Propellor dimensions

S

Sybarite

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Help please.

I need to get a new prop for a Volvo 18 hp 2002 driving a 30' 3 1/2 ton fin keeler.

The present prop seems to drive the boat well but will not allow the engine to reach its max revs : 3600 rph. It peaks at about 2900 rpm.

Is there a magic formula to determine size and pitch? A plain 2 bladed prop is fine for me.

John.

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any prop supplier will do the calcs for you or you can get graphs to work it out from. the Boat Data Book is a good thing to have and contains all the graphs.

as a rough idea, an 18 hp engine will need approx 15" dia x 12" pitch.

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If you\'ve got a few hours to spare...

You could try this <A target="_blank" HREF=http://www.surfbaud.org/zippo/other/surfprop/Introduction/introduction.html>prop calculator</A> program!

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Re: If you\'ve got a few hours to spare...

Used the "Prop Calc" program with great success,
when sizing my new propeller.

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I had my prop repitched from 15 x 9 to 15 x 8, added about 400 RPM to the engine speed, from 2800 to 3200. Much better performance as well. A Perkins Perama 17HP with a 2:1 gearbox on a Jaguar 27.

<hr width=100% size=1>dickh
I'd rather be sailing... :-) /forums/images/icons/smile.gif
 
Why do you want to run your engine at max revs? If you are achieving hull speed at lower revs, then surely your engine is running most efficiently?

I use a Volvo MD2020 (3 cyl 20 HP) and find that 2900-3000 rpm is ideal - hull speed. However, I usually motor at 5 knots, so I'm not bothered.




<hr width=100% size=1>Humperdinck

Email: HJ@Seacracker.org
Website: www.seacracker.org
 
Prop is damaged. Better though for engine life to run at slightly higher revs. A diesel needs to run hot.

John

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