JACK PLATE?

[PANTHERMAN69]

Last year I purchased a 1990 Prince Craft 25' pontoon. The previous owners installed a 2013 Evinrude E90 20" shaft outboard on it. The boat is in excellent shape and the E 90, mechanicly, runs flawless. My problem, this past year it developed a cavitation/ventilation problem, over revving problem at about 4000 rpms. Went to a different prop, no change. About a week ago, with spring approaching, I began reading about a solution to the problem. The cavitation plate sits about 5" above the bottom of the pontoons. from what I have read suggestions run from replacing the motor with an xl shaft to installing a Jack Plate lower on the transom to allow the cav plate to at least sit even with the pontoons bottoms. I also read that a 6" offset Jack would allow the motor to run in cleaner water. Any suggestions?

 

[ahicks]

No suggestions here until I see pics showing the motor install clearly, where it's height can be seen relative to the bottom of the boat.

I will say that installing the motor so low the cavitation plate is level with the pontoon bottoms sounds WAY low.

Also, once you have a solid install where everything is working right, it would be REALLY unusual for a cavitation problem to just appear out of nowhere. There's generally SOMETHING that's changed. That's what I would encourage you to look for, vs. making any changes to your existing setup.

OR, are you saying this install has never been right?

 

[Sea Rider]

Are you boating in a lake, river, open sea environment ? Did the prop aeration issue occurred on flat calm, choppy windy water conditions when at straight or close turns at speed/plane ? In case need to lower the motor is it possible doing so without a jack plate install ?

Happy Boating​

 

[garbageguy]

...this past year it developed a cavitation/ventilation problem...

what changed to develop this problem? or maybe nothing changed, and the problem just became apparent as you had more experience with a fairly new-to-you boat?

 

[gm280]

I am presently making a Jack Plate to raise my '76 40HP Johnson. And I have the angle aluminum to make it already drilled and slotted. If you decide to go that route, you will probably have to install the Jack Plate up side down to get that much lowering ability. Don't know without pictures...