Fiberglass Hatch Repair
Fiberglass hatch repair on an older boat can involve much more than simply stopping a leaking hatch. The fiberglass deck or cabin structure may need to be repaired, rebuilt or modified to provide a strong, flat mounting surface, while the marine hatch itself may need new seals, gaskets, lenses or hardware. In these projects, I demonstrate practical DIY boat hatch repair and restoration, including building and fairing a custom Coosa Board and fiberglass hatch base, correcting deck camber, installing hatches into fiberglass decks, and completely rebuilding older Bomar marine hatches. Whether you’re repairing a leaking boat hatch, restoring an old aluminum hatch or modifying a fiberglass deck for a replacement hatch, these techniques show how to create a strong, watertight installation as part of a larger fiberglass boat restoration.
Restoring an older boat often means deciding whether original hardware can be saved rather than replaced. A quality aluminum boat hatch can cost hundreds of dollars new, while used hatches can sometimes be found for very little money. For my Skipper 20 sailboat restoration, I replaced a homemade plywood forward hatch with a used Bomar aluminum hatch and completely restored it. The process provides a practical example of how an old sailboat or trawler hatch can be evaluated, disassembled, cleaned, resealed and returned to service.
Hatch Repair is not just about replacing a gasket or adding some caulking.
How to Make a Marine Hatch Fit a Cambered Deck
Most marine hatches are designed to mount on a relatively flat surface, but many older sailboats have significant deck camber—the gentle curve from the centerline toward the sides of the boat. If a flat aluminum hatch frame is bolted directly onto that curved fiberglass deck, portions of the frame will be unsupported. Tightening the fasteners can distort the hatch frame, while the uneven mounting surface can make it difficult to create a reliable watertight seal. On the Skipper 20, I solved this problem by fabricating a custom Coosa Board and fiberglass hatch base that transitions between the curved deck and the flat Bomar hatch frame.
Before installing a replacement marine hatch, it may be necessary to modify the camber of the fiberglass deck or fabricate a custom hatch base so the hatch frame sits flat and is supported evenly around its entire perimeter. Most marine hatches are designed for a relatively flat mounting surface, while many sailboat decks and cabin tops have substantial curvature. Installing a flat hatch directly against that curved surface can leave gaps, distort the frame when it is fastened, and make it difficult to achieve a reliable watertight seal. A fabricated Coosa Board, fiberglass and epoxy hatch base can bridge the difference between the curved deck and flat hatch frame, creating a solid mounting surface that can be faired into the surrounding fiberglass and properly prepared for bedding and sealing the hatch.
Building a Coosa Board and Fiberglass Hatch Base
The first step is to determine the actual camber of the fiberglass deck. I make a cardboard pattern of the deck curvature and transfer that shape to the Coosa Board. The hatch base is initially fabricated slightly wider than the aluminum hatch frame, providing enough material to support the hatch completely and allowing the outside edges to later be shaped and blended into the existing deck.
Next, I use a grinder and coarse sandpaper to gradually remove material from the underside of the Coosa Board hatch base until its bottom surface matches the curved fiberglass deck while its upper surface remains flat for the hatch. This requires repeated fitting, grinding and sanding. The objective is to have the composite base follow the deck camber closely while providing continuous support beneath the entire hatch frame.
Once the fit is correct, the base can be installed using thickened epoxy to fill small gaps between the Coosa Board and fiberglass deck. Depending on the installation, the structure can also be laminated into the surrounding deck with fiberglass cloth and epoxy. On the Skipper 20 installation, I mechanically fastened the Coosa base while the thickened epoxy filled the irregularities between the two surfaces.
The final step is sanding and fairing the hatch base into the fiberglass deck. Epoxy fairing compound fills imperfections and creates a smooth transition from the original deck to the new hatch structure. After final sanding, priming and painting, the goal is for the fabricated base to appear as though it were originally molded into the boat. The result is a strong, flat mounting surface that allows a modern marine hatch to be installed correctly on an otherwise curved fiberglass deck.
Should You Restore or Replace a Boat Hatch?
Not every old hatch should be restored. Before beginning, inspect the aluminum frame, hinges, lens, gasket and operating hardware and consider how the boat will be used. An offshore or bluewater boat may justify purchasing a new hatch, while restoring a quality older hatch can make sense for many recreational sailboats, trawlers and cruisers. Replacement gaskets, handles and sealants also add to the restoration cost, so determine what the hatch needs before deciding whether restoration is economical.
Disassembling and Cleaning an Old Boat Hatch
The restoration begins by carefully disassembling the hatch while saving the original hardware, washers and other small components. After removing the lens, all of the old silicone must be removed from both the aluminum frame and the edge of the lens. I use a combination of careful mechanical cleaning and solvent where appropriate. This preparation takes time, but removing the old sealant and contamination is critical because the new sealant will only perform properly if it bonds to a clean surface.
Replacing the Boat Hatch Gasket
Old hatch gaskets become compressed and deteriorate over time and should generally be replaced during a complete restoration. Don’t simply use the removed gasket to determine the length of the replacement because the original material may have shrunk. Instead, fit the new gasket directly to the hatch frame and cut it to the proper length. On this Bomar hatch, I use small amounts of sealant to hold the gasket securely in the frame, particularly around the corners, and seal the butt joint.
Restoring the Aluminum Frame and Hatch Lens and Gasket
Old hatch gaskets become compressed and deteriorate over time and should generally be replaced during a complete restoration. Don’t simply use the removed gasket to determine the length of the replacement because the original material may have shrunk. Instead, fit the new gasket directly to the hatch frame and cut it to the proper length. On this Bomar hatch, I use small amounts of sealant to hold the gasket securely in the frame, particularly around the corners, and seal the butt joint.
Resealing the Boat Hatch Lens
For this Bomar hatch, I reseal the lens using Dow 795 structural silicone, an industrial-grade glazing sealant. The frame and lens are carefully masked before the sealant is applied so the finished joint has a clean edge. The lens is positioned evenly within the frame and allowed to essentially float in the sealant rather than being forced directly against the aluminum. Surface preparation is especially important, and Dow 795 requires considerably longer to reach full cure than its initial tack-free time.
Once the lens has been resealed, the hatch dogs, handles, washers and other hardware can be reinstalled and adjusted so the hatch closes firmly against its new gasket. The result in this project was a restored Bomar low-profile hatch purchased used for about $20, with roughly another $100 invested in restoration parts and materials. Instead of discarding a quality older hatch, the complete process returned it to useful service for a fraction of the cost of a comparable new hatch.
Boat Building How-To Library
The MotorCity Boat Werks How-To Library brings together the practical techniques I use for amateur boat building, including fiberglass and composites, Coosa Board construction, mockups and templating, structural fabrication, woodworking, interiors, tools and materials. These videos and articles document the methods, materials and lessons learned from real boat-building projects. Every video is on topic, hands-on, concise and detailed. I show what works, what doesn’t work–real lessons learned from 30 years building boats. My videos are made for the amateur with information presented for the novice builder, competent amateur, or experienced craftsman.
Don’t Go It Alone. Join the Werkers
Get access to all my tips and tricks, behind-the-scenes-content, and technical Library.