On which type of davit must you turn a crank in order to swing the lifeboat out and over the ship's side?

The correct answer is that a sheath-screw davit requires the use of a crank to swing the lifeboat out and over the ship's side. This type of davit operates through a screw mechanism that allows a lifeboat to be lowered or swung out by manually turning the crank. The crank engages a screw that provides the necessary mechanical advantage to facilitate the movement of the lifeboat.

In contrast, other types of davits function differently. For instance, gravity davits rely on the weight of the lifeboat itself, utilizing gravity to assist in lowering and swinging the boat out without needing to turn a crank. Mechanical davits may use various mechanical systems, but they are typically designed for easier deployment without manual cranking, and they often incorporate other mechanisms such as winches. Hydraulic davits operate using hydraulic systems and do not require cranking; instead, they provide smoother and faster movements compared to manual systems.

Using a sheath-screw davit emphasizes the manual labor aspect of launching lifeboats, requiring specific physical input from the crew, which distinguishes it from other systems that utilize automation or gravitational principles. Understanding these differences is crucial for effective lifeboat deployment and safety during emergencies at sea.