A Treatise On The Principles And Practice Of Dock Engineering

22 DOCK ENGINEERING. be termed the digital. It is illustrated in fig. 2. The suggestion emanated, in the first instance, from the late Thomas Stevenson, but the design in the figure embodies several important modifications of the original sketch, and includes an entrance scheme which has not, to the author’s knowledge, appeared elsewhere. The idea is that the dock is situated on the margin of a tidal river, or estuary, and the dual entrance, as explained in Chapter vi., is intended to permit of the dock being accessible at all stages of the tide. When the flow is up the river, vessels will enter by the upstream locks and depart by the downstream locks. Vice verså, when the tide is running out, incoming vessels will use the downstream locks, and those departing, the upstream locks. In this way the dock will be worked without intermission and without obstruction. It is assumed that the outer sills are deep enough to allow vessels to pass over them at low water. The scheme has been amplified so as to include all the features essential to a dock system. Graving docks of various sizes are arranged between the entrance locks, with ample intermediate space for ship-repairing dépôts. In order to have shoreward connection for these, it will be necessary for the locks to be spanned by movable bridges. The central portion of the dock is semi-circular in form, and designed to afford turning room for vessels up to 1,000 feet in length. There are also four utilisable berths, each 275 feet long. The branches, of which there are five, though irregular in form are all similar, and each provides quay accommodation in pairs of lengths of 1,000, 600, and 400 feet successively, together with an end berth of 350 feet. The indentations permit of ships overlapping, while at the same time berths are afforded for small craft of 100 to 120 feet in length. A further advantage of the indentations is that moored vessels are well recessed out of the way of those passing in and out of the branches ; in faet, provision is made for vessels being attended in their berths by rows of lighters on each side without obstructing the main waterway. The sides of the branches, generally, are lined with sheds, from 100 to 120 feet in width, of varying lengths, and of heights taken at two storeys, but capable of adjustment to circumstances. The sheds are recessed 40 feet from the edge of the quay, to allow of lines for quay cranes and railway trucks. These lines, as well as others at the rear of the sheds, are all in inter-communication by means of a circular i'ailway along the landward boundary of the estate, which is supposed to be connected with trunk lines leading to other towns. Special berths are provided at one branch dock for petroleum and coal, and at another for grain and timber. The petroleum berth has both tank storage and shed accommodation for barrels. The coal berth consiste of an open quay, laid with numerous sidings and furnished with projecting jetties for hoists and tips. Grain is received direct into warehouses, the face line of which is within 5 feet of the edge of the coping. Timber may be discharged into a single storey shed or on to a low quay, or it may be floated