By Frank Lanier
Latitudes and Attitudes (2004)
Most boaters get the big picture concerning boats and water – keep the water on the outside of the hull and you’ll have a lot more fun. It’s easy to imagine the effects generated by a failed through-hull or ruptured hose, however there’s a more insidious side of water most folks don’t even think about. It probably causes more boat damage every year than sinkings, groundings, fires, and alien abductions combined, although you may feel as though you’ve been anally-probed from a financial standpoint as repairs are usually expensive, sometimes exceeding the value of the boat itself. And here’s the scary part – if you’re a typical boater, chances are it’s happening on your vessel at this very moment, unnoticed until the damage is already done. The cause of this lurking horror? Water intrusion into cored decking and superstructures due to poorly bedded or improperly mounted deck hardware.
Yes friends, we are our own worst enemy when it comes to drilling, screwing, and fastening things to our boats – and we’re not alone. A lot of builders, dealers, and other professional folks out there just can’t seem to get their proverbial feces in one sock either when it comes to drilling holes and screwing things into your boat, a situation exacerbated by the fact the problem often doesn’t show up until years later.
The first step in understanding the problem is finding out what the term “cored” means and why water entry is such a problem. The majority of today’s boat decks (along with a lot of superstructures) are cored, typically with materials such as end grain balsa, plywood, or maybe one of the more high-tech foam variations. Cored construction simply means you’ve got an inner and outer skin of fiberglass with one of the above materials bonded / sandwiched between them.
Gone are the days of all solid fiberglass deck and superstructure construction. Capitalizing on the strength of the “I” beam effect, cored construction is both lighter, stronger, and provides better heat and noise insulation than solid fiberglass. It’s also cheaper to build, which is often the real driving force from a manufacturing standpoint. There are real benefits to cored construction, so long as builders respect its limitations and utilize a judicious combination of both cored and solid fiberglass construction in their vessels rather than going hog-wild and coring everything in sight just to save a few dollars.
What this means for the average Joe is that unlike the old days of solid fiberglass construction (when you could drill, mount, and be done with it) chances are you’ll probably be drilling through cored panels and it’s going to take a little more time to do it right. The numero uno thing concerning cored construction is maintaining waterproof integrity in order to prevent moisture from entering the core and causing trouble, particularly with balsa or plywood – wet wood coring can rot, allowing the cored deck to separate, drastically reducing structural integrity. Long term water exposure causes problems with foam-cored decks as well (core separation and even disintegration in some cases) so don’t think you’re totally immune to the problem just because you happen to have foam coring.
Anything and everything penetrating the core has to be properly mounted and bedded to prevent water entry, and I mean EVERYTHING – antenna mounts, windless foot switches, stanchion mounts and yes, especially those innocent looking canvas snap buttons you’ve got screwed allover the cabin top deck and cockpit. Holes left after removing hardware are bad too, particularly when whoever removed them just gooped a dab of sealant over it and called it good. Many boaters fail to realize that drilling a hole into your boat’s deck or cabin top is exactly the same as drilling a hole in the roof of a house.
Anytime you screw or drill through a cored panel, the first rule is properly sealing the core against moisture entry. There are a number of ways to do this, but the best one is to avoid breaching the core material in the first place. In a perfect world, your boat’s manufacturer has anticipated where all deck penetrations are necessary (stanchion bases, cleats, etc) and has “de-cored” these areas by reverting to solid fiberglass, allowing you to mount hardware without drilling into the core. But, in the case of new installations (particularly if you’re lucks like mine) your chances are slim-to-none that any of these areas will coincide with whatever aftermarket doo-dad you want to mount, meaning you’re going to have to do it the hard way. The good new is the hard way is fairly easy, as long as you have access to the underside of the deck where you’re doing the mounting.
What you’re going to do is a little de-coring of your own. The easiest way to remove coring is with a hole saw and a little caution. Let’s say you want to mount a new cleat on your foredeck, but the entire area is cored. First step is marking and drilling the appropriate sized bolt holes. Then, take a 2 inch hole saw (or larger, depending on the size of your backing washers) and remove the coring from the underside of the deck where each bolt is to be installed, being careful NOT to drill through or damage the upper layer of fiberglass (you also have the option of removing a single section of coring large enough to encompass both bolts). I find it works best to drill almost through the coring, but leave the last ¼” or so to be removed by hand (to avoid any chance of damaging that outer fiberglass layer).
Once the cutout and coring is removed, seal the exposed edges of the coring in the holes with thickened epoxy paste. Now all you have to do is mount the cleat using properly sized backing washers and a good bedding compound (under both cleat and washers) and Whaa-la! You’ve got a properly mounted cleat that won’t leak and has no chance of letting water into the core.
I like the above method of dealing with mounting holes in cored panels, but it’s not the only way to address the problem. An excellent reference for this and just about any other type of fiberglass repair or maintenance issue is “Fiberglass Boat Repair And Maintenance” published by Gougeon Brothers, Inc. (517) 684-7286. It’s a good how to booklet and well worth space on any vessel’s bookshelf.
“But Frank,” I hear you say, “This seems like a lot of extra work. Why can’t we just drill, goop it up good, and mount it through the core?” The problem is cored construction isn’t strong enough to handle point loading – tightening up the mounting bolts invariably crushes the core, causing the part to loosen and leak.
Another worthwhile project is inspecting and sealing any exposed coring left over from previous installations. Cutouts for Dorado vents, hatches, chain plates, hawseholes, port lights, etc should be inspected to insure they were properly sealed during the installation.
It’s also a good idea to through bolt the hardware you’re mounting if at all possible. Screws are a horrible way to fasten anything to fiberglass, a brittle material that doesn’t hold screws well to begin with, particularly if the fastener itself will be under a load (canvas snaps being a good example). Anything under pressure and relying on screws for mounting will eventually work itself loose or get ripped out. Squirting sealant under the screw head doesn’t help much either; as the working of the screw also breaks the sealant bond, allowing water to enter. In instances where screws just have to be used, some folks have had tolerable success by drilling the screw hole larger than needed, digging out the core past the edges of the hole, and filling the hole with thickened epoxy paste. This allows you to then drill the screw pilot hole into solid epoxy, thus eliminating the chance of water migrating into the core. That being said, the best solution remains using through bolts and adequately sized backing plates or washers on all hardware whenever possible, particularly those under load.
What about existing hardware? When’s the last time you pulled, inspected, and re-bedded your cleats, chain plates, lifeline stanchions and the like? I’ll let you in on a little know fact – if you haven’t re-bedded in the last 7 years or so, that old caulking doesn’t owe you anything. No one likes to re-bed hardware – it’s a pain, isn’t very glamorous, and doesn’t physically add to the appearance of your vessel like other projects (that new dodger for example). It can, however, prevent some massive repair bills. At a minimum, all deck hardware should be pulled, the deck inspected for damage, and re-bedded at least every 7 to 10 years (more frequently if the situation calls for it). The other thing to remember is that gooping sealant around the outside edges of a chain plate or other piece of deck hardware in efforts to stop a leak or do a “quickie” re-bed job is like throwing sawdust against a waterfall – it has to be pulled and re-bedded or you’re just wasting your time.
Finally, use a good marine grade caulking to bed whatever it is you’re mounting, and use plenty of it. The stuff you get at the hardware store just doesn’t hold up as well, meaning you’ll not only have to re-bed sooner, but you’ll most likely be dealing with leaks in the meantime. There’s a mind boggling array of sealants on the market and what you finally use is a matter of personal choice, however knowing the 4 basic types will help in choosing one that meets your particular needs.
Polysulfides are one of the most versatile of the lot and can be used to bed most anything – except plastic items (deadlights, port light frames, etc). The solvents in it cause polycarbonate, acrylic, ABS and PVC to become brittle and crack, however it can be used with fittings constructed of epoxy, Delrin, or nylon. When used as a bedding compound, polysulfides are flexible enough to allow for movement caused by stress and temperature changes, yet strong enough to maintain a tenacious bond between the two surfaces. It adheres well to oily woods (like teak) and stands up well to the harsh cleaners typically used on them. It can also be sanded once cured and readily accepts paint.
Polyurethane is kind of like the Superglue® of caulking and is as much adhesive as sealant. Fittings and such bedded with polyurethane typically can’t be removed without damage to either hardware or vessel (or both). Polyurethane is a good choice for keel joints, hull-to-deck joints, and through-hulls, however there are differing opinions concerning their use to bed deck hardware. The fact that 3M 5200 is gooey, sticks to everything, and forms such a strong bond is exactly why it should be used according to some. Those against argue that because the fitting can’t be removed without damage come re-bedding time, polysulfides are a better choice, while the other side counters this just means you can go longer without having to re-bed. Weigh the pros and cons and choose what’s best for you, however keep in mind that polyurethane can’t be used on plastic either and can be damaged by teak cleaners, meaning they shouldn’t be used to bed teak rails or decks.
Next up is silicone, the only one of the three major types that can be used to safely bed plastics. It’s also excellent for bedding dissimilar metals due to its insulating qualities, such as stainless steel and aluminum. Silicone is best viewed as a gasket material rather than a sealant however, meaning it works best between two items held together under pressure. Because it relies on compression rather than adhesion, it’s a poor choice for bedding deck hardware.
The final caulking category would by hybrids such as Life Seal, a silicone / polyurethane blend produced by BoatLife especially for use on fiberglass. According to the manufacturer, it’s a “fast-curing, low odor, high adhesion, non-sagging, non-corrosive, non-yellowing formula” that can be used above and below the waterline.
No matter what your boating philosophy a common sense approach to drilling and cutting into your cored deck will go a long way towards protecting your investment. A proactive maintenance schedule concerning pulling and re-bedding of deck hardware is critical as well, so when you mount and screw, don’t forget to spread the goo.