Wrong Prop or Other Problem???

[tlombard]

I recently put a 115hp Mercury ('78) on my 24ft pontoon in place of a smaller outboard and it was recommended by someone to put a 17p prop on it but I'm not sure if I shouldn't step it down to 15p. The boat runs great when the throttle is wide open but seems to bog down at anything lower other than idle or just above which is fine also. When I say "bog down" the engine is running fine but the boat just doesn't seem to want to go. I also don't have a tach so I'm not sure where I'm at on the RPM range at any point. Does 17p sound too high? I haven't seen anything that high suggested on any other forum or site. I need to buy a new prop anyway since my dad takes the boat out also and doesn't exactly avoid floating logs or branches and there are a ton on the river where we have been taking it for not. Not one blade is complete at this point.

 

[Esox]

Re: Wrong Prop or Other Problem???

Not one blade is complete at this point.

That could be the problem. A damaged prop can cause ventilation/cavitation problems under load.​

 

[tlombard]

Re: Wrong Prop or Other Problem???

Thanks for reading my post. We actually had similar performance the first time out also but I know it isn't performing right with the prop in it's current condition and I plan on buying a new one before I head out this weekend, hence the thought I should knock the pitch down a step.

 

[Esox]

Re: Wrong Prop or Other Problem???

Without a tach it's a guessing game. You definitely want to be running at the upper range of the recommended rpm range for your engine. See if you can find a local dealer that will let you try out a few props and give the 15p a try. In the end it will be well worth it. Right now I have 2 SS props that I'm not happy with and a third will be on the way soon since I can't find a place that will let me test some props.​