Management of *backmount* independent doubles?

[tmassey]

After @tbone1004 's recent thread ( https://www.scubaboard.com/communit...ehash-our-discussion-on-primary-donate.575160 ) I was inspired to ask about a scenario that I'm unclear about and would appreciate some different perspectives.

When traveling, it can be difficult or even impossible to get manifolded doubles. I have created travel doubles cam bands (inspired by post #3 here: DIY: travelling twin cam band ) I use my standard backmount doubles regulators (7' hose from right post, 24" necklaced from left, primary donate), and I add a SPG to the right post which goes under my arm and clips off on the right chest D-ring.

I started diving this when I first started with doubles, and had very little experience with the entire configuration period. In the last several years I've gotten pretty good at getting doubles when I need them. (Go popularity of tech diving!) But I've got some nagging questions about this configuration and after the generally constructive perspectives above, I thought I would revisit this topic as well.

I'm open to pretty much any and all discussion about this configuration. However, my primary questions center around gas management and donation/long hose management. But if you have any other thoughts or suggestions about the configuration in general, I'd love to hear them.

First, gas management. When I started doing this, I did research on how to manage the gas usage on independent tanks. The general consensus I could see were one of two things: 1) sip off each tank equally, within 200 PSI or less; or 2) Breathe off of one tanks 1/3 of the way and switch; turn dive at 1/3 of second tank (1/3 total gas); breathe off the second tank 2/3 of the way and switch; breathe the first tank a second 1/3, ending with 1/3 in each -- by doing that, at no point do you violate the rule of thirds. At the time, the two-switch technique was simpler was definitely easier and so I went with that, confident that I was still safe!

At the time I did this research, sidemount was not nearly the thing it is today. I have zero sidemount training, but from what I've gleaned from others is that SM divers are trained in the first option: keep your tanks within 200 PSI of each other. I'm assuming that SM divers don't like having to swap any more than I do, so there must be a concrete, specific advantage to make up for the (admittedly, very low) effort. What is that?

Also at the time, my thoughts and reasoning did *not* contemplate the difference that asymmetric hoses would make in that -- particularly when one hose is *decidedly* unfriendly to use for donation! However, after giving more thought to it, the two-switch reasoning still seems to work -- and if you need to donate from the short hose because of some sort of failure of the long hose you're in for exactly the same situation with either gas management technique.

So, I guess it comes down to that: what is the flaw with the two-switch technique that is solved by the constant-switch technique? And more open-ended, is there a gas management technique that I'm missing that I should be considering -- and why should I consider it?

My second question surrounds long-hose management in a world of independent doubles. I've been taught to clip off my long hose when not in use. With manifolded doubles, the only real time that this would take place (outside of valve drills) is either a failure that disables it or in switching to a different gas. In either case, the long hose is out of commission. (Right? Broken is obviously yes; after a gas switch and it would be primary donate for me, and if I needed to, I would go to the necklace anyway. Am I missing something?)

The problem is that, with breathing down independent doubles, I'm spending half of my time with my necklace in my mouth and my long hose clipped off. That makes me uncomfortable. I now have zero easy-to-donate regs. Honestly, when I first started with the independent doubles I didn't realize that you clipped off the long hose, so I just let it dangle. But now that I know better... I'm not liking the alternatives any which way. So I'm hoping you have one!

From applying @tbone1004 's thread to this, it seems that the preferred solution for many is a frangible link on the long hose snap bolt or variations of open-water octo type of solutions. Right now, I have a DGX Hose Clip Retainer on the long hose snap bolt. It's more frangible than cave line but I don't know if that's frangible enough? This is another area I could use some wisdom. Maybe an octo mouthpiece thingy would be better, though I don't really want to deal with it every time I swap -- especially if you give me a good reason to keep my tanks even.

The other issue is, what do I tell my insta-buddy? With primary-donate, we get to use the line, "Take the one I'm breathing: we know it works!" But in this case, half the time that's my necklace, and they need to take the "octo" clipped off. (And sadly, "Get better skills and equipment so you don't need to mug me" probably won't go over well.... And sadly, "Don't dive with an insta-buddy" won't go over any better: it's either an insta-buddy or no dive. Same thing for "Get a manifold". Would if I could, but I can't so I won't.)

And for the record: independent doubles are not a solution I would use on a tech dive. These are advanced recreational wreck dives, from a boat with a bunch of single-tank divers, so I'm already worlds ahead of what any insta-buddy should expect from anyone. (That's why the independent doubles are so important to me: I want the self-reliance for *me*!)

Thank you very much for reading my quite lengthy post. I look forward to any suggestions -- and reasons behind them! -- that you might have. I really appreciate it.

 

[wetb4igetinthewater]

I think you've come up with a great solution for travel. Is it necessarily ideal? Probably not. I'd be curious to how much the cylinders may shift around on your back. This is something had I not gotten into sidemount, I would try for travel.

You do want to switch regs as you breath them down for the reason that if you have to donate, you and the receiver have about the same amount of air. Not sure how much cylinders that close to the center of gravity would impact balance if you drained one cylinder down and leaving the other full. Less than sidemount cylinders as those are farther out and thus more torque.

As far as donating a reg, you have the same problem as a diver in sidemount. It depends. You have to donate the long hose at all times. I'm guessing you would have the short hose bungeed around your neck. I think you'd tell your buddy, "Let me donate, because if I have the short hose in my mouth, you won't be getting any gas".

I'd be very curious to hear how well this works for you.

 

[ChuckP]

I didn't read all of Tbones other post due to time - what about a magnetic attachment for the long hose? I use one for my second in regular rec diving and was going to use one for the long hose in doubles... Is that bad???

 

[tmassey]

Is it necessarily ideal? Probably not. I'd be curious to how much the cylinders may shift around on your back.

It's the most ideal I can come up with if you presuppose two things: you can't get manifolded doubles, and you've rejected sidemount (which I have for other reasons such as their less suitability for boats, oceans and wrecks). Your mileage may vary. And they shift pretty minimally. With two bands properly tightened, there's really no place for them to go.

You do want to switch regs as you breath them down for the reason that if you have to donate, you and the receiver have about the same amount of air.

I understand why that is certainly might be an ideal, but is it a requirement? As long as I'm guaranteed to have sufficient gas (and with only two gas switches I always maintain that minimum), is there an advantage that can be clearly stated?

Remember: having an uneven (but *always* sufficient) level of gas in two tanks is *superior* to having an even amount of gas in 50% of failures -- because the one that fails might be the one with less (but still *plenty*) gas. So what uneven takes away, it also gives -- plus fewer reg switches.

Not sure how much cylinders that close to the center of gravity would impact balance if you drained one cylinder down and leaving the other full. Less than sidemount cylinders as those are farther out and thus more torque.

I have a feeling that SM gas balancing may have more to do with *that*, than an actual gas-management reason! That's why I'm pushing back on accepted SM-derived wisdom -- not just to be pedantic!

The answer is: not much. Frankly, if I'm doing this, it's gonna be AL80's. So you're talking roughly 2 pound swings at most. Given that it's at your center of gravity, surrounded by your center of lift, it doesn't make too much difference. But thank you bringing that up -- I'll pay closer attention the next time I do this.

I'm guessing you would have the short hose bungeed around your neck. I think you'd tell your buddy, "Let me donate, because if I have the short hose in my mouth, you won't be getting any gas".

Yes, and yes. I just don't like that second answer! (But I'm unable to see a better one that doesn't compromise something else, like having independent doubles in the first place! )

 

[tmassey]

what about a magnetic attachment for the long hose? I use one for my second in regular rec diving and was going to use one for the long hose in doubles... Is that bad???

You tell me! I have zero experience with it. When that was mentioned in the other thread, my recollection is that there was a general eyeroll from those who replied. I didn't see anyone coming to magnets' defense.

Magnets are an interesting answer. You make sure they're as strong as you want them to be (and I'd want them pretty darn strong: you're gonna have to give a *good* tug), but they address my biggest problem with most frangible connections: what do you do when they break when you don't want them to? Magnets re-stick...

Is it "DIR" or whatever? That ship sailed with independent doubles and insta-buddies... so it's only "bad" if it doesn't work... (Though if a GUE type has something more than an eyeroll I'd love to hear it -- even if it's just "You're gonna die because...")

 

[MichaelMc]

There are many mechanisms for attachment. I collected a list with links to some discussions, Sidemount reg stow/release attachment mechanisms, allowing fast OOG response, with the intent to be agnostic to hose routing. Also prompted by tbone's thread. Depends on what works for you.

I started diving tiny independent doubles (AL40s). The reg access for donate issues seem the same as sidemount.

(I'm playing with tiny doubles as tiny (manifold) doubles make sense as DM demo or dive gear, while demoing in sidemount misses the point. Using independent ones now keeps the tanks also free for sidemount.)

 

[PfcAJ]

Travel with a manifold.

Option 1.

Such concessions. Why?

 

[wetb4igetinthewater]

Travel with a manifold.

Option 1.

Such concessions. Why?

We've been over this before and we will at the end have no influence on each other.

With this or similar situations, you can arrive at night on day 1, and in the morning of day 2, you can go straight to the boat, take 2 separate tanks, and go dive. That is not possible if you have to go get cylinders, set up the manifold and get a fill. For you that may be a non issue as it is worth it to have manifolded cylinders. For others, like me, that is a PITA.

Pick your poison. Though I would not say that sidemount is a concession. Pluses and minuses to everything.

 

[wetb4igetinthewater]

It's the most ideal I can come up with if you presuppose two things: you can't get manifolded doubles, and you've rejected sidemount (which I have for other reasons such as their less suitability for boats, oceans and wrecks). Your mileage may vary. And they shift pretty minimally. With two bands properly tightened, there's really no place for them to go.

Sidemount is less suitable for wrecks? Really? Well trained sidemount divers have no issues diving from a boat. See Tomasz Michura. Of course, few sidemount divers approach that level of skill (I don't). Many people say that sidemount is no big deal, but while I have not seen all those people in the water, the ones I have were .... not so good.

I understand why that is certainly might be an ideal, but is it a requirement? As long as I'm guaranteed to have sufficient gas (and with only two gas switches I always maintain that minimum), is there an advantage that can be clearly stated?

Remember: having an uneven (but *always* sufficient) level of gas in two tanks is *superior* to having an even amount of gas in 50% of failures -- because the one that fails might be the one with less (but still *plenty*) gas. So what uneven takes away, it also gives -- plus fewer reg switches.

I have a feeling that SM gas balancing may have more to do with *that*, than an actual gas-management reason! That's why I'm pushing back on accepted SM-derived wisdom -- not just to be pedantic!

I'm not cave trained, but my understanding is that they alternate for 2 reasons: tilt and sharing gas out of a cave (or wreck) in a worst case scenario. Any sidemount cave divers please correct.

If you are doing this for redundancy and solo diving, as long as you have reserve in one cylinder to reach the surface, I think you are good.

 

[tbone1004]

zipping up and down answering so I'll try to keep it chronological

200psi-it's stupid paranoia. In sidemount the moment arms are bigger than in backmount, and I teach and preach that you switch whenever it becomes annoying provided you don't break any gas reserve minimums. Even on LP121's which are BIG tanks, that's usually 500-600psi before the weight shift is big enough to notice. You definitely feel yourself listing and that's when it's time to switch. Breathe that one until you shift the other direction then it's usually about time to turn around.
Part of the key to this is keeping the long hose in your mouth during high probability of needing to share. I.e. always start on your long hose. High probability of a reg failure on descent, then once descent is stable you are zipping around on the short hose, then towards the end of the dive you go back to the long hose when there is a risk of someone running out of gas. That is the practical reason of not switching at some arbitrary pressure interval. The other nice thing is when you get enough hours on them you don't need to check your SPG's until the second switch in OW or at some interval after the first one in a cave. You learn it over time.

With doubles and normal sidemount regs, you can't donate the short hose with it behind your neck. It is trapped by the long hose so it won't donate. On top of that, it's usually on a suicide strap, so you aren't getting it off easily. I say can't, it's obviously possible, but it's really stupid.

You tell your instabuddy to ask nicely for gas, not grab it. Please ask him to signal when it's low on gas at 1000psi or something, which for you is also a signal to get on the long hose, and then you're prepared.

@wetb4igetinthewater indy doubles at least the bands that I have don't shift at all. I don't use them often, but have no issues using them. Backplate still presses against the bottles so it doesn't wobble. I actually find them more useful for sidemount since it lets me keep the two bottles strapped together for easier carrying to/from fill stations.

I've been tempted to try the magnet solution, but haven't bothered as I really like the loops at my shoulder d-rings with the jetstreams. I posted a picture of how I skin that cat in @MichaelMc 's thread.

@kosta diving in NC or any farther north in the Atlantic is certainly infinitely easier in doubles with the swells that we get here. Getting back on some of those boats in sidemount would be something I'd pay good money to see done gracefully. Passing bottles up to the deck is not an option on most boats, you have to climb, or on most days, get thrown up each step if you time it right.
Narrow ladders, narrower gates back onto the deck, pitching decks, etc. It's hard enough with a single deco bottle, combine that with widemount not being practical for going down passages. Doubles are much more suited for vertical wrecks. It's one thing for the guys that are marketing themselves for sidemount to make themselves do it because it's a marketing thing, it's another to be able to admit that doubles are actually a better solution to that problem. If I was doing a wreck trip off of a boat and needed two bottles and doubles weren't available, I'd likely dive a single tank with a stage before I'd dive sidemount. If I'm diving off of flat seas, wide decks, with an elevator, etc. I'd have to be going somewhere that requires bottles off to get thru a snug space or on a wreck that's tipped on its side to justify diving sidemount. The profile of doubles makes much more sense going thru doors and down hallways. Conversely, as there are tons of bedding planes in Florida's caves, the profile of sidemount makes a lot more sense, so it is very rare that I dive doubles in those caves. If it's a cave that's predominantly fissure cracks? Doubles it is because I'd be cursing the sidemount bottles while going thru the cave sideways or with one bottle pushed forward the whole time. Telford is annoying because you are cursing your gear configuration half the time regardless of which one you choose...