I posted a thread years ago about choosing the right propeller pitch
for my sailboat. I've got a 2002 15hp Mercury 2 stroke
on my Pearson
26. Based on the advice I got here, I went with the smallest-pitch propeller
I could find, which was 9.25 x 6.50. It sounded like that was the safest bet to avoid straining the engine
, but I struggled to fully understand all the parameters at the time.
Here is the old thread:
The last poster, hamburking, disagreed with everyone else, but this happened two years after I bought the low-pitch propeller. His rationale was that since my 15 hp motor
is already larger than it has to be, it has more than enough torque to propel the boat
at lower rpms, and that with a greater pitch
I would get the same thrust with less fuel
, vibration, engine
I've put hundreds of hours and thousands of miles on the 9.25 x 6.50 propeller without any probles. Then again, maybe hamburking is right it's still not ideal. His argument makes more sense to me the more I think about it. The motor
sounds a little unhappy above 75% up to WOT, with very little extra speed as throttle increases. Maybe it's over revving? I've also got pretty poor stopping power in reverse, but I always figured it was just normal. Since I'm almost always running it below 75% throttle anyway, maybe I've got torque to spare and a steeper pitch would improve my power and efficiency.
I know that the "If it ain't broke" school
of boat maintenance
may chime in here, but I'm happy to spend $85 to try a propeller with greater pitch and see if it improves things. But how steep should I go? The three choices that I see listed as parts
for my motor are 9.00 x 9.00, 9.25 x 7.00, and 9.25 x 6.50 (the one I already have). Hamburking recommended 9.00 x 9.00, but maybe then I would end up straining the motor like I was trying to avoid in the first place. Should I then try a smaller change and go with the 9.25 x 7.00? Is there any way to know if it's straining or over-revving other than sound and feel? I know there is a formula for pitch, but I don't know how to use it and I don't think it factors in horsepower, which seems like would make a difference.
Anyway here is some other potentially relevant info:
Waterline length: 21.7
: 6000 lbs
Model number: 1015211ZD
I'm not sure what the rpm
range should be on this motor.
Anybody able to offer confident guidance on this? Any help is greatly appreciated.