What size prop should I be running?

[HammondTiger]

I have a 1994 24ft Lowe pontoon boat with a 85hp Yamaha, what size prop should I have on this engine to achieve maximum usage? Obviously I am not looking to go 60mph, just looking for the right pitch/diamter combination to achieve pushing power without burning to much fuel.

 

[bowman316]

Re: What size prop should I be running?

Maybe somewhere between a 19 inch pitch and 24 inch. But it is really just a guess. the more pitch, the more fuel efficent. But too much pitch and your motor will strain, like trying to go up a hill in high gear.

 

[HammondTiger]

Re: What size prop should I be running?

I have never heard of anyone using over about a 14 pitch prop on a pontoon boat. 19 pitch and up is usually what is run on a bass boat and speed boats

 

[curtiscapk]

Re: What size prop should I be running?

this is an excellent little application for props. I bought a 14 x 13 for my 94 merc 115 on a 24 foot tracker does great for me and the turning point props are two piece so it works out cheaper if you ding a blade or spin the prop. I am buying my spare for this year.

http://www.turningpointpropellers.com/

 

[rogerwa]

Re: What size prop should I be running?

You need a stasrting point.. What is your current WOT and prop pitch?

From there we can start speculating on the right size..

 

[HammondTiger]

Re: What size prop should I be running?

WOT is around 6000rpm's
not sure of the current pitch/diameter but i will find out this weekend

 

[rogerwa]

Re: What size prop should I be running?

Good news for you.. Your recommended WOT should be between 4500-5500 so at a minimum you could go up in pitch probably three inches. This will obviously give you better top end speed.

Is this the WOT with the normal load of people and gear??

 

[Silvertip]

Re: What size prop should I be running?

Is 6000 RPM what Yamaha recommends for WOT rpm or is that what you actually observe on the tachometer. If 6000 is what is recommended and 6000 is what you observe, you already have the best prop. Otherwise, go to the Yamaha web site and check performance reports. YOu can select an engine and pick from the boats tested that are identical to or similar to yours. They list the prop used for their testing.

 

[bowman316]

Re: What size prop should I be running?

Just remember,
every inch in pitch you add, you loose 200 RMP's so going up 2 inches will loose you 400 rpm's 4 will loose 800 rpms.

Do pontoon's plane out when you get em up to full throttle, or do they just motor along kinda slow?

 

[HammondTiger]

Re: What size prop should I be running?

Silvertip: 6000rpm's is with only me and about 15gals of fuel. It sounded like it was about to blow up but never went any faster.

 

[HammondTiger]

Re: What size prop should I be running?

Just remember,
every inch in pitch you add, you loose 200 RMP's so going up 2 inches will loose you 400 rpm's 4 will loose 800 rpms.

Do pontoon's plane out when you get em up to full throttle, or do they just motor along kinda slow?

Unless you have some serious hp like the I/O do, most pontoons just plow through the water somewhere beteween 15-25mph.