Motor setup on a Pontoon

[crb478]

I have a new to me 24 foot Crestliner Pontoon boat that has 26 inch pontoons. The prior owner switched motors on it from a 50hp to a 115. The 115 is a short shaft Yamaha 2 stroke and it is lowered down as far as it will go on the transom. The AV plate on the motor is a couple of inches above the bottom of the pontoons and the motor cavatates pretty easily if you start to trim up or turn. The boat does not have lifting strakes. I have noticed that some of the pontoons I have seen seem to have the AV plate close to the bottom of the pontoons, but that has been looking at them from a distance as I ride by boats on lifts.

The prop is a 13 x 15 3 blade Turing point that I just got to replace one the same size that was damaged prior to my ownership. I wanted to see where the AV plate is on most peoples Pontoons in relation to the bottom of their pontoons. Right now I am looking at either making a jack plate to lower the motor or getting a 13 x 13 four bladed prop to see if it will get a better bite.

When I brought the boat home it had a stainless prop on it that was over pitched, but I do not remember having any cavitation issues with it. Thanks for any help or ideas.

 

[Silvertip]

Re: Motor setup on a Pontoon

Your boat, as do most pontoons, needs a long shaft motor. That is simply a fact of life and there is little you can do to eliminate the ventilation issues. On pontoons the motor operates in very turbulent water so the farther you get the prop out of that turbulence the better. Lowering the motor five inches to make it equivalent to the longshaft may result in the powerhead getting wet. Why not just install the proper lower unit and sell the one you have. It may result in a relatively inexpensive fix. In fact depending on your marketing abilities you may actually make a few bucks in the transaction.

 

[crb478]

Re: Motor setup on a Pontoon

Thanks I may be able to pick up a long shaft for cheap as they are not as popular around here. I even know of a rebuilt evinrude from a marina that went under that had a long shaft. I believe it was a 120 if it is still there. I bought a rebuilt 115 johnson for 600.00 so I could probably get the long shaft for the same or less.

 

[Bamaman1]

Re: Motor setup on a Pontoon

I'm in the same position as you, with a Yamaha 115 hp 20" motor--off a bass boat. I often have to ask the "fat women" to move to the back of the boat to minimize cavitation. With 138 hp at the prop, my 24' Starcraft is fast, very silent and efficient while planed off @ 2500 rpm's. My fast cruise is 3500 rpm's.

I have considered removing the engine plate, and cutting it down a couple of inches. But the best way to solve cavitation would be to install an adjustable jack plate. While engines come in 5 inch increments, sometimes solving cavitation is only an inch or two difference. They're just a $350 item.

I think every high dollar, high performance, high horsepower tri-toon should have $1K spent on a hydraulic jack plate to bring about optimal performance. Every time pontoon boats are loaded up, the height of the motor changes--according to how it's loaded.