In February of 1982 the semi-submersible, the Ocean Ranger, was lost with all of its crew in a storm on the Grand Banks off Newfoundland. The Canadian Royal Commission that was established after the disaster contracted with two laboratories to conduct collaborative hydrodynamic model studies. These laboratories, the National Research Council of Canada (NRCC) in Ottawa and the Norwegian Hydrodynamics Laboratory in Trondheim, were asked to simulate the storm conditions on the night of the disaster and to investigate the behaviour of models of the Ocean Ranger. This chapter will (I) review the events leading up to the capsize, (II) describe the hydrodynamic and aerodynamic experiments conducted at NRCC and (III) summarize the results of the experiments and their input to the conclusions of the Royal Commission. The experiments on the Ocean Ranger were the first detailed model experiments on a semi-submersible conducted in Canada. These experiments have been a factor in the recent expansion of Canadian facilities and capabilities for model studies of vessels and offshore structures.
At 3.38 a.m. on the morning of February 15 1982, in a violent storm 315 kilometres off the south-east coast of Newfoundland, one of the world's largest sem-submersible offshore drilling rigs, the Ocean Ranger, disappeared from watching radar screens. In the morning rescue ships found only debris and inverted lifeboats. The Ocean Ranger had sunk to the bottom of the ocean with the loss of all 84 of its crew.
The Ocean Ranger was a modem semi-submersible vessel designed to drill for oil and gas through the bottom of the world's oceans (Fig 1) From the keel of its pontoons to the top of its working deck it was 46 in high Above the deck, the drilling derrick extended another 50 m. Its compartmented pontoons were 121 m long. The deck was supported above the pontoons by eight columns the four comer columns tapered from 11.6 m diameter at the pontoon to 11.0 m at the deck, the intermediate columns were 7 6 m diameter, tapering to 5 5 m The drilling draft at which the Ocean Ranger was working at the time of the accident was 24.1 m corresponding to a displacement of 39 405 tomes.
(Fig 1 is available in full paper) At the time of the accident, Mobil was operating three semi-submersible drilling units on the Grand Banks, fairly close together In addition to the Ocean Ranger, there was the Zapata Ugland of Norwegian Registry, 31 km North and the Sedco 706, 17 km to the North-East
On Friday, February 12, a weak disturbance began in the Gulf of Mexico. It strengthened as it moved North, the centre passing South of Halifax at 8.30 pm on Saturday. Earlier that day weather forecasts to the Hibernia vessels had predicted 60 knot winds and 7 m sea heights by rmd-day on Sunday.
