Caring for Seacocks

Frank Lanier


Considering the excitement a failed seacock can generate, the lack of attention they typically receive is almost criminal. Tucked away in the dim recesses of your bilge, seacocks typically don’t get a second thought with regards to preventative maintenance or inspections – until they fail to operate or even break off in your hand during operation (it happens, I’ve seen it, and it isn’t pretty).

All thru-hull fittings below the heeled waterline of a vessel must be equipped with a seacock, which is simply a valve that controls water entry or discharge through the hull. Acceptable seacocks will be designed and constructed to meet ANSI/UL 1121, Marine Through-Hull Fittings and Sea-Valves and American Boat and Yacht Councils (ABYC) Standard H-27 Seacocks, Thru-Hull Fittings and Drain Plugs.

The most common types of seacocks are the flanged sea valve (a seacock with an integral flange used to support and mount it directly to the hull) and in line ball valve, which is a seacock designed to be supported entirely by the through-hull fitting. You may also see gate valves, but they are not recommended for use as seacocks.

The gate valves I typically encounter while surveying are residential type units purchased at the local big box store. These are constructed of non-marine materials (brass rather than bronze) and are extremely prone to corrosion and catastrophic failure without warning. Another strike against gate valves is they give no visual indication of whether they’re open or closed. Worse still, the valve can fail to completely close due to trash or debris, allowing water to enter the vessel even after being closed.

If your boat is hauled, start your seacock inspection at the through-hull, keeping an eye out for leaks, cracks, broken bedding seams and other such issues. Bronze through-hulls that are bright and shiny or pinkish in color should be inspected further for dezincification/corrosion issues.

Next conduct a visual inspection of the seacock, keeping an eye out for anything unusual, such as leaks, damaged or missing components (handles for example) and corrosion. Verify the installation of a seacock backing block and that the block is tight, leak-free, properly sized (with a surface area greater than that of the seacock flange) and in the case of wood blocks, rot free.

Check the seacock for smoothness of operation. Ensure it not only opens and closes, but can be easily reached in an emergency and that the handle can be moved through its full range of operation. If your boat is hauled, you can verify operation of the seacock visually by shining a flashlight into the through-hull from the outside while someone inside opens and closes it. You can also pull the seacock hose to verify operation, which takes more time, but allows you to better check the condition of the hose itself.

If a seacock is difficult to reach, consider installing a pull rod or other such device. Seacocks that are frozen or difficult to operate should be serviced immediately to return them to full operation.

Old, deteriorated hoses and corroded hose clamps are other seacock-related issues to be on the lookout for. Hoses should be supple with no signs of deterioration (cracks, splits, etc) while hose clamps should be tight and free of corrosion. Installation of double hose clamps is also recommended if there is sufficient hose barb to allow it.

Maintenance should include monthly exercising of the valve and a good greasing (if applicable) in the spring and fall.

Capt. Frank Lanier is an accredited marine surveyor with over 30 years of experience in the marine industry. His website is

Practical Sailor has been independently testing and reporting on marine products for serious sailors for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising or any form of compensation from manufacturers whose products we test. Testing is carried out by a team of experts from a wide range of fields including marine electronics, marine safety, marine surveying, sailboat rigging, sailmaking, engineering, ocean sailing, sailboat racing, and sailboat construction and design. This diversity of expertise allows us to carry out in-depth, objective evaluation of virtually every product available to serious sailors. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser with more than three decades of experience as a marine writer, photographer, boat captain, and product tester. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.


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