formula to find prop pitch from hp and boat size?

[n0ukf]

I've seen information on figuring the speed of your boat based on engine RPM, LU gearing and prop pitch. But is there a formula to determine the optimum pitch based on boat size, and motor hp? <br />A 14' and 15' here, both with 40 hp 'rudes have 10x15 props and a 19' with 75 hp johnny has a 10x10. The 15' runs about 22mph (GPS) but RPM and others' speeds not currently available.

 

[walleyehed]

Re: formula to find prop pitch from hp and boat size?

The only way to determine optimun pitch is a tachometer, and knowing the manufacturers recommended W.O.T. range.

 

[Spidybot]

Re: formula to find prop pitch from hp and boat size?

Yes. The spreadsheet is an estimator to guide you. Pretty accurate, but by no means a replacement for proper testing.

 

[n0ukf]

Re: formula to find prop pitch from hp and boat size?

UU, what spreadsheet?<br />walleyehed, how do I find out the manufacturers recommended W.O.T. range on an older used engine without manuals? For the previous formula, how do I find out the gear ratio?