cavitation/ventilation problem pontoon boat

[RCTJohnson]

I have a one-year old, 22' pontoon boat with 50hp Merc 2 stroke (standard engine, not a "Bigfoot"). Cavitation/ventilation (whatever the precise definition - the prop suddenly spins faster, the engine revs dangerously high, and the boat doesn't move faster) was an occasional problem last year but is more frequent now. The boat is used on a medium-sized lake and floating weeds are a definite problem - more so this year than last. I'm sure weeds are getting stuck on the lower unit and that is part of the problem, but that's beyond my control. From reading other postings on this topic it seems like moving weight to the stern of the boat should help (if I can get my mother-in-law to sit in the back). I don't think I would want to fool around with the engine mounting position - seems like too much time and expense with questionable results (i.e., some say raise it, others say lower it). The idea of a hydrofoil of some sort (Doelfin, Sting Ray, etc.) seems to be an easy solution - almost too easy? Do these things really work to decrease cavitation/ventilation and are they easy to install? Does it matter what type? Any downside to using one? Any advice would be appreciated. Thanks.

 

[Yepblaze]

Re: cavitation/ventilation problem pontoon boat

Weeds in the prop will cause the prop to slip.<br /><br />Maybe the hub has spun in the propeller.

 

[John.F]

Re: cavitation/ventilation problem pontoon boat

I had a simular problem with a friends boat&motor,<br />Every time I went to speed up It would Just rev. realy high and no speed. I needed to change the prop. now it works great. The prop that was on there was damaged,it didn't look like it was to me but it was. Now it works great. Mabye try that.<br />Good luck.......John

 

[Spidybot]

Re: cavitation/ventilation problem pontoon boat

If your prop is working a little high the prop is surfacing (breaking the surface, running in an air/water mix). There are props designed for this (hi performance) but my suggestion is that you get a prop with 4 or 5 blades. Even if surfacing these will have at least two blades in the water.<br />If weed is the problem you could look for a prop designed for this (weedcutting).<br /><br />I have a planing hull and my ventilation problem (due to motor mount and hull/transom design) was completely solved with a 5-blade. I even got much better grip for trim and cornering.

 

[RCTJohnson]

Re: cavitation/ventilation problem pontoon boat

Thanks for the advice - I'll check the prop (or have someone who knows what to look for check it) and may consider a 4 blade prop. But what about the hydrofoil/Whaletail/Doelfin idea? Does the lack of response mean this is a bad or untested idea?

 

[Fouled Plug]

Re: cavitation/ventilation problem pontoon boat

Hydrofoils are a great addition to a lower unit in most cases, but in your instance it may be more of a 'weed magnet' if you tend to drive through the salad a lot.

 

[geezer1960]

Re: cavitation/ventilation problem pontoon boat

HI there<br />I have a 20 foot 1999 Palm Beach pontoon with a Suzuki 1994 85 hp engine on it,,,,,, This weekend i took it out for first time this season and i had a problem similar to yours. I had ran through some lilly pads and the engine started surging and low and high revs... I cleaned off the weeds and thought i had fixed the problem....but no luck,,,,,,,,i got it back to the dock and looked at the prop.....the nut was loose,,,,i had greased the shaft over the winter and just stuck the nut and cotter key on the shaft without torquing it..( i was gonna do it later) .i tightened up the nut and it ran great afterwards.....maybe this will help you... <br />Have a great day

 

[fluidshooter]

Re: cavitation/ventilation problem pontoon boat

experience the same problem with my 24' pontoon. i fish the flats on the big bend of florida, when seaweeds floating we be stalling. agravating but hey i'll put up with it to be one the water!!!<br />my suggestion, just stop, back her up with enough thrust to clear all the weeds from between the logs and then throttle up!!

 

[TELMANMN]

Re: cavitation/ventilation problem pontoon boat

Backing up to clear the prop is always a good idea in weedy areas but make sure it is done in a clear area so you don't foul the propeller all over again.

 

[Hooty]

Re: cavitation/ventilation problem pontoon boat

If it is cavitation and not weeds, the one thing you haven't mentioned is triming the engine down. This doesn't mean you change the mounting position, it means you simply trim the l/u farther in.<br /><br />c/6<br /><br />Hooty