Re: Pontoon motor support (transom)
That's a tough one, especially using the size engine you want.
Have you contacted the pontoon maker?
For that kind of HP, it is going to have to be connected to the toons and the deck.
Welding may not be an option. Some toons are filled with foam. The heat will create a disaster. Also, heat in empty toons can be a problem because it builds pressure.
If your toons have drains and are not foam filled, welding is an option.
At any rate, the motor pad will need to be at least 2" thick using bonded marine plywood. It should be at a 15 degree angle (bottom in) at static rest.
Take a look at factory built pontoon rigs to determine motor pad height. They seem to vary. Some seem to place the motor cavitation plate at about the same height as the bottom of the toons. Others are just above.
Our 20' Starcraft pontoons motor pad is adjustable. It has to be unbolted but it can be adjusted about 2" up or down. We have a 75 HP Merc installed with a 11" pitch prop (high thrust) and a "Mac's River Runner" skeg pad installed. We haven't lost a prop in five years.d
We have it set a little on the low side. I'm sure we lose some speed but we never cavitate.
