Dear Boat Doctor,

I have been battling leaks in my deck hatches for years. First I thought there was a leak around the plastic lens, so I removed and resealed it. When it still leaked I replaced the gasket to no avail. I am fed up and I just want to replace the two large hatches. I like the look of the Lewmar Ocean hatches, but they don’t quite fit the hole cut for the old hatches. The opening required is roughly a quarter inch larger and the corner radius is slightly different.

I have basic woodworking skills, but this feels a little more complicated than just breaking out my jig saw.

Harry Barnes

Annapolis, Maryland

Dear Harry,

I’ve been down the same road and at some point it makes sense to stop chasing leaks and just replace old hatches. Lewmar Ocean hatches are a good choice. There are fancier stainless steel and glass hatches out there, but boats have sailed around the world countless times with Lewmar hatches.

You have two options on the Ocean hatch, a flat base or flanged base. This refers to the base frame that screws to the deck. The flat base sits on the deck, the flanged base slides into the deck about an inch. If you have enough deck thickness, I would recommend the flanged base as it’s much stiffer.

Most decks are cored with a skin of fiberglass on the top and bottom, and filled with core material. The core can be plywood, balsa or foam. Your deck is likely about an inch thick, and probably framed thicker around the hatches. You can tell a lot by opening the hatch and taking measurements from the top and bottom.

To use a slightly larger Lewmar hatch, you’ll need to inset the hatch into the deck by cutting a groove around the opening. The easiest and most precise way to do this is with a router and a template. Build a wood frame the exact size of the inset you want to cut. You can make this from ¾-inch plywood or build a frame with ¾-inch dimensional lumber. Your new hatch will come with a paper template, or you can simply trace the hatch profile.

With the template built, you just screw it to the deck in the exact location you want and cut the hole with the router. The trick is to use a template cutting bit with a guide bearing at the top. The bearing will ride on your template, and the bit will cut the deck away. Take your cuts a little at a time until you get to the depth you need. You’ll need to seal the cut edge with epoxy to make sure everything stays watertight. 

Your new hatch should slip right into the inset. Then just seal with a deck sealant and screw the hatch to the deck with stainless sheet metal screws (or through-bolt if you have access).