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Maintaining Bronze Seacocks

Sturdy bronze seacocks may look like impenetrable lumps of metal down in the bilge, but they are actually finely machined valves that must be lubricated periodically to prevent the tight-fitting surfaces from "freezing" mechanically. Many skippers, unfortunately, tend to forego the recommended inspections in favor of a somewhat less rigorous maintenance philosophy: "Out of sight, out of mind." The results are predictable. A poll of marine surveyors found that almost 42% of the bronze seacocks they inspected were mechanically frozen, either open or shut.

Question: How do these negligent skippers close thru-hulls in an emergency or when they will be away from the boat for extended periods? Answer: They don't.

Claim #911273. "During a period of heavy November rains, the vessel took on water. It should be noted that the vessel was not fitted with an automatic bilge pump. Although the head intake and discharge valves were fitted with seacocks, they appeared to be inoperable. With the valve in the open position and in conjunction with the heavy rains in this area, the vessel took on water to the point where the head back-siphoned into the hull and the vessel sank."

The first line of defense against flooded heads, burst hoses, and many other dockside calamities is an operable seacock. A 1 1/2" hole in the hull will admit 71 gallons of water a minute into the boat, which will quickly overcome a bilge pump. The good news, at least for skippers of boats with frozen bronze seacocks, is that a stuck seacock can probably be rejuvenated fairly easily. And if the seacock is already in good operating condition, it can be kept that way with only a few dabs of waterproof grease every spring. All you'll need is a wrench, a wood mallet, kerosene, an emery cloth, waterproof grease, and a few cotton rags. For a badly frozen seacock, you may also need a pipe that fits over the end of the adjustable wrench. And if the drum is badly scratched, you'll need a valve grinding compound.

Disassembling the Seacock

With the boat out of the water, remove the large nuts at the end of the barrel (opposite the handle) and tap the stem lightly with the wood mallet until the barrel is loosened. (If all you have is a metal hammer, use a block of wood to absorb the blow.) Resist the temptation to clobber the stem, as this could damage or bend the threads. If tapping fails to dislodge a stubborn drum, you can reassemble the seacock and use a large wrench (not the bronze handle) at the end of a long pipe to get sufficient leverage to loosen the drum. You can also try tapping the wrench or pipe with the hammer. Be forewarned, however, that unless the seacock has a wide, flanged body that sits on a backing block (contoured and bolted snugly against the hull), you run the risk of seriously damaging the fiberglass. It would be wise to replace the seacock with one that is properly flanged and backed (see diagram).


Once the drum is removed, use the kerosene and rags to clean salt, old grease, gunk, etc., from the drum and seacock passageways. Scratches and roughness, if any, should be smoothed with the emery cloth. Deep scratches can be smoothed by spreading a valve-grinding compound evenly on both the drum and the interior of the seacock. The grinding can be done by reassembling the seacock and moving the handle back and forth a few times. Too much grinding may do more harm than good. After grinding, use the emery cloth to smooth the drum. As an alternative to emery cloth, you can use wet sandpaper, starting at 220 grit and going to a finer 600 grit paper.

Once the drum is reasonably smooth (slight scratches and pitting can be tolerated), you should clean the surfaces again with kerosene and then wipe on the waterproof grease. Teflon is also acceptable. Be liberal; the grease not only keeps the drum limber, it also helps prevent leaking.

To reassemble, tighten the nuts sufficiently so that the seacock will still be operable but the drum won't be loosened by vibration. Make sure two stainless steel hose clamps are used to secure on the hose. Finally, a soft wood plug tied next to the seacock is excellent insurance against an unexpected catastrophe.

Greasing without Hauling

Between annual inspections, a grease (zerc) fitting screwed temporarily into the seacock's drain hole will allow you to lubricate the drum with a grease gun while the boat is still in the water. This should be done with the seacock open, or the grease will just empty into the hole. A grease fitting that will fit the drain hole (typically 1/8") can usually be found at an auto supply store.

Defining a Proper Seacock

All thru-hulls below or near the waterline must have a valve that can be closed in an emergency or when the boat will be left unattended for more than a few days. Traditional bronze seacocks are acceptable, but gate valves and many plastic thru-hulls should not be used at thru-hulls below the waterline.

Gate valves have internal parts that deteriorate and snap off. And unlike a seacock, which has a handle that is clearly open or closed ("positive action"), a gate valve's wheel may or may not be closed. Even turning the wheel will not confirm that the valve is closed. The internal mechanism could have become jammed open by debris, for example, but feel as though it had been closed.

Plastic seacocks are brittle and can be easily broken by an errant foot or a stowed anchor. The exception is Marelon thru-hulls, which are made of glass-reinforced plastic and are acceptable for thru-hull installations below the waterline. Marelon seacocks have been tested (most sizes) and approved by Underwriters Laboratories. While probably not as prone to mechanical freezing as their bronze counterparts, Marelon seacocks must also be taken apart, inspected, and lubricated periodically.

Finally, some boat builders have recently been installing ball-type bronze seacocks that use a Teflon-coated ball (either plastic or stainless steel) instead of traditional tapered drums. These newer valves are acceptable, especially if they have a flanged base and are mounted on a backing block. The ball valves are not inclined to mechanical freezing, but the models that can be taken apart (some can't) should be inspected occasionally to make sure they haven't become clogged by debris.