Anchor (Gr. Lat. anchora, Ger.
Anker), a metal hook of suitable form and of sufficient weight and strength to enable a ship, by means of a chain or cable attachment, to lay hold of the bottom, and thus remain fixed in any desired position. The form of the anchor has undergone but slight modification since the time of Anacharsis, the Scythian philosopher, about 594 B. C. Before him anchors with one arm or tooth had been a short time in use, but he first added the second. The later Greek anchors were of iron, but originally they consisted of large wooden pipes filled with melted lead. In the heroic times of Greece, large stones were sunk into the water by ropes to hold the ship; and a little later bags of sand and baskets filled with rocks were used. Every ship was supplied with from four to eight anchors. The largest of them was termed the sacra, and was only used in times of great danger; hence the proverb, sacram anchoram solvere, to fly to the last refuge. The Chinese anchors, now as in ancient times, are only crooked pieces of heavy wood. - With the exception of Spain and certain of the South sea islands, where copper is occasionally employed, the metal used in the construction of anchors is the best of wrought iron.
The form of the common wrought-iron anchor, with the manner in which it "lays hold" of the sea bottom, may be best understood by a reference to fig. 1. It is evident from the direction of the strain that any forward movement will cause the lower fluke and arm to be buried still deeper in the earth. Anchors are called solid or ordinary when the shank and arms are wrought into a body; they are called portable when they can be taken to pieces. Each part of an anchor has a distinct name. The shank or the central part of the instrument is a round or octagonal bar of iron tapering toward one end, where it becomes square; the arms are two curved pieces projecting from the heavy end of the shank at right angles with it, and in opposite directions; the stock is a transverse beam, of wood or of iron, fastened to the square end of the shank at right angles with it and with the arms, and serves to cant the anchor when the arms fall on the bottom in a horizontal instead of a vertical position; the square is the square end of the shank, which at the extreme end, just beyond the place where the stock is fastened, is bored through for attaching the shackle by means of a pin; the shackle is a ring, by means of which the cable or chain is attached to the anchor; the crown is the extreme end of the shank, or the external part of the arms, on which the anchor falls when let go in a vertical position; the palms or flakes are parts of the arms, of a shield-like form, which arc near their extremities, and constitute the holding surface of the anchor.
The angle of the face of the palm with the shank is 51°. The arms extend from the shank in a curve the outside radius of which is 35. That part of each arm which sustains the palm is called the blade, and the part which projects beyond the palm, and has to open the ground, is named the point, peak, or bill. If 100 be taken as the unit of length for both the stock and shank, then 40 will represent the average length of each arm from the crown to the bill. The relative weights of these several parts may be roughly estimated as follows: The shank, 5/10 of the whole; each arm, 2/10; two palms, 1/10; stock, 1/5; shackle, 1/15. When an anchor is let go from the ship, it falls vertically through the water, and, should the bottom be an even one, the crown will strike first; but a rocky bed may compel one of the arms to receive the full force of the fall, for which reason any cross section of an arm should represent an ellipse, with the line of its greatest diameter vertical to the point of probable contact, thus receiving the heaviest strain in the direction of the greatest strength. After striking the ground the anchor falls sideways, the arms lie flat, and the stock rests on one end.
A length of chain proportional to the depth of water, and so calculated that the hardest pull of the vessel will not lift it entirely from the ground, is permitted to run out. The action of the current or of the wind on the vessel soon makes her exert a traction on the chain, and this lying on the ground pulls down the shackle, bringing the stock flat on the bottom, and the arms perpendicular to it; this is called canting the anchor. The longer the stock and the shorter the arms, the less force will be required to perform this operation; hence in all anchors the stock is longer than the arms. After canting, the anchor will be dragged or will hold. Quick holding depends on the sharpness of the bill and the angle of the palm with the ground. For "weighing anchor," the chain or cable is taken in by aid of a capstan, till the bow of the vessel is brought over the shackle; here an increased pull is necessary to trip it, and the anchor is raised to its place. The property of quick tripping depends on the curve of the arm, and on the angle of the palm; they have to be such that when the shackle is pulled up vertically, the bill cuts open a short curved circular way in which the palm and arm follow.
When the palm is out, the ground is torn open by the arm, which is comparatively sharp, and acts with a more advantageous leverage than the palm would. More than two thirds of the ruptures of anchors happen in the operation of weighing. We have said that the arms ought to be thicker in the dimension parallel to the shank, to resist shocks against rocks. The same is necessary to resist the strain in tripping. The shank is exactly in the same circumstances, and has to be thicker in the direction of the arms, and to decrease in size from the crown to the square. Though theory indicates rectangular sections as best for the arms and shank, they are in practice made round or oval, or at least the angles are much rounded. This has been found necessary for the preservation of cables, which often take a turn around the anchor when the vessel changes its direction with the tide or wind. - The forging of an anchor requires the constant superintendence of an educated engineer, while the workmen should be chosen with an eye to their skill and judgment, as well as muscular strength.