In a sea going vessel, navigational officers control the ship’s navigation system from bridge and engineering officers control the propulsion plant from the engine room. Bridge is right on top of the ship, hence the officer on the bridge does not know about the condition of the propelling engine and marine engineer in the engine control room does not knows where the ship is heading as the engine room is situated below the water line of the ship. Hence a fail-safe communication is required in between the navigation and engineer officer to ensure smooth and safe sailing of the ship.
As the word describes, the telegraph on board ship is used as a communicating device to transfer orders of change in speed or direction from the bridge to the engine control room.
