Patching holes in a fiberglass hull

[dorsett59]

Hello.
So, the lower unit on my old engine crapped out, so I'm updating from a 1959 Evinrude 50hp to a 1979 Mercury 70HP. The problem (okay, ONE of the problems!) is that the holes drilled in the transom to attach the bottom end of the mounting bracket do not line up. Go figure.

So, the question I have is this. How should I fill two holes about 7/16 inch dia that are sometimes below the waterline in the transom?

Additionally, how should I drill and plug the NEW holes I get to put in my boat? The previous owner kindly left a few pieces of aluminum diamondplate angle stock for a brace so I don't overtighten the bolts.

I've already mounted a bilge pump in case this doesn't work. Personally, I'd rather not have to use it!

Thanks in advance!

 

[danond]

Re: Patching holes in a fiberglass hull

What kind of hull? Type of boat? Any pictures? Not enough info to go on here.

 

[dorsett59]

Re: Patching holes in a fiberglass hull

From my username, the boat is a 1959 Dorsett Catalina.
From the title, the hull is fiberglass.
I do not know exactly what the transom is made of, but the previous owner reinforced portions with 2X2 aluminum angle diamondplate. The top screw mounts are attached to diamondplate. Lower on the transom, there is fiberglass covering I'm not sure what. The previous owner used a one foot section of the diamondplate mentioned above as a brace and as a washer to spread the load and to prevent crush damage on the inside. Externally, the previous engine through-bolts had what looks like neoprene gaskets sealed with some blue sealant. It worked very well, as the boat would not make any water.

I am looking to seal the hole externally, so that water does not get to whatever is under the fiberglass.
To mount the new engine, I also need to drill two to four new holes through the transom.

I do not have any photos.

For drilling the new 7/16 ich holes for the 3/8 inch engine mount bolts, should I use a regular drill bit, hole saw, or something else? Should I cover the fiberglass to prevent splintering?