Cavitation

[BOWTECH.JUSTICE]

I have a 2000 Monark Seville 240 which has the larger toons. Outboard is a 60 hp mercury with a 22" driveshaft. Transom mount is as low as it goes and I still have problems with it spinning out. I can hardly allow many people to ride up front. What is the solution to this?

 

[ahicks]

Move some people to the rear would be simplest, but you might also consider notching the top of the transom, assuming that it would still be tall enough to support the lower part of the engine mounting bracket. You wouldn't want that hanging below the transom.

Taking that idea a step further, it might make sense to shim the entire motor pod downward.

Hard to say without seeing it.

Too, the design of your prop may be counter productive. A large diameter pontoon prop may not be as susceptible to the problem.

 

[HotTommy]

Not enough information for me. For example, how high is the engine cavitation plate relative to the bottom of the engine pod? Also, have you compared the engine speed / gear ratio / boat speed to determine the slippage? ... Cavitation can be caused by several things and sitting too high in the water is only one of them.

 

[H20Rat]

ventilation, not cavitation... ;-) Highly unlikely a 60hp on a pontoon is cavitating. (very different processes/problems)

Going to sound obvious, but trimmed all the way down?

 

[Scott Danforth]

of all boats that need a powered jack plate, a pontoon is the one that needs it the most.

prop depth is the biggest bane of 'toon owners. too shallow and the prop ventilates. too deep and the motor performance suffers. and every time someone steps on or off the boat or changes where they sit, the prop depth changes

 

[BOWTECH.JUSTICE]

Yes, ventilates, but you knew what I meant. Trimmed down. I should've posted a pic but I'm not with the boat. Will investigate the prop and look into notching the transom. Is that a common practice?

 

[BOWTECH.JUSTICE]

It's getting old when everytime I ask people to move to the back they have to ask if I'm saying they're fat

 

[HotTommy]

Perhaps you can ease their guilt by reminding them that moving has double the effect of their weight. It reduces the load on the bow AND increases it on the stern. You might also remind them that as captain of the boat, you were being more polite than required when you disguised your command as a request.

 

[ahicks]

It's getting old when everytime I ask people to move to the back they have to ask if I'm saying they're fat

I agree. Some seating arrangements just do not work out well when the boat gets loaded up. I just tell them that if the shoe fits wear it. It is what it is.

Notching not common, but yours would not be the only boat that's ever been done.

Boats with big tubes are often set up with larger/heavier motors in mind. That might be a solution if that's a direction you've been considering as well. Maybe time to go 4 stroke if that's not already been done. Extra weight hanging on the back acts as a counterbalance. Downside may be a new issue with how low the back end rides when the boat is lightly loaded....

 

[SuperGlenn]

I have the 4.3L I/O in my 24' Seville. I sometimes have the same issue.