Transocean 3

Rig:

Transocean 3

Date:

02 Jan 1974

Location:

UK Continental Shelf

Operator:

Mobil North Sea Ltd.

Summary

Built in Hamburg, Germany in 1973 for the Transocean Drilling Company, the Transocean 3 rig was reported as a 'special self-elevating semi-submersible design', modified for use in the North Sea. Late-December storms in 1973 prevented the new rig from being moved to its first drilling location for Mobil, so the rig was anchored in 342 feet of water about 100 miles east of Shetland.

Between 29 Dec 1973 and 01 Jan 1974, the rig suffered progressive structural damage resulting from the storm conditions, leading to the evacuation by helicopter of 38 of the 56 crew at around 1800 hours on 01 Jan 1974. The remaining 18 crew were then evacuated by 2300 hours on 01 Jan 1974. The crew were transferred to the nearby Transworld 61 and Transworld 58 rigs. Four tugs were on stand-by to tow the Transocean 3 to Norway for repairs, but continued bad weather sank the rig in the early hours of 02 Jan 1974 before this could be performed.

HSE documents from the UK state that a jackable leg broke away from the machinery house, leading to the subsequent capsize and later sinking of the vessel. Weather conditions at the time were winds of 21m/s with waves of 6m. A later report for the Department of Energy concluded that the failure was caused by the inadequate performance of rings of wedges which were used to transmit bending movements between columns and cross-girders (location not mentioned, presumably on the legs - editor).

Sources:

The Times (UK): 02 Jan 1974 'North Sea rig sinks after crew taken off'
The Times (UK): 20 Jun 1975 'Structural defects blamed for loss of rig'
HSE: Review of issues associated with the stability of semi-submersibles PDF document