I recently wrote an article that documents Northern Marine’s approach to securing the deck to the hull of its new 57-foot trawler yacht. The custom builder takes considerable time to fiberglass the hull and deck together. The result is a superior and permanent bond that results in essentially one big fiberglass part completely glassed together.

While exploring related subjects of installing and bedding hardware, ports, and windows, I found numerous threads and comments regarding owner experiences with various bonding products. Many reported these bonds often failed after so many months in paradise, from the extreme UV and from the boat constantly flexing under way. Most interesting was the common and mistaken assumption that these bonds would be permanent.

The reality is that no adhesive, sealant, or caulking will last forever, even if properly applied under ideal conditions. According to subject matter expert John Schmidt of BoatLife, any bond, even when meticulously cleaned and installed to the exact specifications, will last 15 years or so. It is just the nature of boats and the materials that keep them together and the water out. Cut corners while cleaning the materials, however, or apply the product in conditions outside the recommended environment to cure properly, and one will not get anywhere near that longevity before there is a leak or the beginning of a bond failure.

The many products referenced by owners included Sikaflex products; 3M 5200, 4000 UV, and 4200; Dow Corning 756 and 795 adhesive sealants; BoatLife’s Life Seal and Life-Calk; numerous brands of silicone; butyl caulking tape; and mixtures of epoxy and fillers to rebuild original window tracks. Pettit also recently announced its new line of sealants and adhesives under the Anchortech label. All have their place on boats, but with different roles and most are generally not interchangeable.

Seen below: BoatLife's Life Calk can normally be found at West Marine.

boatlife life-calk

There are three product categories to consider when bedding and sealing hardware and boat parts. There are adhesives, sealants, and caulking products.

Adhesives (and adhesive sealants) provide a strong bond between mating surfaces where the adhesive not only keep the water out but keep the parts connected.

Then there are sealants, which create a waterproof barrier between mating surfaces. They are best for bedding hardware and windows and ports. Sealants expand and contract as the temperature changes and can serve well in situations that involve some amount of movement.

The third category are caulking products, used to cover the edges and borders of sealed surfaces. They fill in the seams of joints, and while they remain exposed to the elements, they continue to provide excellent sealing characteristics while resisting UV and chemicals.

Seen below: This porthole is an excellent candidate for rebedding or replacement. Photo taken at Port Annapolis Marina.

porthole need of repair

I considered going over the basics of how to use the products, but there is a significant amount of published material already out there, and one needs only to spend a couple of minutes on a computer to find articles, manuals, videos, and catalogs that cover these in great detail. West Marine, BoatUS, 3M, Sikaflex, and BoatLife all have guides and product catalogs to help wade through the choices, and how to best match the products for each task.

The only product that I feel compelled to make specific mention is the polyurethane 3M 5200. Long considered the industry standard for permanent bonds, its strength is also its downfall. It is well known to be permanent, but over time even this adhesive sealant has been known to leak. In the tropics, some boat owners find that it fails within 18 months in the tropical sun. Unfortunately, it is not UV resistant, unlike its more moderately adhesive sister products.

But consider what is “permanent” on your boat. The hull and deck joint is certainly permanent. And 5200 does a great job for that application. But today there are other products that work well for most other adhesive applications, and which represent more realistic solutions, as they are removable when that becomes necessary.

Seen below: The aft cabin window of an older Grand Banks Yacht can be easily sealed with the right product.

window on grand banks yacht

Because it is exceedingly difficult to remove, 5200 is not popular among experienced cruisers. (One of my cruising friends calls it the “Death Paste.”) Many boat owners and service yards shy away from 5200, and even refuse to have it aboard. Removing hardware installed with 5200 usually requires the destruction of fiberglass and hardware, and many hours of hard work, it is that tenacious. Using it to bed windows and deck hardware, such as cleats, particularly when this hardware is fastened by nuts and bolts that sandwich the hardware on both sides of the fiberglass deck structure, is a bad practice. It is such a poor choice for bedding hardware and windows that you should not be surprised if a service yard tends to avoid projects that involve its use.

There are many other products suited for these purposes that provide years of trouble-free service. And when it is time to renew the material after its long service life, it is not a big deal.

If I shopped for my next boat and found that a potential boat’s previous owner liberally used 5200 to fix leaks around the boat, I would have reason to pause. Knowing the headaches in front of me is asking for trouble. What about hardware in areas not as easily inspected? Did the owner use 5200 to put hoses on seacocks? I shudder to think of that nightmare…

Seen below: Being proactive about leaks on older boats, like this classic trawler yacht, is a great best practice to follow.

trawler boat

All of this leads me to the following conclusions. Given that bonding projects in the marine environment should never really be considered permanent, why not accept that fact so it just becomes part of the boat’s maintenance program? If a window on my Mainship trawler begins to leak, or water seeps in behind the molded shower fixture in the aft cockpit, once I determine the best method to seal it, I should recognize that this needs to be included in my boat’s maintenance program. If I bought a Valiant 42 sailboat (one of my favorites, but now 25 years old) and I noted that a saloon port leaked, I would plan to rebed them all, adding this task as yet another one of those projects needed to be done every so many years. Using the right product to seal the ports removes most of the hassle and it just becomes another boat project, like rebuilding the winches or putting anti-seize paste on bolts in the engine room that are removed annually.

Maybe it is just me, but knowing that everything on my boat will need attention at some point in the future, including the bonds that hold things together, makes me feel better that it is one more thing I’ve figured out and can stay on top of. And that feels good, because when it comes to maintenance, about the only thing that is permanent is my commitment to keeping the boat in top form. Rebedding hardware, hatches, and windows with the proper materials is not a big deal, if one has access to do it right. Ah, yes, the issue of accessibility comes up once again.

The more we learn about our boats, and the best way to take care of them, the more we are confident they will perform at their best when conditions are at their worst. No mystery, no anxiety, all is well. Trust me, it is a particularly good feeling. Leave those sentiments of cheating death to the other guy, the one who believes in permanent bonds.

I do want to include comments from the technical experts of BoatLife. They offer the following remarks that spell the difference between success and failure on your next bonding project:

1.) Only use fresh products that have not expired. I am appalled how much money I have wasted over the years carrying tubes of these products that sat undisturbed in a locker or toolbox. In those days, none had manufacture dates printed on the packaging or product tubes. One never knew if a tube was good or way past its operational shelf life. Today there is no excuse. Manufacturers print the useable shelf life beyond the manufactured date in their product literature, which is now clearly printed on the tube.

Manufacturer Date On Tube

2.) Read the instructions that come with each tube. They define the best operating conditions for effectively using the product and to get the best cure. A common statement is for an ideal environment of 70 degrees, and a relative humidity of at least 50 percent. Applying the product well outside these conditions can easily affect curing time and how successful the bond will be.

3.) Thoroughly wash all surfaces, pieces, and fasteners. Do not assume brand new fasteners are clean. Filth and dirt from the manufacturing process remain with the fasteners when they ship. Use a product such as Life-Calk’s Solvent and Cleaner to thoroughly rinse the fasteners in solvent or acetone. You will be surprised how much dirt will settle in the bottom of the container.

4.) Be careful when determining the suitability of materials to bonding product. Not all products work with all plastics, acrylics, and other materials. Plastic parts are not a good fit with Life-Calk, for example. Do you research.

Seen below: An older boat, but in great condition. You'll notice the sealant around the S2's windows is old, so these windows need to be rebedded once leaks begin.

leaking windows on a boat

If I owned an older sailboat or trawler, one approaching 20 years or more, I would carefully chart out the many parts on the boat that I will need to document with their bonding requirements. While this may sound tedious, it is only a one-time effort (much like creating a schematic for the boat’s electrical systems) to get a handle on what windows, ports, hatches, fittings, and deck hardware will need inspection to be sure to catch any issues or leaks well ahead of causing damage. Some leaks may not be obvious, as the water may run down the inside of a fiberglass panel or enter the core material of the surrounding deck or cabin side. A moisture meter is a good tool to catch core intrusion as soon as possible.

Once one understands the different roles and proper application of these bonding products, and the reasonable expectation between maintenance intervals, they have made a huge leap forward in the context of periodic maintenance. Replacing the concept of “seal it and forget it” with a more realistic approach that simply puts that item into the work file of preventative and routine maintenance is a more enlightened approach to boat ownership.

And that brings its own rewards as you create memories with your boat for years to come.