200 



RENNIE'S DOCKS AND HARBOURS. 



PART VII. 



and three minor engines for other purposes, such as 

 grinding mortar, working the pile-engine, and landing 

 materials from the jetty an application of steam power 

 as an economist of labour which Mr. Rennie was among 

 the first to introduce in the execution of such works. 

 The coffer-dam for the main entrance, and the excava- 

 tion of the Docks, were begun in the spring of 1802 ;* 

 after which time the works were carried forward with 

 great vigour until their completion on the 30th of 

 January, 1805, when they were opened with consider- 

 able ceremony. 



At a subsequent period Mr. Rennie designed the 

 present westernmost or Hermitage entrance lock and 

 basin, the former of which is 150 feet long and 38 feet 

 wide, with the cill laid two feet below low water of spring 

 tides ; the basin and main dock covering a surface of 



1 The locks were founded upon 

 piles driven firmly into the soil, with 

 rows of grooved and long-end sheet- 

 ing piles in front of and behind the 

 gates, in order to prevent the water 

 from getting under them. The cham- 

 ber between the lock-gates was formed 

 by an inverted arch of masonry 2 feet 

 6 inches thick, strongly embedded in 

 brickwork. The side- walls of the 

 lock recesses and chamber were 7 feet 

 thick, with strong counterfoots be- 

 hind at the proper intervals. The 

 whole of the locks and chambers 

 were built of fine masonry, com- 

 posed principally of hard blue sand- 

 stone from Dundee. All the retain- 

 ing walls of the basins and docks 

 were made curvilinear in the face, 

 drawn from a radius of 80 feet, the 

 centre being level with the top of the 

 wall, and the bottom being inclined 

 at the same angle as the radius. The 

 wall was of a parallel thickness of 

 6 feet, except three or four footings at 

 the back, where there were also 

 counterfoots 3 feet 4 inches square, 

 15 feet asunder. The dock walls 

 were founded generally upon a strong 

 bed of gravel, which rendered piling 

 unnecessary, and were built upon a 



flooring of beech and elm plank 6 

 inches thick. Under the front and 

 back of this flooring ran a strong cill 

 12 inches square, to which the planks 

 were firmly spiked. The walls and 

 counterfoots were built of brickwork, 

 the front, for 14 inches inwards, 

 being formed of vitrified pavier 

 bricks, and the remainder of good 

 hard burned stock, the joints being 

 a quarter of an inch thick in front 

 and three-eighths thick at the back ; 

 the whole well bedded in excellent 

 mortar made by a mill. There were 

 two through or binding courses of 

 stone, 14 inches thick in front, in- 

 creasing in thickness backwards ac- 

 cording to the radius of the front of 

 the wall. The whole of the locks 

 were furnished with cast iron turning 

 or swivel-bridges erected across them. 

 The works were generally done by 

 contract, but the locks, which re- 

 quired greater care, accuracy, and 

 completeness, were executed by day- 

 work, under the engineer's immediate 

 direction. [For further particulars as 

 to these docks see Sir John Rennie's 

 able work on 'British and Foreign 

 Harbours ;' Art. London Docks.] 



