Image Credit: www.libramar.net
The stern tube is a hollow tube-like structure at the stern or rear part of the ship. A ship needs the propeller to drive it forward in water. The propeller, located outside the ship, needs to be connected to the engine inside the ship’s engine room. The propeller shaft is used for connecting the ship’s engine and the propeller. The stern tube is a narrow hole in the hull structure at the rear end (aft peak) of the ship, through which the propeller shaft passes and connects the engine and propeller.
Stern tube bearings serve two main functions:
1. To properly connect the propeller to the ship
2. To keep water from leaking into the stern tube (and lubricant from leaking out)