98 50 hp Bigfoot RPM surge problem

I have a 98 Seagull Nautico Cat with a 50 hp merc bigfoot. Problem is at WOT (approx 5100 rpm on this sled) the motor will surge to 55 or 5700. Mainly when the waves are at stern. When waves at bow, or with a few weight adjustments in boat, problem stops. Hub checked out fine. Clutch maybe, but doubtful. Almost seems like prop is breaking surface. Powertech 11 P prop by the way. Any suggestions welcome!!! PLEASE!!!

Re: 98 50 hp Bigfoot RPM surge problem

That boat is known to have cavitation/ventilation issues with single engine setups. Cool looking boat though.

What size do you have? I would assume 18, in which case you are significantly underpowered. There are people running twin 50's on those boats.

Is this engine new to the boat or is the boat new to you? This is probably a hull specific problem rather than an outboard performance/maintenance issue. I would suggest posting your issue in a cat forum and I am sure you will have lots of hits.

BTW, your WOT is posted on the engine (independant of the vessel). Running an engine as hard as you can while not reaching within 100-200 RPMs of WOT is called "lugging" and is a good way to re-power your boat. I assume your engine will have 6,000 posted on the plate, but you will have to check.

Re: 98 50 hp Bigfoot RPM surge problem

thanks for the reply! Have had the boat for about 6 years but have only been running now for the last year and a half. Thought about going twin but was told that with the particular year model of my boat, the transom is not designed to support twins.. odd.. a buddy of mine in Virginia has twin Honda 75's on his... and yes, mfg's specs say 5500 - 6000 rpm is ideal range. I have a 60 hp Suzuki 4 stroke that i'm mulling over installing. Just dont want to go through all of that mess if it's not gonna help at all. Thoughts, suggestions? Thanks again reload!!!

HJ