The Thistle SALM (Single Anchor Leg Mooring) was a tanker loading facility that allowed oil from the Thistle oilfield to be transported to land where a submarine export pipeline did not yet exist. It was also the site of the August 8, 1979 Wildrake diving accident that killed two divers. and the January 21, 1981 Stena Seaspread diving accident (non-fatal). Development In February 1975, Burmah Oil made the decision to develop the Thistle SALM. It was conceived by Exxon Research and Engineering of New Jersey, designed by Single Buoy Moorings, Inc. of Monaco, and built by Motherwell Bridge Offshore in Leith, Scotland. It cost $6.4 million to build, and in March 1977 it was set into position by divers from Sub Sea International. The SALM had three major components: a 182-foot upper section called the buoy, a 335-foot long middle section called the riser, and a hex-shaped gravity base which anchored the facility to the seabed to prevent it from drifting away. From head to toe it was 545 feet long. Two articulated “universal joints” allowed the buoy and the riser to pivot in rough water. During operation, the Thistle Alpha platform fed oil to the SALM through a pair of 16-inch pipelines. This hard piping ran up the base from opposing sides and terminated at the bottom of the riser near the first U-joint articulation. From that point the oil bridged the articulation through a pair of very thick 16-inch flexible jumper hoses, then continued up the riser through more hard piping, and over the riser-buoy articulation through another set of jumper hoses. From there, the oil flowed through product hoses to the shuttle tanker which was moored to the buoy. Damage The SALM was installed in March 1977, but did not go into operation until February 1978 when Thistle Alpha began producing oil. Then, on October 15, 1978, a pin-hole leak was discovered in some pipework on the inside of the buoy during a routine maintenance inspection. Preparations were undertaken to fix the leak, but poor weather conditions interrupted the repair work. Over the winter months the pin-hole leak developed into a split, and a crack in the 16-inch pipework outside the buoy allowed water and oil to flood the central trunkway. This caused the buoy to lose more of its buoyancy. The loss of buoyancy in turn caused the upper U-joint to go into compression which allowed