144 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



The blocks were constructed of rubble-stone masonry, set in 

 cement mortar, consisting of 1 part of cement to 4 parts of 

 sand. The size varied, averaging about 16 feet long, 9 feet 10 

 inches wide, by 8 feet 10 inches high. The average contents 

 would therefore be 53 cubic yards, equal to about 100 tons in 

 weight. The blocks were built in a specially arranged yard 

 above high water, each on a separate timber platform, or carriage, 

 resting on an inclined slipway. 



The slipway consisted of three longitudinal timbers, placed 

 about 7 feet 6 inches apart centre to centre, rounded on the 

 upper surface, and laid at an inclination of 1 in 16 feet 6 inches. 

 Bearing-pieces hollowed out to the same curve as the rounding 

 on the longitudinals were fixed to the under side of the plat- 

 forms, which were thus enabled to slide down the ways without 

 risk of lateral movement. The slip was 380 feet long and could 

 accommodate twenty-eight to thirty blocks. 



The blocks, when sufficiently consolidated, were removed to 

 the lower end of the slip to low-water level by means of endless 

 chains, which traversed the whole length of the ways, one on 

 either side of the block. 



After submersion, and when the tide had risen to a con- 

 venient height, the blocks were lifted by a barge, and transported 

 under water to the work. 



For lifting the blocks, T-headed rods were used, suitable 

 rectangular openings being formed vertically in the mass. The 

 heads, when turned, took a bearing upon pieces of hard wood 

 covered with sheet iron on the under side built into the block 

 about 1 foot above the base. 



For lifting the blocks, one of the hopper-barges employed in 

 depositing the rubble mound was used, the dimensions being 

 92 feet long, 16 feet 6 inches wide, with a draught of 1 foot 8 

 inches light and 4 feet 6 inches loaded. With the view of the 

 barges being used for this purpose, the hopper doors were so 

 arranged that when open, their lower edges did not project 

 below the bottom of the barge. 



To prepare the barge for lifting purposes, four baulk timbers 

 were placed on the deck in pairs over two of the hopper openings, 

 each pair of timbers having a clear space of 15 inches between 

 them, so as to admit of the free passage of the suspending bars and 

 chains. Each pair of baulks carried two winches fitted with pitch 

 chains, which connected up with the tops of the suspension bars. 



