Quote:
| Originally Posted by big_si Ok, so at my stage of diving at present (Adv Nit + Dec Proc) I'm happily planning dives and planning my gas useage to rule of 1/3's for back gas and rule of 1/2's for deco gas so should I or my buddy have an issue then then other person is carrying enough gas for the other person to come up safely too. Obviously this is a form of gas being a team resource.
As dives get deeper and deeper and gas requirements get more and more then obviously these volumes get higher.
I understand that the expedition style diving would be based on more than a buddy pair and this overage of gas is distributed more amongst the team so you don't all need to carry a squillion cylinders, there would / could be support divers / deco trapeze.
I was just wondering at what sort of stage does this sort of planning start to become more necessary / sensible? And what sort of form does this planning take?
Would a simple example be something like diving in a 3, deco gas you would plan to use 2/3 and the extra 1/3 (x2 buddies) would be for the diver with the issue? Obviously a good buddy system focused / skilled team would be necessary for this technique to be usable. When would or Would you use a gas plan of this kind?
What are people's thoughts? |
The most deco / bailout tanks i will ever carry is three 10ltrs or Ali 80s. Past this I cant get to my equipment properly.
The point is reached where thats not enough gas to get to the surface. Once you reach this point you need to decide on the following three options.
CCR and teem bailout
CCR/OC and staged gas
CCR/OC and support divers.
Each option has its own inherent risks.
Teem Bailout: On a ccr you can carry teem bailout so two divers have enough gas to get one diver to the surface. The dangers are obvious.
1: Can you rely on your buddy to stick with you no matter what?
2: What if your buddy also has a problem
3: What if you lose your buddy and then have a problem
I used teem bailout on a 90m sea cave and had a unit failure at max depth. I went to bailout and exited the cave at max speed. My buddy for what ever reason decided not to follow me. He later said he couldn't see the point in both of us getting bent? Perhaps he forgot he had my gas. A subsequent down load of the dive showed my ballistic ascent rate to be 7m/min.
Had I not fixed the CCR problem id be dead now.
Ill never dive team bailout again.
CCR/OC and staged gas:
This requires the diver to make it back to the shot line/deco station. If not then the diver should have a yellow bag and wet notes attached to tell the chase boat what depth to drop the drop tanks to.
Again if on CCR it relies on buddy cooperation. The buddy also has three tanks on so at a push if your gas runs out you can go teem bailout and use the gas your buddies carrying to prolong the time waiting for the support boat.
This system requires careful planning good buddy skills and quality surface support.
On CCR you assume that the unit will work so the staged gas is for emergencies only. The temptation therefore is to stage one set of bailouts for a large number of CCR divers. The obvious down side is when you need the gas someone else has removed it from the line already.
On OC the risks of the system are greatly expanded. Now your option of buddy support is gone and both you and your buddy are under great stress if you fail to make it back to the shot. The chase boat is now a life or death support system.
Safety / Support Divers:
Again this is a return to shot dive. A system based on safety divers will always include a chase boat and drop tanks. QED all the previous problems related to chase boats will apply. Will they see your SMB will they be preoccupied dealing with someone else, have they rigged the drop tanks correctly.
The added issues with safety divers center around the quality of the safety diver. Why arn't they doing the dive? Have they not got the experience? If so do they understand your needs? Do they actually have the skills required to deal with any problems you might have?
As you can see there are a lot of risks as soon as you pass the point where you cant carry enough gas to get to the surface. For me that means you need to be on CCR as it gives you expanded options for bailout.
More bottom time to find the shot, SCCR, pure 02CCR and access to the gas your buddy is carrying. All that has to fail before you become reliant on OC
However no matter which way you look at it, its bloody dangerous diving.
ATB
Mark