Mostly, vessel doors are designed around the movement and protection of people. But some doors, like on some ferries, are designed and built to protect vehicles and cargo. 

When the Bridgeport & Port Jefferson Steamboat Co. built the 300', 1,000-passenger, 120-car ferries P.T. Barnum and Grand Republic in 1999 and 2003 at Eastern Shipbuilding, Gilbert Associates Inc., a naval architecture and marine engineering company based in Hingham, Mass., came up with a unique door design for the car deck. 

Instead of going with a curtain-style door or clam-shell-design where the stresses that occur where the door breaks are significant, cars go on and off the bow beneath “a giant guillotine door,” said the company’s John Gilbert. “The whole thing slides up like a sled,” on heavy steel casters and rollers. 

The door’s up-and-down movement is controlled with winches instead of relying on hydraulically powered cylinders. “With cylinders the pressures are gargantuan, especially at the knucklehead,” said Gilbert. The winches are “more economical, easier to maintain and have better longevity.”

The wire comes off the winch and goes over a vertical block above, then back down to the freight deck to a solid connection on the door. The door slides up on heavy steel rollers, and there’s a locking pin to support the door, “so it’s not just hanging on the wire,” Gilbert said, and it keeps the door from coming down if the winch fails. 

The door measures 19'x19', is made of 5/16" plate and framed out with 10"x8" stiffeners on 5' centers. A 14"x8" steel beam runs down the center. 

Longevity is good for this type of door as there aren’t many moving parts and preventive maintenance basically requires replacing the wire on the winch every few years.