speed formula?????

[longshot]

I read somewhere the other day that used the gear ratio, prop pitch and other things to figure the max possible speed. WHat was that formula exactly.<br />thanks<br />longshot

 

[JB]

Re: speed formula?????

Howdy Longshot.<br /><br />Calculating top speed by using rpm and prop pitch assumes too much. You don't know what the ideal prop pitch for your boat is and you don't know how much prop slip you will have.<br /><br />You can get very close with this equation:<br /><br />Square root of (HP/Gross weight) X 180.<br /><br />Example: 70 hp on my Montauk, which weighs about 1500lb wet. <br />70/1500=.0467. <br />Square root of .0467 =.216. <br />.216X180= 38.8mph<br /><br />GPS measured top speed of my Montauk is 38.5mph.<br /><br />Good luck.

 

[Clay]

Re: speed formula?????

Try this site<br />www.go-fast.com/boat speed predictions.htm

 

[dihwp734]

Re: speed formula?????

http://www.boatramp.com/prop_applet/PropAnalyzerAppletG.html

 

[Hooty]

Re: speed formula?????

...are you can multiply your prop pitch times engine revs, divide that by lower unit gear ratio and divide that by 1056. That will give you your theoritical speed. Then ya gotta subtract slippage which is anybody's guess (0-20%).<br /><br />c/6<br /><br />Hooty