Fishing forum > Transom Strengthening for higher HP

Author Topic: Transom Strengthening for higher HP

How would someone go about strengthening the transom of there boat to accept a higher HP motor? Im not talking much more. Only on a 12' Aluminum with a rating of 10hp. I would like to go up to a 15hp or possibly 20hp.
How would it be done to strengthen the transom?

Not a good idea. The boat is designed for a specific engine size and rated for it by the government. More horsepower equals more weight and with the operator in the stern, you will greatly reduced freeboard plus manoeverability issues. I tried a 9.9hp Honda on my 12ft Princecraft and I had to be very careful not to take water over the transom.

You could look into modifying a 9.9. I've heard a carb swap will give you 15 from a 9.9 Then you're not changing the size/weight ratio, just the power. As for modification that would be necessary, my boat has some brackets that go from the top of the transom diagonaly down and mount 6-8" out on the flood. They're riveted in place. Maby look into supports like this? That way the flex of the transom is dispersed pushing down on the floor.

Good points, however I will be at the bow of the boat with an extension bar connected to the tiller. So all the weight wont be in the stern, it will be equally distributed throughout the boat. I have been boating for a number of years and safety definitely comes first. I would not do such a modification unless I find the proper way of doing it.
Secondly I am getting a 04 15hp Yamaha. In this particular year the 9.9hp & 15hp weigh about the same. So this will not affect the transom at all I think. Though I wouldn't mind strengthening it some just in case, just to be safe.
In your guys' opinions, would a piece of 1/2" thick plywood cut to size be a good means of strength for the transom?
fisher 696

Be VERY careful about exceeding rated power levels. Having said that I think that you may need to look at transferring the additional power through the side rails and into the floor. I feel that the addition of a piece of 1/2 inch ply would have little effect. Attaching plywood to aluminum can be difficult. Good luck with your efforts

I would be very careful, if you get stopped by fisheries, they can fine you and take your boat for exceeding the engine size for the boat.

If you are still going to do it take a look at getting a piece of 3/8 Aluminum plate and add that to the transom. Them use sica flex to seal the holes.

Fishing forum > Transom Strengthening for higher HP


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