Volume Five - The Age of Decline & Crass Stupidity - How do you lose a pontoon 115 metres long? . . .

The radial arm booms mooring the pontoon to the dockside had met with the burning torch shortly before the valves were opened to berth the pontoon at the bottom of the dock. I recall this fact clearly from conversations with other engineering staff at the works during 1969-70. I feel sure that the RSJs and associated pipework etc. would have been well worthy of reclamation.

We must remember that the pontoon structure was of a flat bottomed design 345’-11¼” (105.44m) x 75’-0¼” (22.9m). The total area of the underside of the pontoon is no less than 2,410 m2. Since she was capable of lifting ships with a draft of 18’–0” we can assume that there would have been a depth of water below the hull of at least 24’–0” (7.3m).

So, for the pontoon to sink to the mud and silt below it would have to displace approx. 17,625 m3 of water with say, a density of 1.025 which would require a displacement approx. 18,000 tonnes of water.

It is not known at what velocity or how long it took for its final dive but it is reasonable to surmise that the displacement of such a large volume of water from below the vessel, which is now free to move in one lateral, one longitudinal and definitely in only one vertical direction, would impart a velocity to the pontoon in a direction away from the quayside, thus propelling it outwards and backwards toward the centre of the dock.

The “wall”, its superstructure 305’-10¾” (144.5m) long x 27’–3½” (8.3m) x 8’–6” (2.6m) wide was situated along of the starboard side of the vessel. This structure was removed prior to her scuttling. It contained two boiler plants, pumps and ancillary equipment.

For stability, ballast would be required on the port side to ensure that the vessel was not listing and that she was also in trim from stem to stern. Remove the superstructure and we have a list to port. I cannot image that the ballast was adjusted prior to sinking but the list would have facilitated the displacement of water from below the hull at her starboard side thus imparting a greater thrust of water towards the quayside as she sank.