What is "bilge keel"

Keel \Keel\, n. [Cf. AS. ce['o]l ship; akin to D. & G. kiel keel, OHG. chiol ship, Icel. kj[=o]ll, and perh. to Gr. gay^los a round-built Ph[oe]nician merchant vessel, gaylo`s bucket; cf. Skr. g[=o]la ball, round water vessel. But the meaning of the English word seems to come from Icel. kj["o]lr keel, akin to Sw. k["o]l, Dan. kj["o]l.]

1. (Shipbuilding) A longitudinal timber, or series of timbers scarfed together, extending from stem to stern along the bottom of a vessel. It is the principal timber of the vessel, and, by means of the ribs attached on each side, supports the vessel's frame. In an iron vessel, a combination of plates supplies the place of the keel of a wooden ship. See Illust. of Keelson.

2. Fig.: The whole ship.

3. A barge or lighter, used on the Tyne for carrying coal from Newcastle; also, a barge load of coal, twenty-one tons, four cwt. [Eng.]

4. (Bot.) The two lowest petals of the corolla of a papilionaceous flower, united and inclosing the stamens and pistil; a carina. See Carina.

5. (Nat. Hist.) A projecting ridge along the middle of a flat or curved surface.

6. (Aeronautics) In a dirigible, a construction similar in form and use to a ship's keel; in an a["e]roplane, a fin or fixed surface employed to increase stability and to hold the machine to its course. Bilge keel (Naut.), a keel peculiar to ironclad vessels, extending only a portion of the length of the vessel under the bilges. --Ham. Nav. Encyc. False keel. See under False. Keel boat.

   1. A covered freight boat, with a keel, but no sails, used on Western rivers. [U. S.]

   2. A low, flat-bottomed freight boat. See Keel, n., 3.

      Keel piece, one of the timbers or sections of which a keel is composed.

      On even keel, in a level or horizontal position, so that the draught of water at the stern and the bow is the same.
      --Ham. Nav. Encyc.

      On an even keel a. & adv., steady; balanced; steadily.

n. (context nautical English) a strake, or small keel or blister, running along much of the length of the hull. It is used to reduce the hull's tendency to roll. They are typically fitted one on each side, low down on the side of the hull, so as not to increase the draft of the vessel. In battleships they were often quite large and used as part of the torpedo protection system.

n. either of two lengthwise fins attached along the outside of a ship's bilge; reduces rolling

A bilge keel is used to reduce a ship's tendency to roll. Bilge keels are employed in pairs (one for each side of the ship). A ship may have more than one bilge keel per side, but this is rare. Bilge keels increase hydrodynamic resistance to rolling, making the ship roll less. Bilge keels are passive stability systems.

On commercial shipping the bilge keel is the form of a strake, or small keel or blister, running along much of the length of the hull. They are typically fitted one on each side, low down on the side of the hull, so as not to increase the draft of the vessel. In battleships they were often quite large and used as part of the torpedo protection system.

A bilge keel is often in a "V" shape, welded along the length of the ship at the turn of the bilge. Although not as effective as stabilizing fins, bilge keels have a major advantage in their low impact on internal ship arrangements. Unlike fins, bilge keels do not have any components inside the hull that would adversely affect cargo or mission spaces. Like fins, bilge keels have the disadvantage of increasing the hydrodynamic resistance of the vessel, thus hindering forward motion.