Motor depth?

[weekendfunchaser]

I bought a pontoon boat recently with a 70hp mercury 2-stroke on it.. I removed it to put a 125hp force 2-stroke motor on it. My motor sits way too low in water now.. When I took it out it throws water out the sides of the lower unit. It's not even close.. I think I need to modify my transom to allow me to raise the motor about 6".... My big question is what is ideal motor depth on pontoon motor to get best performance? Should whale tale be right at water level when trimmed down while sitting in water or at cruising speed? Or does plate have to be even with bottom or transom???

 

[kazeej]

Re: Motor depth?

Hey weekendfunchaser! Welcome to the forum.

I'm dealing with the opposite problem. I think my motor is too low. I'm fairly new to pontoons, too, so I sought the advice of the wise ones here. (wise ones - not wise guys). Take a look at the motor while you're moving. The cavitation plate should be about 1 to 3 inches below the waterline when underway.

Jack
South Florida

 

[Rancherlee]

Re: Motor depth?

I bought a pontoon boat recently with a 70hp mercury 2-stroke on it.. I removed it to put a 125hp force 2-stroke motor on it. My motor sits way too low in water now.. When I took it out it throws water out the sides of the lower unit. It's not even close.. I think I need to modify my transom to allow me to raise the motor about 6".... My big question is what is ideal motor depth on pontoon motor to get best performance? Should whale tale be right at water level when trimmed down while sitting in water or at cruising speed? Or does plate have to be even with bottom or transom???

Basically its nothing short of playing "mad scientist" to figure out the right height on a 2 log pontoon. You could set it up for the cavitation plate to run at the surface like a V hull boat and it will work good on a calm lake but get into some rollers and it will lift the prop up to high and you will suck air. Leave it down to low and it will get good bite in all situations BUT you give up 2-3mph. Its all about trial an error and what your preference is. Trust me, My pontoon started life as a 2 logger with tiny 19" pontoons so I played around a lot with motor height and lowering/raising the transom.

 

[MH Hawker]

Re: Motor depth?

Tuning motor height is a bit of work on a pontoon, because of all of the turbulence created in the back. A bit deep is often better than a bit to high. Its often trial and error and a good GPS to get the real speed. The sort of normal standard is just under the surface while your running at WOT. What most to is to watch your tach and GPS at the same time and slowly bring up the RPM and watch speed. If you hit a point where the speed dosnt increase as the RPM`s go up then it needs to a big deeper because its not hooking up to the water. If it is hooking up all the way to max RPM then your golden.
Whale tails are all most useless on a pontoon. They may help a small bit if its captivating, but that's a sign it needs to be deeper in the first place.