Deco on an umbilical compared to OC?

[Noel Johnson]

Good morning all,

I have a quick question, which is possibly stupid, but as I don't know the answer for sure I'm going to ask it anyway.

I have been watching the new series of the Sea Hunters on Nat Geo and the episode based on the wrecks of the Dardanelles (sp?) near the Gallipoli peninsula raised a question for me.

On the first 2 dives Mike Fletcher went down in a stage, with a hard hat and umbilical to the wreck. As it was deep he was on mix which was controlled by the operator above him (in this case his son Warren (I think)) When he began to ascend he was put onto nitrox, again by the operator, at the first deco stop. However he was brought to the surface instead of doing the long stop on o2 and put in the vessels recompression chamber for a couple of hours. This was shown in the episode twice.

Later on in the program, he and his son do a similar wreck round the corner at the same depth, but on OC. This time no recompression chamber was needed as they did all the deco in the water.

I'm presuming that heavy boat traffic was the reason for using the deco chamber instead of in water deco. Does this sound correct or is it impossible to provide high 02 percentages through an umbilical?

As I said, probably a daft question so if it is, sorry.

[zepp]

can supply anything through umbilical, but yes it was probably the heavy traffic for the reason to do one inside the chamber...or to make the program more interesting

[BJ]

See Bikini Atoll diving or look at: Bikini Atoll- April 2002 - DIVERNET from Diver Magazine

There are also very strong currents in the Dardanelles - enough to make t difficult for a WW1 era submarine to make progress.

See: The second Gallipoli disaster

[wolf_diver]

could it also be that in the first dive that they where diving surface suppled and the deco and dive profile for what is in effect a commercial dive means less bottom time, faster ascent rates and if slow on the ascents (IE not in lifting cage) time & tables changed and on surface deco undertaken. (so he might have made a boo boo ) open circuit gives more freedom and its easy to do in water deco under the bag, just more failure points.

[The complete goggler]

I doubt that a boo-boo occured - there's far too much experience involved. The reason for comitting to surface deco (SurDO2) will most likely be that the bottom time was in fact 'greater' than that acheivable on scuba - as the vast amount of gas available on suface demand makes this possible. This would lead to a fairly extreme deco profile - one which you wouldn't want to complete in-water in a shipping lane. Depending on which tables they were using DCIEM or US Navy there most probably was an O2 stop in-water - this is usually the last stop (Jeese it's nice when that warm gas comes through).
Once a diver is blown-down in the DDC you obviously have ultimate control of his wellbeing - something you don't have in the water.

Edit here:- Another reason for the two differing dives is that there may well have been only 2 umbilicals available - so when Mike wants to dive with his lad for continuity they'll be on scuba while the cameraman works on SD.

[NotDeadYet]

The boats I used to use at Key West Diver had O2 supplied by 2nd stages on umbilicals to 6m. It was a brilliant system. I've also used it in France with some French cavers. They just left a j-bottle of O2 on the surface and strung an umbilical down to 6m. I've got 20m regulator hose in my garage.