The “Ailsa Craig” was a 120,000 DWT per permanently moored storage tanker known as a Floating Storage Unit (FSU) modified to handle the storage of the Emerald crude in longer wave motions of the North Sea. The vessel was converted and updated to meet the the UK continental shelf offshore regulations and was capable of storing 900,000 barrels of produced crude oil. The vessel had a sophisticated offloading oil transfer system and was fitted with a bow mooring point arrangement which
allowed for a 360° swing around the Single Point Mooring (SPM). The SPM consists of a tripod, clump block and
chains, all installed on the seabed. Produced oil is transferred from the FSU storage tanks to shuttle tankers through
a catenary-moored loading hose, astern of the FSU.