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Author Topic:   Another prop conundrum
tomol posted 08-07-2001 07:12 PM ET (US)   Profile for tomol   Send Email to tomol  
I'm tweaking. I have a Yamaha 4 stroke on an old Montauk. Top speed is 36 knots at 5900 rpms, although I rarely run that fast. I usually find myself at about 4000 rpms (21 knots).

I would like to pare off 400 to 500 rpms if possible. I would still be running within the manufacturer's recommended range, it would save a little gas and hopefully engine life.

When I bought the motor last year a friend gave me a gorgeous stainless prop. I know it was pricey so I would hate to just discard it. Does anybody know if I can get it reworked or possibly trade it in for one with slightly more pitch?


Laguna Beach, CA

Bigshot posted 08-07-2001 10:16 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Have it reworked! Local Marina or prop shop can have it done. Try General or Hill propeller in national mags.
Clark Roberts posted 08-08-2001 10:05 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Dittos on reworking prop. Generally speaking, a stainless prop can be repitched once up to 2" either up or down.. and each inch of pitch translates to approx. 200rpm (either up or down) so if you had pitch increased by 2" you would loose approx 400rpm at top end. BUT a higher pitch doesn't always mean higher mileage as you may introduce laboring at your cruising speed and this would hurt milage and engine life! Personally I prefer to prop and engine so that it will rev slighty over (maybe 200rpm) the suggested max rpm. Then when boat is laoded it will still perform good and not "bog down". Also at cruise speed the engine runs "more freely and relaxed" with less internal stress and mid-range accelleration is optimum. There are loads of opinions on this subject but don't give up because the prop is what puts the power to the water! Happy Whalin'.. Clark.. Spruce Creek Navy

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