Patching Deck Hatch Leaks

The drippy evidence of a leak can be a long way from its source at a leaking hatch. Follow these procedures to find and fix the leak.

FIND THE LEAK. Leaks commonly appear from four different routes.
Route 1 Through the hatch lid.
Leaks between the lens and frame first show up here.	At hatch dogs or fittings that pass through the hatch lid. Look for drips off the bottom of the handle shaft
Route 2 Via deteriorated rubber gasket.
Rubber gasket between the hatch lid and base.	This locker hatch gasket looks dubious.
Route 3 Under the hatch base and/or through the base mounting fasteners.
A leak between the hatch base and the deck may show here.	A leak can also emerge at one of the hatch frame fasteners.
Route 4 Out of the deck core or inner liner exiting at the hatch cutout.

Repairing a leaking hatch is not always as easy as it sounds. You can’t stop a leak until you find the source and therein is the challenge. Waiting for a day of steady rainfall to help you pursue leak sources may not fit your detection and repair schedule. Leaks can be prodded into action with the “rain” from a garden hose.

Standard leak hunting technique using a hose requires teamwork. Up on deck, you begin with the hose irrigating the lowest fittings first. Below, your spotter keeps watch. Water is gradually pointed to higher fittings until the spotter calls out that water is getting inside. Careful inspection usually determines the origin of a hatch leak. Armed with a paper towel and a flashlight, follow the wet trail back from where the drip forms, dabbing it dry as you go, until you see the first sign of seepage out from under or between parts of a hatch.

Leaks arriving by Route 4 (as described opposite in “Find the Leak”) are the most difficult to trace. They originate at some other fitting and can travel a long way between the liner and deck or through the deck core before exiting at a vulnerable point in the hatch cutout on deck. Brown water seeping from around the edges of the hatch hardware or the headliner edge trim is a symptom of wet balsa (or plywood) core and is bad news requiring prompt action. Time to bring in a moisture meter or call a surveyor or repair yard you trust.

Tame the Leak

Repair techniques vary depending on the source of the leak. Leaks through the lid, as found in Route 1, are caused by either the lens or lid fittings. Framed lenses commonly leak at the flexible bedding around the plastic (acrylic) lens. A proper repair requires complete removal and rebedding of the lens using a high flex glazer’s silicone. A Band-Aid approach won’t work. [Ed: See DIY 2001 #4 issue for complete hatch lens repair details.]

Any type of hatch lid can leak where holes have been drilled for fittings. Hinges and latches on frameless hatches take a beating and should be periodically tightened and rebedded with a polyurethane sealant. Many anchor locker and cockpit locker lids are Balsa cored so it’s important to keep the fittings well sealed.

Hatch dogs fitted through plastic lenses differ as they usually rely on Orings and rubber washers that keep them sealed while allowing them to rotate. Dismantle the hatch dog assembly and replace all O-rings whether they look worn or not. If possible get the hatch manufacturer’s repair kit. Cut sealing washers from scrap rubber or neoprene. Thoroughly clean (don’t use solvents on plastic/acrylic lenses) the surface where the O-ring rides. Apply a light coating of Teflon grease or sail track lube to the Orings during reassembly to help them seal and to prevent sticking.

Rainwater leaks by Route 2, between the hatch lid and base, are usually not a problem with a typical framed hatch because they are designed to shed water. These are left open a crack for ventilation and still things can stay dry, but don’t try this when underway in rough seas. The pressure of green water on deck will blast water violently through the slightest gap. To ensure a hatch stays sealed under these conditions, the neoprene gasket between the lid and the base must be in good condition and the hatch dogs properly adjusted to maintain firm clamping pressure.

Over time the neoprene gasket deteriorates and gets crushed flat and the dogs no longer clamp tight. Most hatch dogs are adjustable but eventually you run out of adjustment and then it’s time to replace the gasket. This entails peeling and scraping off the old gasket and glue from the hatch and gluing a new one in place using contact cement or a combination sealant glue, such as Rule’s Sudbury Elastomeric Marine Sealant. If gasket material is not available from the hatch manufacturer, use generic neoprene weather stripping of approximately the same size and shape. You’ll also need to readjust the hatch dogs to suit the new gasket.

Where leaks occur via Route 3, exit-ing along the hatch base, the culprits are usually loose hatch base fasteners. Any that turn easily with a screwdriver must be resealed. Remove suspicious fasteners and any sealant residue, clean both surfaces, tape the repair area to reduce clean-up, then rebed using a polyurethane sealant, such as 3M 5200. Don’t skimp on the goo. If in doubt as to exactly where the flange is leaking remove and reseal the entire hatch base flange. This may not be easy. Try tapping a putty knife under the edge to cut the sealant and then gently wedge it up a bit at a time with a broad chisel. Indiscriminant prying will result in a bent hatch flange or worse.

Carefully clean off all old sealant from the deck and base flange. Apply sealant to the individual fastener holes and run a continuous bead all around the flange. A well-bedded flange should squeeze sealant around its perimeter as it’s bolted (or screwed) down. (Masking beforehand helps to eliminate clean-up.) If you think you might someday have to remove the hatch or its fasteners use a polysulfide sealant, such as 3M 4200. This class of rubbery sealant doesn’t have the ferocious adhesive strength of polyurethane but on a large bedded surface will seal almost as well.

Leaks manifesting from Route 4 are difficult to identify, tricky to trace and are a sign of trouble brewing. If a slow leak continues to appear under the hatch at the lower edge of the deck or headliner opening, even after the hatch base is rebedded, you should suspect other hardware as the culprit. Look for wet spots on deck with a moisture meter or if in doubt rebed all the fittings on deck. This is preventive maintenance that should be done at least every 10 years and could save your deck.
-By Nick Bailey

Steps to replace a gasket.
Loosen gasket on frameless hatch lid.	Press gasket back in place	Apply Sudbury Elastomeric sealant.

RESEALING A HATCH FRAME
Break the seal by gently driving a putty knife between the hatch base and deck.	After hatch base is removed, scrape off the old sealant.	Apply new sealant, being careful to plaster each fastener hole well.