Dickerson Harbor Yacht Service Committed
Dickerson Harbor

Marine Seacock Maintenance

Groco seacock

Seacocks are your first line of defense against water entering your boat. They open and close for a reason and if they don't operate properly they are an accident waiting to happen. If a hose bursts you must be able to close the seacock. To ensure proper operatation, you must maintain them on a regular basis. What is involved depends on the type of seacock you have. Some seacocks are maintenance free, such as Apollo and Conbraco brands, while other require maintenance such as Perko and Groco style. The maintenance free styles should be operated frequently to ensure they don't get stiff or stuck. Most of the other types have similar maintenance requirements.

Disassembling the Seacock

Maintenance style seacocks require disassembly of the seacock, which obviously has to be done while the boat is out of the water. The perfect time for this is when you are laid up for winter storage. While disassembing, we can ensure the seacock is properly bedded and fits snugly to hull. Also if the seacock is mounted on a backing block, we will make sure that it is stable and shows no signs of deterioration.


Once the seacock is disassembled, we clean clean salt, old grease and other debris from the drum and seacock passageways. Sometimes grit from sand will score the drum which will allow leakage through a closed seacock. This will need to be slightly sanded to allow a water tight fit. We then lubricate the drum with the proper lubricant and reinstall the drum in the seacock.

Other Types of Seacocks

We have seen all styles of seacocks on boats here in the marina. There are some we will immediately recommend replacing. First off, any gate valve mounted on a thruhull should be replaced, regardless of the use. Gate valves are succepticle to lots of problems and most do not have all rust proof parts. We would also recommend most plastic thruhulls below the water line be replaced. Some styles such as the Forespar, which is made from plastic impregnated with fiberglass, are heavy duty and are used primarily where weight is an issue such as in racing sailboats. Other boats don't have the same restrictions and should stay with heavy bronze for the least amount of problems.

We also see thruhulls with a ball valve mounted on them. While this works, it is not really an acceptable practice. All seacocks should be mounted to the hull which will negate the possiblity of it getting broken off as a ball valve could be.

Seacock Strainers

Groco strainer

There may actually be two kinds of strainers on a seacock. One is on the outside of the hull and could be a scoop strainer or just a strainer cover. These keep larger debris from entering though the hull. It should also eliminate most jelly fish from getting sucked in. Maintenance on these strainers should be done while the bottom is being painted and simply involves removing from the hull, cleaning and painting inside and out to eliminate barnacles.

The other kind of strainers are basket strainers and could be mounted right to the seacock or remotely. In either case, these will need to be maintainted. There are no moving parts so lubrication is not an issue, but cleanliness is. These have glass or heavy plastic so you can visually inspect for debris. If you can't see through them, clean them immediately. Secondly, most have baskets inside. Groco makes 2 types of baskets — monel or plastic. We prefer the plastic. Aside from being cheaper, they do not corrode over time as the monel do. We have removed baskets with holes the size of golf balls in them. These will allow debris to enter the system and essentially negating the strainer from the system.

You also want the strainer to be leak-free which will mean occasionally you will need to replace the seals. Most strainers have 3 seals - one at the top and bottom of the glass and one under the removeable lid. The one on the lid is the most usual one to replace since you will be opening the strainer a lot to dump the basket (hopefully).

bad strainer basket

On the left is a strainer basket we found during the winterization of a boat. The use of plastic baskets will eliminate this type of deterioration. The owner obviously has not been maintaining these.

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Dickerson Harbor
3831 Trappe Landing Road
Trappe, MD 21673