Show Your Seacocks Some Respect

A ‘Proper’ Seacock

The American Boat and Yacht Council (ABYC) recommendations state that “all thru-hull fittings or hull penetrations designed to accept pipes, hoses, or valves, with any part of the opening below the maximum heeled waterline when inclined from the static floating position, shall be equipped with a seacock to stop the admission of water in the event of failure.”

Should a new seacock need to be installed, or an old one replaced, a proper seacock is one that’s flanged (for added support) and meets UL 1121 and ABYC standards and recommendations. These include operation by a lever-type handle (operating through a 90-degree arc), which gives a clear indication of whether the seacock is open or shut, and a mounting that can withstand a 500-pound force applied at the inner end of the attached fitting.

While unflanged inline ball valves (photo 1) screwed directly onto a thru-hull are permitted for use as seacocks per ABYC standards, care must be taken to ensure thread compatibility between the valve and thru-hull. Many ball valves use NPT (national pipe taper) threads, which are not compatible with the NPS (national pipe straight) used in most thru-hull fittings (unless the thru-hull fitting is machined with “combination thread”).

Installing an inline valve onto a NPS thru-hull fitting creates a mismatch of threads, resulting in a weaker, less waterproof joint. As it has no mounting flange, an inline valve can also turn or loosen from the thru-hull fitting due to vibration or through normal use.

Based on my observations as a marine surveyor and my personal experience, I prefer a good quality, flanged, marine-grade bronze seacock, rather than an inline ball valve.

When replacing a seacock with a new unit, replacing the corresponding thru-hull fitting is also recommended to prevent the possibility of thread mismatch. Seacocks and their respective thru-hulls must also be of the same material (more on this later).

Types Of Seacocks

The most common seacock styles are tapered plug, expanded-rubber plug, and ball-valves. Gate valves (valves with a wheel-shaped handle like you see on many outdoor faucets) are notorious troublemakers and not recommended for use as a seacock. The ones I typically encounter while surveying are residential-type units purchased from a big box hardware store (6c). These are constructed from non-marine-grade materials (i.e., 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.” Material-wise, seacocks should be constructed from either marine-grade bronze or a suitable marine-grade composite (such as Marelon).

Inspections

Backing plates should be stable, leak-free, and properly sized, with a surface area greater than that of the seacock flange. If made of wood, the backing plate should be free from splits, checks, or deterioration (4).

Next, check the seacock for smoothness of operation and that the handle can be moved through its full arc of operation without being blocked by equipment or vessel structural components. Boats are constructed and assembled in stages, with thru-hulls typically being one of the first things installed. As such, it’s not unheard of for a seacock to be blocked from full operation by cabinetry or other equipment installed later during the build process or during aftermarket installations (5a & 5b).

I once surveyed a vessel with an aftermarket generator installed directly over and completely preventing physical or visual access to the seacock providing cooling water to it. As installed, to simply operate the seacock required removal of the generator – a dangerous situation should seacock or hose failure occur. With that in mind, if a seacock is difficult to reach, consider installing a remote pull rod or other such device to facilitate easier operation.

Other installation problems include the use of PVC fittings or components (6a), as well as any composite (plastic)-to-metal connections (6b). In addition to the very real possibility of thread mismatch, metal and composite components have different expansion and contraction ratios, which can result in composite component failure due to cracks or splits.

Also keep an eye out for installations that include a section of pipe or hose between the seacock and thru-hull (6c). This introduces a potential failure point inside the hull that is unprotected by the seacock.

Finally, any seacock that is no longer in use must be properly capped (7). During your annual haulout, shine a flashlight into the thru-hull from the outside and observe its operation while someone inside opens and closes it.

Another option is removing the seacock hose and looking through the seacock to verify operation and to spot blockages. Removing the seacock hose takes more time, but doing so allows you to better check the condition of the hose itself.

Seacocks that are frozen or stiff and difficult to operate should be serviced immediately to return them to full operation. If unable to be repaired, they should be immediately replaced.

Inspect all seacock hoses for kinks, damage, and deterioration while also verifying that they’re of the correct type (i.e., marine-grade and approved for use on thru-hull fittings below the waterline). As a marine surveyor I see plenty of incorrect hoses pressed into seacock service, from fuel hose to the clear, reinforced vinyl hose typically used for potable water systems (6b).

All hose has a limited lifespan and while recommendations vary among manufacturers, a good general rule is to replace all seacock hoses at 10 years of age, regardless of condition (8).

Finally, each end of the seacock hose should ideally be secured with double stainless steel or titanium hose clamps, with the following caveats:

Install double hose clamps only where there is sufficient length of hose barb/nipple available and hose end overlap to allow it.

No hose clamp should be installed closer than 1/4 inch to the end of the hose, and it must fully engage the hose barb or fitting. Any clamp that extends over the end of the fitting and is cutting into the hose (9) or forcing the hose to be internally cut by the fitting is an incorrect installation.

Separate clamps by at least 1/4-inch (1/2-inch if possible) with screws located on opposite sides of the hose. If the seacock hose barb fitting is of insufficient length to install two hose clamps, a single, more robust clamp should be used. Another option is to replace the existing hose barb with one long enough to accommodate two hose clamps.

Maintenance

While specific requirements will vary based on the type of seacock (plug, ball, bronze, composite), in addition to regular inspections, general maintenance should also include a good greasing with manufacturer-recommended grease at least twice a year, even for so-called “maintenance-free” units. Some seacocks have grease fittings to simplify the process, however, those that don’t can be greased by following these steps when the vessel is hauled:

1. Disconnect the seacock hose.
2. Swab a suitable waterproof grease onto the ball and cycle (open and close) the seacock a few times to spread the lubricant.
3. Check the seacock hose and clamps for issues, then reinstall.
4. Follow manufacturer instructions. You can also grease the seacock from outside the hull via the thru-hull. Simply use a wooden dowel topped with grease to reach the ball and apply the lubricant, then cycle the seacock a few times.

Final Tips

Now that you’re showing your seacocks the love and respect they deserve, here are three closing thoughts on attaining true seacock nirvana:

1.  Label each seacock as to its function (e.g., engine raw water, livewell).
2. Locate soft, tapered wood plugs or expansion style plugs of appropriate size at each and every seacock. Tapping a plug into a failed seacock will staunch the powerful gushing of incoming water. These plugs can be attached to the seacock with light line or stowed in a portable “Damage Control” kit (along with a hammer for wooden plugs) that should always be kept in an easily accessible location and ready for instant use.
3. Post a diagram of the vessel showing all seacock locations in an easily visible area (above the chart table for example). It’s an excellent “knowledge is power” device, one that’s handy during your predeparture safety briefs as well as those discussions that begin with, “Where’s all this water in the bilge coming from?”