Boat anchors can either be temporary or permanent. A permanent boat 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 boat anchors which may be of different designs and weights. A sea anchor is an unrelated device: a drogue used to control a drifting vessel. A stockless anchor being broken out is another boat anchor.
Boat 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 boat 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 boat 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 boat 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 boat 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 boat anchor. If necessary, motoring slowly around the location of the boat anchor also helps dislodge it. Boat 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 boat 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 boat 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).
Boat Anchor | The Evolution of
The earliest boat anchors were probably rocks and many rock anchors have been found dating from at least the Bronze Age. Many modern moorings still rely on a large rock as the primary element of their design. However, using pure mass to resist the forces of a storm only works well as a permanent mooring; trying to move a large enough rock to another bay is nearly impossible.
The ancient Greeks used baskets of stones, large sacks filled with sand, and wooden logs filled with lead which, according to Apollonius Rhodius and Stephen of Byzantium, were formed of stone; and Athenaeus states that they were sometimes made of wood. Such anchors held the vessel merely by their weight and by their friction along the bottom. Iron was afterwards introduced for the construction of anchors, and an improvement was made by forming them with teeth, or "flukes", to fasten themselves into the bottom.
Admiralty Pattern Boat Anchor
The Admiralty Pattern, "A.P.", or simply “Admiralty", and also known as "Fisherman", is the most familiar among non-sailors. It consists of a central shank with a ring or shackle for attaching the rode. At one end of the shank there are two arms, carrying the flukes, while the stock is mounted to the other end, at ninety degrees to the arms. When the boat anchor lands on the bottom, it will generally fall over with the arms parallel to the seabed. As a strain comes onto the rode, the stock will dig into the bottom, canting the anchor until one of the flukes catches and digs into the bottom.
The basic design of the boat anchor has remained unchanged for centuries, with the most significant changes being to the overall proportions, and a move from wooden stocks to those of iron. Since one fluke always protrudes up from the set anchor, there is a great tendency of the rode to foul the anchor as the vessel swings due to wind or current shifts. When this happens, the boat anchor may be pulled out of the bottom, and in some cases may need to be hauled up to be re-set. In the mid-19th century, numerous modifications were attempted to alleviate these problems, as well as improve holding power, including one-armed mooring anchors. The most successful of these patent anchors, the Trotman Anchor, introduced a pivot where the arms join the shank, allowing the "idle" arm to fold against the shank.
Handling and stowage of these mooring anchors requires special equipment and procedures. Once the anchor is hauled up to the hawse pipe, the ring end is hoisted up to the end of a timber projecting from the bow known as the cathead. The crown of the anchor is then hauled up with a heavy tackle until one fluke can be hooked over the rail. This is known as "catting and fishing" the anchor. Before dropping the boat anchor, the fishing process is reversed, and the anchor is dropped from the end of the cathead.
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