My Stage Diving Strategy

[kensuf]

The math is really not that difficult to figure 1/2+2 but the advantages are big because you're transferring 15-25 cubic feet problem solving gas into your back, giving you options including the ability to jettison an empty stage earlier (making a speedier exit), or share that problem solving gas with a teammate.

Let's use North Florida standards (LP 85s, 95s and 104s for back gas) and standard AL 80s (stages) for our math. If you look at the pressure deltas for 1/2+2 versus 1/3rds for the realistic usable pressure ranges of an AL80 stage (~2400 psi to 3500 psi), you're looking at a shift of between 5 and 12 cubic feet of penetration gas from the bottles on your back to your stage. That means you're looking reducing the usable penetration gas from your back gas by either 100 psi or 200 psi, depending on starting pressure of the stage.

The switch points for 100 and 200 psi depend on the size of your back gas cylinders and the starting pressure of your stage bottle (for 104's, those switch points are 3200, 3400 and 3500 psi). But if you want to make it super simple, reserving 200 psi from your back gas to account for the gas used in a stage, you're guaranteed to be as or more conservative over diving straight thirds in the stage (as long as you're in 95's and 104's).

If you're using 85's and feel the need to stage, then my recommendation is first get bigger back gas cylinders and skip the task loading involved with staging, or reserve 300 psi from your penetration gas. You can get substantially more gas by going from 85's to 104's, and skip the entire task loading bit in the process.

There is some sense in carrying the stage bottle further after you've hit your drop pressure and shut the bottle down, you're effectively turning it into a safety bottle at that point, but you can accomplish a similar goal by shifting that emergency / problem solving gas to your back by using the 1/2+2 strategy.

Finally, I want to re-emphasize Kelly's point. The rule of thirds is for turds and is not conservative enough to be suitable for two person dive teams. It was designed around the idea of a 3 person team and an OOG diver getting usable gas from two different divers on the exit. Most people fail to recognize this. Additionally, that "1/3rd" is not just buddy sharing gas, but in reality it is problem solving gas. More gas on your back = more time to solve a problem.

 

[Jack Hammer]

I dive 1/2 + 200 with a reserve of what's used held back from usable BG. I prefer having more gas on me to allow extra time to deal with any unexpected circumstances. That extra gas also allows a deeper reserve to get back to a stage.

 

[rjack321]

what was the recent incident?

 

[CptTightPants21]

what was the recent incident?

There was a double cave fatality in Mexico.
Third post, page 4 has a summary of the information.

Two German divers drown at Gran Cenote Kalimba at Tulum

 

[rjack321]

I guess I thought this was <another> navigational mistake at the old snap and gap spot but I had a hard time, even sketch right with Kim's description, understanding what they did (or why)

My understanding is that when they returned to the bos chen jump they took the line down paso towards Grand which is the way the arrows point at that spot. If anything this is more of a discussion about should the arrow at the old snap and gap spot continue to point at Grand.

Having bigger reserves would have been good but the camera seems to have distracted them and this isnt a stage bottle issue its a navigational problem

 

[rddvet]

I guess I thought this was <another> navigational mistake at the old snap and gap spot but I had a hard time, even sketch right with Kim's description, understanding what they did (or why)

My understanding is that when they returned to the bos chen jump they took the line down paso towards Grand which is the way the arrows point at that spot. If anything this is more of a discussion about should the arrow at the old snap and gap spot continue to point at Grand.

Having bigger reserves would have been good but the camera seems to have distracted them and this isnt a stage bottle issue its a navigational problem

Agreed. Based on what I've read if its accurate, this was a navigational screw up. Stage really wasn't a factor.

 

[kafkaland]

I guess I thought this was <another> navigational mistake at the old snap and gap spot but I had a hard time, even sketch right with Kim's description, understanding what they did (or why)

My understanding is that when they returned to the bos chen jump they took the line down paso towards Grand which is the way the arrows point at that spot. If anything this is more of a discussion about should the arrow at the old snap and gap spot continue to point at Grand.

Having bigger reserves would have been good but the camera seems to have distracted them and this isnt a stage bottle issue its a navigational problem

I agree that it was likely a navigational error, but not at the Kalimba T (the old snap and gap). That's where they dropped their stages and never came back to. Also, that T is labeled exceptionally well. My best guess is that they turned left, instead of right, when they came out of Mutch's maze. I don't know how they marked their jump, but the permanent arrow their points to Grand, not Kalimba, as it should. So they should have reversed the arrow with a cookie or REM, and not just jumped off the arrow, but I have no way of knowing if they did. Still, they should have sufficient gas to make it to Grand or Ho-Tul. If their sidemount tanks were full at the Kalimba T (likely as they breathed down their stages to half-plus), they would turn in Mutch's with 3/4 gas, and out to the main line with maybe 1900 psi. If they turned mistakenly towards Grand, they would reach Paso de Lagarto with maybe 1000 psi, and then it's not far to Ho-Tul. But that jump at Paso de Lagarto is very long (70 ft) and if you already know at that point that you messed up your navigation, it's easy to see that someone loses faith there, turns around, perhaps checks out the jump to Lithium Sunset in an increasingly desperate attempt to find a way out, instead of making that very long jump. So if there is any change to the lines and markers, I wouldn't significantly shorten the Paso de Lagarto jump so that the continuation of the line is visible, and label it conspicuously like the Kalimba T and the Box Chen jump.

 

[rjack321]

If this were "my cave"...

The Kalimba, Bos Chen, Paso intersection would have large plastic markers on each leg. E.g.
"Kalimba line"
"Bos Chen this way"
"Paso Line, Grand Cenote 1,400ft" (or however far it actually is)

And the Paso to Grand jump would be within visual distance not around behind the big beehive shaped rock.

 

[boulderjohn]

If this were "my cave"...

The Kalimba, Bos Chen, Paso intersection would have large plastic markers on each leg. E.g.
"Kalimba line"
"Bos Chen this way"
"Paso Line, Grand Cenote 1,400ft" (or however far it actually is)

And the Paso to Grand jump would be within visual distance not around behind the big beehive shaped rock.

There was another recent (and highly suspicious) death in that area because of a diver getting lost. I believe the big gap is due to the theory that it is unsafe to have cave lines visible within a cavern zone, and since there is a nearby cenote, that qualifies.

I am not a believer in that theory. There was a thread a few years ago in the Cave Divers Forum about extending the cave line at Jackson Blue into the cavern area. The people opposing it simply repeated the theory that unqualified people entering the cavern area might be tempted to follow the cave line into the cave. The people supporting that idea listed about 7 total benefits, and they argued convincingly that it was actually safer to have the line there. No one opposed to the idea even attempted to refute any of the arguments in favor of extending the line, but their opinion still prevailed.

I believe that area would be much safe with permanent, well marked lines, but I have no expectation that will happen.

 

[rjack321]

There was another recent (and highly suspicious) death in that area because of a diver getting lost. I believe the big gap is due to the theory that it is unsafe to have cave lines visible within a cavern zone, and since there is a nearby cenote, that qualifies. .

The jump from the Grand/Ho Tul line onto the Paso line is well within the cave zone. There's no logical reason for this jump to be 75 or 80ft. If it were me I would be happy to T these two line together but that wont happen either.