Replacing old 15HP for 25HP OB

[carlosproa]

I have an old EDELCAT33 with a place for an outboard at the nacelle. The transom is 3 pieces of glued wood circa 1991? And is very strong for the current 93 lbs 2 cycle manual start Yamaha 15HP. I recently purchased a brand new 25 HP HT Yamaha of 146lbs electric start. So there is a 53 lbs difference, and dimensions just a bit bigger.
Since this engine will be bolted on, and since I would need to bring the transom closer 2” forwards, and 2” higher and wider, I decided to make a new transom.
Target thickness is 2.5” and I am looking for rot resistant hardwoods to avoid using marine plywoods.
The idea is to epoxy 3 pieces of wood and wrap it with 1708 biaxial cloth and epoxy.
So questions to the group:
- which are wood to get? Spanish cedar? Mahogany?,or?
- is it worth just doing two pieces of marine ply?
Here is a picture of the current transom. The idea is a new piece taller and 2” closer forwards

[carlosproa]

Well, since I got no answer, I took a swing at it. By the way, those stoping in Miami and need provisions, look at US-1 and 27th Avenue for Shell Lumber for all your wood and metal, and Crook&Crook for boating related. There is West Marine about 1/2 mile at US-1 and sw40th street.

Back to my story, turns out the wood making the transom in question was determined to be walnut, a very hard wood that dulled by reciprocator saw blade fast. There was no way to save the piece to get to the threaded rods, but a 4x3x7 pi ce cost me $80.
So now, I am making a mockup of the measurements with cardboard before cutting the wood. My biggest concern is being able to perfectly align the 4 holes securing the transom to the body of the boat via a metal plate, as they are in and angle and I have to drill into about 6” of wood.

[Bullshooter]

Looks tricky. Can the bolts be removed? It looks like maybe you cannot access them from the outside of the stern?

I think I would get some plywood and clamp it in place and have a go at getting the holes right before risking the walnut.

Some waste wood from a dumptser or something may be worth using at first. If you drilled over-sized holes that would match the bolt locations, you could put it in place, then use it as a template to figure out if the angles and locations are right.

I would have to be there, but maybe there is a way you could cover the bolts with vaseline and then put some quick-setting compound in the hole around the bolt. When it dries, take the board with the large holes filled with bolt impressions as a jig to drill your walnut.

I did not explain that well but maybe it will give you some ideas. Good luck with your project.