Advice, hose routing for mirrored left and right second stages

[kensuf]

Absolutely the OOA diver is up front, I thought my post was clear on that but I apologize that it wasn't. My issue is that if I'm diving with you and YOU have a 5ft hose.....I can't count on you for help. Swapping tanks is simply not feasible, so you've now doomed me. In open water, I have yet to hear an argument for 2x5ft hoses that I buy.

Just quoting for emphasis.

To summarize:

1. Tank swapping is not realistic for gas sharing.
2. 5' hoses are not realistic for gas sharing in an overhead environment.

 

[victorzamora]

I find discussions of 5' hoses in sidemount interesting.

If the majority of people agree that you should have a 7' hose on backmount doubles for overhead (cave/wreck) penetration in order to share gas, why would anyone use a hose that is 2' shorter coming from a valve that is also an additional 12" farther away from your out of gas buddy?

Everyone diving in an overhead needs a single 7' hose for gas sharing.

I know it's an unfair position to take, but I wish that 7ft hoses were more like 7.5ft.....but I otherwise agree.

In a solo-diver-only mentality, I can see using shorter-than-7ft hoses but I don't understand why the need to go as long as 5ft.

 

[kensuf]

I know it's an unfair position to take, but I wish that 7ft hoses were more like 7.5ft.....but I otherwise agree.

In a solo-diver-only mentality, I can see using shorter-than-7ft hoses but I don't understand why the need to go as long as 5ft.

You can be solo diving and still encounter an out of gas diver.

Back in 1996 I was diving with some friends at Little River. As we were heading in, we ran into a guy that flashed us down and wrote on a slate that his buddy was trapped. We went back and found him at the 3-way split, in zero vis, entangled in the line. We got him out, but he ran out of gas at the chimney and I had to give him a gas share through his deco.

If I was sidemount and using a "solo diver mentality" he'd be ******.

 

[tbone1004]

@Dan_P high pressure manifolds have been accepted going much farther back than the 80's, hell the original scuba regulator patent had a high pressure manifold.
There is nothing consistent about the rationale for a HP manifold and the rationale for a LP manifold.
HP manifold rationale is really simple

• I am far more likely to encounter a first stage failure than any other failure in the breathing system
• If I lose a first stage, I lose access to all gas in that tank
• If I manifold them together, then I can access all gas in that tank

The LP manifold does not give you that benefit. In recreational and "light" technical dives that are conducted without stage bottles it gives you the ability to donate a long hose from whatever you are breathing 100% of the time vs 50% of the time. You keep saying the system is scalable. How do you scale the concept of "always donate the long hose in my mouth" to CCR when there is no regulator in your mouth? You have to go through the same donation protocol for CCR with a LP manifold as you would if you just swapped tanks. You now added thousands of dollars and a lot of complexity to a system that doesn't actually scale to the pinnacle of gear requirements. Sure it is scalable between single, double, and stage tanks as long as you are diving open circuit, but it doesn't translate to CCR.

As far as organizational wide lack of skill in UTD. Yes, there is a deeply entrenched lack of skill in UTD with the ability to use critical thinking


see image of cave diving pioneers. note image is from 1986. Note HP manifold

See image of same cave diving pioneer, interestingly at the same cave. Note picture is from 1980. Also note HP manifold

I'm sure I can find older than that, but don't think it's necessary

 

[leadduck]

Just quoting for emphasis.

To summarize:

1. Tank swapping is not realistic for gas sharing.
2. 5' hoses are not realistic for gas sharing in an overhead environment.

As I wrote above, I meant extreme restrictions where single file swimming and gas sharing on a long hose is not realistic. The kind of places where sidemount or no-mount is must-have, where backmount divers wouldn't go. Crawl space, sump diving. At least they could in a wider space or in a dry part of the cave swap tanks before exiting through the restrictions, or not?

About the guy you saved in Little River 1996: is the chimney wide enough that a sidemount diver could share gas with the backmount guy on a 5' hose during deco (i.e. not swimming single file) as well? Could you as a sidemount diver hand over one tank to the backmount guy like a stage before both swim through the maze independently?

 

[Dan_P]

So all gas must be available from one valve, that's your argument. How does that ressonate with indies (backmount/sidemount)? You would advocate something on the lines of Lola valves from the valves, or not diving sidemount at all?

And, following up, please explain to me the scenario where having all gas available on one valve would be necessary with a Z system?

In recreational and "light" technical dives that are conducted without stage bottles it gives you the ability to donate a long hose from whatever you are breathing 100% of the time vs 50% of the time.

...and when I'm in "heavy" technical dives, it gives me the ability to donate a longhose from whatever I'm breathing 100% of the time, as opposed to, say 25% of the time if at 75m on backmount. If diving staged penetration, it gives the ability to do the same 100% of the time.
That's the point.

As for CCR, you do know that there is no donating from the loop on any CCR, but the MX has donation from 1) a longhose, and 2) an onboard platform. That's the point, the breather is a gas extending plugin to the base we already have in place.
There's a chain of links to understand, in order to grasp the reasoning behind the MX, but rest assured, it's not without thought.

And I would urge you to challenge the notion you seem to have all but accepted, that UTD-trained divers are incapable of critical thought.

 

[leadduck]

You're definitely envisioning something different than I am. With a straight-up hose routing, you can't lose as much length without it being a problem as if you had more slack...right?

With behind-the-neck, I doubt you'd snag a reg hard enough and long enough that you'd pull it backwards behind your neck, then left across your back, then forward over your shoulder, then continue pulling down. That's a lot of convolution to get the reg out of reach. With straight-up hoses, you don't get that. If the hoses get pulled, they get pulled out of reach.

I was thinking about the hose loop in my waist belt getting caught on something between my knees during a slow crawl in a tight restriction, not allowing me to move on. A strong pull on the reg is something I'd notice immediately and can stop moving, no matter how long the hose is. Why would I continue crawling with no air until the reg gets pulled out of my reach? The point of the short hose is just that there's a lot less hose that can get stuck, and if it does, then the stuck hose section is in reach of my hand.

Absolutely the OOA diver is up front, I thought my post was clear on that but I apologize that it wasn't. My issue is that if I'm diving with you and YOU have a 5ft hose.....I can't count on you for help. Swapping tanks is simply not feasible, so you've now doomed me.

Yes, misunderstanding on my side. Agreed, single file swimming in overhead with 5' hose, or in your case even with a 7' hose on your buddy, won't work. What are the reasons why swapping tanks is not considered feasible? Won't work obviously inside a narrow section, but else?

 

[tbone1004]

@Dan_P the hose on stage bottles and deco bottles is long enough to be able to donate from the mouth in an OOA scenario if you have to, but think about what must go wrong in order to have to donate from those.

Independent doubles are not commonly used because the risk of an isolator failure is minimal compared to the risk of a first stage failure. First stage failure is really the only solid argument for the manifold in the first place and the Z system does nothing to address that failure.

I do not advocate lola valves because they are unable to be swapped underwater due to water ingress to the tanks and tying those tanks together would make bottle off restrictions very complicated if not impossible.

SCR is a gas extended. CCR is not. If you admit that donation of the long hose from the CCR is not possible, then why is it relevant to a "scalable" system where you always donate from the mouth? That is the argument for the manifold in the first place.

@leadduck the point @victorzamora was trying to make is that the initial jerk that makes you realize you got caught is enough to pull the regulator out of your mouth if it isn't crossed behind your neck.

If 5' single file air sharing won't work, why have the 5' hose? Why not use a shorter length hose that allows you to make a direct ascent and not have the hassle of the looped hoses? 7' hose is enough for Victor and I to get out together but we are really getting to know each other in the process. I don't like him that much, so I have a 9' hose so I don't have to have my head in his crotch on exit. He apparently likes me enough to not worry about changing ;-)

On swapping tanks. Try it with anything other than an AL80. It's essentially not possible which is why the Toddy System mandates use of AL80's.

 

[victorzamora]

I was thinking about the hose loop in my waist belt getting caught on something between my knees during a slow crawl in a tight restriction, not allowing me to move on. A strong pull on the reg is something I'd notice immediately and can stop moving, no matter how long the hose is. Why would I continue crawling with no air until the reg gets pulled out of my reach? The point of the short hose is just that there's a lot less hose that can get stuck, and if it does, then the stuck hose section is in reach of my hand.

Often enough, getting through restrictions means pushing and crawling. Sometimes, it's not overly clear what's stuck...so you push on. As for there being less hose: there's still quite a bit of hose, and there's more overall hose in 2x5ft than 30"+7ft. Either way, the point remains that it takes a lot less to lose your reg with hoses straight up than it does to go behind your neck.

Yes, misunderstanding on my side. Agreed, single file swimming in overhead with 5' hose, or in your case even with a 7' hose on your buddy, won't work. What are the reasons why swapping tanks is not considered feasible? Won't work obviously inside a narrow section, but else?

Swapping tanks in ANY circumstance is a terrible idea, imo. Tight spaces, there literally may not be enough room...this one is obvious. BUT most caves are big enough that physically fitting tanks isn't that big of a deal, but the tank swap technique is still likely to go wrong. First of all, think of the mental state you're in if you've got not one but TWO independent sidemount tanks that are empty. You're probably not very calm or stable, no matter how much experience you've got. That stress will add to the difficulty of whatever else you're doing. Also, sidemount tanks are rarely going to exchange well. In my friends group, none of us can easily swap tanks and have decent looking SM bottles. That's more than aesthetics in that sagging bottles can drag in the mud, get caught in restrictions, and generally be problematic. Another issue is that SM divers, especially SM cave divers, often use their primary tanks as part of their ballast. I'd be SOO off trim if I completely removed one of my tanks. For a while I was sidemounting LP104s. My buddy was diving Faber LP85s. There's like a 7lb difference between them, which would've made it absolutely miserable.

But onto the logistics of switching tanks, once everything else is handled: you're in a cave big enough to switch (or OW), with a buddy you trust and have practiced it with, that's at least mostly mentally capable of doing this and isn't in a panic, with tank setup that's similar enough and tanks that you could theoretically remove and still survive the dive. That in-and-of-itself is a lot of ifs, but we'll pretend like all those are met. Now you have to hope that the floor and ceiling aren't soft. There are caves (common, "tourist" caves) where looking at the floor wrong can blow it out for hours. Swinging tanks around is a surefire way to force yourself into a blind exit. Oh, speaking of....all of this has to be done with good visibility. Okay, but let's pretend you're in a cave with enough flow to clear what you stir up, big enough to pass tanks around easily with a stable top. Oh wait, high flow would also make this a hilariously dangerous endeavor for what I think are fairly obvious reasons. So we have to knock out high flow passages. We also essentially have to knock out OW because if you don't have a floor (or have a fragile bottom or muck/mud/gross bottom) you could lose your tanks forever. Same with the soft cave bottoms....there's a few caves I know of with silt so deep you can EASILY lose your tank in them. Now you're buddy-breathing off one tank containing half the required gas to get two level-headed divers out.

Okay, back to the top: You have to assume you are in a cave big enough to switch with a stable ceiling and a hard bottom with enough flow to clear out but not so much to complicate things and a buddy who is mentally stable enough to keep his wits, while having tanks of similar size/buoyancy and leash/attachment setup. Now you still can't drop the tanks, though there will be two tanks unclipped during the procedure. With AL80s that might be feasible (though still woefully impractical), but try it with LP104s or LP121s. Plus, now you lose the psychological benefit of comforting the OOA buddy (who, as we've covered, is clearly not in a great frame of mind) during the now-notably-more-stressful exit.

All of the time it takes to switch tanks before going about your now-slowed exit is definitely longer than simply exiting single-file, which can be done with pretty impressive speed. Besides the rest of the problems, you gain essentially nothing from it. As stated earlier, 2x5ft hoses is more hose than 7ft+30" hose - my current setup. It's not much, just 6" different, but the "less hose" argument is certainly not one the 2x5ft hose setup has going for it.

 

[Dan_P]

@tbone1004 Again, please if you will, explain to me a scenario where a first stage issue is a real problem on the Z system and not on manifolded backmount?

Independent doubles are not commonly used because the risk of an isolator failure is minimal compared to the risk of a first stage failure. First stage failure is really the only solid argument for the manifold in the first place and the Z system does nothing to address that failure.

I believe this concern is followed up best by repeating the question above - kindly describe a scenario where first stage failure is a problem on Z system but not on manifolded backmount?

I do not advocate lola valves because they are unable to be swapped underwater due to water ingress to the tanks and tying those tanks together would make bottle off restrictions very complicated if not impossible.

Yes. So, if manifolding, it would make sense to do it on LP side if one wants flexibility to rotate tanks (scale) but still maintain the same platform.
As for the concern of being able to access all gas on one valve, I wouldn't mind expanding as soon as you've described a scenario where it's a bigger concern on Z system than on manifolded backmount.

SCR is a gas extended. CCR is not. If you admit that donation of the long hose from the CCR is not possible, then why is it relevant to a "scalable" system where you always donate from the mouth? That is the argument for the manifold in the first place.

Let's not lose essence over semantics.
It was obvious to me that I mean the CCR layer in the MX-Z is a gas extending plugin, conceptually.

You have your Z-system except, there's a canister with a loop plugged into it.
In the event of a CCR failure, you turn the BOV and you're back to what you've done since day one.

The bailout is the base that we've used all along. Hence scalable to CCR in that sense.

If you want me to say it, sure:
On Z-system, we always donate from the mouth on O/C.
On CCR, it's never possible to donate from the mouth.
That's a far cry from saying the rig is not scalable to CCR, and a far cry from saying it has no strengths in the MX configuration.