Just to add my bit - ship captains commonly hand over navigation to a pilot when entering a tricky area such as a tidal estuary, where the channel is always changing. The pilot joins the ship from a cutter at a recognised spot where the channel meets the open sea. If the ship gets into difficulty or runs aground, the pilot takes the flak as the appointed expert - there have been many cases of that in the past. Especially tricky with sailing ships (plenty of those in the 1880s) as they were much more at the mercy of tide and wind.
Less essential these days with aids like sonar for judging depth of water.