A Treatise On The Principles And Practice Of Dock Engineering

INITIAL COST. 467 could be placed upon an estimate for a slipway to accommodate modern ships of from 20,000 to 30,000 tons, with lengths of 600 to 700 feet, especially when the largest slipway in existence is one with a cradle of only 330 feet and a power of 5,000 tons. So, too, with graving docks. One at Newport (Mon.), built in 1890, cost £70 per lineal foot, or 10s. per square yard of internai cross-section below high water; another at Biloela, New South Wales, completed about the same date, cost £440 10s. per lineal foot, or 26s. per square yard of section ; for a third at Halifax, finisbed in 1889, the figures were £233 and 15s. 6d. respectively. No useful purpose, accordingly, can be served by attempting to fix the unit of expenditure. The kind of material (whether concrète, timber, brickwork, or masonry), the mode of construction, the nature of the foundation, the state of the labour market, and the cost of transport—all these conflicting conditions combine to render nugatory calculations based on existing data. The fluctuation in the price of iron and steel, more than anything else, influences the cost of a floating dock, but there are often special features to be taken into account. Not infrequently a site has to be specially prepared by dredging for its reception. Shore connections and approaches are required, more particularly for the type known as the “ off-shore dock.” Also for docks built in this country, to be located at Colonial or Conti- nental ports, there is the cost of freight or of towage and insurance. Herr Howaldt* of Kiel, estimâtes the cost of composite floating docks of wood and iron, designed on his system, at 110s. to 120s. per ton of lifting power, if built in the west of Europe, and at 170s. to 200s. per ton if built in the east of Europe. For docks altogether of iron, he estimates the cost at 180s. to 200s. and 230s. to 270s. per ton of lifting power, in the west and east of Europe respectively. Messrs. Clark and Standfield state “an all-round figure of £10 per ton of lifting power for floating docks of medium size.” At first sight it may appear that the cost of a light, hollow iron structure, built amid the conveniences of the shipbuilding yard, must inevitably be less than that of a masonry or concrète dock, involving a deep excavation, with expensive gates and other appurtenances. Such, however, is not necessarily the case. Undoubtedly, there are circumstances ot site and foundation which would render the construction of a graving dock an inadvisable, if not an impossible, proceeding, but it is not improbable that the same conditions would equally preclude the construction of such essential adjuncts to a floating dock as a jetty and a shipbuilding yard. These circumstances åre generally abnormal and, in the main, local con- ditions are favourable to either type. Speaking roughly, but upon a basis of experience, the cost of a graving dock constructed in this country, under normal conditions, to accommodate a vessel 700 feet in length, should not greatly exceed £200,000. The * Howaldt oii “Floating Docks,” Int. Nav. Cong., Dusseldorf, 1902.