Need more gas - now what?

[tbone1004]

@Dan_P most divers doing that 30m/30min profile in the US are doing them in jackets and single tanks. Most is done with a 17l/250bar tank which is a roughly 130cf tank.
It is exceptionally rare to see doubles or twin tank sidemount in the US for that type of diving.

 

[Gareth J]

In the time I've spent diving (admittedly, much less than most on here) I've seen precisely zero divers who were diving with more than one tank at a time, and zero rebreathers. I'd wager money that the overwhelmingly majority of all people who get certified to dive never progress to doubles or a rebreather. That some of the most passionate divers eventually progress on to tech diving doesn't mean that "the vast majority of divers" have a need for any such thing. I've dived to recreational limits and didn't surface thinking "darn, wish I'd had a second tank with me".

You need to keep in mind that diving is like any other pass time.
Rather like visiting the countryside, there are those who go for a walk or hike in the hills with a pair of boots and a waterproof, and those that hike across the Andies, or climb Mount Everest.
The percentage involved in the first is significantly higher than the percentage involved in the last.

With diving it also relates to where you are located. In a warm tropical area, you are likely to see a lot of single tanks and tourist divers. In a more temperate area there will be far fewer tourist divers, a much more enthusiastic group, more inclined to spend on more specialised equipment.
Also, in more temperate water with lower visibility, divers are more inclined to equip themselves with redundancy to mitigate the risk of buddy separation.

My late partner was not interested in deep dives. She wanted to take photographs.
But she dived twins, and will do as much as 15 minutes of decompression on a dive, if she is getting good pictures.
Twins give her redundancy if we get separated, which is a high likely hood with two photographers. Especially when she will indicate shes is going left, then change her mind and go right as soon as I look away .
For her a dive should be 60 minutes - because that was when the batteries started to give out. (As long as it was inside her air allowance and maximum of 15 minutes of deco' - and she wasn't cold).

Not all passionate divers move to technical diving. They may take up photography, marine life survey/conservation, or even archaeology.
I watched a photographer in Malta diving in 10m (30ft) on his own. He was wearing twin 10l cylinders so that he had redundancy in case of equipment failure, so that he could solo dive!

Gareth

 

[Bob DBF]

Of course, a diver who never advances beyond DSD or OWD, won't need the extra gas

I can understand that with the DSD, since he would be limited by depth and the DM he has to have with him to control the dive. If you could explain how an OWD wouldn't need more air as he gains experience.

In my experience, the majority of those who progress, end up on a different solution than jacket style BCD and single tank.

Considering the diving in Scandinavia, I can understand why divers would go to a BP/W or other similar solution, however in less demanding environment there are a lot of choices to make a jacket suitable to carry more gas.


Bob

 

[Trace Malinowski]

Scaling Hogarthian OC:

0 - 100 ft: use a single AL80
100 - 150 ft: convert AL80 to Nitrox50 bottle + doubles
150 - 200: add AL40 oxygen + Nitrox50 bottle + doubles
200+: add another AL80 bottom stage + AL80 Nitrox50 + AL40 O2 + doubles

And, you can problem-solve an isolation manifold behind your head:

 

[Dan_P]

I think the extra huge tank solution is a real problem only if there's a reliance upon a BCD to work - other than that, my only concern about it is that it won't scale anywhere else.
But of course, I understand that a lot of divers never progress to tech, that goes without saying.

 

[Dan_P]

Scaling Hogarthian OC:

0 - 100 ft: use a single AL80
100 - 150 ft: convert AL80 to Nitrox50 bottle + doubles
150 - 200: add AL40 oxygen + Nitrox50 bottle + doubles
200+: add another AL80 bottom stage + AL80 Nitrox50 + AL40 O2 + doubles

Makes sense.

Most of the divers I see, start out on a 12L or 15L steel tank, which is of course less recyclable than the AL80 later on (unless building a 12L into a doubles set by adding another and a manifold).
Of most I've seen progress to technical courses, the majority usually go for an AL40 as their first deco bottle, but I like the way you've recycled really well through the progression.

Another option:
0-60ft: 1x AL80
60-100ft: 2x AL80
100-150ft: 2x AL80 + 1x AL40
150-200ft: 3x AL80 + 1x AL40
200+: 4x AL80 + 1x AL40

 

[rjack321]

Makes sense.

Most of the divers I see, start out on a 12L or 15L steel tank, which is of course less recyclable than the AL80 later on (unless building a 12L into a doubles set by adding another and a manifold).
Of most I've seen progress to technical courses, the majority usually go for an AL40 as their first deco bottle, but I like the way you've recycled really well through the progression.

Another option:
0-60ft: 1x AL80
60-100ft: 2x AL80
100-150ft: 2x AL80 + 1x AL40
150-200ft: 3x AL80 + 1x AL40
200+: 4x AL80 + 1x AL40

Don't you have steel over there in Scandinavia? Why oh why would you use stages of backgas plus al80 doubles for a those 130ft+ dives (unless you are someplace without them)

 

[Dan_P]

Don't you have steel over there in Scandinavia? Why oh why would you use stages of backgas plus al80 doubles for a those 130ft+ dives (unless you are someplace without them)

It doesn't matter how many of them I need, I'm on the same rig, and the way I interact with them is 100% consistent.

Why would I swap over for first one steel tank on a single-tank rig, then a twinset on a doubles rig, and then abandon it to add off-board tanks?
I don't need to buy two rigs, only one. And for a 130ft dive, I'll have 3 tanks that have the same 1st-stage on them, so I have redundancy if my deco tank first-stage fails.
And, I can gasshare my deco tank.

Also, as you hint to, an operator may not have twinsets for rent where I travel to.

 

[tbone1004]

@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

 

[rjack321]

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.