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BALDT, Inc.
801 W. 6th Street
Chester, PA 19013
phone: 610-447-5200 fax: 610-874-8599
chain@baldt.com
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A History of Anchors from a 1902 Scientific American article
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This interesting article, from a 1902 Scientific American Supplement, chronicles the technical development of anchors between 1800 and 1860
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Anchors in the 1700's
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The ships' anchors in general use, up to the beginning of the last century, consisted of a long, round, iron shank, having two comparatively short, straight arms, or flukes, inclined to the shank at an angle of about 40 degrees, and meeting it in a somewhat sharp point at the crown. In large anchors, the bulky wooden stock was built up of several pieces, hooped together, the whole tapering outward to the ends, especially on the after or cable side.
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Early 1800's: A Simple Change To Anchor Design
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About the beginning of the last century, a clerk in Plymouth naval yard, Pering by name, suggested certain improvements, the most important of which was making the arms curved instead of straight. At first sight, this simple change may seem of little value, but consideration will show that this is not the case. The holding power of an anchor depends on two principal conditions, namely, the extent of useful holding surface, and the amount of vertical penetration.
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Curved Arms Over Straight Arms
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The old-fashioned straight arm retained a more or less horizontal direction in the ground, until the leverage derived from the effective length of shank became very much reduced. Again, with straight arms there exists considerable resistance to penetration, because the entire anchor must move longitudinally before the arm can bury itself; but with curved arms the weight alone of shank and upper arm suffice to bury the anchor in soft bottoms without longitudinal displacement. This last consideration, which has some bearing in the case of modern stockless anchors with two blades, was again referred to when dealing with the Martin's type of anchor.
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Technical Dynamcis of the Design Change
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Some inclinaton of the arm must have, in order to bring about penetration; yet the more at right angles to the shank, the greater the penetration. These two opposing conditions are reconciled by curving the arm to the arc of a circle having its center in such a position that the radius of the curve is about a third of the length of the shank. Two minor advantages also accrue. During the process of tripping or breaking out the anchor, the buried arm continues its curved path in the ground until the shank is nearly vertical and the pea ready to emerge with the least possible resistance.
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Why Change Was Necessary
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The latter quality is necessary on account of the nature of ordinary sea bottoms, the surface layers of which are generally less tenacious and resisting than is the ground a short distance below. Now the measure of penetration, and also, to a limited degree, that of useful holding surface, is the vertical distance from the lower portion of shank to the pea, or extreme end of the arm, when fully buried. The distance evidently depends on the length and on the inclination of the arm.
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Trotman's Anchor Reigns Supreme in the Mid-1800's
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A great numer of patents for anchors were taken out prior to the great exhibition of 1851, and public attention having been called to the models there shown, in the following year a committe was appointed by the admiralty to report on the qualifications of anchors of the various kinds. Practical trails were then instituted and, as a result, Trotman's anchor took the highest place out of eight competitors, Roger's anchor being second on the list. Some of the tests to which the anchors were of doubtful value, such for instance, as "facility for sweeping." Nowadays, at all events for deep ships in shallow harbors, it is considered an advantage for an anchor to offer as little obstruction as possible above the ground. In this particular test, as also in some others of small importance, Trotman's anchor was handicapped as against those of ordinary form, yet came out first owing to its undoubted superiority in holding power.
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1831-1860: Chain Cables & The Admirality Anchor
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In the year 1831 chain cable began to supersede the hempen ones, with the result that the long-shanked anchors hitherto in vogue were no longer necessary, and anchor with shorter shanks and with heavier and stronger crowns gradually came into use. In consequence of these changes, a commission was appointed in the year 1838 to inquire into the holding power of anchors, and a principal result of their labors was the adoption of the so-called admiralty pattern anchor, which continued to be used in the navy up to 1860. The invention of the steam hammer in 1842 made the welding of heavy masses of iron a comparatively easy and reliable process, so that from this time onward the strength of anchors fully kept pace with that of the chain cables which had come into general use.
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