Hedderwick: Marine Architecture (1830)


The Chains, by which the shrouds are attached to the side, consist generally of the three links; the uppermost being very large, is rounded and made of iron, 3-16ths of an inch thicker than the other links; it embraces the dead-eye, and is called the strap of the dead-eye. When this link is pretty thick at the top part, the dead-eye is not so apt to split with the strain. The link joining to this, at the under part of the channel, is long and narrow, and has its sides parallel to each other; it is called the middle link. The next link is made with a small bend the side way, so as to allow the lower end to lie flat against the ship's side when the upper one is in the direction of the middle link, pointing to the outer ege of the channel. The two sides of the lower link are set close together, at about 1-3d of its length from the lower end, where the opening is worked to a round of proper size to take in the chain-bolt, which is drove through it, and thus connects the chains and dead-eye to the ship's side. There is also a stout plate made to fit over the lower end of this link, with its upper and lower ebds fitting close to the plank, so as to take a bolt in the lower edge of the next plank, below that in which the chain-bolt is driven; this plate is called the preventer-plate, and is of great service in keeping down the outer end of the chain-bolt, which also passes through the upper end of the preventer-plate.

All the chain-work should be made of the very best iron, as they are continually exposed to very heavy strains by the tightness of the shrouds which are attached to the dead-eyes. A certain strength of shrouds is required, and the chains should always be in proportion to them. If the chains have a diameter of 1-8th part of an inch for every inch of the circumference of the shrouds, they will be sufficiently strong.

(Note. — In proceeding with this part of the work, it will first be necessary to know the size of the shrouds; therefore see subsequent article on the strength of ropes and dimensions of the standing rigging.)

Thus, for a 6-inch shroud, the diameter of the chains will be 6-8ths or 3-4ths of an inch, which is sufficiently strong for the strength of the ropes; but when we consider that the iron corrodes and wastes, it will be safer to make them a little stronger than the above proportion. The chain-bolts should be made of the best iron, perfectly sound, and well hammered round at the neck, to prevent the rust from taking so much hold of them. Their diameter at the outer end should be about 1-5th of the circumference of the shrouds attached to them. They should be made with a taper from the middle to the point, which allows them to go easily through the timber, with less risk of splitting than when they are made parallel. They should always be a little thicker at the neck than in the middle, which gives more strength, and fills up the rimming of the plank.

It has been observed, that the chain-bolts should always be thicker than perhaps what is actually necessary to bear the strain of the shrouds; for although a smaller bolt than the common might be sufficient to hold till the shroud gave way, yet as the frequent, heavy, and inconstant strains to which they are subjected by the rolling of the vessel, added to the regular strain of the shrouds and their bearing on a small portion of the timber, wears or bruises the fibre of the wood on the upper side of the bolt at the outside of the plank, the bolt-hole becomes wide outside; the bolt is then less supported, soon grows loose and leaky at the lower side; consequently it is better to have them a little thicker at the neck than is barely sufficient for their strength, according to that of the shrouds.

The above proportions and observations may be considered as applying more particularly to square-rigged vessels, and therefore it is necessary to give the proportions, and a few observations on those for one-masted vessels, such as smacks, cutters, &c. In the first place, it is evident, that in this rigg [sic] the weight of the masts, spars, ropes, and every thing therewith connected, is much greater in proportion than when the sails are supported by two or more masts, and having two sets of shrouds &c.; for, independent of the mast of smacks being so much higher, making the angle of the shrouds with it very small, it throws a greater strain on the shrouds to support it than if they were equally spread as a brig's shrouds. The leverage power of the sail is also increased; and having only half the number of shrouds, with half the angle of support, the strain on the shrouds of a smack is tripled in comparison to that on those for two-masted vessels. Now, the shrouds and chain-work connected with them must be in proportion to the strain to which they are subjected, and this being so much greater than for brigs, the former rules or proportions given will not answer both.

To illustrate the proportions requisite for smacks, or any vessels similarly rigged, I shall first state the dimensions of the shrouds and iron-works for a smack of 190 tons register.

A smack of 180 or 190 tons, has four 9-inch shrouds on a side.

Smack have only chain-plates, instead of the linked chains as used in brigs, for connecting the dead-eyes to the side.

The chain-plates are made of strong plate or bar-iron, of about 3 or 3¾-inch iron in breadth, and about 3 feet in length, from the upper part of the channel downwards; they are about 1½-inch thick, and tapered to 5-8ths of an inch thick at the lower end. Above the channel the breadth is worked to a round of about 2 inches in diameter, forming the hook, the point of which is truned inwards; it is also bent inwards close at the top of the channel, to stand with the inclination of the shrouds. The strap of the dead-eye is made of 1¾-inch iron; the crown of the hook of the chain-plate is 1¾ inch in diameter. The plate is bolted to the side with three 1 3/8-inch bolts.

Taking the above as a medium, the proportion of the chain-work of these vessels is as follows:—

1st, The size of the shrouds is found by the method pointed out in the article on the standing rigging. (See next chapter.)

2d, The diameter of the iron for the strap of the dead-eye is 10-8ths of an inch for every inch of girth of the shroud, calling the product eighth parts of an inch.

3d, The diameter of the back part of the crown of the hook of the chain-plate is 1-5th of the circumference of the shroud.

4th, The diameter of the chain-bolts, supposing three in each chain-plate, should be 9-8ths of an inch for every inch of the girth of the shroud, the product being considered eighths parts of an inch.

5th, The breadth of the plate should be twice the diameter of the hook, or about three times the diameter of the bolts.

6th, The thickness of the plate at the under side of the channel is 5-8ths of the diameter of the hook, or 1-3d of their breadth.

Peter Hedderwick: A Treatise on Marine Architecture, containing the theory and practice of shipbuilding, with rules for the proportions of masts, rigging, weight of anchors, &c including Practical Geometry and the Principles of Mechanics; observations on the Strength of Materials, Hydrostatics, &c. with many valuable tables calculated for the use of shipwrights and seamen; also the proportions, scantlings, construction, and propelling power of steam-ships. Illustrated with twenty large plates, containing plans and draughts of merchant-vessels from fifty to five hundred tons, with mast and rigging plans; plans and sections of a steam-boat of eighty-horse power; and eight quarto plates of diagrams, &c., by Peter Hedderwick.
Printed for the Author, Edinburgh, 1830. pp 324-325.

Transcribed by Lars Bruzelius

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