Anchors

An anchor is a heavy object, often made out of metal, that is used to attach a ship to the bottom of a body of water at a specific point. There are two primary classes of anchors—temporary and permanent. more...

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A permanent anchor is often called a mooring, and is rarely moved; it is quite possible the vessel cannot hoist it aboard but must hire a service to move or maintain it. A temporary anchor is usually carried by the vessel, and hoisted aboard whenever the vessel is under way; it is what most non-sailors mean when they refer to an anchor. A sea anchor(q.v.) is a related device used when the water depth makes using a mooring or temporary anchor impractical. The hole through which an anchor rope passes is known as a hawsepipe.

An anchor works by resisting the movement force of the vessel which is attached to it. There are two primary ways to do this — via sheer mass, and by "hooking" into the seabed. It may seem logical to think wind and currents are the largest forces an anchor must overcome, but actually the vertical movement of waves develop the largest loads, and modern anchors are designed to use a combination of technique and shape to resist all these forces.

An interesting element of anchor jargon is the term aweigh, which describes the anchor when it is hanging on the rope, not 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).

Development

The earliest 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. It simply works. 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.

A simple anchor using a pair of wood arms under a rock mass is a primitive anchor which is still in use today. The wood arms are pointed to penetrate the bottom, and the mass will overcome normal movement forces. Together they comprise what may have been the first successful attempts to hook into the seabed and use the strength there to prevent a vessel from moving. Almost all future anchor developments combine these two elements—a penetrating point and a reasonable mass.

In the western world the vast majority of anchors worked on the concept of the grappling hook—multiple points on arms such that at least one will be aimed toward the bottom. Suddenly the concept of the stock, a bar placed perpendicular to the hooking arm at the other end of the shank which would roll the anchor over so the point would penetrate the bottom, was developed and within a single century became the standard anchor type.

Read more at Wikipedia.org