A Treatise On The Principles And Practice Of Dock Engineering

342 DOCK ENGINEERING. suitable composition for the bronze alloys of the varions parts as adopted at Liverpool is as follows :— Copper. Tin. Zinc. Pivot , 16 ozs. 2J ozs. Bail/ ........................................16 » 3J » Heel-hoop.....................................16 ,, 2 ,, J oz. The addition of a small portion of phosphorus is said to have the effect of preserving the surface of the metal from corrosion. Aluminium bronze, containing 90 parts of copper to 10 of aluminium, is a very strong alloy, which does not readily corrode, but it is very expensive. Manganese bronze is another compound possessing equal durability and strength. Steel is quite out of the question. It is speedily destroyed by the sait water. Plan of Base of heelpost inverted. Fig. 286. Fig. 287. Check chains from the mitre-post to volute or other suitable spring at the square quoin of the gate recesses, are a useful means of checking the impetus of a gate at the sill and preventing distortion. Examples of Dock Gates. It only remains to conclude this section with a few selected examples of wood and iron gates. Liverpool is par excellence the port of wooden gates. Throughout the vast system controlled by the Mersey Docks and Harbour Board, there is not a single iron gate in existence up to the time of writing. Several of the locks and entrances are no less than 100 feet in width, but they are all fitted with wooden gates. A pair of gates closing a 60-foot entrance bas already been treated. By way of exemplification of the larger structures, the plan and vertical section of a leaf of the Canada Lock gates are shown in figs. 288 and 289. The timber is greenheart, connected by galvanised iron straps and bolts. The principal feature of the gates along the great waterway leading to the Port of Manchester is their great solidity. Perhaps this is also their most essential requirement, for several serious accidents have already taken place in connection with them. For example, a few years back a steamer, improperly controlled, ran into a pair 01 gates and drove one leaf completely