Can you calculate boat speed from prop pitch and rpm?

T

trickasabrick

Cadet
Joined
Apr 28, 2005
Messages
9
I tried it with my prop. Taking into accout the pitch, gear ratio, and using about 15% slip, I came up with 43 mph at 4500 rpm, which is about what my speedo says. Anybody have any reasons why that wouldn't get you at least in the ballpark?
 
L

Limited-Time

Vice Admiral
Joined
Mar 30, 2005
Messages
5,820
Re: Can you calculate boat speed from prop pitch and rpm?

taab,<br />It should get ya in the ball park. I'm not sure about your slippage number, sounds close. A lot of other variables effect top speed, hull design, weight, load distribution, water conditions, and air temp. to mention a few. Your best bet is a GPS. If nothing else it will tell ya how far off your speedo is
 
Boatist

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: Can you calculate boat speed from prop pitch and rpm?

My question is how do you know what the rpms will be for a new prop.
 
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