To be precise, the pilot was the harbour professional official whose speciality would be to guide a ship from harbour to open sea, up to which point, as he would be conversant with the harbour's depths and shallows &c, he would be regarded as in command. Once clear, he would be "dropped", ie would descend the ladder into a boat which would row him back, and the captain would take over command from then on. Hence the famous Punch cartoon: "Dropping the Pilot is a political cartoon by Sir John Tenniel, first published in the British magazine Punch on 29 March 1890.[1] It depicts Chancellor Otto von Bismarck, as a maritime pilot, stepping off a ship (perhaps a reference to Plato's ship of state),[1] watched by a young Wilhelm II, German Emperor. Bismarck had just resigned as Chancellor at Wilhelm's demand, as their political views were too different for Wilhelm." Wikipedia -- see this entry for repro of the cartoon.

~M~