A Treatise On The Principles And Practice Of Dock Engineering

TIMBER. 147 Gates and Cloughs. —Greenheart, Jarrah, Mora, Oak, Pitchpine, Pine, and Fir. Deckings (for wharfs and bridges).—Greenheart, Oak, Teak, Elm. Venders. —Elm. Temporary Dams.—Pitchpine. Timbering for Excavations. —Pitchpine, Spruce deals, Greenheart sheet- ing piles. Graving Doch Blocks.—Oak, Birch, Elm, Pitchpine. As indicative of their comparative values in maritime situations, the following classification of timbers for shipbuilding purposes, by a committee of Lloyd’s, will be useful : — TABLE XIL Estimated Durability in Yeai's. Tiniher. 12 Teak, British oak, mora, greenheart, ironbark, sal. 10 Bay mahogany, cedar. 9 European Continental oak, chestnut, blue gum, stringy bark. 8 North American white oak and chestnut. 7 Larch, hackmatack, pitchpine, English ash. 6 Cowrie, American rock elm. 5 Red pine, grey elm, black birch, spruce fir, Englisli beech. 4 North American hemlock, pine. Greenheart is a product of British Guiana and the north coast of South America. It is a wood of extreme hardness and durability, with a colour ranging from green to black. Its resistance to crushing is enormous, but it is very brittle and splits under the least provocation. Particularly is this the case during the months of April and May. Great care is therefore required in working it, and when a log is about to be sawn in two, it is often advisable to bind it on each side of the proposed cut with chains and wedges. The wood has a very fine grain and exhibits no distinct annual rings. It is very heavy, ranging from 62 to 75 Ibs. per cubic foot, so that it does not float in water. It contains an essential oil which is very poisonous, and which apparently confers upon it some immunity from the attacks of sea-worms. The evidence on the last point, however, is not conclusive. Greenheart is obtainable in logs from 12 to 24 inches square and up to 70 feet in length. Mora is a light red wood with similar uses to greenheart and is a native of the same district. It is very tough and close-grained, difficult to saw and split, and extremely durable. It can be obtained in logs 18 to 24 inches square and as much as 100 feet in length. Purpleheart, another neighbouring tree, is also noted for its qualities of durability and strength. It is hard and close-grained, and its colour is