Air lock diving-bell plant

[1][2][3][4] It was designed by Siebe Gorman & Company of Lambeth and Forrestt & Co. Ltd of Wivenhoe in Essex, who built and supplied it in 1902 for the British Admiralty.

The heavy harbour moorings have three chains extending out radially along the seabed from a central ring, each terminating in a large anchor.

[6] The bell was built by Siebe Gorman at their factory in Lambeth of steel plates, with cast-iron ballast, and its total weight was about 46 tons.

[10] It was electrically lit and fitted with a telephone for communicating with the air-compressor and lifting-winch rooms on the barge,[6] and a compressed air rock drill.

The wire ropes for lowering and raising the bell worked over pulleys mounted on a lifting frame superstructure erected over a well through the centre of the hull.

This company, established in 1788, had a long track record in the construction of specialized vessels and naval equipment for the Admiralty, as well as the War Office, Crown Agents, and the Royal National Lifeboat Institution.

[8] Her trials took place on the River Colne before September, and she was the "subject of great interest to the fish, numbers of which attracted by the light (from within the bell), swarmed around it".

[15] Shortly after its delivery, back home in England, the Essex Newsman reported: "Henry Turner, mariner, was charged with being drunk and disorderly at Wivenhoe, on 1 September 1902.

[6] An illustration of the plant was included in the influential 1909 Diving Manual by Sir Robert Davis, who was head of design at Siebe Gorman at the time.

The barge would then return to its original position and four men in the chamber would commence digging a hole big enough for placement of the anchor.

[5] Working in dank, dingy, pressurized conditions, the men would skim off a thin layer of mud and attack the rock, first with pickaxes; as the hole deepened, one man would hold a crowbar for another to swing a sledgehammer.

[17] Moorland was fitted with two 10-ton winches capable of heavy lifts from the seabed, and carried all the cables and anchors required for laying the moorings.