Stage planning in caves

[RTodd]

So somewhere around 4 stages it gets to the point where you might as well not even bother using backgas (from AL80 doubles). Maybe 5 stages for bigger backgas tanks.

So I think I understand the general progression from dives where using stages + "1/3" of backgas is plausible/logical (a couple stages) to the point where backgas is all reserve (alot of stages).

Thanks fellas

You guys are focusing on thirds and missing a very important concept here. Once you are doing dives on two or more stages, the nature of the dives generally dictate all of the backgas is a reserve. For newer divers with relatively high consumption rates this might not be as intuative. But, once you have any business using 2 plus stages the bottom times they will give you is significant.

Also, swimming with two stages isn't really that much fun and trying to do it with more than two is really just a bad idea. So, for discussions of more than two stages should be assumed to include scooters. At this point you are at a level of diving where 1/3rd is completely indequate to cover the amount of gas you might need to get out.

If you are ever unfortunate enough to see a stressed buddy have to go to his 120s back gas reserve at 285', you will be amazed how much gas gets used compared to the relaxed sipping of a stage while scootering in on the entrance. Answer, if it is true gas loss issue of the stage and breathing rate has spiked - all of it.

 

[rjack321]

(There is the obvious caveat of placing safeties on long exploration dives where back gas isn't enough of a bailout but this was not being discussed.)

So its somewhere around 6 or 7 stages where backgas is now no longer adequate reserves for the dropped stages and safeties start getting placed?

 

[rjack321]

Also, swimming with two stages isn't really that much fun and trying to do it with more than two is really just a bad idea. So, for discussions of more than two stages should be assumed to include scooters. At this point you are at a level of diving where 1/3rd is completely indequate to cover the amount of gas you might need to get out.

So its more like 3+ stages = scooter
Scooter requires more reserves, just start using all stages.

Did I get that about right?

 

[RTodd]

So its more like 3+ stages = scooter
Scooter requires more reserves, just start using all stages.

Did I get that about right?

While there could be exceptions, yes. But, I can't think of many situations where even swimming with two stages I would breathe any significant amount of my back gas. Once I start going that far into an overhead, thirds starts sounding less and less like a good idea. But again, this view is based on experience and how far I would generally go on just two stages on a swim dive in shallow water. In deeper water, I would be on a scooter and the distance would also be great enough to want a higher buffer. My view is that if you aren't covering the types of distances where you want more than thirds on multi stage dives, your skill set probably isn't where it should be to be doing multi stage dives in the first place.

 

[Mike Edmonston]

You guys are focusing on thirds and missing a very important concept here. Once you are doing dives on two or more stages, the nature of the dives generally dictate all of the backgas is a reserve. For newer divers with relatively high consumption rates this might not be as intuative. But, once you have any business using 2 plus stages the bottom times they will give you is significant.

Also, swimming with two stages isn't really that much fun and trying to do it with more than two is really just a bad idea. So, for discussions of more than two stages should be assumed to include scooters. At this point you are at a level of diving where 1/3rd is completely indequate to cover the amount of gas you might need to get out.

If you are ever unfortunate enough to see a stressed buddy have to go to his 120s back gas reserve at 285', you will be amazed how much gas gets used compared to the relaxed sipping of a stage while scootering in on the entrance. Answer, if it is true gas loss issue of the stage and breathing rate has spiked - all of it.

At what interval would you or the team have the safeties placed? and how many safeties would you drop at each station or is that completely team dependant?

Thanks

 

[RTodd]

At what interval would you or the team have the safeties placed? and how many safeties would you drop at each station or is that completely team dependant?

Thanks

Too many variables - depth, syphon or spring flow, locations in the cave where a safety depot can be placed, etc. For a big operation, a good starting point to consider would be to start placing them at stage drops. For a fairly large dive that requires some setup, possibly just the team doing two dives, somewhare around the second stage drop is an okay rule of thumb. But, really impossible to answer since it is so location and objective dependent. You want the safeties fairly far back but you should also be building plenty of bailout into the dive team so taking them all the way to the last drop of the push team usually isn't very practical since there should be enough back gas and other bailout to get a fair distance back towards the exit.

 

[lamont]

1st rule - never violate thirds with total gas. A previous post advocating doing just this. You can arguably get away with this on easy dives where you are staying in the kiddy pool and spend most of the dive in high flow areas. Then again, you can get away with diving 1/2 on most cave dives too. But, it is a bad habit and will eventually bite you.

by extension, for scooters and stages, would you never want to be violating 1/6ths on total gas?

diving two stages (to 1/2+200) and reserving all of backgas would consume 33.4 cu ft out of 2 stages and would then mean you need to carry in 400 cu ft of gas which is (just) satisfied by 2 stages + double-130s in backgas (414 cu ft total, not much left over for deco).

diving three stages (to 1/2+200), reserving all of backgas (2x130) violates 1/6ths and puts you closer to 1/5ths of total gas at your turn.

 

[coldsmoke]

I wish we saw more threads like this. I have enjoyed it and learned somthing too! Thanks to all who have contributed.

 

[SparticleBrane]

I agree. Best thread in here in awhile. Thanks for the insight, guys.

 

[dsteding]

What is interesting to me is you start to see when RB80s start to come into play, RTodd, where is that in terms of amount of stages? I imagine gas planning is the same, but the RB80 effectively reduces consumption rate . . . but my head is spinning a bit.

Good thread.