Prop pitch recommendation

[macca123]

Hi

I purchased a 1982 mariner/ yamaha 40hp model no 40e 6e9l 405360, the prop is stuck on solid tried everything except burning off or cutting it off, the prop is pretty rough anyway so it wouldn't hurt to buy a new one. The current prop no is 48 73136 a4 13p best I can tell, what pitch should I go to as in the test run the engine got to maximum revs very easy, my boat is half the weight of what it came off also how many splines does my shaft have as I cannot remove the prop so I cannot count them, I would like to get my new prop before removing the old one, can anyone give me a part no of one to buy.

many thanks

keith

 

[Silvertip]

Re: Prop pitch recommendation

Getting to max revs real easy is not a number. It will not hurt to over rev the engine for a short burst to see how much pitch increase you need. Was the test made with what you consider an average load. If not, run the test again loaded the way you will normally run. If you test light, the engine will be lugging when you load it up. The prop you have is a 13 pitch. If you stay with the same Merc prop design, engine rpm will come down 150 - 200 rpm for each inch of pitch change. So unless we have some rpm numbers (what you actually observe on the tach) that's the best we can do.

 

[macca123]

Re: Prop pitch recommendation

Thanks for the reply, all up weight approx 800lb, at least half the weight of the boat the engine originaly came off, all I have to add is a couple of rods, so yes the payload will be about the same. It just seemed to get to maximum speed far too easy, maximum speed was reached at 4800 revs, I put the throttle forward to give more revs which it did it reved to 5500 but no more increase in speed 26knots was the max speed. So judging by the numbers you gave me I probably need a 15 pitch prop ?? and also is it a 13 spline shaft for that model.

thanks

keith

 

[DuckOfDeath]

Re: Prop pitch recommendation

If you couldn't exceed 5500 RPM at WOT your current prop pitch is fine. Unless it's beat up and not allowing the engine to reach max RPM at that pitch level. I'm not familiar with model numbers but as long as it's not the big foot model it should be 13 splines.
http://boatpropellers.iboats.com/Ma...r=1982&**********=390612006&*******=736192695