Recently, I helped a dockside neighbor tighten a flush rod holder to the covering board in his boat’s cockpit. He had landed a nice tuna, but the fight had loosened the fitting. Often, rod holders or other deck hardware benefit from a reinforcement plate on the underside, but his relied on screws biting into the teak and going into the fiberglass substrate below.
I removed the flush rod holder and noticed there was no sealant on the underside of the face plate. I knew that every time he washed the boat, the teak near the rod holder’s base always seemed to take longer to dry than the rest of the wood. Now, I understood why. Without sufficient sealant lining the base to repel the water, the moisture would remain until the sun heated the metal to evaporate the trapped water.
The remedy required more than simply padding the bottom side and fastener holes with sealant. The plywood core, which is designed to reinforce the fiberglass laminate, had been soaking up water for several years. The previous owner had installed the teak covering boards but never sealed the freshly exposed end-grain of the coring before mounting the rod holders. In addition, there was no sealant inserted into the screw holes before fastening the rod holder in place.
This woeful fish story ended with the current owner having to pay to have the bad wood removed, and new coring installed and properly sealed along with each fastener, before reinstalling the rod holders. A $20 tube of caulk could have prevented this $1,000-plus ordeal.
Anywhere a hole is drilled into a boat, a leak can occur. When you wash your boat, do some thorough sleuthing. A rust stain or similar discoloration trailing from a fastener or metal fitting is begging for attention. See if the stain is caused by the fastener, or by a soaked piece of wood or coring material behind it.
Removing the rust with a specialized cleaner or gel is only the first step in the process. Once the surface area is clean, the fasteners should be removed, and the cavity fully dried with acetone to absorb any lingering moisture. Caulking products can also seal moisture in. Make sure all surfaces and materials are dry.
Inspect the fasteners carefully. Lesser grades of stainless steel are prone to discoloration and corrosion, but what helps most is coating the fastener threads with sealant to insulate the metal from moisture. Marine sealants basically turn into a rubber-like material when cured, so they also act as a shock absorber.
Diverting water away from the fasteners not only prevents rust, but also ensures that moisture is unable to infect the substrate. This is especially critical if your boat is exposed to winter conditions where moisture could freeze and expand the substrate, causing serious damage to metal, wood and fiberglass.
Choosing the correct sealant or caulk is mandatory. Read the label before you purchase any product. Are you using the caulk above or below the waterline? For a permanent or temporary solution? Some products can be painted over, while others cannot. Cure time is another factor depending on air temperature and humidity. Not all sealants are compatible with plastics, ABS, glass and Lexan. Other sealants may not be compatible with oily woods such as teak, unless the wood is primed. And not all sealants play nicely with harsh teak cleaners.
Caulking products basically fall into two categories: a sealant that creates a water- and airtight seal, and a sealant that incorporates an adhesive. Above the waterline, a bedding sealant that can be removed later is the right choice. Underwater hardware needs polyurethane compounds for permanent and leak-free installations.
Polysulfide sealants are versatile and popular, and likely can do most sealant chores topside and underwater. One- and two-part formulas increase its usefulness. Liquid versions are good for sealing cracks and seams. However, polysulfides are not recommended for bonding plastic materials. Cure time is around 24 hours.
Polyurethane sealants are noted for permanent installations and are often chosen for boatbuilding operations including the hull-to-deck joint, running-gear hardware and rub rails. Cure time with these products can take a week, though some versions offer a faster cure. A blend of polyurethane and silicone is a popular option among boaters, combining good adhesion qualities with ease of removal without destroying the substrate.
Pure silicone sealants are generally suitable for Lexan and acrylics, topside fiberglass, metal and wood. Unpaintable and unsandable, the color choices are white, black or clear. Silicones tack up quickly, and generally clean up with soap and water. They are not a suitable choice for underwater or teak-deck seams.
Marine sealants are pricey. You can save unused quantities by taping off the insertion tip with two layers of duct tape, and storing the cartridges in the refrigerator. Small tubes generally have a screw-on cap that should be wrapped tightly with tape and chilled. If you decide to keep a small tube aboard the boat, store it in a latex glove to prevent or contain leakage.
This article was originally published in the October 2023 issue.
