Sterndrive Transom Plate For Aluminium Boats

[Willallison]

Would anybody have some pics / drawings / info on how the transom plate is typically setup in an aluminium boat? Clearly, you don't use 55mm plate!!
I've attached a pic which just shows the transom plate template extruded to the required thickness, but I'm sure this isn't how it's typically done.....

[CDK]

Two pieces of 24 mm plywood, several coats of epoxy resin until you're sure the surface is completely sealed, then bed it with Sikaflex.
That's the way I would do it.

[gonzo]

All the ones I've seen have two layers of 3/4" ply with an aluminum skin on the inside.

[Willallison]

Hmm - ok... no brackets etc back to the engine beds etc?

[gonzo]

The engine beds usually end up at the transom, just like on a wooden or fiberglass boat. The engine beds are welded or riveted to the bottom and transom.

[Willallison]

Yes.. I know.. sorry... didn't explain that very well....
I meant brackets between the engine bed / transom stiffeners etc and the thicker area of the transom where the cutout is

[gonzo]

That depends on how you design the structure. There can be brackets, it can be welded/riveted to the outer or inner skin. You can engineer it in a variety of ways. The beds only have the weight of the engine and torsion. There is no longitudinal forces on them. However, if you think of the hull as a box, attaching the beds or stringer to the transom helps to transfer the torsion load to a transverse member.

[CDK]

Originally Posted by Willallison

Hmm - ok... no brackets etc back to the engine beds etc?

None.
The engine rests on two spring washers on the bracket of the transom housing and one or two adjustable front engine mounts. The load is almost static, just half the engine weight plus some vibration.
The transom has to absorb the thrust as if you had an outboard engine, but the area is larger and lower positioned; I see no problems there.