Bigfoot 60hp on Fisher pontoon

[oldMarine6367]

I'm having a problem with a Merc Bigfoot 60hp on a Fisher pontoon. This complete package is an older 2004 model. Motor idles and runs smoothly. I had an old banged-up prop, so I decided to upgrade the prop. Bass Pro 'boat specialists' put a new prop on. It runs well except occasionally it loses thrust, the alarm system starts beeping, the tach races to 6500rpm. I quickly pull the throttle back and motors idles down and runs smoothly. This doesn't happen often. Usually on a smooth lake I can run at 5200rpm without a problem. The Fisher pontoon has oversized pontoon logs. I'm beginning to think that I may be experiencing a cavitation problem because the prop is not deep enough in the water. My thinking is based upon the larger logs keeping the pontoon sitting higher in the water and the motor shaft is just not long enough to fully keep the prop down. This is happening with the motor trimmed up just a little to attempt to get on plane better. Any thoughts? Thanks ..... Bill

 

[Faztbullet]

You want the biggest diameter you can get to hold water.

 

[oldMarine6367]

You want the biggest diameter you can get to hold water.

Thanks for the response. Apparently the Bigfoot props need to have a 'cup' on the prop blades for correct thrust. They (Bass Pro) originally put a 'standard' 14" diameter 10-pitch on there to replace my old banged-up prop. Had all kinds of thrust and alert problems above 3500rpm with that prop. After doing their research they selected a BlackMax ExtraCup Pontoon-Work prop 14"diameter 10-pitch. I think that's the correct prop for the motor. Seems to run and thrust correctly except on rare occasions. That's why I'm thinking that something is related to that prop coming out of the water or picking up cavitation when the boat is underway with some conditions. Maybe I'm too picky but I expected it to run correctly 100% of the time if it runs correctly 95%.

 

[Alumarine]

Did it ever work well with the original prop?
If it did, why not get the same prop?