How to Install Underwater LED Boat Lights Part 2: How to Drill Through Gel Coat

This is Part 2 of our series on How to Install Underwater Boat Lights, to continue to Part 3, click here. Or, if you need help picking a mounting location for the underwater lights, you can go back to Part 1, click here.

In Part 2 we walk you through how to drill through gel coat when wiring LED lights on a boat. During the video, we teach you about best practices for safely drilling through the gel coat on your boat as we prepare to install a set of Liquid Lumens Mavericks Underwater Boat Lights on a Supra SL550. If you want to skip ahead to one of the key steps in the process, here are the timestamps for the step-by-step:

0:41 – Step 1: Start drilling in reverse to begin the hole.

1:06 – Step 2: Finish drilling in forward.

2:08 – Step 3: Feed the wire(s) into the boat and test fit the light.

2:25 – Step 4: Visually align the light and check for issues.

3:00 – Step 5: Drill the first mounting hole.

3:42 – Step 6: If you used tape, remove it now.

3:47 – Step 7: Partially install a screw while maintaining back pressure.

4:13 – Step 8: While positioning the light, drill the second hole.

4:26 – Step 9: Partially install the second screw while maintaining back pressure on the drill.

4:30 – Step 10: Drill the remaining mounting holes.

4:54 – Step 11: Partially install the remaining screws.

4:57 – Step 12: Check final position of the light housing.

Congrats, you’re done drilling holes in your boat! Probably not nearly as scary as a lot of us thought it would be the first time we did it, right? Continue to How to Install Underwater LED Boat Lights Part 3: How to Use 3M Marine Adhesive Sealant to Install Boat Lighting for the next step in your install. Additional Underwater Light Installation Instructions are available here.

Comments and questions are always welcome. Let us know how your own installation went and if there is any other content you’d like to see us share in the future. Thanks for watching!

Transcription of Video

A couple of things to consider when drilling gelcoat.  It is very fragile and does not like drill bits.  If you drill in the forward position it will chip away at your gelcoat.  You may end up with a crack that could run out from the screw hole off the side of the light and have a damaged boat.  So, there are a few tricks that you can do to avoid letting your gelcoat crack.  

One is using some tape in the area that you’re going to drill.  We’ve put down some high temperature masking tape that we use for our powder coat process here.  You can also use blue painter’s tape or even just some basic masking tape.  

STEP 1:  Drill in Reverse to Start

We’re going to put the drill into the reverse drill position.   So instead of drilling forward, we’re going to drill backwards as we break through the outer color layer of the gelcoat.  By doing that, it will allow us to get through the outer color layer and avoid chipping.  Once we’re into the fiberglass, then we’ll put the drill into forward and finish the hole.  

STEP 2:  Finish Drilling in Forward

As you can see, we’re well into the fiberglass now, we’re through the gelcoat so we can put the drill into forward and drill right through.  Now we’ve got a nice pilot hole.  We still want to avoid letting this other hole that’s pre-existing let the drill bit wander.  Normally, we could move from here right up into the 3/8” size.  We’re going to step up a couple of drill sizes just so we can keep the hole centered where we want it and make it all the way through.

So, as we step up in drill size anytime, we need to repeat the process.  We’re going to drill in reverse at first and then we’ll switch it to forward, avoiding any cracks in the gelcoat.  Now we’re ready for our final drill size – 3/8”.    

We’ve got two nice holes, obviously this hole is plenty big to handle whatever we need.  The other wire should fit nicely here.  We’re going to test that now.  Before we drill any of the screw holes, we want to feed the two wires into the boat, position the light, make sure everything looks good.

STEP 3:  Feed Wire(s) into Boat

We’ve got our first Mavericks light here, we’ve unbundled the wire, we’re going to feed it into the boat.

STEP 4:  Visually Align the Light and Check for Issues

You can see with the position we’ve selected we like how the lights position on the boat and where it’s sitting.  We’re running into one problem.  This surf exhaust is getting in the way of our drill getting a nice clean 90 degree angle into the gelcoat, so rather than trying to drill on an angle or cause a problem, we’re going to run over to the hardware store and snag a 90 degree angle drill head so we can have the proper tools for this install that is a little bit unique.  

STEP 5:  Drill the First Mounting Hole

We’ve got our 90 degree angle drill head that we snagged at the hardware store and I’m using a friend here to help me position the light just the way we need it.  He’s got it visually lined up the way that it gives us about the same clearance on one side as the other.  We’ve put tape underneath this very first corner screw hole and we’re going to follow the same process as drilling the wire hole.  We’re going to put the drill bit in reverse.  We’re actually going to use  the light housing as the drill template now because it will align the screw straight into the gelcoat.  We’ll drill in reverse to start and then all the way through.  

Use one hand to give back resistance so as you break through the fiberglass you don’t run your drill into the light housing and put a scratch in your paint. This isn’t our final mounting.  We’re just going to secure that first hole in position for drilling the other hole so we can more easily secure the light.  

STEP 6:  If You Used Tape, Remove it Now

So move it out of the way for just a second.  We’ll get this masking tape off.  

STEP 7:  Partially Install a Screw While Maintaining Back Pressure

We don’t need to go all the way in.  We’re just going to get it set far enough into the gelcoat that it will secure the light for us to pivot and position the other holes.  

Gelcoat and fiberglass are incredibly strong.  We drill that hole just slightly undersized so that you have good purchase into the material with these mounting screw holes, so be sure to maintain good back pressure on the drill as you’re going in, otherwise you’ll end up stripping the heads on your screws.  

STEP 8:  While Positioning the Light, Drill the Second Hole

We’ve got one screw started into the gelcoat to help us with the pivot and now, again I’m going to start drilling in reverse and prep us a hole for the second screw.  

STEP 9:  Partially Install the Second Screw While Maintaining Back Pressure

Now I don’t need a friend.  I’ve got two screws set.  I’m just going to drill the last two holes.  

STEP 10:  Drill the Remaining Mounting Holes

We’ll set a couple of screws in them.  Make sure everything aligns then we’ll pull all four screws out, clean the housing, put our Marine Grade sealant on it then put it all back together.

STEP 11:  Partially Install the Remaining Screws

STEP 12:  Check Final Position of Light Housing

The housing is where we want it.  Everything is lined up nice.  We’re going to pop the screws out, clean it up, put the sealant on it and put it back together the final time.

Continue to Part 3