Wiktionary
n. (context nautical English) A valve in the hull of a vessel used to let in water, either to clean the bilges, flood a ballast tank, or scuttle the vessel
Wikipedia
A seacock is a valve on the hull of a boat or a ship, permitting water to flow into the vessel, such as for cooling an engine or for a salt water faucet; or out of the boat, such as for a sink drain or a toilet. Seacocks are often a Kingston valve.
Seacocks are left open or are closed depending on the situation. Seacocks feeding into or out of a closed system, like the engine cooling system, are almost always left open. Seacocks connected to something open, such as a sink drain, might be opened up in port but closed when at sea. The reason for this is that when the boat is level, the drain or other opening will always be above the waterline, and so water will only flow out. At sea, when the boat rolls in the waves, the opening may sometimes be below the waterline. If the seacock is open, water may flood the boat.
Some seacocks on warships are designed to flood the ship when opened. Typically, this is done to magazines to prevent detonation of the ammunition in the event of fire, or to maintain trim due to battle damage (counterflooding). Additionally, opening the seacocks is one of the main methods used to scuttle a ship so that it cannot be captured by the enemy.
Usage examples of "seacock".
He looked around for another opportunity but saw none, so he opened both seacocks and watched the sea water gush onto the engine room floor, then he went forward and did the same for the seacock at the ship’s toilet.
The valve was joined to the cooling water pipe by two flanges—one on the seacock and one on the pipe.
He closed the seacock, selected the proper socket, and went to work on the six bolts holding the two flanges together.
They reversed both your bilge pumps and opened the seacock to your head.
If a plastic bag hadn't been sucked up by the intake and blocked the seacock, you would have sunk far before shore.
Pitt didn't have to be told that the seacocks in the bilge had been opened.
He found a screwdriver and loosened the clips that held the water hoses onto the seacocks, then he pulled the hoses free.
Finally, he opened the seacocks for the port and starboard engines, and he had two more three-inch blasts of water pouring into the engine room.
Open the seacocks, push her away and abandon ship, he said, so we did.
We opened all the seacocks and she went down like a stone in a thousand fathoms.
Before I leave, I open the sailboat's seacocks, shake my head at the necessity of having to sink such a fine craft.