Tuckunder:
I'm afraid I don't have any North Sea rig experience or knowledge so I'm really not at all qualified to answer your question. I also have to admit that I haven't read all 22 pages of this thread, just picked up on the last few pages
But I would still argue all the way down the line that it's quantifiably better to have a free swimming diver in a rescue chopper than not. It's just not necessarily possible to quantify it from the rescue reports. I'l give you another example:-
In about '80 or '81 another 771 cab went to find Simon Le Bon trapped inside his yacht ("Drum" I think it was called). The free diver went down under the upturned hull, shared his air and dragged the lad out. (Dreams of front row seats disappeared when a Duran Duran tee shirt turned up, as I remember!).
What would have happened if it had been a Crab machine?
(a) somebody else turns up and gets him out because he's lucky that the air has lasted another half hour = report summarises to "rescue was a success"
(b) somebody else turns up and gets the body out half an hour later, in which case the pathologist or coroner is unlikely to have the impetus to look into the comparison between time-of-death and time of helicopter arrival.
My point is that unless one of the helicopter crew has previous experience of working with free divers the report is unlikely to include the phrase ".....and we might have got him out if we'd had a free diver on board". It just doesn't come up on the radar if you've never had the benefit of it.
If anybody currently at 771 has access to the last few years of rescue reports I reckon they would find at least half a dozen lives saved every year in Cornwall alone where you could reasonably conclude that it was a free diver who made the difference. Anybody at 771 watching "Neighbours" right now with half an hour to spare????
P.S. Thanks Angelonawire, nice summary.