Metal Fastenings.

168. Metal fastenings consist of either copper or iron, Copper is used below the water, and to about two feet above its surface, and at the bows all the way up; and iron in the remaining part of the upper works. Formerly, ships were fastened with iron throughout; but thus species of fastening, after the bottoms of the ships were coppered, was soon destroyed, and though great pains were taken to prevent the communication of the two metals, still oxidation took place very fast, when subject to the action of salt-water, and the iron was soon destroyed.*

169. Ships seldom have their planking entirely fastened with metal; but when this is the case, then only ships built of fir and a small class of vessels; each strake is then fastened wither double or double and single, with dump metal bolt nails, commonly so called, or with nails, with one through-bolt placed in about every fourth timber, instead of the nail or dump-bolt, driven on a ring and clenched. The butts of the planking, in metal fastened ships, are secured in the same way as those with treenails, excepting that there is a nail or dump-bolt in the butt, instead of the treenail.

170. Treenail fastenings will better resist any transverse strain than metal, according to the present proportion of the diameter of the bolts with the treenails; but the metal will better resist the direct strain or separation; therefore, if the treenails are used in numbers, as the bolts are in treenail-fastened ships, and bolts or screws the same as treenails, there is no doubt of increased strength and greater durability; for, since the resistance to separation is the same, but the fibres cut off by the fastening less, the strength must be increased, and the greater the number of joints of wood and wood, not in close contact, the greater the exposure to decay.

* A much greater degree of oxidation goes on when the iron fastenings are subjected at the same time to the action of salt-water and to that of the acids contained in the oak, than when exposed only to the oxygen of the atmosphere, or in fresh-water; but an active galvanic arrangement is produced, and oxidation goes on still faster when the bottom is coppered, and there are iron fastenings; because then there are two metals possessing different degrees of oxidability, combined with a fluid (fresh or salt water) that is capable of oxidating either.
John Fincham: Outline of Ship-Building in Four Parts.
Whittaker and Co., London, 1952. Part II, pp 42-43.

Transcribed by Lars Bruzelius

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