Seacock Maintenance

By Andrew Spaulding

Seacocks are those bronze or plastic things in the bilge that keep the water out while making handy foot-holds. What they really do is start and stop the flow of water through a thru-hull fitting. In some cases the seacock and thru-hull are separate pieces threaded together, and in others the seacock and thru-hull are manufactured as one piece. The first thing we need to discuss is that they should NEVER be used at foot-holds. Stepping on them, while often very convenient, can cause them to weaken and crack or break off entirely which, as you can imagine, causes a bit of a problem.

Thru-hulls are one of the more neglected pieces of equipment on the boat given their location and purpose. There isn’t often a reason during the standard boating day to open or close a seacock, so they get ignored. However, ignoring your seacocks can be very dangerous. If a hose connected to a thru-hull breaks or a strainer basket housing cracks, the only thing stopping the boat from sinking is the seacock. I don’t think that it’s a stretch to call your seacocks emergency equipment. When you need them to work, you NEED them to work.

There are many types of seacocks, but they all basically work the same. The seacock is made up of a valve body, which is what you see, with a cone or ball valve inside the body attached to a handle. The cone or ball has a hole through it and when the hole is oriented in-line with the thru-hull, water flows through the seacock. When the hole is perpendicular to the thru-hull the flow of water is stopped.

The best way to keep your seacocks in good working order is to “exercise” them. Exercising your seacocks is marine industry vernacular for operating them through their full range of motion – all the way closed, all the way open and back to their original position. As the years pass, the seacock’s lubrication begins to wear away causing them to become more difficult to operate. Once this process starts, it is time to re-lubricate your seacocks. For most boat owners this will be sufficient to keep them operating fine for many years. If you ignore your seacocks, they may become so stiff that you cannot exercise them. Once this happens, it is time for a rebuild.

Seacock maintenance is best done out of the water for obvious reasons. It is a good idea to lubricate them annually and exercise them once a month during the boating season. Apply lithium grease to the ball or cone from the outside with the seacock closed. It is also a good idea to apply some to the inside. However, this will require removing the hose that is attached to the seacock. If you decide to remove the hose from the seacock, be careful as this process can crack older hoses. Although, if your hose is in such poor condition that it may crack, you may want to take this opportunity to replace the hose. Once the lithium grease is applied, exercise the seacock until it frees up.

If you can’t get the seacock to move at all, greasing it up won’t help – it is time for a rebuild. The easiest types to rebuild are the cone-type that uses a bronze cone and a bronze valve body. Ball-type seacocks typically can be taken apart and cleaned, but not rebuilt as many of them have plastic sealing rings. I suppose the plastic bits could be replaced, but since ball valves are comparatively inexpensive, most boat owners choose just to replace the valve. There are also plastic seacocks that are not serviceable and must be replaced once they aren’t working. If you have non-serviceable or ball-type seacocks make sure that you follow a strict exercise and lubrication policy, since your option is replacement, not rebuilding.

During the winterizing process, it is important to pay attention to your seacocks. Some seacocks trap water when they are moved from the closed position to the open position in the water. If this type of valve is not exercised on land after the boat is hauled, freezing temperatures can rupture the valve.

Once upon-a-time there were many manufacture of the bronze cone-type seacock that we would consider the “traditional” seacock. Spartan Marine Hardware located in Maine is the only company left in the United States that makes them. You can view their catalog by clicking here. Once there, click on the “Seacock Maintenance” link on the left hand side of the page. This will take you to a page that describes in detail how to maintain a cone-type seacock.