Thanks for that Martin, very interesting insight.
I have never really had much to do with oil rigs, closest I came was when I was a young bloke and working for Fremantle Dive Co. A local joint venture had built a rig in a big 'man made' lagoon right next to the coast not far from where I am now living.
The base of the rig was constructed first and chocked to the base of the then dry lagoon. When that part had been completed, they flooded the lagoon and floated out the rest of the assembly welding each components in place as they went. When we came in the rig was all but done but still fixed to the bottom of the lagoon.
Our job was to dive the 60' odd foot to the bottom of the lagoon and release the rig for a test float. Once released and floated, positioning of the rig in the lagoon was to be done via 4 x massive diesel winches that were evenly spaced around the edge of the lagoon.
We released the rig mid morning and they pumped the bilges and up she floated just as planned. However we spend the rest of the day watching a ridiculous tug-o-war take place between the 4 winches, the wind and the rig as they jockeyed to re-centre her in the lagoon and allow us to go back down and remove any debris from beneath the hulls before they set her back on the bottom and secured her ready for the pending launch.
The rig ended up winning the tug-o-war with one of the big kick-ass diesel winches being pulled from it's skids and onto it's side where upon it caught fire. The operator had jumped free of the winch as it tipped but had left it in gear, so the burning winch then pulled itself down the bank of the lagoon and into the water with the rig. Talk about a will to live, the winch may have put it's flames out but when you got no fins or tail and weigh that many tons your sure to drown if you go for a swim
Anyhow this was back in the 70's and the rig was called the Ocean Endeavour, have you heard of her? We eventually made the dive back down to clear the way and she was successfully launched a few weeks later when they re-floated her, knocked out the sea wall of the lagoon, and she made her way out into Cockburn Sound with the escaping waters of the lagoon. All pretty clever really.
So I can't say I have ever been 'on' a rig, but I have been 'under' one and I can confirm they are big suckers, especially when diving through the gap between the hulls and the bottom whilst she's sitting about 2' from the bottom. Those pipes seem to never end as you move from one side to the other and it's a very uneasy feeling as you swim along waiting for the arrival of light from the reverse horizon of such a massive steel pipe, good money though
Cheers
Kim
, sheep 
