|A few notes on Timber - as used in ship building. |
The Timber chiefly used in the construction of a ship is oak, elm, fir, teak, larch, and mahogany. Timber is purchased by the load, a measure which contains 40 feet of rough timber, averaging in weight about one ton. An 80-gun ship consumes as many as 2000 trees, averaging about two tons each.
Timber is divided into three sorts, viz., square, which is the full size of the tree, having only its sides squared off ;thick stuff; which is square timber cut into different thicknesses from 4½ inches to 10, but the whole depth of the tree; and plank, which runs from 4 inches down to 1½ ; all under that size being called board.
Deals occur in lengths of 10,12, and 14 feet, varying in thickness from 3 inches to ½ inch, and averages 9 inches in breadth.
Those which are ½ inch thick, are flat deals; 1¼ inch are whole deals.
Kyanising and Burnettising are somewhat similar processes, by which timber, canvass, and cordage are so readily seasoned as to be preserved from the injurious effects of dry rot, mildew, &c., and premature decay.
In the former of these, the article is steeped for a certain length of time in a solution of corrosive sublimate and water. In the latter, as used in Her Majesty's dockyards, canvass and cordage are immersed for 48 hours in a solution of chloride of zinc and water, in a wooden tank, in the proportion of 1 pound of the chloride to 4 of water. Timber is placed in a wrought iron chamber, which contains about 20 loads at once; and after the air is exhausted from both timber and chamber, by means of an air pump which is worked by a steam engine, the solution is forced into the timber by a Bramah's forcing pump, which exerts a pressure upon it equal to 150 pounds on the square inch for eight hours.
Unless wood is previously well seasoned, to char or paint it accelerates decay by preventing the natural escape of the juices; seasoning requires from two to eight years.
The difficulty and expense involved in procuring suitably curved timber for ship-building purposes, as well as the labour and waste incurred by "conversion," seem about to be diminished by timber-bending machines. In these, straight timber, having gone through a process of steaming, is bent into the desired form; not only increasing its value, but economising time, and avoiding that impairment of strength which is consequent on cutting wood against the grain. We are told, for instance, that in one of these machines a piece of straight oak, 14 feet long and 16 inches square, whose value is about £3., after being bent into the requisite angle is enhanced to three times its value, and that ten such pieces may be thus shaped in as many hours.
MECHANICAL PROPERTIES OF MATERIALS USED IN CONSTRUCTION - TIMBER
Timbers are joined; together by scarphing, morticing, halving, dovetailing, &c. and when great strength is required, it is usual to make use of coakings, bolts, and iron bracings.
The strength of timber is variable, being affected nut only by its place of growth, but degree of seasoning. Trees that have been grown on mountainous districts are stronger than those grown on plains. Roots and trunks are stronger than branches.
Source : A Manual for Naval Cadets By John McNeill Boyd c. 1857.
^ back to top ^