Diving Deco/Stages to 1/3

[battles2a5]

Well, there are a lot of stage strategies. But one is to breathe a 1/3 in, 1/3 out, 1/3 reserve. In this case, you breathe a 1/3 in, and instead of breathing the 1/3 out off the stage, you just keep using back gas. You still have the same amount of total reserve gas, it's just in a different place. Again, it depends on where you want your reserve gas, but the bottle just rides a little nicer this way.

To answer your second question, this approach keeps the reserve in the stage (see the point above), so you aren't reserving BG for stage contingency. As I stated in the first post, this approach tends to break down as you add bottles, but is fine w/ 1, maybe 2 bottles.

 

[gr8fuldiverNC]

i have asked myself this question as well. the rule of thirds originated with cave divers. for penetration you use 1/3 in (of the smallest bottles used if team members have different bottles), then turn, and use 1/3 out, that way the remaining third is donated to an out of air diver and both can make it out. this of course assumes no deco on back gas. best i can figure is that tec procedures just adopted this inappropropriately for deco cylinders too. dsat teaches that you should have a 3rd in reserve, but of course this would not be enough for a teammate to deco if a bottle was lost. i agree with meng tze that the rule of thirds applied to deco cylinders comes from a misunderstanding of the reasons behind the rule of thirds. to have a useful back up for deco would require having half the deco gas in reserve for a buddy. of course, a 1/3 back up is better than nothing, but it just seems kind of arbitrary.

as far as cylinder handling goes, the rule of thirds really has nothing to do with this.

 

[Dive-aholic]

I do 1/3s on my stage bottles, but not my deco bottles. But I'm also one of those solo sidemount divers...

 

[Bismark]

The concept of diving 1/3's seems to be thrown around a lot by those who wish to consider them selves tech divers without the training. Invariably, when pressed, their knowledge of diving 1/3's will sound like "1/3 in, 1/3 out, and 1/3 for my buddy". However, when you ask them what they plan to do to resolve an emergency just as they reach their first 1/3, and how this is going to affect their ability to exit the dive, they usually have no answer. Moreover, this issue is made even worse (if that is indeed possible) when a "wreck" diver trained to the high standard of some of our recreational agencies in wreck diving, quotes the same 1/3's rule as our diver above. Sadly, they have no conception that they will have no gas left to actually do their ascent from the point of penetration, assuming they actually make it back. Failure to incorporate a rock bottom or minimum gas strategy into their 1/3's plan is a fairly good indication that they don't know what they are talking about.

It would seem to me that if someone needs to breath down an Al 80 to 1000 psi to make it "more manageable" they should be reconsidering their use of stages.



There is indeed a good deal of utility in allowing for a 1/3 reserve in your deco gas in a team of three. Assuming one team member loses their deco gas, their is sufficient gas on hand to complete the deco with the proper rotation of deco/back gas between the 3 team members. However this is not using "1/3's" per se.

There is also some serious risk analysis to be done on the view of carrying one AL 80 deco bottle with 50% versus two AL 40 bottles, one with 50% and one with 100%. If you are doing a dive in the 150 range, you are most likely to save yourself a very small amount of time by bringing the 02 along. This should be weighed against the extra task loading and skill required to properly manage and dive with 100% 02, as well as the more serious CNS issues. If you are diving with a team or even a single buddy with the proper deco gas reserve, in my view it becomes more advantageous to do a single dive in this range with one deco gas only. If an AL 40 doesn't do the job, by all means, take an AL 80.

It is at the deeper depths with extended shallow stop times (or the second dive in a series where you have extended your shallow stops) that bringing 02 becomes the most beneficial. Of course, it goes without saying that by the time you are doing dives in the 200' plus range, you should have solid bottle manipulation and gas switching skills to start with so the addition of the extra bottles should pose minimal issue.

Just my 2 cents in response to some of the posts above.

I know zero about side mount diving..............

 

[battles2a5]

It would seem to me that if someone needs to breath down an Al 80 to 1000 psi to make it "more manageable" they should be reconsidering their use of stages.

Nobody said they need to breathe down 1000 out of a stage to make it manageable. I said an AL80 swims nicer with 2000psi (of air/nitrox) than it does with 1000, and you can choose to continue swimming on backgas instead of switching back to the stage. This was not instructions on how to dive 1/3's in stages, it was anecdotal information gained from my instructor (as I stated). I was trying to find an example that would match ucf's question and this was the only example I could think. I was also very clear that this approach breaks down when you are start adding multiple stages.

 

[Bismark]

Nobody said they need to breathe down 1000 out of a stage to make it manageable. I said an AL80 swims nicer with 2000psi (of air/nitrox) than it does with 1000, and you can choose to continue swimming on backgas instead of switching back to the stage. This was not instructions on how to dive 1/3's in stages, it was anecdotal information gained from my instructor (as I stated). I was trying to find an example that would match ucf's question and this was the only example I could think. I was also very clear that this approach breaks down when you are start adding multiple stages.

My post was directed towards the cave instructor you mentioned.

In my view, doing anything with a stage other than breathing it down until it is used up completely and then switching to backgas is the wrong use of a stage. Also, if you are using a bottom stage, you are probably also using at least one deco gas, which, for me, is placed on top of the bottom stage on the same side. Being basically lazy, I am quite happy to have an empty bottom stage which now supports the negative deco gas bottle on that side. If I am doing a big enough dive to warrant a bottom stage and two deco gases, I would then move my empty bottom stage to my leash and switch with my 02. My empty bottom stage now rides nicely behind me and out of my way completely. If we are doing drifting deco with good surface support we would also probably shoot the empty stages up the line for surface retrieval.

This procedure outlined above does not break down with multiple stages.

 

[battles2a5]

My post was directed towards the cave instructor you mentioned.

In my view, doing anything with a stage other than breathing it down until it is used up completely and then switching to backgas is the wrong use of a stage. Also, if you are using a bottom stage, you are probably also using at least one deco gas, which, for me, is placed on top of the bottom stage on the same side. Being basically lazy, I am quite happy to have an empty bottom stage which now supports the negative deco gas bottle on that side. If I am doing a big enough dive to warrant a bottom stage and two deco gases, I would then move my empty bottom stage to my leash and switch with my 02. My empty bottom stage now rides nicely behind me and out of my way completely. If we are doing drifting deco with good surface support we would also probably shoot the empty stages up the line for surface retrieval.

This procedure outlined above does not break down with multiple stages.

If you read my original post, I said this was from a CAVE instructor. The procedure you described above is an OW strategy. I agree with (and utilize) your approach in OW, but that does not work in caves. Deco bottles and stages are dropped in the cave as they are used and retrieved on the way out. There is absolutely no utility in carrying around a bunch of empty bottles in a cave.

 

[Bismark]

If you read my original post, I said this was from a CAVE instructor. The procedure you described above is an OW strategy. I agree with (and utilize) your approach in OW, but that does not work in caves. Deco bottles and stages are dropped in the cave as they are used and retrieved on the way out. There is absolutely no utility in carrying around a bunch of empty bottles in a cave.

I understand. So please understand my confusion here: you mention that you breath your stages down to 1000 psi to make them eaiser to handle, yet you also state that "in the cave as they are used and retrieved on the way out". And, "There is absolutely no utility in carrying around a bunch of empty bottles in a cave." So if I interpret you correctly, there is no use in carrying around empty bottles but it is okay to carry around bottles with 1000 psi because they handle better than full bottles? (he asks while scratching his head.........??)

 

[battles2a5]

I understand. So please understand my confusion here: you mention that you breath your stages down to 1000 psi to make them eaiser to handle, yet you also state that "in the cave as they are used and retrieved on the way out". And, "There is absolutely no utility in carrying around a bunch of empty bottles in a cave." So if I interpret you correctly, there is no use in carrying around empty bottles but it is okay to carry around bottles with 1000 psi because they handle better than full bottles? (he asks while scratching his head.........??)

No, you definitely do not understand what I am saying. You are promoting an OW stage strategy. You typically don't drop bottles in open water so there is no reason to breathe down to "x" psi then drop the cylinder. So your version works there.

In a cave, you are most like coming out of the same hole you came in. So let's say for the sake of argument, I am diving a set of 104's with 1 AL80 stage. There are two primary strategies for diving that stage. You still need to adhere to the rule of thirds, so you either breathe down 1/3 of the stage, drop it, and continue the dive on back gas to 1/3's. OR you breathe the stage to 1/2 + 200-300psi, then add the required reserve to your backgas which is roughly 500 psi in this case. In either case, you are going to drop the stage when you hit the desired pressure so you can lose the drag from that stage. On the way out, you pick it back up and either breathe the next 1/3, or finish breathing it down (depending on how you are planning your gas).

What I was describing in my previous post is that if you breathed that stage down 1/3 and pick it up, you still have you full 1/3 in your BG, so you can just continue to exit on BG rather than breathe the next 1/3 out of the stage. The stage should be flat nuetral and just sits nicely.

Now in your scenario, you breathe that stage down ALL the way and keep carrying it farther into the cave as you breathe down your backgas. You are just carrying dead weight that can do nothing for you and you've also placed all your eggs in one basket by draining that stage on the way in.

 

[Bismark]

No, you definitely do not understand what I am saying. You are promoting an OW stage strategy. You typically don't drop bottles in open water so there is no reason to breathe down to "x" psi then drop the cylinder. So your version works there.

In a cave, you are most like coming out of the same hole you came in. So let's say for the sake of argument, I am diving a set of 104's with 1 AL80 stage. There are two primary strategies for diving that stage. You still need to adhere to the rule of thirds, so you either breathe down 1/3 of the stage, drop it, and continue the dive on back gas to 1/3's. OR you breathe the stage to 1/2 + 200-300psi, then add the required reserve to your backgas which is roughly 500 psi in this case. In either case, you are going to drop the stage when you hit the desired pressure so you can lose the drag from that stage. On the way out, you pick it back up and either breathe the next 1/3, or finish breathing it down (depending on how you are planning your gas).



What I was describing in my previous post is that if you breathed that stage down 1/3 and pick it up, you still have you full 1/3 in your BG, so you can just continue to exit on BG rather than breathe the next 1/3 out of the stage. The stage should be flat nuetral and just sits nicely.

Now in your scenario, you breathe that stage down ALL the way and keep carrying it farther into the cave as you breathe down your backgas. You are just carrying dead weight that can do nothing for you and you've also placed all your eggs in one basket by draining that stage on the way in.

Looks like we are talking apples and oranges here. I was not advocating anything for caves, while you were. I have zero cave experience so I find this quite interesting. If I re-read all your posts with the background that you are referring to cave diving, and then read mine with the view that I was talking about open ocean diving, things become more clear. The only overlap then comes with wreck penetration.........but that opens up a 'whole other can of worms.......