What size props?

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Guest

Guest
I'm looking for some advice! I have just had a new engine installed in my Fairline Sprint, a V8 Volvo 225. Prior to this I had a V6 205 running thru a 290 leg with a B5 duo prop. I found that with the "new" engine the revs were very high (admittedly the rear prop has a bit of damage) and despite resetting the rev counter for a V8, the situation continued. I am currently running a a B8 set which now only revs to 2700 but cruises comforably at 2000 doing 25 knots. My question is how can I best determine the optimum prop size for the boat, engine and leg combination? Any help, advice or contacts would much appreciated.

Thanks

David
 
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Guest

Guest
When I was trying to do this with my Sealine I got a lot of help from Volvo Penta in Watford. Sorry dont know their number but they have a lot of technical details regarding boat types and engines.
Give them a call.
 
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Guest

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interpolation

You can interpolate to get the right answer. You get 2700 at WOT with the B8 props, and much higher (you didn't say how much, but let's say 3700rpm as an example) with the B5s. You need to find out out the manufacturer's rated rpm of the engine at WOT from the engine data sheets. Say it was 3200rpm to make the maths easy. You therefore need props whose pitch is exactly midway between the pitch of the B8 and B5. (I have no idea what the pitch of these props is cuz B5 and B8 is volvo-jargon). That will give you roughly 3200rpm at WOT.

It is important to get the max rpm at WOT right - if the motor spins too fast it will get knackered and if it spins too slow you will not develop the full horsepower even if you are at WOT, and you will also belch much smoke
 
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