AS 1799 is not a mandatory standard)

On the other hand, if you are looking at determining the expected speeds for a given installed power, crouches formula, though very simple will give reasonable results. The key is of course, having an accurate constant in the equation from another vessel of similar type.

If you wanted to get further into it, then I'd suggest that you google "Savitsky". Savitsky is the grandfather of planing vessel resistance prediction, but be warned, if maths is not for you, then don't even go there. There are a few online calculators/spreadsheets around, but unless you have quite a bit more data on your hull shape and parameters, then you aren't going to have all the information required. Interesting fact: Savitsky's work was initiated many moons ago, to determine the resistance of Seaplane floats and hulls and thus powering requirements for takeoff.

Finally, if you have lots of money, the most accurate method is model tank testing. This is expensive, and well beyond the amateur fisho but is done during the design phase of many commercial vessels.


I'd suggest that you stick with crouches formula, but check it against another known boat to compare. The other methods are really the realm of NA's and other technical/engineer types. Obviously, what I've said here is only scratching the surface.

confused now? good

CBS

[Jimbo00]

The following web page gives a formulae used by the United States Coast Guard to calculate hp as it relates to hull characteristics.
http://newboatbuilders.com/pages/hp.html
Cheers