A master of a ship is, without exception, a highly skilled seafarer, who understands the capabilities and limitations of the ship he/she commands. But in some waters, local knowledge of tide, swells, currents, depths and shoals that might not be easy to spot on nautical charts is also necessary and it is in these areas that another expert is brought in to safely steer the ship. Known as a Pilot, these professionals, often masters, will guide the ships through narrow, shallow and/or dangerous coastal waters between a harbour and the open sea. As an individual with specific knowledge of a particular harbour, canal, river or other waterway, the pilots will take over the position of the master when pilotage is compulsory, and on other occasions will act as a guide to the Master. Some pilots have a wider expertise than the surrounding waters of a port, for example there are pilots that act as guides through the busy waters of the and the North Sea and the English Channel, known for heavy traffic and sandbanks. While sea pilots may stay on a ship for ten days or more acting as a sort of consultant to the master about the navigation between ports, and the ports themselves. A particularly perilous part of the pilot’s job is the boarding and disembarking of the ship, which could be via a pilot boat and a swaying rope ladder sometimes up 40 feet to the deck of the largest containerships and tankers. Some arrive and leave by helicopter!