A Treatise On The Principles And Practice Of Dock Engineering

304 DOCK ENGINEERING. 3. Initial Cost.—Generally speaking, gate materials may be placed aa regards cost in the following order, commencing with the most expen- sive :— Greenheart, iron, oak, and creosoted pine. The exact proportion, of course, depends on current prices. At the présent time, greenheart logs of large size can hardly be obtained for less than 3s. 6d. to 4s. per cubic foot, and for great lengths, the price will run as high as 5s. or 6s. Under such circumstances, greenheart gates, for entrances ranging between 60 and 100 feet in width, may be expected to cost, under normal conditions, from 40s. to 50s. per superficial foot of gate. Oak may be priced in this country at 3s. to 4s. 6d. ; red pine at 2s. 3d. to 3s. 3d.; and pitch pine at Is. 3d. to 2s. 3d. per cubic foot. Gates of these last named timbers will be relatively cheaper with a corresponding decrease in durability and strength. The cost of iron gates has fluctuated somewhat. In 1857 the Dublin graving dock gates cost 46s. 9d. per square foot of gate area, but the figure is a high one, and due, no doubt, to special and, possibly, local circumstances. The price of iron was certainly inordinately high about the year 1873, for the original intention of fitting the Avonmouth Lock with iron gates was abandoned in favour of wooden gates for that very reason. Iron gates constructed at Antwerp in 1873-74 cost 46s. lOd. per square foot. But in 1879, when estimates were obtained for a pair of gates at Dunkirk, the tender for ungalvanised iron had fallen to 21s. per square foot, and for galvanised iron it was only 26s. per square foot, including in both cases four coats of paint. About the same period Mr. Harrison Hayter, Past Pres. Inst. C.E., stated in the course of a discussion,* that he was in the habit of estimating the cost of wrought-iron gates at from 30s. to 40s. per square foot. Within the succeeding decade a pair of steel gates was erected at Limerick Dock entrance for 25s. 4d. per square foot. At the present time, allowing for market fluctuations, a pair of iron or steel gates might be expected to cost from 25s. to 30s. per square foot, with a slight margin in favour of steel. On the Manchester Ship Canal, two pairs of gates were recently constructed for the same lock—one pair of greenheart and the other of steel. A statement (Table xxiv.) of their actual cost will be useful, if only as affording a basis of comparison between the two materials.f From particulars of the cost of seventeen gates of oak for small entrances at German seaports, ranging between 25 and 45 feet in width, Messrs. Brandt and Hotopp have deduced 15s. per square foot as the average cost of such gates.J They further state that “ the proportion in the cost of wooden gates to that of iron or steel gates may, under present conditions, be taken as 4:5, within the limits fixed for comparison.” * Min. Proc. Inst. C.E., vol. lv., p. 72. t Hunter on “Lock Gates of Greenheart and Steel,” Min. Proc. Ninth Int. Nav. Cong., Düsseldorf, 1902. Î Brandt and Hotopp on “Iron, Steel, and Wooden Gates,” Min. Proc. Ninth Int. Nav. Cong., Düsseldorf, 1902.