Need more gas - now what?

[AfterDark]

tbone 1004 and rjack321 you guys should take your rigs to Scandinavia and see how well suited those rigs are there where the OP is diving. You guys tell the OP all about VA and WA where he isn't diving, you guys should try diving where he is diving.

 

[Dan_P]

@Dan_P start cave diving in Florida, you'll realize REAL fast that AL80's don't work and you pretty much need steel tanks. Also saying that 1x large steel is better than 2x al80's, when al80's are actually pretty meh tanks to begin with is a little ridiculous. Al80's actually represent one of the most inefficient tank designs in terms of weight:buoyancy:gas capacity so shoehorning yourself into only using them is not a great idea for most diving

Yet, I like it and it works well. Will hit you up for a dive next time I'm in Florida. Maybe I'll find that in that venue, different tanks would make sense. I don't generally love the bouyancy caracteristics of steel indies, but that's on a more general note.
You're telling me that in Florida, sidemounting steel tanks is sensible - bene. I simply don't understand why is all.

I like that the AL80s are near neutrally bouyant and for this and their size, find them easy to handle.
Would a 12L steel tank hold more gas? Sure, a whopping 0,9L.
But I personally think even a 7L steel tank is aweful to reposition, let alone a 12L.
If I don't need steel in icewater, what is the reason I need them in Florida?

That said, it's not like I don't appreciate a use - I like a 12L for single-tank backmount, for instance.
But I can't use that single 12L for anything else than shallow rec diving. And it requires a separate rig.
I can, however, use a single AL80 for light rec diving, deeper rec, tech, stage or deco application. And have only one rig for all my diving.
That's one reason I prefer that setup.

All those AL80s will not work for a 200+ft dive in Puget Sound in ripping current on a scooter with dry gloves. Plus lord knows how much lead you'd need, 40+lbs easily. I wouldn't even let you on my boat if you showed up with all that full of 15/55. Forget it.

PS if you showed up with a Z system for anything other than a recreation dive you are also staying on the dock. Sorry that thing is stupid and the gas switches are especially problematic.

I dive dry gloves exclusively.
If you can't handle your gear with dry gloves, that's the core issue;
A perception that the Z system - or any other gestalt in this case - has anything to do with causation, in this logic, is flawed by what I'd best describe as an associated reversal of effort heuristic.
And I've never heard of anyone who needed 40lbs of lead..

But of course, it's your prerogative to invite anyone you wish, onto your own boat.

It's been my experience that people who concern themselves with their minds' negatives surrounding the Z-system, generally haven't ever even tried one on.
In my view, the gas switch is no more problematic than a gas switch is as a baseline when there are multiple deco tanks to pick from. On a side note, that is a general problem. One that has to be solved with a protocol in all cases.
Are you familiar with the gas switch protocol employed when using a Z-system?

tbone 1004 and rjack321 you guys should take your rigs to Scandinavia and see how well suited those rigs are there where the OP is diving. You guys tell the OP all about VA and WA where he isn't diving, you guys should try diving where he is diving.

 

[rjack321]

4 x al80s is + 16lbs of buoyancy at the end of a dive. MANY drysuit divers here need roughly 35lbs to sink, in a single hp100 (in salt water). More in a single 80, which are exceptionally unpopular for that exact reason. Not much gas, buoyancy that has to be offset by extra lead someplace else. You have 3 more al80s.

And you're going to be a cluster for no good reason at all when you could use a set of steel 95s or 130s for your 200ft dive and skip 15lbs of back crushing lead.

 

[Dan_P]

4 x al80s is + 16lbs of buoyancy at the end of a dive. MANY drysuit divers here need roughly 35lbs to sink, in a single hp100 (in salt water). More in a single 80, which are exceptionally unpopular for that exact reason. Not much gas, buoyancy that has to be offset by extra lead someplace else. You have 3 more al80s.

And you're going to be a cluster for no good reason at all when you could use a set of steel 95s or 130s for your 200ft dive and skip 15lbs of back crushing lead.

I don't agree at all;
When I'm diving the coldest saltwater, I'll wear 26lbs to two AL80s for an hour of diving, and be neutral with near empty tanks.
With 4 AL80s, that would be 35lbs in the very coldest environments. "Easily past 40+", is well off.

On a separate note, speaking purely of back crushing, I'm pleased not to drag a massive set of doubles around... Not saying it's a bad solution, just saying...

 

[Gareth J]

I read with interest the negative view on aluminium cylinders (ALi80's).

When I started using stages, as a general rule, they where always steels. They where a real pain in the water, because of the negative weight. Handing them off, dropping them was a skill we all mastered.
During a trip to Asia, I had to use Aluminium cylinders, initially we added 1kg (2Lb) weights to make them negative. The experience however did change my view.

I now dive a CCR, using a steel stage is horrible. I am happy to carry two, or even three Ali80's, I hate carrying even one 7litre steel stage.

If your premise is that when empty a Ali80 is positive, that is no real issue.
In the first place, in a pedantic world, a stage always has 50% remaining (rule of thirds for back gas and 50% for stage).
Granted a regularly carry stages (bailout) on 'recreational dives with only 100bar of gas ( enough to get me or my buddy back to the surface).
In the second In my case, if carrying multiple stages, if one is empty (positive), I can either hand it off, or send it up the DSMB line, then use the second (or third) Ali80. Granted you CAN'T DO THIS IN A CAVE.

My preference, either using CCR or OC, is to use aluminium cylinders for stages.
If the issue of weight change is a concern, then with an aluminium you can add weight, with a steel you can't remove weight!

Just on a point of weight carried.
Diving twin 12's (steel) and a drysuit a carried 4kg weight around my waist in addition to the trim (V weight) on the twinset. That was my sea weight.
Diving the CCR 12lb is my total sea weight, 4lb top, 2x2 lb trim weights and 4lb around my waist.

Gareth

 

[Imla]

Now... as a perspective... the "norm" in the area where Dan_P dives (assuming he hasn't relocated) is:
OW class (usually done in a drysuit)
10L 300Bar.
AOW 10L 300Bar
Then people start looking around and seeing what others dive.
So... when they buy their own gear, they usually get a BP/W variant depending on the shop they are taught at.
With this BPW, they usually get:
Girls or guys under 170cm, a D7 300/232 Bar.
Girls or guys over 170cm, a D8,5 232 Bar
Big guys, D12 232.

There might be a disproportionate amount of divers in this area going with technical/cave-diving. Also among girls.
So, usually ppl end up with a D12, then a 7L alu stage, then S80s in variant numbers until they reach C1 levels. (Cave/mines are usually GUE or IANTD). Gas restrictions and cave/mine environments causes people to move to D18s.

So... In my basement... you'll find:
1 D18 32%
2 D12s (One for 32% and one with TriMix)
4 S80s (50%, 21/35 or 32%, 18/45, 15/55)
2 7Ls (50% and 100%)

(And soon to come... a little baby JJ...)

In other words... diving Alu bottles for backgas in Norway is HIGHLY abnormal. (I think I have only seen two guys doing it, and I have about 650 dives here...)

 

[Dan_P]

For me, steel/alu is a matter of whether the tank is backmounted or slung, and/or whether in warm or cold water.

I.e. my logic goes:
Steel tanks make sense when backmounted and one needs the weight due to thermal protection.
Alu tanks make sense when backmounted and one does not need the weight.
Alu tanks make sense when slung due to handling, in my opinion.

@Imla is right that the norm in Scandinavia, is steel - in my opinion that's because of thermal protection and backmounting.
I've never seen anyone in Norway dive alu backmounted. All of Scandinavia, for that matter.

The reason I prefer alu is because I'm not diving backmount, but rather Z-system, so the bouyancy characteristics make a difference in terms of handling.
As all my tanks are "identical" in how they work, I don't care if I'm on a designated "backgas" or stage (bottom gas).
Same gas, and same protocols. Therefore, I don't personally need bigger tanks. Hence, and because of the bouyancy characteristics, I prefer AL80s.

That said, if I were diving backmount, I'd definitely go with steel, too.

In my arsenal:
4 AL80s + 1 AL40.

 

[tbone1004]

@Dan_P

why? It's real simple. My dives right now take a pair of lp121's cave filled, which are 19 liters filled to 250bar, and a pair of al80's. If I tried to do that dive with al80's only, then I would need 6 al80's.
6 al80's are heavier to begin with, require more lead on my rig, and create so much more drag that I would not get nearly as far in the cave despite having the same amount of gas.

Those same 19l's can be used on my same Dive rite Nomad whether they are banded together as doubles, slung on the sides as sidemount, or solo on my back for singles, the rig handles them all just fine.

You don't need them under the ice because your dive time are incredibly short in comparison, you don't have to carry nearly as much reserve gas, etc etc. which is where it shows that you are not a cave diver. You see all of these reports of guys diving Razor rigs with al80's in Mexico, but the average depth in Mexico is shallower than our decompression stops in Florida. You get to choose whether more small tanks, or less big tanks are better. Less big tanks are cheaper, easier to dive, less drag, less handling, and less weight so there is literally no one that I can think of that dives al80's in the Florida caves because they don't make sense.

Regarding your handling comment. You shouldn't be "handling" your primary sidemount tanks. They are essentially permanently attached to you once the dive has begun, hence the long hose. Stages yes, leave them aluminum because you don/doff them in a cave, but the only time your primary tanks get "handled" is before the dive, after the dive, and if you have to do a bottle off restriction. Those restrictions aren't that difficult to do, even with 19L steels because you aren't just swimming around with them pushed in front of you like most sidemount instructors would have you believe. You're wiggling through a snug passage, then as soon as you're back in swimmable passage, you put them back.

As backmounted tanks, they make no sense for single tank either. An al80 is 32lbs empty and holds roughly 80cf of gas. A HP100 is 34lbs empty and holds 105cf of gas. The AL80 requires 6lbs more lead than the HP100. Total rig weight is 4lbs heavier, but only has 75% of the gas capacity for diving. Oh, they're also a couple inches shorter which is more comfortable for anyone under 6' tall.
Why would you PREFER to dive al80's in backmount?

 

[Gareth J]

I can't really add a sensible contribution with regard cave/cavern diving. Its not something I am trained for, or something I have participated in. Although it would be a very sensible thing to do the training to then apply the techniques to wreck diving.

To be frank, I don't think I would even consider using OC in a cave system. The risk of running out of gas compared to an 'infinite' supply on CCR makes OC a non starter for me. I have been lost in a wreck a few times on OC, now I would be very cautious about wreck penetration on OC. Having used CC, the ability to just sit and wait, with no concerns about running out of gas is a wonderful luxury (granted the deco clock is still running).
One of my friends got heavily into cave diving, mainly in the UK and France, but also in the USA and Mexico. He wouldn't consider it on OC, but then he was heavily into risk analysis - it was part of his doctorate.
I still struggle to see what attracted him to crawling through zero vis cave systems in the UK - the clear waters of Florida and Mexico are another matter altogether.

Gareth

 

[Dan_P]

You don't need them under the ice

I've extracted heavily from your - may I add, very enlightening - post, with the above quote. You're absolutely right that the specific requirements to which you apply LP121s, is one foreign to me. From my perpective, for both economical and logistical reasons, a rebreather sounds like a reasonable alternative in the scenario you describe, depth and duration-wise.
Would you not agree?

Regarding your handling comment. You shouldn't be "handling" your primary sidemount tanks. They are essentially permanently attached to you once the dive has begun, hence the long hose. Stages yes, leave them aluminum because you don/doff them in a cave, but the only time your primary tanks get "handled" is before the dive, after the dive, and if you have to do a bottle off restriction. Those restrictions aren't that difficult to do, even with 19L steels because you aren't just swimming around with them pushed in front of you like most sidemount instructors would have you believe. You're wiggling through a snug passage, then as soon as you're back in swimmable passage, you put them back.

But I do handle my tanks. They're all interchangeable, which is in the nature of that configuration, and one reason that I appreciate diving it. They're not permanently attached.
I can swap the tanks around - without having to swap regs, change the donation procedure, having to deal with two longhoses, or alternatively fiddle an inflator and figure out how to hand off a permanently attached tank during a donation.
In either case, mine aren't static when donned, I swap them around freely. Which I find handy when boat diving, but that's another matter entirely.

I'm not saying that makes "me right and you wrong" or vice versa.
I'm saying it's certainly interesting to hear about the needs that you see in your diving, that's all. I hope you too understand that mine differ.

In either case, we're both speaking about each other's respective back yard - if I travel to yours, I'll need to rent tanks anyway, and can pick whichever one I deem most sensible for that specific job. And vice versa.
I think the same principle holds true, as does to sidemount/backmount dedication - aluminum tanks don't make sense to a new dedicated backmount diver in Scandinavia to start up diving with, unless aiming for it's application at tech 2 level. Little we agree or disagree on here, will be universally applicable.

But the AL80s make a world of sense from my perspective.

As backmounted tanks, they make no sense for single tank either.

If your end goal is LP121s, bene, get an LP121 for your first tank in backmount - if your end goal is AL80s and rebreather, it kind of does make sense to start off on an AL80 at OWD level. At least when your rig can support both backmount and sidemount, surely? And allows feasible interchangeability of all your tanks?