pontoon prop question

[jo65lg]

I have recently purchased an 18ft older model Grumman pontoon. It has a 2005 mercury 50hp 2 stroke with an 11 pitch black max prop. I noticed on the water im running 5600 rpm at 3/4 throttle. I max out at around 6400 rpm at full throttle but see no speed increase or added performance , just a louder motor. I have been told that this model engine has a ideal WOT of between 5200 and 5500 rpm. When doing the ideal prop quiz on mercury website it recommends the prop I have now with the same or lower pitch but everything I read indicates I need I higher pitch prop to lower my WOT rpm. Any suggestions??

 

[Sea Rider]

Re: pontoon prop question

Welcome to Iboats,

Try a prop pitch that gives around 5500 if that's the max wot rpm factory stated for that engine at that given boat load. Right now, you're increasing rpm and losing best torque when at full wot.

Happy Boating

 

[MikDee]

Re: pontoon prop question

You're 900rpm too high at WOT? I hope your tach is right? Is so, you need to prop up 2 levels IMO. I would say you need at least a 15" pitch Black Max.

 

[Scott Danforth]

Re: pontoon prop question

are you testing with only yourself on the pontoon? will you be running with 4 or 5 people or yourself mostly?

If it will just be you, then I would re-prop with a higher pitch. If it will be you and a half dozen people, I would test it first with a half dozen people.

 

[jestor68]

Re: pontoon prop question

I would verify the tachometer accuracy first.

Any dealer/shop can hook up their "shop tach" and check it for accuracy.

Or it could be that the prop is slipping so badly that it allows the rpm to over speed.

The Mercury Spitefire 4 blade is supposed to be a good pontoon prop. The prop selector recommends a 12 pitch.

 

[steelespike]

Re: pontoon prop question

It would help to have your wot gps speed to help evaluate your setup/rpm.

 

[steelespike]

Re: pontoon prop question

It would help to have your wot gps speed to help evaluate your setup/rpm.If your tach is indeed accurate;at 6200 you would be doing over 26 mph at 25% slip your probably actually at about 20 mph.
I do suspect the tach is high. Is it set correctly?

 

[jo65lg]

Re: pontoon prop question

I have not verified the tach is correct. I did this test with 4 people onboard, being that will be the norm.

 

[jo65lg]

Re: pontoon prop question

It would help to have your wot gps speed to help evaluate your setup/rpm.If your tach is indeed accurate;at 6200 you would be doing over 26 mph at 25% slip your probably actually at about 20 mph.
I do suspect the tach is high. Is it set correctly?

Im actually waiting for the river to drop before I test again. I will gps my speed so I have that info.

 

[jo65lg]

Re: pontoon prop question

It would help to have your wot gps speed to help evaluate your setup/rpm.If your tach is indeed accurate;at 6200 you would be doing over 26 mph at 25% slip your probably actually at about 20 mph.
I do suspect the tach is high. Is it set correctly?

I would verify the tachometer accuracy first.

Any dealer/shop can hook up their "shop tach" and check it for accuracy.

Or it could be that the prop is slipping so badly that it allows the rpm to over speed.

The Mercury Spitefire 4 blade is supposed to be a good pontoon prop. The prop selector recommends a 12 pitch.

That is actually what I wanted to put on, which lead me to this forum and pitch question. a friend told me about the spitfire