Underwater LED Light Install

I am looking for some feedback on installing some LED underwater boat lights. All of these lights require a hole drilled through the hull. The installations that I have seen demonstrated on YouTube are all on fiberglass hulls, where there would not be any issues related to core damage due to leakage.

My question is what should be done on a cored hull, either plywood or foam? I feel like following the Gougeon method, of drilling a larger hole than is required, backfilling with epoxy, and then drilling the hole the correct size is the way to go here to insure there is no possibility of some sort of water leaking around this light causing the hull to rot. Thoughts?

It seems like all of the installations are using 3M 4200 marine sealant. Would you trust that?

Thanks!

 

You are on a good plan.

I would consider doing the filling from the inside to take advantage of the gravitational assist instead of fighting it from the outside.

Paul

 

Thanks Paul, these were my thoughts exactly. They make the installs look so easy and I suppose they are when you don't have to worry about saturated core materials. In the case of the sealant failing on a fiberglass hull you just get some water in your bilge, and you have your alert the seal has failed. With a core you could have a major repair in store if you don't go through the hull correctly.

I just don't trust these silicone sealants. I know there in wide use now days, but I have my doubts none the less. Has anyone done an install and had the silicone fail after a while?

 

use a kevlar thckened epoxy paste to fill the hole. If you grease your bolts or screws with grease you can remove them when the epoxy sets up and have a perfectly threaded hole.... see wet dry 700 epoxy