Shaft tunnel
The shaft tunnel is the space in the hull of a ship through which a drive shaft is guided from the ship's engine through the ship's side to the propeller . Its shape and characteristics depend on the shape of the ship's hull.
Ships with multiple drive shafts also have multiple shaft tunnels. In larger ships, a shaft tunnel is often a walk-in space that can be separated from the engine room by a watertight bulkhead . As the shaft bearings used to have to be checked and lubricated frequently, it was important to be able to see and maintain the shaft over its entire length inside the hull.
The shape of a tunnel - and hence the name of this room - results from the structural conditions: At the bow end of this room, the ship's hull still has a relatively large cross-section, which corresponds to the rear wall of the engine room. Normally, ship hulls taper continuously aft : on ships with a propeller, the side walls converge at the exit point of the drive shaft - the cross section of the ship hull almost disappears at this level. The result is a wedge-shaped space with rounded outer walls and partially rounded bottom, which must have a maintenance passage for the drive shaft in the middle. This space could be put to good use in classic shipbuilding by guiding the shaft through a tunnel-shaped passage and the “misshapen” spaces around it being used for fuel bunkers or for ballast tanks . This is particularly useful due to the proximity to the engine room.
Only ships with classic propellers and shafts have shaft tunnels. On ships with diesel-electric propulsion, there are shaft tunnels from or from the traction motors to the propeller. The traction motors do not necessarily have to be located in the engine room near the generators, but for practical reasons and reasons of ease of maintenance they are usually still. Ships with pod drives do not have a shaft tunnel in the classic sense, but rather a cable duct. There, the electrical current to drive the traction motors must be conducted from the generators in the engine room to the pods. The mounting points of the pods on the fuselage must be accessible for maintenance work, but not necessarily directly from the engine room.