Changing boats - changing props?

[revkab]

I currently have a 1985 35 hp Merc on a 14' aluminum v hull boat. I would like to put this motor on a 1985 Bass Buggy pontoon (18'). (No, I cannot afford a new 50hp). My question is, do I need to change to a different prop for the pontoon? If so, what might be a good diameter/pitch?

 

[RogersJetboat454]

Re: Changing boats - changing props?

You may...

But your motor is the best one to answer the question. First off make sure your motor is in good tune, and has no running issues. Install it on the pontoon boat. If your motor does not have a tachometer, you will need to get one. Something like this will fit the bill;
http://www.amazon.com/Tiny-Tach-Hour-Meter-TT2A/dp/B0045L9GA0

Throw the boat in the water, and open the engine up to WOT, observe the tach. Your engine should be able to reach the specified WOT RPM range. If it falls short, you will need to drop the pitch of your prop accordingly, so the engine is able to get in the proper RPM range at WOT.

 

[revkab]

Re: Changing boats - changing props?

You may...

But your motor is the best one to answer the question. First off make sure your motor is in good tune, and has no running issues. Install it on the pontoon boat. If your motor does not have a tachometer, you will need to get one. Something like this will fit the bill;
http://www.amazon.com/Tiny-Tach-Hour-Meter-TT2A/dp/B0045L9GA0

Throw the boat in the water, and open the engine up to WOT, observe the tach. Your engine should be able to reach the specified WOT RPM range. If it falls short, you will need to drop the pitch of your prop accordingly, so the engine is able to get in the proper RPM range at WOT.

Thanks - this sounds like good advice. If I find out that I do need to change the prop, is there any formula or general approach to figure out the change, other than buying several different pitches? How about the diameter?

 

[steelespike]

Re: Changing boats - changing props?

There really isn't a formula but the rule of thumb is 200 rpm for each inch change in pitch. Go to a lower number to increase rpm.
On a pontoon the rule doesn't exactly apply. but is a place to start.
Look under your prop nut or near the base of the blades for your numbers _ _ X _ _ diameter X pitch.