Why ships are louder close inshore

How far can submarines hear surface ships, and why do they sound different near shore?

Range depends on conditions, but harbour manoeuvring uses additional machinery that makes ships much louder than they are at sea.

Sonar range depends heavily on conditions, so dramatic anecdotes should not be treated as fixed performance figures. Surface ships operating near harbour use machinery that may be unnecessary in the open ocean. Bow thrusters are a vivid example: they are loud enough to disturb nearby accommodation and create a conspicuous acoustic source. A ship heard during close-in manoeuvring may therefore sound very different once it settles into efficient sea-going propulsion. Harbour observations cannot be used directly to judge normal wartime quieting.