Plugging screw holes below water line

[Mooker]

Hey all, I'm the new owner of a 2006 22' Angler. Previous owner had an intense relationship with his screw gun and added extras everywhere on the boat, and now I'm removing redundant lights, PA speaker, horns, etc.

My current project is the removal of two fishfinder transducers and install of new. I'm looking for advice on how to plug the old holes on the transom below the water line. And, of course, none of the old holes line up with the new transducer bracket.

Also looking for what to use to remove old silicone caulking without harming the finish.

[thataway]

For the screw holes, I would screw/glue a block of 3/4" thick Starboard or similar plastic over the areas of bad screw holes. I have used old screw holes as an "extra:" for keeping the Starboard block. Use a small dovetail bit in a Dremel tool to under cut the surface of the starboard, Make some under cuts also, rough up the back surface, and flame harden it, use G Flex epxoy to glue the Starboard to the transom.

Before you do this, Over drill all of the holes you want to fill, under cut the core, and then fill with thickened epoxy--even for the screw holes you are going to use. Use a piece of paper to mark the holes to dill with a drill press on the piece of Starboard. Paint the edges of the holes with neat epoxy, Then quickly thicken the epoxy with cabosil and medium density filer, or some milled fibers, if large holes.

The starboard will allow you to put transducers the rest of the boat's life, without any chance of compromise of the transom core.

Or for $50 you can buy a "Stern Saver"kit.

Back side of Starboard


Below is screwing one of the early blocks of 1/2"--I found that the thicker was better, and should go right to the edge of the transom.



Dovetail Dremel bit.

[Mooker]

Thanks for the info!
However, I realized I may have a conflict as I intend to add trim tabs and the starboard tab would mount over the existing holes.
So, just fill holes as previously explained or handle differently given the board wont be covering the holes with another layer of sealant?

[WCF]

My opinion: Just fill your holes with thickened epoxy after countersinking them and/or pulling out rotten core, like any other hole repair. You'll get to skip the cosmetic part of the repair since it will be covered up.

FYI: I recently had to remove a section of HDPE boat board that was bonded with thickened (fumed silica) G-Flex only. The HDPE was sanded to 60 grit and then flame treated; no pockets created, no mechanical fasteners. It took the gelcoat and some fiberglass with it when it was removed.

[Mooker]

I figured removing the board would also take some glass with it, so that's why I wanted to make sure and place the new transducer away from where the tab would mount.

Thanks again for your help.

[WCF]

Sorry if my point was lost: I was just pointing out that the pockets and mechanical fasteners (The extra work of doing drill-fill-drill) might be overkill for some applications when working with G-Flex/HDPE in my experience.