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1799 - Dockyard Works

No. 2 Boathouse built.

Work continues to the South dock (No. 1 Dry Dock) (£25,000 being voted by Parliament). £3548. 0s. 4d.

March 11th. The first stone was laid to the invert arch for the entrance to the Great Ship Basin. (£47,680 voted by Parliament to carry on the great national works).

The new entrance to the Basin would be 64 ft. 9 inches wide at the top and 33 ft deep and was of a new and novel design, for Bentham proposed doing away with the traditional method of closing a dock or basin by using lock gates and substituting it with, what at the time was called the Green Land Boat. It was shaped similar to that named vessel in that it was pointed at both ends. It had a large protruding keel on the outside that ran through its centre and up to the top deck at each end. This keel was designed to sit in a grove in the masonry on the newly constructed basin entrance. The vessel would be towed into position and then seacocks would be opened to flood and sink the vessel into the groves of the basin entrance. The pressure exerted by the falling water level on one side or the other, due to the tide, kept keel in the grove watertight. The main advantage of this new system was in the roadway top deck that when sunk in position became part of the road, allowing horse and wagon traffic carrying considerable loads to cross it. Whereas, the old system of lock gates only allowed foot traffic. In terms of traffic movement around the yard this was a vast improvement. To remove the caisson, the seacocks were closed and men worked a crankshaft that operated chain pumps, all within the caisson that cleared the water from the ballast tanks and allowed the caisson to float. It is said that this operation took less than an half an hour. To day we know this invention as the Caisson. New visitors to the Dockyard also call it the Caisson but they soon pick up the old Dockyard word for it, which is pronounced Cassoon and that is exactly how Bentham spelt it when it was built in the dockyard. Since that time the world has copied the caisson and it can be seen in operation around the world.

21st December. 12 hp Steam Engine proposed and installed to drive dock pumps. It was an engine called “Sadler” after the man who invented it and who was said to have been on Bentham’s staff. It was first set to work at Redbridge and was the first steam engine erected and used in Hampshire (1795).

Works on the walls for the enlargement of the Basin with the new entrance from the harbour, together with entrances to the two new docks (No’s 2 & 3 Dry Docks) according to General Bentham’s plans £19039. 11s. 4d.