Question The Right Dive Tanks: Autonomy vs. Tradition

[Njord fr]

Diving in cold quarries and already looking forward to the possibility of training to see those amazing caves you have in France? Listen to your fellow divers!

Which ones ?
The ones in my club who tell me that cave diving is suicide and diving in quarries in february with 7 degrees water is for mentals ?
Or the ones who want to explore, with a lot of training, redundancy and security ?

 

[Njord fr]

Can someone who speaks European and American tell us if the D12 is the same or nearly the same as an HP100? Is it filled to 232 bar?

If so, that would make the 15L basically the HP120. Is that really a standard for single tank in France? The standard here would be the HP100 or Aluminum 80 (11L at 207 bar), with the HP120 not uncommon, but regarded as kind of a specialty tank for air hogs.

The standard in France is 12 or 15 liters @ 230 bars, every club has these (uysually 12 liters for student and 15 liters for instructor btw).

 

[Lorenzoid]

Which ones ?
The ones in my club who tell me that cave diving is suicide and diving in quarries in february with 7 degrees water is for mentals ?
Or the ones who want to explore, with a lot of training, redundancy and security ?

You referred to these fellow divers in your original post:

Fellow divers (all into cave diving) suggest purchasing two tanks, either 7.5 liters, 10 liters, or 12 liters, for reasons including:
- More autonomy (obviously)
- More possibilities for progression (sidemount, double tanks, independent back mount, etc.)
- The ability to consider cave diving with my own equipment soon

If you want to do the kind of diving they are doing, then follow their suggestions for an equipment and training path to get you there. From other replies here, it sounds like D12s would work nicely.

 

[Mod63]

2xD12s for colder water sidemount.

Don't think so - I have yet to see someone sidemounting with a "D"ouble 12 on each side.

 

[inquis]

tell us if the D12 is the same or nearly the same as an HP100?

D12/232 bar is a little smaller than our HP100/12.9L: 6.75" diameter and ~92 cuft each at rated pressure.

 

[rjack321]

D12/232 bar is a little smaller than our HP100/12.9L: 6.75" diameter and ~92 cuft each at rated pressure.

D12 = lp85 overfilled in Americanish

 

[Njord fr]

the choice of which tanks to use is greatly influenced by the type of sm rig you will be diving, is it fresh or salt water, and the water temps you will be in.

some sm rigs are better suited for heavy steel tanks, while others may be best using allum.

I am going to buy a Hollis sms 100 to a friend.
Do you know it ?

 

[Caversluis]

I cold water diver from Denmark here. I am a certified Master Scuba Diver with deep + self reliant diver certificates. I own my won tanks: 15L, D10, D12, 7L stage tank, 10L stage tank. Happy to share my perspective.

On autonomy
Autonomy is good, but it can be achieved in many ways. For regulator failures, you can use a single tank with a dual outlet valve. This allows you to mount 2 first stages on one bottle. I have that on my 15L tank.
Twinset are great for redundancy, but only if you can reach your valves.

On tank size
I use mostly my D10. The D12 are just heavier, for most of my dives I have more than enough gas. Therefore there is no neeed to use the D12.

On economy
In advanced diving, the cost of your tanks is only a very smal portion compared to the other equipment (stages, drysuit, BP/W). Furthermore, you buy tanks second hand. With that in mind, you can change your afterwards without a big cost. Just sell the tanks that you bought second hand, and buy something else second hand.

Backmount or sidemount
Please note that you cannot just take a twinset and split it into 2 sidemount bottles. You will have to change the valve on one of the bottles.

Further thoughts
In terms of redundancy, you can use a 15L tank with a smaller (like my 7L) stage tank. As you have an ambition to do deep technical dives, a stage tank is likely unavoidable anyways.

 

[Njord fr]

On autonomy
Autonomy is good, but it can be achieved in many ways. For regulator failures, you can use a single tank with a dual outlet valve. This allows you to mount 2 first stages on one bottle. I have that on my 15L tank.
Twinset are great for redundancy, but only if you can reach your valves.

That's what I am doing currently, that's a good setup frankly, but I had an adventure with a second stage that got stuck and emptied my tank in 20 seconds... that's why I'm interested in the 'two tanks' setup

On tank size
I use mostly my D10. The D12 are just heavier, for most of my dives I have more than enough gas. Therefore there is no neeed to use the D12.

Noted !

On economy
In advanced diving, the cost of your tanks is only a very smal portion compared to the other equipment (stages, drysuit, BP/W). Furthermore, you buy tanks second hand. With that in mind, you can change your afterwards without a big cost. Just sell the tanks that you bought second hand, and buy something else second hand.

My plan

Backmount or sidemount
Please note that you cannot just take a twinset and split it into 2 sidemount bottles. You will have to change the valve on one of the bottles.

Yeah, but the plan is to have two independant bottles even in backmount, without a manifold.

Further thoughts
In terms of redundancy, you can use a 15L tank with a smaller (like my 7L) stage tank. As you have an ambition to do deep technical dives, a stage tank is likely unavoidable anyways.

Noted


Thank you so much for taking the time to respond, it's greatly appreciated!

 

[inquis]

you cannot just take a twinset and split it into 2 sidemount bottles. You will have to change the valve on one of the bottles.

I split mine without changing valves, although I did have to remove/reinstall one of them.