When ships get close to a port, they need to pick up a harbour pilot to guide them in unless the captain on board has been to the port many times before. A pilot provides local navigation advice to the ship's captain. The ship must book the pilot 24 hours before it either arrives at a port or is due to sail from a port. Before the ship gets to the port, the pilots board ships where the crew needs assistance. When the ship is at sea, pilots use a boat or helicopter to get on board.
The pilot has special local knowledge of the channels and how currents and winds can affect ships. Ships are large and can't stop and turn quickly. The pilot knows when to start a turn and if the wind and currents will push the ship off its course. The pilot is a guide to the ship's captain and officers and does not take over the controls. If the pilot makes a mistake, the ship's captain and crew are still responsible as they control the ship at all times.