Trim with 3 deco cylinders?

[kensuf]

Lake Jocassee, South Carolina. Working out of the Lake Jocassee Dive Shop. I.e. diving off the LJDS boats.

If you know the lake, our dives were all on or off the Chinese Junk wall.

I may actually be diving there in 2 weeks myself.

 

[stuartv]

I may actually be diving there in 2 weeks myself.

I heard. I wish I could invite myself along and be there. But, I have another commitment for that weekend. Lucky you! LOL

 

[inquis]

Why not switch to backgas between bottles? Two hoses (plus your long hose) around your neck at the same time with three different gasses is a ginormous cluster. Strongly disagree with how PADI and TDI teach it in this manner.

Old thread, I know; but the system suggested I check it out. My recollection was that PADI also teaches switching to back gas, in contrast to the part I bolded. (TDI's support for switching to back gas was noted a few posts later.) The PADI student materials have this to say:

If you’re switching from another stage or another deco cylinder, go to your back gas momentarily, close the
first cylinder valve, retuck the second stage hoses into the bands, and then go through NO TOX as you switch to the new cylinder.

 

[inquis]

My primary reason for resurrecting this thread was to discuss why it was seemingly universally recommended to go to back gas between deco gases. I was taught to try them both (switch to back gas as well as going direct) and see which worked better for me. I came to a similar conclusion as Stuart pointed out:

I have practiced switching directly to one deco gas from another and it didn't seem any harder than switching from back gas to a deco gas. Maybe easier. There's a lot less gas switches that way too, which seems like a good idea. And no frequent clipping and unclipping of the primary back gas 2nd stage.

With two slung and breathing from the top cylinder, there's zero possibility of mixing up which is the next gas. (There's only a single second stage available.) After pulling that second stage out (holding it in my right hand) and turning gas on (with my left), it's trivial to remove the regulator from my mouth with my left hand and pull the hose over my head. Loop the hose behind my neck with the right and insert into mouth. It's very efficient. After that, just stow the hose in your left hand (it's the top cylinder, so easily done).

This seemed to capture the spirit of the issue (as best I can tell):

Two hoses (plus your long hose) around your neck at the same time with three different gasses is a ginormous cluster.

However, at no time are there two deco hoses around your neck in what I described.

I have the utmost respect for the various voices advocating "switch to back-gas" so I'm honestly trying to understand what the problem is. Is the worry that one might simply mix up the order and cross the hoses? Does the issue surface later with more cylinders? I haven't yet pursued trimix, but after switching, it seems reasonable to me to shift that top (used) cylinder to the leash or nose-clip to hip ring and bring the the next cylinder forward underneath the one I'm currently using. For that matter, it's even a little easier to stow the hose with the cylinder out in front of me (part way through the rearward shift when it's still clipped to the chest ring).

@stuartv, have you switched your approach in the last year? If so, what changed your mind?

 

[Jack Hammer]

My primary reason for resurrecting this thread was to discuss why it was seemingly universally recommended to go to back gas between deco gases. I was taught to try them both (switch to back gas as well as going direct) and see which worked better for me. I came to a similar conclusion as Stuart pointed out:

With two slung and breathing from the top cylinder, there's zero possibility of mixing up which is the next gas. (There's only a single second stage available.) After pulling that second stage out (holding it in my right hand) and turning gas on (with my left), it's trivial to remove the regulator from my mouth with my left hand and pull the hose over my head. Loop the hose behind my neck with the right and insert into mouth. It's very efficient. After that, just stow the hose in your left hand (it's the top cylinder, so easily done).

This seemed to capture the spirit of the issue (as best I can tell):

However, at no time are there two deco hoses around your neck in what I described.

I have the utmost respect for the various voices advocating "switch to back-gas" so I'm honestly trying to understand what the problem is. Is the worry that one might simply mix up the order and cross the hoses? Does the issue surface later with more cylinders? I haven't yet pursued trimix, but after switching, it seems reasonable to me to shift that top (used) cylinder to the leash or nose-clip to hip ring and bring the the next cylinder forward underneath the one I'm currently using. For that matter, it's even a little easier to stow the hose with the cylinder out in front of me (part way through the rearward shift when it's still clipped to the chest ring).

@stuartv, have you switched your approach in the last year? If so, what changed your mind?

In short it is about developing and reinforcing solid habits to reduce potential bad switches if/when you carry multiple bottles. Same reason to follow a gas switching and verification procedure when only carrying one bottle. Plus it is simpler to clean up the first bottle and stow the reg without the reg from the second deployed.

 

[rjack321]

My primary reason for resurrecting this thread was to discuss why it was seemingly universally recommended to go to back gas between deco gases. I was taught to try them both (switch to back gas as well as going direct) and see which worked better for me. I came to a similar conclusion as Stuart pointed out:

With two slung and breathing from the top cylinder, there's zero possibility of mixing up which is the next gas. (There's only a single second stage available.) After pulling that second stage out (holding it in my right hand) and turning gas on (with my left), it's trivial to remove the regulator from my mouth with my left hand and pull the hose over my head. Loop the hose behind my neck with the right and insert into mouth. It's very efficient. After that, just stow the hose in your left hand (it's the top cylinder, so easily done).

This seemed to capture the spirit of the issue (as best I can tell):

However, at no time are there two deco hoses around your neck in what I described.

I have the utmost respect for the various voices advocating "switch to back-gas" so I'm honestly trying to understand what the problem is. Is the worry that one might simply mix up the order and cross the hoses? Does the issue surface later with more cylinders? I haven't yet pursued trimix, but after switching, it seems reasonable to me to shift that top (used) cylinder to the leash or nose-clip to hip ring and bring the the next cylinder forward underneath the one I'm currently using. For that matter, it's even a little easier to stow the hose with the cylinder out in front of me (part way through the rearward shift when it's still clipped to the chest ring).

@stuartv, have you switched your approach in the last year? If so, what changed your mind?

"Breathing from the top cylinder" is the start of where you are going amiss here. What happens when your cylinders are reversed? You've dropped them and picked them up in a cave and reversed their clipping. Or the skipper helped you put them on and you fail to discover they are backwards. You never want to be using cylinder position for anything. Also "put the next cylinder underneath" My recommendations is to stop using cylinder position as indicative of anything right now.

Switching to an unbreathable gas is the #1 way OC tech divers die.

In this whole post you havent once mentioned checking the MOD. Nor have you mentioned confirming the reg in your right hand is associated with the cylinder valve in your left hand.

If you switch to backgas after every stage or deco gas you: 1) are going to the only gas on you that you don't have to verify before you put it in your mouth and 2) starting each switch from exactly the same place with a "clean" set of stages on the left.

 

[Miyaru]

Recurring theme....and reading all the arguments I get the impression that the whole dives is about procedures, trim gas switches.
On a planned techdive, there is something that you have loads of: time.

Last week I went through the Canyon in Dahab with a local instructor. Not particularly deep, but we took 2 deco gasses anyway. Which gave us loads of extra time. The dive was all about the Canyon, swimming through it, watching how the breaks continues in the deep and enjoy the sunlight seeping through the cracks in the coral.

When you have all the time in the world, simply relax, double check what your buddy or team member does and when he's done, do your own switches as relaxed as possible. It's usually the fastest switch as well.

Intermediate switching to backgas - do you do that on the last switch, e.g. switching from 50% to 100%? With 10/70 on your back?
I don't.
Take the 50% back from around your neck, put the 100% around your neck and continue breathing. That stop is the longest and there is loads of time to stow your 50%. No rush, no entanglement, no clusterfcuk. I want to enjoy the reef, that's why I did a dive there.

 

[stuartv]

My primary reason for resurrecting this thread was to discuss why it was seemingly universally recommended to go to back gas between deco gases. I was taught to try them both (switch to back gas as well as going direct) and see which worked better for me. I came to a similar conclusion as Stuart pointed out:

With two slung and breathing from the top cylinder, there's zero possibility of mixing up which is the next gas. (There's only a single second stage available.) After pulling that second stage out (holding it in my right hand) and turning gas on (with my left), it's trivial to remove the regulator from my mouth with my left hand and pull the hose over my head. Loop the hose behind my neck with the right and insert into mouth. It's very efficient. After that, just stow the hose in your left hand (it's the top cylinder, so easily done).

This seemed to capture the spirit of the issue (as best I can tell):

However, at no time are there two deco hoses around your neck in what I described.

I have the utmost respect for the various voices advocating "switch to back-gas" so I'm honestly trying to understand what the problem is. Is the worry that one might simply mix up the order and cross the hoses? Does the issue surface later with more cylinders? I haven't yet pursued trimix, but after switching, it seems reasonable to me to shift that top (used) cylinder to the leash or nose-clip to hip ring and bring the the next cylinder forward underneath the one I'm currently using. For that matter, it's even a little easier to stow the hose with the cylinder out in front of me (part way through the rearward shift when it's still clipped to the chest ring).

@stuartv, have you switched your approach in the last year? If so, what changed your mind?

Regarding other replies to this, and in case you haven't figured this out yet, picking something that you did not address at all and assuming you're doing it wrong, then flaming you for it is The ScubaBoard Way.

I assume when you say "breathing from the top cylinder" (just as an example), you are just speaking in a short, convenient way, to convey your point - not that you are actually using cylinder position as your basis for your gas switches, while ignoring fundamentals like checking MOD, verifying regs, etc..

In answer to your question, no, I have not changed the way I do it.

The most cylinders I have carried - beyond either back gas doubles or a CCR - is 3 x AL80.

With OC doubles, I carry 2 on the left and 1 on a leash from the left waist D-ring.

With CCR, I carry 2 on the left and 1 on the right. All sidemount-style. That is how I was trained in my MOD3 course yet and I haven't been diving in that config enough yet to say "I have mastered it this way and I'm going to change it." Not sure if I will even ever WANT to change it. So far, it feels pretty good. I just have to figure out how to carry/manage my camera rig when kitted up like that. I am used to carrying it on my right side.

In either case, I still change directly from one to the next.

I never have 3 hoses around my neck. (Actually, I would have 3 hoses around my neck on OC, because there's the deco mix, the long hose, and the alternate - I'm just counting the way it was talked about earlier in this thread. The real point is I would never have 4 hoses - never 2 deco mixes - around my neck, as has been implied by others.)

If I get a half twist on two hoses as I switch, it is totally simple to straighten them out after I get breathing on the new reg. One of the simplest scuba skills there is after OW training. It's just not hard, and you generally have no pressure to rush, either. You're on deco.

I never switch to a hypoxic mix at 20'. Sure, you CAN breathe 10% at 20'. But, sometimes shtuff happens. I am not super comfortable with the notion that analyzed mixes are accurate +/-1% (so a 10% mix could actually be 9%) and any number of "things" could happen that might result in you getting shallower than intended. Being a few feet above my ceiling for a minute (if shtuff happened) is not generally that big a deal - unless it results in me breathing 0.12 ppO2.... All in all, this is a minor risk, as it's a short time window that you'd be on back gas at 20' and generally unlikely that you'd get any significant amount shallower during that time. Still, it's a small chance (with a big, bad consequence) that I don't expose myself to.

With 3 deco gases, I do 3 gas switches. That seems better than doing 5 gas switches.

With only 2 gases, going directly one to the next means, as long as you get the first one correct, there is basically zero chance of switching to the wrong one on the next switch.

On OC, where I only have 2 gases "up front", the chances of switching to the wrong gas is also pretty much zero. That is, as long as I manage the cylinders and rotate them correctly. There is no shortcut to verifying cylinders/regs per normal protocol at the time of actual switching.

I.e. just because you "know" you clipped your O2 to your leash, so when you switch to your intermediate mix, you "know" that it's the intermediate mix because it's the only other reg "up front", that doesn't mean you don't still have to verify that you are switching to your ACTUAL intermediate mix when the time comes to actually switch.

Once I am switched and the hoses don't have a half twist, stowing the reg I was using before doesn't seem like any big deal, whether I'm breathing off the other cylinder on that same side, or breathing off my primary back gas reg. I think, at the level of diving where you'd be carrying that many cylinders, it really SHOULDN'T be a big deal to stow a reg like that.

Now, all that said, I fully recognize that there are a number of posters responding here who are WAY more experienced than I am, including at diving with multiple deco gases, etc.. So, it is entirely possible that some day I will have more experience and come to appreciate a different way of doing things than how I do them now. The only thing I feel pretty confident about is that, no matter which way I'm carrying my cylinders or whether I switch to back gas in between or not, I am PROBABLY not going to kill myself because I failed to verify that I am switching to the correct gas. I think I'm pretty OCD about that.

And in the end, that seems to be the fundamentally important part. The rest is really just discussion of opinions on the best way to set yourself up to succeed in doing that one thing - verify your mix and make sure it's right before you start breathing it. Discussion of human factors, if you will.

 

[rjack321]

Intermediate switching to backgas - do you do that on the last switch, e.g. switching from 50% to 100%? With 10/70 on your back?
I don't.
Take the 50% back from around your neck, put the 100% around your neck and continue breathing. That stop is the longest and there is loads of time to stow your 50%. No rush, no entanglement, no clusterfcuk. I want to enjoy the reef, that's why I did a dive there.

Yes although how many OC 10/70 dives have you actually done? The closest I have been to OC 10/70 is 12/65 for a ~290ft dive quite a few years ago.

The most reliable way to do this is in the last few (~5) mins of your 30ft stop you switch from 50% back to backgas. You will need a low ppO2 break for a few minutes at this point anyway. Stow the reg for the 50% stage bottle. Rotate the 50% bottle back on your leash, it's not full anymore and will float up from your butt nicely alongside your bottom stage. Move the o2 bottle forward. Now you are ready to move up to 20ft. You are still breathing on your long hose, you are finishing your air break, you are not switching stage to stage, and your left side is completely fresh and cleaned up.

Now you are free to do your backgas to 100% switch like any other gas switch

 

[inquis]

My recommendations is to stop using cylinder position as indicative of anything right now.

I don't use cylinder position as indicative of anything. The actual switching procedure -- noting depth, confirming MOD on tank, pulling reg, tracing hose back to the regulator/valve, turning that specific valve, etc. -- wasn't my point of confusion. I do those things regardless of where tanks might be, though I appreciate you pointing out the importance of such. I completely agree with you.

Regardless, at the end of the day one of the tanks WILL be on top. I might as well put the first one I'll use there from the get go -- verify placement at that time and verify again before, during, and after deployment (with further checks during & after by the buddy).

I don't see that as any different than arranging for a "clean" set of stages as you described. Even when on back gas, it's easier to switch to and clean up a bottle when it's on top. Don't you strive to do that as well?