An anchor is an implement for securing, or holding fast, a ship or other floating vessel to prevent it from drifting.
It is a heavy device which, when attached to the end of a chain or rope, automatically grips suitable ground on the chain or rope being subjected to tension.
The earliest anchors were stones or baskets filled with stones tied to small boats with ropes.
How Anchors Work
The simplest and commonest form of anchor consists of a straight bar having at one end a straight crossbar, called the stock, and at the other a pair of curved flukes. It is easy to see that, as the anchor lies on the ground, a pull on the chain tends to cause the fluke to dig into the ground. The object of the stock is to cause the anchor to take up the most favorable position when thrown to the ground in any way.
The purpose of the chain is to weigh the anchor when the cable is pulled. For this reason rope is very unsatisfactory as a substitute; and an anchor will hold a ship satisfactorily only if the chain cable is of sufficient length to allow of the anchor lying with its shank on the ground.
The greater the pull on the anchor (from wind or tide), and the deeper the water, the more chain must be let out from the ship. On the other hand, if the anchor chain is of excessive length, an anchor is more easily "fouled" when the direction of wind or tide changes.
The fouling is caused by the chain becoming wound round the upper or free fluke, whereupon the anchor is at once pulled out of the ground.
Large vessels no longer use this type of anchor, but one in which the flukes are swiveled on the shanks, there being as a rule no stock. Both flukes bite into the ground at once, and that they are induced to do so by a projecting shoulder, which turns their points downwards as the anchor drags along the ground.
The "ground tackle" consists of anchors, chain cable, and the necessary shackles and other fittings.
Types of Anchors
The common anchor is now used only on small boats and has largely been replaced even for this use by more modern types. It consists of a shank with two curved arms that end in spadelike points, called flukes. At the top of the shank is a ring for the anchor chain or rope. Just below it is a bar, called the stock, that crosses the shank. Its function is to turn the anchor so that one of the flukes can hook into the bottom.
Various types of anchor are used for permanent moorings, such as ferro-concrete blocks, long screws and mushroom-shaped anchors. The mushroom anchor is shaped so that it will sink easily into a muddy bottom but will resist being pulled out.
The grapnel anchor is used in small boats that anchor on rocky bottoms.
The sea anchor is an emergency device that is let out from the bow of a boat in a storm. It acts like a parachute to create a drag that keeps the boat headed into the wind and waves. This minimizes the danger of the boat's being swamped by waves breaking over its side.
A sea anchor is a drogue used by small craft to hold their head to wind and reduce drift in bad weather. Anchor buoys mark the position of an anchor on the sea-bed.
The stockless, or navy, anchor is the type used on large ships. It needs no stock because its flukes pivot on the shank and dig into the bottom together.
Admiralty pattern anchors, which were used for many years, have been replaced by Stockless types which are easily stowed in hawse pipes.
The Danforth anchor is famous for its holding power. It has broad sharp flukes that penetrate deeply into the seabed. The Danforth anchor has no stock, but it is stabilized by a short bar through the base of its flukes. The Danforth anchor is frequently used for oil rigs.
Another anchor used on small boats is the plow anchor, which has a single fluke designed to right itself and dig in as soon as it is pulled by the rope.
Merchant ships carry two bow and a spare anchor, the weight being governed by Lloyd's rules.
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