Story and photos by Jan Mundy Deck hatches usually have lenses made of acrylic or polycarbonate. Boat cleaners, sunlight and pollutants gradually degrade these “plastics” until a web of crazing clouds the view through them. Removing the old lens and replacing it with a new one isn’t difficult, if you know how. Fred Blair of Custom Marine Services (Tel: 416/282-8083), a mobile boat repair service based in Ontario, kindly agreed to share his expertise with DIY readers. Warehouse Plastic Sales (Tel: 800/268-6784; Web: plastic4boats.com) supplied the project boat and the replacement material.

Twelve years in the Florida sun had literally “baked” the lens on this J35’s foredeck hatch. The lens appeared cracked and scarred, but surprisingly the surface was smooth to the touch. Repeatedly cleaning with an ammonia-based product, combined with intense UV exposure, apparently had caused the damage.

This job is best done off the boat on a sturdy surface. The first task is to remove the hatch top from the deck frame, then remove the lens. This took less than two hours. Fortunately, fasteners weren’t corroded, and nuts were exposed so it wasn’t necessary to remove the cabin liner. There was no need to replace the gasket as it was in good shape. While working on the hatch, you’ll need to cover the opening in the boat with plastic sheathing, or devise some other protection to the interior.

Measuring 63cm (25") square and 9mm (3/8") thick, the replacement lens in bronze Acrylite cost $100. The milling charges for WPS to cut and drill fastener holes was $50. If you don’t have the proper tools to fabricate plastic, this job is best done by the supplier.

Follow these procedures for a leak-free hatch lens. A professional budgets six to eight hours for this job and charges up to $600 installed.

Step 1 Remove the original caulking from the groove in the hatch frame using a sharp chisel. Be careful not to nick the inside gasket. Removal could take hours, depending on what compound was used. It’s not necessary to remove all the compound, just the loose residue, to ensure good adhesion. Lightly sand with 80-grit paper to remove loose bits. Clean the groove with a whisk or vacuum.

Step 2 Mask the frame edge. Fred uses 3M 233 tape in 19mm (3/4") width for this job. Overlap each piece and extend the tape ends to provide a good grip later when removing it. Tape across corners, then using a sharp, single edge razor blade, “saw” the tape following the contour of the frame. Press tape down firmly. This way the caulking won’t run under the tape, and you’ll achieve a straight, finished caulking line. As most hatches have a separate gasket, normally, you would mask the outside and inside edges. Since this hatch has an overlapping gasket that wraps around the inner aluminum frame, any sealant that oozes out can be trimmed later.

Step 3 Place the new lens on a protective surface (Fred used bubble wrap), and remove the paper mask. Once the paper is removed, handle it carefully as plastic scratches easily. Before starting, remove wristwatches and slide belt buckles to the side. Determine which is the front, back, etc., and put a piece of tape on the underside, or whatever suits best, for reference later. Mask the lens edge, using your thumb to feel the edge and position the tape. Alignment isn’t critical, but the neater you get it the straighter the finished edge. Trim the corner with a razor blade using a sawing action.

Step 4 To caulk plastics, Fred uses only GE1200, a construction-grade silicone available in black, clear or white. This product requires no prep, it has a working time of one hour, and cures overnight. Again, because of the gasket, application differs from other hatches. Normally, you fill the groove with sealant and any excess oozes out onto the taped edges (see Step 2). Instead, Fred carefully caulks the outside frame edge so it just overlaps the bottom ledge. He’ll fill in the gap from the top, once the lens is placed. With two mating surfaces, the bottom and sides, chances of getting a good joint are good. Smooth with a gloved finger to remove the lumps and spread the sealant evenly.

Step 5 Lay the lens in the frame, carefully checking the front and back positioning before dropping into place. Center the lens in the frame. This silicone has a working time of just 20 minutes at 10°C (50°F); with normal summer temperatures, you’ll need to hustle. Lightly press down, applying just enough pressure to seat the lens in the frame. If the hatch frame is bowed, then you’ll need to weigh down the lens. For this, Fred uses a wooden block placed over a protective cloth in the center of the lens, then lays a batten across the block and clamps it to the frame.

Step 6 Caulk the gap between the lens and frame edge. Apply pressure to squeeze the caulk into the gap and remove any air. Run a 25mm (1") putty knife along the tape to smooth the caulking. Hold the knife at an angle so it doesn’t run off the masking tape. There is often a height difference between the frame and lens. When the lens sits lower, run the knife flat along the frame edge, leaving a slight bevel up to the lens. Recaulk any low spots or air pockets, and level with the putty knife. On hatches with a narrow gap, run a finger along the edge for a neater finish. Don’t do this where the gap is wide (in this case) or you’ll make a definite groove.

Step 7 Remove the masking tape now. Don’t wait until the silicone hardens or the tape may lift it. Start at the corners, pulling back the top tape layer on the frame. Then pull up the tape on the lens side, join the two and pull off both at the same time. This prevents caulking strands from dropping off the tape onto the frame or lens. Angle the tapes back when pulling, not up, which may pull out the caulking or lift the lens. Wait until the sealant cures to remove any tape or sealant residue, then scrape off with a razor blade. Hold the razor blade flat when trimming. To remove caulking off the lens, let it cure, then rub with your finger and it will roll off. Uncured sealant can be removed with Varsol, if needed. If it leaves a film, clean with a specialized plastic cleaner when the silicone has fully cured.