The word “bilge” is a nautical term which is used to refer to a several concepts. It dates from 1513, when “bilge” was first used to refer to the lowest compartment inside the hull of a ship, where the two sides meet at the bottom. However, the term is also used to discuss the matter which collects in the bilge: water drains from the decks of the ship into the bilge, dragging detritus from topside down below. The water that collects in the bilge is usually brackish and also has a foul odor, so bilge has also come to be a term which refers to anything foul or unpleasant. A bilge pump is a device which is used to remove water from the bilge.
The bilge is a collection point for water which overflows on the decks of the ship, along with water which enters through small leaks along the hull before they have been noticed and repaired. Especially in storms, the decks of the ship cannot drain to the sea quickly enough for the decks to be safe to walk on and so the excess water is routed into the bottom of the ship to be handled by a bilge pump, or several, in the case of a large boat. Because the water drains from the decks, which are not always completely clean, the bilge also collects detritus like urine and feces from seabirds and unscrupulous sailors, tar, food material, and other dirt that has accumulated on deck. The contents of the bilge can get quite acidic and it is usually painted with a protective seal to prevent the bilge water from eating through to the sea. The bilge pump must also be carefully monitored to ensure that it is not clogged or damaged by the bilge water.
Because bilge water gets understandably foul, the task of cleaning the bilge was often assigned to junior sailors. Periodically, ships are hauled into dry dock for service and repairs, and cleaning and resurfacing the bilge is a vital part of this procedure, but not a very pleasant one. The linkage between bilge water and unpleasantness caused the term to be used generically among sailors for people speaking nonsense and foul tasting drinks.
Before the introduction of mechanization to sailing, the bilge had to be bailed or pumped by hand. In emergency situations like storms, the bilge could fill quite quickly, potentially posing a risk of sinking. For this reason, sailors were stationed to keep an eye on the bilge at all times during hazardous weather, and to pump it continually. If the contents of the bilge were overwhelming, everyone on the ship would be enlisted to help avert catastrophe. Mechanized bilge pumps on modern ships greatly reduce this risk, although an electric bilge pump can still fail, so hand pumps are kept on board. Maintenance for the bilge pump is also crucial, to minimize the risk of failure at a crucial moment.
Responsible sailors consider the bilge pump to be vital to the integrity of a ship, and usually have at least one backup pump in addition to the regular bilge pumps to ensure coverage at all times. A number of things can go wrong at sea which cause the hull of a ship to rapidly fill with water, and properly installing and maintaining a bilge pump could make the difference between losing a ship and making it back to port. Numerous sizes and styles of bilge pump are available, depending on the size of the ship and the way in which it is built.