propping a pontoon boat

[bob johnson]

does standard prop rules apply for a pontoon boat?

seems they dont plane...or do they?

my buddy wants to change props...he is currently only running about 5000rpms at WOT on his 80 merc 2 stroke.

the boat is a full 25 feet long..

he said he thought he went a lot faster with his older 88 special...( and it had issues)...

I dont know what his current top speed is..

but he said he thinks he has a 17 pitch and wants to go and put a 21 or 22 pitch on..

I told him he needs to get his rpms up to about 5500 at WOT..

seems he might go backwards with more pitch....right


second question:

is there a benefit to go bigger with a prop( larger dia) material and pitch being the same..

say on a light weight aluminum 20 foot CC( about 1200 lbs) 12 degree dead rise, 72 " at the chine... with a 115 hp 2 stroke?

thanks

bob

 

[junior1113]

Re: propping a pontoon boat

really need speed and rpm to calculate prop slip. agree go down in pitch to get around 5500 rpms. i'd put a 14 pitch 4 blade. or a 15 pitch 3 blade with no cup. for best performance and engine life

 

[Silvertip]

Re: propping a pontoon boat

five inches of pitch change will drop his WOT rpm by rougly 800 to 1000 rpm and lug the be-jeepers out of the motor in the process. Chances are he would lose speed, have terrible hole shot and be looking for a new engine not long after installation of a prop with way too much pitch for the application. Speed is what you get when the engine is propped to put it in the manufacturers recommended WOT rpm band. While you may gain a MPH or two by different prop designs (stainless vs aluminum for example) you will not make a hot rod out a pontoon.