Volume Twelve - Pre-Victorian to the Present Day - further aspects - 1898 - A Clever Piece of Engineering . . .

The work being done on one pair of gates, the dams and the shoot were shifted so as to utilise them for the adjoining pair, when similar operations were carried out. The three months mentioned as being occupied by the work, included the time required for both pairs of gates, but as neap tide did not ebb low enough to clear the dam, not more than half the number of tides could be worked.

The available depth of water for draught of ships passing was reduced 2 ft. 6in. for the time being, but this, as it happened, did not stop any ships that wished to pass.

As shown in Figs. 1 and 2, the boilers were placed on the quay wall, but the pumps were submerged every tide. Water was let in by opening the sluices. The dams were double sheet with 12-in. timber. When it was required to move a dam it was shifted bodily, the clay being taken out so that it could be easily floated to its new position. The middle dam, however, remained in the same position throughout the job.

The entrance having been made good, the next point was to change the lock gates, which had been long in use. With sound outer gates it was possible to use the basin as a lock, and Mr. Riches accordingly first shifted the inner lock gates.

The manner in which this was effected is illustrated by Figs. 13 and 14, which show the method of slinging the gate and attaching the pontoon presently referred to.

Figs. 15, 16, and 17 are enlarged views of the sheerlegs ; the old rails used as ballast, however, are not shown in position in the latter views.

Figs. 18 and 19 show the method of getting the gates out of the water and up on to the land for repairs.

Fig. 20 shows a detail of the stop used when lowering the gate.

The method of operation was as follows:

First a pair of old egg-end boilers were provided and made into a pontoon. These answered the purpose admirably, as it did not matter so much if they were dragged under water through mishap or a rapidly rising tide, under which circumstances barges would have been sunk.