Anchor

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Anchor selection.jpg

Origin

Middle English ancre, from Old English ancor, from Latin anchora, from Greek ankyra; akin to Old English anga hook — see angle

Definitions

  • 1: a device usually of metal attached to a ship or boat by a cable and cast overboard to hold it in a particular place by means of a fluke that digs into the bottom
  • 2: a reliable or principal support : mainstay
  • 3: something that serves to hold an object firmly
  • 4: an object shaped like a ship's anchor
  • 5: an anchorman or anchorwoman
  • 6: the member of a team (as a relay team) that competes last
  • 7: a large business (as a department store) that attracts customers and other businesses to a shopping center or mall
  • 8: a fixed object (as a tree or a piton) to which a climber's rope is secured

Description

An anchor is a device, normally made of metal, that is used to connect a vessel to the bed of a body of water to prevent the vessel from drifting due to wind or current.

Anchors can either be temporary or permanent. A permanent anchor is used in the creation of a mooring, and is rarely moved; a specialist service is normally needed to move or maintain it. Vessels carry one or more temporary anchors which may be of different designs and weights.

An unrelated device is a sea anchor, a drogue used to control a drifting vessel.

Background

Anchors achieve holding power either by "hooking" into the seabed, or via sheer mass, or a combination of the two. Permanent moorings use large masses (commonly a block or slab of concrete) resting on this seabed. Semi-permanent mooring anchors (such as mushroom anchors) and large ship's anchors derive a significant portion of their holding power from their mass, while also hooking or embedding in the bottom. Modern anchors for smaller vessels have metal flukes which hook on to rocks on the bottom or bury themselves in soft bottoms.

The vessel is attached to the anchor by the rode which is made of chain, cable, rope, or a combination of these. The ratio of the length of rode to the water depth is known as the scope. Anchoring with sufficient scope and/or heavy chain rode brings the direction of strain close to parallel with the seabed. This is particularly important for light modern anchors designed to bury in the bottom, where ratios of 5-7 to 1 are common, whereas heavy anchors and moorings can use 3 to 1 or less.

Since all anchors that embed themselves in the bottom require the strain to be along the seabed, anchors can be broken out of the bottom by shortening the rode until the vessel is directly above the anchor (at this point the anchor chain is "up and down" in naval parlance). If necessary, motoring slowly around the location of the anchor also helps dislodge it. Anchors are sometimes fitted with a tripping line attached to the crown, by which they can be unhooked from rocks or coral.

An interesting element of anchor jargon is the term aweigh, which describes the anchor when it is hanging on the rode, not resting on the bottom; this is linked to the term to weigh anchor, meaning to lift the anchor from the sea bed, allowing the ship or boat to move. An anchor is described as aweigh when it has been broken out of the bottom and is being hauled up to be stowed. Aweigh should not be confused with under way, which describes a vessel which is not moored to a dock or anchored, whether or not it is moving through the water. Thus, a vessel can be under way (or underway) with no way on (i.e., not moving).[1]