HC Deb 07 July 1976 vol 914 cc592-3W
Mr. Hooley

asked the Secretary of State for Energy what hydrographic surveys were carried out for his Department before the first deep draught concrete production platform to have been built in the United Kingdom was towed from the Clyde to the Frigg field; what was the draught and value of this platform; who carried out the surveys and what hitherto unknown hazards were discovered during the surveys; and when the route had last been surveyed.

Dr. J. Dickson Mabon

Her Majesty's surveying ships carried out a total of four surveys to assist the safe passage of the concrete gas treatment platform TP1 from the Clyde to the Frigg gas field. The route passed through three critical areas and had to pass outside the 200 metre depth contour to the west of the Hebrides and north of the Shetlands since the area closer inshore had not been surveyed. In the three critical areas the following hazards were found:

  1. (a) Firth of Clyde to Ailsa Craig. Last surveyed by Her Majesty's survey ships in the mid 1960s—using sonar still generally used by Her Majesty's surveying ships—and by a French commercial company in 1975. The 1976 surveys by HMS "Hecla" and "Woodlark" showed a depth of 59 metres where 72 metres had previously been found by older methods. Less water was found in a small area close to Ailsa Craig with a least depth of 40 metres not found in previous Naval or commercial surveys.
    2. 593
  2. (b) North Channel. Last surveyed by Her Majesty's survey ships in the mid 1960s and by a French commercial company in 1975. HMS "Hecla", in 1976, confirmed shoal depths, widened the surveyed route in an area of difficult cross tidal stream and resolved previous inconsistencies.
  3. (c) East Shetlands Basin. Never systematically surveyed until HM survey ships "Hecla", "Herald" and "Fox" surveyed a route five miles wide and about 155 miles long from the 200 metre line north of the Shetlands to the Frigg gas field site. The bathymetry, whilst complicated, had no natural hazards for the platform, but 13 wrecks or other obstructions were located and examined, of which the most hazardous was the wreck of a World War I U-boat with a least depth of 90 metres over it.

This platform had a minimum draught of 36.5 metres during tow out to the Frigg field. Its value was in excess of £60 million.