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Replacing a Hatch in 7 Easy Steps

Replacing a Hatch in 7 Easy Steps

For our first night together on Polynya there was a heavy downpour. There are a few minor leaks that need to be addressed, mostly around ports that need to be rebedded, but the worst leak, needed more dramatic attention. The forward hatch, above the v-berth, let a lot of water in, quickly filling buckets. Our attempts to add sealant were never successful so we resolved to replace the hatch. We considered just rebedding the hatch but when we watched the hatch in a rainstorm it was obvious that the leak was coming right through the frame around the glass. Being such an old hatch we decided it made more sense to just replace it. We decided on a Vetus Magnus which is an ocean rated hatch able to open 180 degrees. It has 4 dogs that can be opened from above or below, and the hatch can be locked from below in a fully closed or partially vented position. Our forward hatch is the largest available size, approximately 25” square.

1.) Remove Old Hatch

The first step is to remove the old hatch. Loosen the screws around the hatch, being careful not to strip them. Our screws came out fairly easily but we decided to replace them with new screws as the heads showed signs of wear. Once the screws are out, lift the hatch out of the opening. More than likely, the hatch will be stuck in place by the sealant. A small scraper carefully wedged under the hatch, all the way around, will help to break the seal. Slowly work the hatch up from the deck, being careful not to damage the hatch opening. In places where the sealant was particularly persistent, I used an oscillating multitool with a scraper attachment to break the seal.

The old, leaky hatch.
The old, leaky hatch.

2.) Clean the Hatch Opening

Use a scraper to remove any leftover sealant around the hatch opening. It should come up fairly easily, but be careful not to damage the surface below. Any damage to this surface will diminish the quality of the seal on your new hatch. Remove any remaining residue with acetone, leaving a clean smooth surface.

3.) Enlarge the Hatch Opening

Now that the hatch opening is clean, do a test fit of your hatch. If the hatch fits nicely in the opening you can skip step 3. In our case, the new hatch was of a slightly different design which required enlarging the opening by approximately 1/4” on all sides. Our opening has a teak coaming all the way around so this was an easy process. If you have to enlarge a fiberglass opening that will entail additional steps, not discussed here, to ensure the opening is properly sealed.

I used a circular saw set to the exact depth of the wood to neatly remove the 1/4” all the way around the opening. After a quick dry fit I found I needed to remove a little more material on one side. I used a sharp chisel to remove small amounts of wood where needed until I had a snug fit.

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The view from below during a dry fit.

4.) Fill Screw Holes and Prep Hatch Opening

To prevent water intrusion, and ensure a good seal, it is important to fill the old screw holes. For this I used a thickened filler. While I was filling the holes I decided to use a little extra filler to fair the topside of the coaming to maximize the quality of the seal. Once the filler is dry, sand the the entire coaming to a smooth, fair surface. I then used a little acetone on a rag to remove any remaining dust and give the opening a final clean.

Coaming filled and faired.
Coaming filled and faired.

5.) Dry Fit the Hatch

With the opening preparation complete, test the fit of the hatch to make sure nothing has changed after fairing.  If everything still fits flush, pre-drill your screw holes all the way around the hatch. Be sure to drill straight, with an appropriately sized bit, to avoid crooked screws or a split coaming. Screw size will depend on your specific installation, but be sure to use stainless. In our case I used the same size screw as previously used, which was long enough to pass through the coaming and bite into the deck itself.

Dry fitting the hatch. Note protective coating still in place on the glass.
Dry fitting the hatch. Note protective coating still in place on the glass.

6.) Apply Sealant

The next step is to remove the hatch and apply sealant to the opening. A variety of sealant options are available, and you should choose what you are comfortable with. We decided to use butyl tape, but whatever you choose, make sure it is appropriate for a marine environment.  We like butyl tape because it is much cleaner to use, eliminating the messy process of cleaning oozing sealant after the install. I carefully laid the butyl tape around the opening, paying particular attention to the corners to ensure there were no overlapping seams.

7.) Final Fit

With the butyl tape in place, wipe down the bottom of the hatch and carefully lower it into the opening. Any debris between the tape and the hatch will compromise your seal so it is important keep the surfaces clean. The hatch should fit snugly, but will be slightly raised due to the thickness of the butyl tape. As the screws are tightened the tape will compress and the hatch will lay flush. Before installing the screws put a dab of 4200, or similar sealant, into the opening. This will ensure the screw hole is sealed and the materials below are protected. There is no specific order to put the screws in, but I tried to work evenly around all sides. A little patience while working your way around the hatch will improve the chance of a solid seal as the pressure is evenly applied around the opening. As the butyl tape compresses it will slightly squeeze out around the edge of the hatch. Once all screws are tight the extra butyl tape can be easily trimmed with a knife, leaving a clean, professional installation. With the hatch secured, the job is complete! Test the operation of the hatch and spray it down to check for leaks. If you’ve worked carefully, there should not be any leaks. If there are, however, do not panic. Simply remove the hatch, clean away all the sealant, and rebed.

Hatch installation complete!
Hatch installation complete!