What happens to a ship when the lock shaft is engaged?

When the lock shaft is engaged, it effectively disconnects the main propulsion system from the ship’s drive train. This means that the ship's engines can produce power, but without the ability to engage propellers or thrusters, the ship loses its propulsion capability.

In this state, the vessel is unable to maneuver or sustain any form of movement under its own power, which necessitates external assistance from a tugboat if travel is required. This condition is particularly relevant in scenarios where the ship is either docked or preparing to enter or exit repairs. Thus, the pressing need for tug assistance confirms why the ship cannot move unless towed.

Other options suggest varying states of mobility or operational readiness that are not consistent with the engagement of the lock shaft. The ship does not achieve full speed or reverse capabilities when the lock shaft is engaged, nor does it enter a dry dock in the traditional sense of a vessel actively maneuvering itself. Dry docking typically involves a ship being secured and brought to rest, rather than being impelled by its own power systems.