Hatch Replacement 101

Upgrading a hatch will improve a boat's looks and kill that annoying leak.

Reasons to replace a hatch are manifold. The most common reason is a leak, which is typically caused by faulty seals. Even if a hatch is made out of high-impact polypropylene, though, the fact it’s on a boat means it’s been exposed to extreme conditions, which can compromise its integrity. Plus, people tend to walk on them or try to jam things through them that are too large.

We replaced this particular hatch for three reas

• Better aesthetics
• Provide more light
• Create a larger opening, so larger items could fit through it
We chose the Bomar 900 Series polycarbonate hatch sold at West Mar

ine for $399. The original hatch was the ubiquitous white polypropylene hatch with twin dogs. For that install, we started by finding a flat spot with no critical component underneath it and taped down the supplied template. Then we used a circular two-inch hole drill bit in all four corners to give the jigsaw easy access to cut the hole. Starting with round holes in the corners helps prevent any cracks from spreading.

The boat’s owner and my friend, Meade Gougeon, who died a few months ago, wasn’t sure he would keep the original genericlooking hatch. To make sure he could remove it easily, he didn’t use the usual heavy marine sealant. He decided to install the hatch using WEST SYSTEM epoxy thickened to a mayonnaise-like viscosity with 410 Microlight Filler. (All the West System epoxy products referenced in this article are included in the 105-K Fiberglass Boat Repair Kit that retails for $33.35.) He reasoned that the lower-density epoxy/410 combination would be flexible enough to stay attached to the epoxy-coated plywood deck and to the plastic trim ring that defines the perimeter of the hatch. The trim ring’s bottom edge had grooves to help bedding compounds adhere and assist in sealing out water.

He did have some concern about the differing coefficients of thermal expansion for the plastic trim ring and the plywood deck. Common flexible sealants handle this nicely, because “they go along for the ride.” He wasn’t sure if the epoxy/410 would be able to handle these forces, but the hatch would also be installed with a number of screws that would address these loads nicely. Over the course of two years, the hatch performed successfully, never exhibiting leaks or other issues. Plus, it looked a lot neater.


To remove the old hatch, we unscrewed all of the mounting screws and were pleased to find that if we lifted up on just one of the corners of the hatch, the whole thing came away with little effort (1).

Most of the time it takes a bit of effort to unseat an old hatch, sometimes requiring DIYers to tap a series of small wooden wedges around the edges to break it loose. All the epoxy originally used to install the hatch was left on the deck, creating an exact molded profile of the bottom edge. Obviously, the bond between the plastic flange and the epoxy was not very strong, but it was adequate to prevent any leaks over its two years of service.


To prepare the area for the new hatch, we got rid of what was left from the last install. The epoxy/410 Microlight mixture was easily removed with a low-angle block plane (2). Epoxy thickened with Microlight carves and sands like low-density wood. Because it worked so well the first time, we decided to use this compound again to install the new hatch.


Because the new hatch was larger than the old one, we had to widen the hole with a jigsaw. Like the original installation, we taped the area to protect the gelcoat (3), taped down the template, made our cuts and put the trim ring down, so we could use it as a template for drilling the holes for the mounting screws.

To prepare the surface, we lightly sanded the area, so the epoxy/Microlight mixture would adhere better. After thoroughly cleaning the area with alcohol, we coated the freshly cut edges of the gelcoat, fiberglass laminate and core with unthickened epoxy/hardener to seal it. With the trim ring still in place, we taped the area outside of the ring with clear packing tape (coating it with cooking spray would work too), to make it easier to remove any excess epoxy.


We thickened the epoxy with West System 410 Microlight, until it attained a consistency like mayonnaise. Then, using a small brush, we applied a 4- to 5-mil coating around the perimeter of the opening (4).


Now it was time to position the hatch into place and squeeze out any excess epoxy. After applying a small amount of marine silicone sealant, we screwed in all the screws (5). Be careful not to overtighten the screws, though, or the plastic or gelcoat underneath can crack.


Using a West System Reusable Mixing Stick that has a chisel point that won’t damage brittle gelcoat (6), 


we cleaned off the excess epoxy (7). 

Remember to pull the clear packing tape while the epoxy is still curing, and wipe the surrounding area with alcohol and cheesecloth.


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