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8hp prop pitch worth changing?

J

Jack Blant

Member
Hi, I have an 8hp mariner (1991) and it is a very powerful motor. On my old boat it would push me along at 17 Mph and on the smaller, lighter Zodiac C310 (3.1m) it gets up to 23 Mph, but with the drop in weight, the engine seems to be revving much higher than it used to do (stock prop) and I wondered if adding a higher pitch prop would help drop Rpm's and boost top end speed? I think the stock prop is 7" and would a stainless 8-9" prop (Solas 3 blade) be a good idea?

Thanks, Jack :)
 
kimcrwbr1 said:
You need to find out the WOT rmps first on the light boat. A 2 inch pitch is alot for a small motor I doubt you will gain much if any as far as speed goes. If you want faster bigger is allways better.
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Hi, thanks for reply, I will get a tachometer on the engine when I finish rebuilding it and find out the wide open rpm's and see what it's like. At some point I may do the same as I did a while back With another 3.1 sports dinghy and strengthen the transom, add a console to the floor boards and add a 25hp Yamaha I have sitting around.....

But for now its my little boat for pottering around in the river in Shaldon! :)
 
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kimcrwbr1 said:
Rule of thumb is 200 rpm per inch of pitch but with all the variables the only sure way to adjust pitch is trial and error, you want to get the rpm closer to the upper WOT rpms with a light load that way you have the power when you load er up.
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Hello, think I may try one of these if my rpm is high when I get 'round to trying it, which one would you go for?

http://boatpropellers.iboats.com/Solas-Amita-Propellers/1111-093-08/

Or: http://boatpropellers.iboats.com/Solas-Saturn-Propellers/1121-093-08/

Thanks again! :)
 
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