Prop Suggestions - 21' Party Barge

[mayorjones]

I have a 2008 21' Sun Tracker pontoon with a 50 hp Merc (I don't believe it's a big foot). Anyway, I am having a lot of cavitation problems, and have read through here and other similar sites that a standard 3 blade prop isn't the best choice for a pontoon, so I think I'd like to try a four blade. It currently has a 12.5x9. RPM wise it's pretty good - don't think we need to change much there. The motor is mounted as low as possible (I think?), but it still cavitates quite easily, even when a majority of the weight is in the back and the motor is trimmed all the way down.

Any suggestions on what I should buy? This is all very new to me, so I apologize for my ignorance. If I bought the same size/pitch but four blade vs three would I be better off, or isn't it that simple?

This is very frustrating - embarrassed to take anybody out because I can only go a few MPH or the problems start...

Thanks!

 

[Frankenstien]

Re: Prop Suggestions - 21' Party Barge

12.5 inch prop with a 9 inch pitch is about rite, if you could could move up to a larger prop that would be great. I think (but not sure) if its a big foot you can got up to a 14" that would give you more blade surface. I would suggest moving to the largest blade size that will fit your lower unit. Are you sure its cavitation and not prop slip? its possible that it has "spun itself" on the hub. It would be like having a week clutch, as long as the load of the motor is light you can cruise as expected, however once you put the power to it, ... the motor goes but the boat doesn't. I have a boat about the same size as yours, however at more than twice the hp , and a few other things... I run up to a 13.75 inch at a 20 pitch and hit around 45 mph. hope this helps.

 

[curtiscapk]

Re: Prop Suggestions - 21' Party Barge

sure sounds like a spun prop to me.

 

[mayorjones]

Re: Prop Suggestions - 21' Party Barge

But if it were a spun prop, it would do it wherever people were in the boat, right? If I move everybody to the back I can run it wide open. If people start working their way to the front, even say 40% of the passenger weight, it starts acting up. I'd think a spun prop would cause problems at take-off no matter where people were in the boat?

 

[rrhodes]

Re: Prop Suggestions - 21' Party Barge

Can you post a picture that will show us where the prop is in relation to your tubes? I don't know if another prop will help because it sounds like the prop is not deep enough in the water.

As far as a spun prop, Take a marker and make a line across the hub and rear edge of the prop. Run it for a few and check to see if the line has moved.

 

[schwarztot]

Re: Prop Suggestions - 21' Party Barge

I think I'm having the same issue. I have a 24' Sunliner with an 85 Yamaha. When the boat hits some wake or some good chop, I'm getting pretty bad cavitation. My motor is lowered as far as it will go. Any suggestions on lowering the transom with spacers or anything else that would make the motor sit a little further in the water?

Thanks,
Travis

 

[DMAN1968]

Re: Prop Suggestions - 21' Party Barge

I have had the misfortune of a spun prop on my toon--twice. It's not sounding like mine did. With a load and the spun prop you weren't going anywhere...just screaming rpm's. I did have cavitation issues when I ran the 50 hp as well. Like the others have said, get the biggest diameter prop you can and make sure the motor is set at its lowest setting. That's the place to start.

Mine came with a doelfin on the motor when I got it. I took it off once to see how it would perform without it and the cavitation issue got much, much worse. Needless to say I put it back on. Maybe adding one to your motor will help. It's relatively easy and inexpensive and may solve some of your issues.

Good luck.

 

[captkevin]

Re: Prop Suggestions - 21' Party Barge

Doesn't sound like a spun prop to me. Sounds like you need to get a bigger prop if possible. Or if you can't get a bigger one is it possible to get a 4 blade? Not sure if they make them in smaller sizes but if so that would help.

 

[mayorjones]

Re: Prop Suggestions - 21' Party Barge

How would I determine max prop size? Anybody have any suggestions on how to measure so I buy something that works?

 

[DMAN1968]

Re: Prop Suggestions - 21' Party Barge

Is that a 2 stroke or a four stroke?

 

[mayorjones]

Re: Prop Suggestions - 21' Party Barge

2 stroke

 

[Frankenstien]

Re: Prop Suggestions - 21' Party Barge

Start Here....

http://boatpropellers.iboats.com/?dz=55011

 

[hvachillbilly]

Re: Prop Suggestions - 21' Party Barge

i have i 2003 fishin barge with 60 hp big foot runs a 14x 10 prop dont know difference between your two stroke and my four stroke though