drilling a hole below the waterline

[checkeredflags]

I have a 16" aluminum boat and I need to drill two holes through the aluminum 1/2 " in diameter in order that I can install two extra bolts to secure a 25 horse engine. There are two bolts going through the transom above the water line that go through the wood; however I need aditional reinforcement and this will require that I drill two holes through the thin aluminum below the wood transom to bolt the lower portion of the engine mounting bracket. I thought I would use a thin piece of steel on the inside like a steel plate...drill the hole and run 1/2" bolts through the aluminum and the plate and bolt it down. My concern is leakage since this will be right at or a bit below the water line...not sure what to do.

 

[Solittle]

Re: drilling a hole below the waterline

3m 4200

 

[Chris1956]

Re: drilling a hole below the waterline

Checkered, if you use a couple of fender washers on the lower bolts, it will be strong enough. Steel will only rust in time. You should use all stainless steel, BTW. use some silicone sealer on the washers and under the motor to keep it from leaking.