Pitch Understanding

[mwhitten]

I have a 24" pontoon that I have propped to reach it's max rpm with a typical load. In doing so I lost about 5mph. No big deal I'm not out for speed, just wanted the right pitch for the engine. Help me understand what is going on with the engine when the pitch is to big and not able to reach max rpm and why it's important to be able to reach the max rpm range. Even today I only cruse at about 3,000 - 4,000 rpm or less.

 

[Dunaruna]

Re: Pitch Understanding

Lugging the motor will kill it prematurely and in most cases you will not know it is happenning, especially a 2 stroke. If you do not prop for WOT, you are in danger of lugging the motor through a wide RPM range, this is especially true for a planing hull but not so much for a displacement hull, depending on a few other factors.

A gearbox would solve the problem but unfortunately marine engine manufacturers have not yet devised a reliable/affordable/small enough multi ratio gearbox for domestic use. The only way to alleviate lugging through the entire RPM range is to prop for WOT. That doesn't mean you have to use WOT.

Pontoon boats, especially heavy displacement pontoon boats, pose a slightly different set of challenges in regard to prop pitch but the basic rule still applies, prop for WOT.

 

[junior1113]

Re: Pitch Understanding

over pitching lugs the motor meaning more gas per revolution and will shorten life of power head. max rpm at wide open throttle should be within limits to make your motor last and save you money in gas. do you want speed or your motor to last. i know the answer hope this helps

 

[steelespike]

Re: Pitch Understanding

What motor are you running?
Lugging the motor can cause coking, carbon buildup and premature engine problems.On any boat the motor is working like its hauling the boat uphill.
So it needs to be able to reach its max rated rpm.or your adding even more stress.In my opinion you should be able to maintain most if not all of youre original speed. What prop were you running and the max rpm and speed?Present prop max rpm and speed?All props are not created equal.
There are props intended for pontoons and other hard to push boats.
For best efficiency the boat needs the most speed possible.

 

[mwhitten]

Re: Pitch Understanding

I have a 2004 Merc 115. I went from a 14 pitch to an 11 to get within my range. Both props are Merc props. I lost about 5mph. My max speed for the 24" is 21 mph. Speed is not an issue with me. I like to enjoy my time on the lake. I just wanted to do what is right for the motor. I have a better understanding now. My local mechanic thinks I'm nuts.

 

[steelespike]

Re: Pitch Understanding

You may need a pontoon dedicated prop Just because you prop for max speed doesn't mean you have to run that speed.Usually the right prop will deliver more speed at what ever rpm you select. delivering the best economy at most speeds.Most Pontoons deliver the best mileage at 9mph or less.
and at these speeds are very competive the planing hulls at the same speed.