Updated: Marine hatch in the bathroom

**Townesw** · May 14

I have been wanting to do this modification for a few years now and actually bought the hatch a few years ago but just got around to installing it before this recent trip.

I never have liked the shower caddy/shelf in the bathroom vanity. I’ve had it out at least 2 times to work on the faucet and to replace the sink drainpipe. I needed to tighten the nuts on the bolts that go through the propane enclosure and are accessible only under the sink so I took the opportunity to install the marine hatch.

Picture of caddy removed and cleaned up using ASI 0240 adhesive remover and plastic razor blades. I never have cared for the way the factory drills holes in the gelcoat. Every factory screw hole I have seen has cracked gelcoat around it.

Vanity front taped up and template taped in place. I actually lowered it after this picture was taken.

The door doesn’t detach from the flange, and even if it did you couldn’t reassemble it after the flange was mounted. This and the small space that you are working in makes the hatch and flange difficult to position accurately. It helps to make the opening just large enough for the flange to fit into, then you can modify the hole if needed to square up the hatch.

I used a coping saw to cut the fiberglass and a sanding drum in a drill to shape the hole. I cut the opening a little small at first but it was easy to open up a bit using the sanding drum and a sanding block. I marked and drilled pilot holes, then screw-sized holes, then chamfered the screw holes with a 1/2 inch chamfer bit. I also cleaned up the factory holes using my chamfer bit. You’ll want to locate and drill 2 holes, one on each vertical side, then temporarily mount the hatch so that you can better mark the remaining holes. Holes not shown in this picture.

I placed one layer of butyl tape all around the flange then an additional layer of butyl along the vertical sides. I did this because the front of the vanity has a slight curve and I didn’t want to pull the vertical sides down to meet the vanity surface.

I used 10-24 x 1inch stainless steel oval head machine screws, #12 stainless steel flat washers (because that what I had), and 10-24 Stainless steel Nylock nuts to secure the flange to the vanity.

Picture after the butyl is through oozing and trimmed flush with the flange. You can’t trim the butyl behind the hinge so be careful how you apply it to the back of the flange on the hinge side. I suggest keeping it back away from the edge 1/16” and hopefully it will extrude evenly as you tighten the machine screws. I’ll talk more about this area later.

Taped off for caulking with ASI 335 sealant

You can’t caulk the edge behind the hinge.

I wasn’t pleased with the way the butyl looked behind the hinge…

…So I used a paint stirring stick that had dried latex paint on it (this sealed the end grain of the stick) to “tool” the butyl behind the hinge. This produced a finish that I was pleased with

Picture of open hatch. I have yet to relocate the pump switch and light. I am thinking about putting them in a stainless steel bracket just inside the top right of the opening so that the switch can be accessed while seated.

Notice the pump switch and light hanging over the p-trap. I’ve got it cable tied there for this trip.

Marine hatch used. I think I ordered it off Amazon.

I am very pleased with the way this modification turned out and being able to very easily access the area below the sink. I don’t intend to store anything under the sink, I just like being able to see in as many places as possible.

Again, apologies to any of my High School English teachers who may be reading this.

Bill

Edited 21 hours ago by Townesw