Here is the Pentagone semi-submersible Petrolia in the Cromarty Firth back in 2005. This rig type was constructed in large numbers back in the 1970s, mostly at shipyards in France. Internally they were very like the jack-ups of the same vintage with a central area containing the sack store the bulk tanks, a control space and a window overlooking the moonpool (Not likely to be allowed today). The five legs had a sort of bulbous space on the bottom. When the Alexander Kielland broke apart in the North Sea in 1980 (Full summary in my book "A Catalogue of Disasters") Norwegian rigs were required to remain afloat with one leg missing, and this rig had been modified to conform.

Photo taken by Victor Gibson in 2005 and posted here on 8th June 2018.

 

 

 
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