Jetty Engineering

ENGINEERING, JETTY, CANALS and PORT OPERATION.

Early Dock Construction.

Some account of ancient har bour works will be found in the article HARBOURS. The earliest quays or wharves in the Port of London were probably the "hithes" of Saxon times. These were small cuts formed in the bank of the river, their sides being protected by rude piling. The word is still preserved in place names, such as Queenhithe. Dow gate dock and Puddle dock were ancient hithes but the word dock was not used in the sense of a closed dock until the i5th century.

There are records in 1434 of an elementary form of dry-dock at Southampton which seems to have been a narrow embayment in which a ship was placed at high tide and then, as the tide fell, enclosed by a temporary wall of clay, timber and brushwood built across the mouth. The first permanent dry dock, with primitive gates staunched with clay, was built at Portsmouth in 1496. This dock was large enough to take in the "Sovereign," the biggest warship of the time. Later the dock was enlarged and in 1523, the "Henri Grace a Dieu" of i,000 tons was docked in it.

In the Port of London no dry docks, other than those of the early temporary kind, were constructed until the middle of the i 7th century when there were dry docks with gates at Deptford, Blackwall and Woolwich, as well as at Chatham. One such was made at Bristol as early as 1626 and remained in use until 1687; and in 1656 a larger dry dock was built at Portsmouth.

Open tidal basins formed by excavating in the banks of a river, such as the Thames, and surrounded by wharves or primitive timber faced quays, had been in use since the 15th century, and these were sometimes known as docks. But the first closed wet dock was one at Blackwall, which is mentioned by Pepys in 1661; and at Dunkirk a wet dock of 42 acres with closing gates was made in 1686. An Act of Parliament was obtained in 1696 for the building of the Howland dock at Rotherhithe on the Thames, which was later absorbed in the Surrey Commercial docks.

The earliest wet dock at Liverpool, the Old Dock, was built about i 708-1 o—the exact date is uncertain—and was the pio neer of the great series of docks since constructed in the river Mersey. Bristol followed with a wet dock, begun in 1712 ; but at that port, the "Trench," an artificial cut forming a new channel for the river Frome into the Avon, with quays and wharves along its bank, was made as far back as 1247. This cut became the harbour of Bristol and from its quay Cabot sailed in 1497, on the voyage which resulted in his discovery of the mainland of North America. (For details of early history see The Development of Harbour and Dock Engineering, Sir C. R. S. Kirkpatrick's Ver non-Harcourt Lecture, Inst. C.E. 1926; and Belidor's Architecture Hydraulique, Paris, . ) It was not until the beginning of the 19th century that the era of systematic dock construction began which kept pace with the steady development of shipbuilding and maritime transport throughout the past century, and still continues to do so.

Dimensions of Shipping.

In designing new port works, it is essential to look forward to the possible future requirements of vessels. The necessity for such forethought is shown by the pro gressive increase in the size, not only of the largest ocean liners but, also, of cargo carrying ships. The "City of Rome," launched in 1881, was 5 6of t. long, 5 2 2 f t. beam and had a maximum draught of 2 72f t. ; the "Campania" and "Lucania," of 1893, measured 600 by 65f t. At the close of the I 9th century a cargo vessel of over roof t. in length did not exist : the limiting draught of the Suez canal was 2 71f t., and the largest merchant ship afloat, excepting those in the Atlantic trade, was 53o by 61 ft. and 28ft. draught.

The period of 15 years which preceded the World War was marked by great advances. In 191 o the largest merchant ship afloat was the "Mauretania" of 30,696 gross tons, 762ft. long and 88ft. beam; but, excluding transatlantic liners, the largest cargo carrying ship did not exceed 13,00o tons. In 1914 merchant ships far exceeding the dimensions of the "Mauretania" were either afloat or building. Harbour authorities, not only of those ports which accommodated the great transatlantic liners but in many other parts of the world, were engaged in increasing their facil ities to serve shipping of far larger dimensions than any which had hitherto used their navigable waters. During the war period harbour development throughout the world was arrested and con fined, in the main, to works of a nature essential to the objects of the belligerents.

Since 1914 no ships of greater dimensions than the largest of those built or building at that date have been laid down; and, although the advent of the 1 000f t. ship having a draught ap proaching 45ft. must be contemplated, it is unlikely that the next few years will see any great increase in the maximum dimensions of transatlantic liners. The dimensions of the largest of these, the "Majestic" (ex "Bismarck"), laid down before the war but not completed until 1921, are 56,551 gross tons, 915.5ft. length, zoo.' ft. beam, and maximum draught 38.9ft. The "Leviathan" (ex "Vaterland") has been loaded to 41 ft. draught. On the other hand a considerable increase is likely in the number of cargo-carrying ships of large capacity. In 1899 the largest general cargo vessel afloat had a gross tonnage of under 8,000 and was 47oft. in length. In 1928 ships of this class over 600ft. long and 7 2 f t. beam and of 18,000 to 20,000 tons gross were not uncommon. (See SHIP