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Old 06-25-2002
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Mounting Deck Hardware

This article was originally published on SailNet in February 2001.


By properly mounting deck hardware, particularly heavy items like windlasses and cleats, you can ensure years of trouble-free service and a leak-free deck.
The wide-open expanses of deck on a new boat seem to invite additions. Indeed, some cruising boats collect so many fittings attached to the deck that finding a place to stand can be difficult. Sometimes an installation error is obvious on the deck, as when a genoa sheet doesn't line up with its winch. But it isn't until you're inside the boat, slithering through the lockers with a flashlight, that you can tell whether most of those added deck fittings were properly installed.

Deck fittings fall into a number of major groups and some of these have widely different mounting requirements. Before we get to the details, let's recap the types of mounting that may be desirable on the deck of your boat.

Safety gear includes lifeline stanchions, pulpits, handrails, jackline and harness tether-attachment points, as well as pedestal guards, and life raft cradles.

Sail-handling gear can be quite plentiful, including all winches, turning blocks, tracks for cars, travelers, sheet and control line cleats, deck pads for dead-ending running rigging, and spinnaker pole and whisker pole chocks.

Ground tackle and mooring gear consists of windlasses, chocks, cleats or bitts, hawse pipes, rollers, chain stoppers, and anchor tie-downs bolted to the deck.


For Dorades and ventilation boxes, it's imperative that they be mounted in a watertight fashion.

Ventilation presupposes that hatches, portlights, Dorade boxes, and other ventilators will decorate the deck, some requiring hasps or security locks.

Storage often dictates that padeyes be installed to lash gear down on deck, that locker lids be installed, or deck-plate access be added.

Comfort items include mounting bases for bimini tops and dodgers, snaps for cockpit cushions and sheet bags, cockpit tables, stereo speakers and the bric-a-brac that personalizes a boat and makes it more "sailable" for its owner.

There are two principal requirements for mounting deck hardware. Each is sufficiently important to merit a separate section in this article:

Watertight Integrity    Regardless of its size, location, or the required strength, every deck fitting must be bedded for two good reasons. Decks and fittings are not perfectly smooth and flat, and will allow water to be trapped in the cracks and crevices left if they are simply bolted together. This moisture is destructive to many metal fittings and will eventually find its way inside the boat, resulting in an even more annoying and destructive leak. If the deck is built of plywood or balsa-cored fiberglass, water will penetrate the core, requiring an expensive repair in later years. Bedding compound is cheap by comparison.


Hardware that lives near the waterline and is subject to movement, like gudgeons and backstay fittings, needs to be securely fitted and mounted with sufficient bedding so that water will not penetrate the hull.

Use a good-quality, marine-grade caulk from a recognized company when installing deck hardware. These products have UV and other inhibitors added that cheap, home-center products do not. Most sailors rely on 3M, Sikaflex, and LifeCaulk for these caulks. Be aware that there are three distinctly different marine caulking/bedding products on the market. Silicones have limited applications and are good where unloaded plastic parts, such as a bulkhead compass, are to be installed in the cockpit. Many silicones cure very fast and can be hard to work with. At the other end of the spectrum are the polyurethanes, which are listed as adhesive sealants. These are only for permanent bonding, such as a hull to a deck, and should not be used to bed down any piece of gear that you'll ever want to remove for replacement or repair. Lastly, the polysulfides are usually the best choice for most deck installations. Read the manufacturer's information for the item you are installing as well as the instructions on the tube of caulking—there are special considerations with some things like plastic portlights where the bedding compound may be incompatible with the fitting material. There are specialty and blended caulking compounds to suit these applications.

Bedding is a messy process when done incorrectly. The stuff can spread like wildfire, and if allowed to contact a porous fitting such as a teak handrail, caulking will be very difficult to remove. The proper way to avoid a mess is to dry fit the piece of hardware after the holes are drilled. This allows you one last chance to ensure that the holes line up, that you have all the proper backing plates, washer, nuts, and that the bolts are the proper length. When all is in good order, mask the deck around the fitting leaving just a barely-visible line of deck showing (if it is round, use lots of little overlapping pieces of tape).

Now remove the fitting, clean up your drill holes in the deck with a small countersink, and mask the edge of the fitting leaving that same hair's width of metal or plastic showing. Make sure the deck and fitting are cleaned of any drilling chips, dry, and free of any grease or oil—a swipe with an acetone rag won't hurt. Then, slather the compound on. When you put the fitting on the deck, rotate it and slide it around to ensure an even coating between them. Then insert and tighten the fasteners all but the last turn. With bolts, please note that this takes two people, so have your helper lined up first or you'll be wandering around the docks looking for help, spreading caulk along the way.

"Setting bolts takes two people, so line up your assistant beforehand or you'll find yourself wandering the docks looking for help, spreading caulk along the way."

Before the bedding that has oozed out all around the fitting has time to get stiff, assemble lots of paper towels and a waste bucket lined with a plastic bag. If you're squeamish about using your fingers to wipe away the excess caulking and shape it, wear a latex rubber glove or use a shaped tongue depressor—but nothing works as well as a bare finger and acetone will get most of it off later. Keep wiping the excess onto the paper towels until you see clean masking tape, then remove the tape (carefully and under complete control to avoid spreading caulking everywhere) and throw it in your waste can. Voilà! A perfectly clean installation. Now throw the waste bag away before it blows overboard.

Notice that you didn't turn that last bit on the fasteners. Many caulks shrink a bit as they cure. When fully mature, you will have a custom-made, form-fitted rubber gasket under your fitting. In about a week for most caulks, you can take that last turn on the fasteners and put the gasket in compression, giving you a leak-resistant joint that will last for years.

Strength    We have to assume first that you have chosen the correct fitting. I have come across 20-foot daysailers with 12-inch mooring cleats and 65-foot sloops fitted with 2,000-pound working load padeyes for the running backstays. Too big is a waste of money and space—too small is dangerous. Marine hardware manufacturers spend thousands of dollars on catalogs, computer programs, and sales training to help you select the correct deck hardware. But after the part has been purchased, two questions remain: can it be simply screwed to the deck or must it be through-bolted, and should you use a backing plate?


The builder of this vessel provided raised, reinforced bases for mounting winches, which makes good sense since hardware like this operates under tremendous loads.

A few parts can use screws to fasten them to the deck. The criteria used must include the fact that the part is never too highly stressed and that the mounting surface is thick enough to give good support. Looking at our list of items, safety gear, sail handling items, and ground tackle/mooring gear are always highly loaded, and so must always be bolted. It is in the ventilation, storage, and comfort areas where individual decisions must be made. For instance, a low-profile ventilator under the dodger might be screwed down while a 12-inch, high-cowl vent near the mast should be bolted. Many snaps can be screwed in as they are lightly stressed and failure would be insignificant. When installing with screws, the deck must be thick enough so that flesh-tearing screw points don't protrude into a locker inside the boat. Any piece of hardware with fastener holes larger than a No. 10 should be bolted—the manufacturer is telling you something about the stress on the part. And use the proper fastener, for cryin' out loud. If it was designed for flat heads, don't use a pan head and fill the gap with caulk.

Decisions on backing plates fall into the same category. Certainly, all safety, anchoring, and mooring items should have backing plates, and most highly stressed sail-handling gear should too. Backing plates spread heavy loads over wider areas of the deck and prevent the nuts from being pulled into the deck material. In many pieces of hardware, only a few of the fasteners are loaded at a time, making it doubly important to use a backing plate.

The best backing plates are made of aluminum in a thickness to match the load on the fitting (1/8 inch for light loads up to 3/8 inch thickness for heavy loads on big boats), with holes drilled to match the piece of hardware. Many builders hate them though since they require that the holes drilled through a thick deck be perfectly true if the holes are to line up. Having removed a good number of deck fittings, I can say that the holes in many cases were drilled, and re-drilled, and reamed out until the bolts would line up—not a pretty picture.

"Even with backing plates, you should use washers and aircraft nylock nuts or lock washers to ensure that a fitting is securely mounted."

And so, many builders use plywood for backing plates. This way they can drill through the deck and backing plate simultaneously and be guaranteed that the bolt will fit even if the hole is not exactly straight. This practice is OK if the plywood is good quality, dense-wooded, marine-grade ply with no voids, and is at least 3/8 inch thick for light loads and up to 3/4 inch thick for heavier loads. I recommend coating it with epoxy to harden its surface and eliminate the possibility of rot in years to come.

Some items make it very difficult to install full backing plates. I list genoa T-track in this category, since it is long, has lots of holes, is generally out at the edge of the boat where there is little room to work, and is often curved to boot. Long travelers can be difficult too. Often these long pieces can have the backing plates installed in pieces.

Even with backing plates, you should use washers and aircraft nylock nuts or lock washers. For plywood backing plates, I prefer fender washers, which are larger in outside diameter than standard washers and are available in stainless steel. These prevent stress from pulling the nuts into the wood, which loosens the fitting. Fender washers are also a good choice for those lightly stressed fittings that don't need a full backing plate, and I often use them for things like flag halyard cleats, cam cleats for traveler control lines, or eyestraps for tying down a jerry jug on deck. If in doubt as to the loads on a part, bolt it and use a backing plate.

Functionality    I say this partly in jest, but too often deck hardware is installed in the wrong place, interferes with working on the deck, provides an unfair lead to a winch or turning block, or is in the way of another fitting. I detest bimini supports that won't allow a full turn on a winch handle. Toe-snagging headsail hardware is not well thought out. Foot blocks not on risers or angled blocks often make the genoa sheet chafe on the coaming on the way to the winch. Consider lashing or taping a new piece of gear in place and using the boat that way for a week before bolting it down permanently. All additions to running rigging should be laid out with a piece of line running through the whole system. And measure too—it's not nice to drill into the top of a bulkhead or wiring chase down below. I once installed a ventilator on the foredeck only to find that the angle of the genoa sheets forced them to catch the cowl every single time we tacked—and in the five years we owned that boat, I made a lot of trips to the foredeck.


Suggested Reading:

Choosing and Using Sealants by Don Casey

Drilling and Filling Holes in Your Boat by Sue and Larry

Refitting an Older Boat by Sue and Larry

SailNet Store Section: Stanchions and Rail Fittings

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