Hatch Seal Replacements 

Part 1: Bigger Isn't Always Better

--Blogpost written by Bob

We decided to replace the seals for our forward hatch (lower area of image) and
our mid-ship hatch (upper area of image) during the winter
as part of our boat's 30-year retrofit.

This will be the second time seals were replaced for these two hatches. The first time (about 15 years ago), 1/2-inch diameter closed-cell foam neoprene seals were used--this time around I increased the diameter to 5/8-inch (thinking that bigger is better).

The seal material was purchased from Atkins & Hoyle, the original manufacturer of the hatches.
I specified that they be 5/8-inch diameter after I found out that two diameters were available,
the other and more standard being 1/2-inch.  This was a BIG mistake!

Removing the Hatch Covers

Since I'm replacing the seals during the winter, I made a temporary plywood cover for the hatch
so that I could bring the hatch cover home and adhere the new seal in my home workshop
where the temperature would be more suitable for curing (so I thought anyway).

Removing the Old Seals and Adhesive

Removing the old seal material (mostly the old caulk) was the most time-consuming part of this project--it took about 2 hours for the forward hatch cover.

First, I cut out the majority of the old seal with a razor knife.  The groove (shown at the
bottom of this image) still contains some of the remaining seal.

The second operation was scraping out the old adhesive and seal remnants with a 1/4-inch wide wood chisel.  Some remnants of the adhesive were still in the groove of the hatch cover and I tried to remove them with various tools in a Dremel but the wire brush wheel and the burnishing tools wore out very quickly.  I went back to using the 1/4-wide wood chisel and continued to remove the old seal that way--it wasn't fast but it was effective.

Removing the old seal and adhesive was very difficult and time consuming.
The groove is shown here taped off to prevent the messy
adhesive from getting on the hatch frames.

Installing the New Seals

I decided to use Sikaflex #291 for the adhesive to hold the new seal in the groove in the aluminum hatch cover--the cured adhesive has an elongation property of greater than 400%.  To assure satisfactory adhesion to the anodized aluminum frame, I had to wipe the frame with Sika #205 cleaner/activator and then, within 2 hours, apply the sealant.

I taped off the inside and outside edges to minimize the sealant from getting on the hatch frame--this turned out to be unnecessary.  The Sikaflex #291 is thick and messy--I should have worn disposable rubber gloves!

I started to adhere the seal (within 30 minutes after applying the cleaner/activator) starting in the middle of the frame (opposite the hinges) and working around each side to the hinged side of the hatch frame.  I allowed the seals to temporarily overlap in the middle of the hinged side and I cut thru both ends of the seals at roughly 45 degrees with heavy shears.  I applied adhesive on the two 45-degree cut ends and brought them together--the junction was not very pretty and there was an irregular gap--next time I will use a hack saw.  I allowed the adhesive to cure overnight and then, attempted to remount the forward hatch cover on the boat--next time I will allow the adhesive to cure in place while the hatch cover is mounted.

The 5/8-inch diameter seal appears significantly bigger than the old 1/2-inch
diameter seal--it's actually TOO big!

Not only was the new seal bigger, but without being clamped during curing,
the seal did not fully seat into the groove in the hatch cover.

Results

When I remounted the hatch cover I couldn't get the hatch closed.  I felt that the largest obstacle to closing was nearest the hinge--the seal diameter was simply too big and not fully seated in the groove.  So, I removed the hatch cover, reinstalled the temporary plywood cover, and removed the new seal that I just installed.  I ordered replacement 1/2-inch diameter seals (the proper size) and I'm waiting for them to arrive--they should be here in about a week.

I hope someone else can learn from my mistakes on this project.  Installing the proper size seals will be covered in Part 2.

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