What is a watertight door?
A watertight door is a door between compartments of a ship that prevents water from a leak in the hull spreading to other parts of the ship. A watertight door seals tight enough that water can't get through.
The History of Watertight Doors
Watertight doors were first used in China during the Han dynasty, well over a thousand years ago. They were fitted in Chinese ships called junks, which were divided into compartments so that flooding could be controlled and less ships would end up at the bottom of the sea. In the following years, the idea of watertight doors and compartments would spread across Asia and Europe, becoming the standard in ship building.
What is a watertight door made of?
Watertight doors are usually made of stainless steel for its water and corrosion resistant properties. Stainless steel was discovered in the early 1800's when people created a chromium-iron alloy that resisted rusting. Since stainless steel was invented, it has been pivotal to ship construction; it is used for many parts of the ship, but especially for watertight doors because it is so strong and is less likely to wear down with exposure to salt and water. Some watertight doors feature peepholes or windows which make it easier to assess the condition of the compartment once the door is shut. The glass used for these windows is high pressure glass, like the kind used for giant fish tanks, that can stand up to the water pressure that the window might experience.
There are many different reasons watertight doors are needed on a ship. Here are a few reasons why watertight doors are used:
War- Watertight doors have been used for years in submarines and warships to protect against sinking when the hull has been breached by torpedoes or cannonballs. Without watertight doors, pumps would likely not be fast enough to remove the water from a leak before the ship's buoyancy was compromised.
Collision- When two ships collide, or when a ship hits a foreign object like a reef or iceberg, the hull can be damaged. Without a watertight compartment where the water can be quickly sealed off, the ship could sink. Watertight doors can seal off a breach.
Wear and Tear- Sometimes, a ship is not well looked after, and wear and tear can cause a leak that can quickly get out of hand without a way to contain it. Watertight doors can help save a ship and its passengers.