Standard 80cft side-mounted tanks for CCR?

[Bernie_U]

Most back-mounted rebreathers are equipped with two small tanks for oxygen and diluent. I am not a certified rebreather diver, only tried CCR (JJ, Se7en, Inspi, SF-2) and SCR (Horizon) in a pool. Different to the CCRs and common SCRs, the Mares Horizon SCR uses standard 80cft tanks side-mount. Now, I wonder whether someone dove his back-mounted CCR with side-mounted tanks.

Please apologize if the statements I am going to outline now were incorrect. As mentioned above, I am not a certified rebreather diver. The concept of taking a CCR on air trips, as far as I know, is:

Leave the small tanks at home, travel with the bare CCR to the destination and rent small diluent and oxygen tanks. When you go deeper, you also rent bail-out tanks from the dive center. Normally, everything will be okay and no gas from the bail-out tanks is used. At the end of your trip, you pay the rent for the four or more tanks and the gas fillings of the small back-mounted CCR tanks only.​

However, if you planned to dive non-deco profiles (just EAN, no Tx) on CC: Wouldn't two side-mounted standard tanks be sufficient to serve twice, as diluent and oxygen supply in CC mode and as bottom gas and deco gas in an OC mode? Anyone who tried that?

 

[tbone1004]

@Bernie_U
Sidemounted bailout tanks are the norm in cave diving. One of them will often be used as the diluent bottle which is how sidemount CCR's are run.
You don't need any more O2 than the 2l or 3l that is on the unit, so going to a bigger bottle is not really beneficial.

Most destinations that support CCR's will have at least 2l and 3l bottles for rent in addition to sorb, so finding them is not that big of an issue.

The Horizon is a SCR so the 3l bottles that you'd normally mount to the sides of a Revo are almost enough together, but getting the plumbing right is complicated for that, plus you'd still need enough bailout gas. Makes much more sense to use the big bottles for that.

 

[rjack321]

However, if you planned to dive non-deco profiles (just EAN, no Tx) on CC: Wouldn't two side-mounted standard tanks be sufficient to serve twice, as diluent and oxygen supply in CC mode and as bottom gas and deco gas in an OC mode? Anyone who tried that?

If I understand you correctly you are suggesting not using the 3L bottles at all and just side mounting a diluent and O2. This means that if your diluent regulator fails you have no way to dive the CCR and no way to bailout either. Or if your oxygen regulator fails you cant use the CCR and also have no deco gas.

So no, its not don't this way.

 

[doctormike]

You need bailout whether you are going deep or not. I suppose that in a very shallow pool dive, you don't really need bailout since you could probably stand up more easily than you could deploy your bailout (especially if you don't have a bailout valve).

Many rebreathers use "dilout", which is something like what you are suggesting. That is, your dil and bailout are the same bottle. You only use dil for maintaining loop volume on descent (or for a dil flush - a contingency procedure). So you don't need a lot of it. Both your deep bailout and your dil need to be breathable at your maximum depth, whether or not you use dilout.

There are different ways of configuring dilout. I have a JJ, and I dive it in the standard fashion, with a separate bottle for dil and bailout. The dil and O2 are in small backmounted tanks, and my deep bailout is in an AL80 slung sidemount style on the left. If I am doing something with more deco, I will also take along a richer mix in case I need to bail out with a significant deco obligation (generally an AL40 of O2). But the GUE configuration is to take two 50 CUF tanks, mount them on the back of the unit (de-inverted) with a manifold between them, and then to use that as dilout with no sidemounted tank at all unless you need a rich mix for deco.

 

[a878bob]

Your making this so complicated.
2 small cylinders for your unit, air, and o2.
Sling an al80, done.

 

[tbone1004]

@Bernie_U also, please keep asking random questions! if we start getting grumpy it's because we are all getting stir crazy and bored out of our skulls. Questions like this may seem obvious to those of us that dive these things on a regular basis, but it's good to be able to open real discussions and start explaining the why's of what we do

 

[jale]

Hi
Indeed Dilout and sidemounting tanks is the answer.for using local ressources that are not always perfect for CCR diving.
Of course, it needs to be adjusted to the kind of dives you are doing.
As an example, for my last trip to the Philippines, I wanted to use my RB for some rec dives.
I just went to a rec center offering Nx where I got a s40 filled at 100 bar with O2 (they didn't have a booster) and another s40 with air.
It was perfect for my week.
Often, you can only get s80. A bit bulky but manageable.
Of course, i brought my lime with me but you only take that you need.
Anyway, flexibility is going to be the key word if we are lucky enough to be diving again...

 

[Bernie_U]

Thanks to every-one for your sincere input! Didn't note any grumpiness so far.

Rjack 321 got me right, I consider not using the 3L bottles at all. It is as risky as recreational OC diving with a single tank / one valve / one 1st stage. The Mares guys decided that would be alright for the Horizon, and they suggested these limits for their latest SCR:
- non-decompression dive, max 30 meters, one tank (EAN appropriate for target depth)
- max. 25 minutes decompression, max 40 meters, two tanks (1x EAN28 for 40 meters, 1x EAN50 to EAN99 for decompression)

According to Doctormike and jale, dilout is used in some situations, but probably not widely spread. Would you also use the oxygen for accelerated deco on the shallower stops (max pO2 = 1.6 bar)?

 

[tbone1004]

Thanks to every-one for your sincere input! Didn't note any grumpiness so far.

Rjack 321 got me right, I consider not using the 3L bottles at all. It is as risky as recreational OC diving with a single tank / one valve / one 1st stage. The Mares guys decided that would be alright for the Horizon, and they suggested these limits for their latest SCR:
- non-decompression dive, max 30 meters, one tank (EAN appropriate for target depth)
- max. 25 minutes decompression, max 40 meters, two tanks (1x EAN28 for 40 meters, 1x EAN50 to EAN99 for decompression)

According to Doctormike and jale, dilout is used in some situations, but probably not widely spread. Would you also use the oxygen for accelerated deco on the shallower stops (max pO2 = 1.6 bar)?

if the O2 bottle was sufficiently large to use for that dive, then yes it would be used as an OC deco bottle.

 

[W W Meixner]

Bernie...

You might like this...

This a chest mounted Triton...clipped off to the front of any standard rec or modular BCD...using standard back-mount cylinder as diluent/bailout...

Attached also...are two photos of the Triton in side-mount configuration...

You can see the small oxygen cylinder is mounted via cam band and S/S mounting plate horizontally to the bottom of the Triton cover-bag...

This is an MCCR...Dive Rite is about to introduce something similar...which is ECCR... called the Optima CM...

They are not as as expensive as a typical back-mounted CCR...but having said that...they're not cheap either...Dive ready...you can plan to spend $6000...USD...

Personally...Between the two...I prefer the manual Triton...

W.M...