An anchor is a device, normally made of metal, used to connect a vessel to the bed of a body of water to prevent the craft from drifting due to wind or current. The word derives from Latin ''ancora'', which itself comes from the Greek ἄγκυρα (''ankura'').〔(anchor ), Oxford Dictionaries〕〔(ἄγκυρα ), Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus〕
Anchors can either be temporary or permanent. Permanent anchors are used in the creation of a mooring, and are rarely moved; a specialist service is normally needed to move or maintain them. Vessels carry one or more temporary anchors, which may be of different designs and weights.
A sea anchor is a drogue, not in contact with the seabed, used to control a drifting vessel.
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 the 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 seabed.
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 scopes of 5– to 7-to-1 are common, whereas heavy anchors and moorings can use a scope of 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 rope 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.
The term ''aweigh'' describes an anchor when it is hanging on the rope and is 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 the vessel is moving through the water.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』