Question Bailout gas configs for tech/deep chestmount rebreathers

[flymolo]

What is the GUE rebuttal?

This is getting a bit pointless..

 

[justinthedeeps]

This is getting a bit pointless..

The point is to think mate. That is the point of this thread.

Telling people "just use our Standard Gases" and that it's not worth thinking about it is pointless... but there's been plenty of that in this thread.

 

[flymolo]

The point is to think mate. That is the point of this thread.

Telling people "just use our Standard Gases" and that it's not worth thinking about it is pointless...

Oh, gee I never thought of it like that. Fanks mate

 

[LFMarm]

Given that the discussion is getting more in the details, here is more context on the gas plan I was describing before:

• Depth: 100 m
• BT: 15 min
• GF: 70/85
• Gases (all in sidemounted independent tanks):
  • 10/70 in AL80
  • 21/35 in AL80
  • 50% in AL80
  • O2 in AL80
  • O2 in AL13

In case of bailout:

• In case of loss of 10/70 while at the bottom with CCR still working, ascend to first stop and plug 21/35
• In case of failure of CCR AND one of the gases, I will need bailout gas from one of the team members

I don't pretend this is the best or safest plan but it's one I am comfortable with.
Very open to hear suggestions from others on how to improve it and increase the safety.

 

[rjack321]

80% is also missing, the advantages of which both Cio and I have pointed out. What is the GUE rebuttal?

If you bring actual O2 you can cover the loss of CCR O2. 80% you can sorta, but you end up needing to flush the N2 away which lowers your fO2 so its a big messy ascent with likely lots of yo-yoing from all the flushing and adding and flushing. There are ample other reasons to bring O2 BO on 100m a CCR dive. The only people doing 100m dives with air, 32% and 80% BO are fools on the internet - that went out of fashion for good reason 20 years ago.

 

[rjack321]

Given that the discussion is getting more in the details, here is more context on the gas plan I was describing before:

• Depth: 100 m
• BT: 15 min
• GF: 70/85
• Gases (all in sidemounted independent tanks):
  • 10/70 in AL80
  • 21/35 in AL80
  • 50% in AL80
  • O2 in AL80
  • O2 in AL13

In case of bailout:

• In case of loss of 10/70 while at the bottom with CCR still working, ascend to first stop and plug 21/35
• In case of failure of CCR AND one of the gases, I will need bailout gas from one of the team members

I don't pretend this is the best or safest plan but it's one I am comfortable with.
Very open to hear suggestions from others on how to improve it and increase the safety.

Or I dunno just acknowledge that a unit CM isn't the right tool for the 100m ocean dive in the first place?

 

[justinthedeeps]

If you bring actual O2 you can cover the loss of CCR O2. 80% you can sorta, but you end up needing to flush the N2 away which lowers your fO2 so its a big messy ascent with likely lots of yo-yoing from all the flushing and adding and flushing. There are ample other reasons to bring O2 BO on 100m a CCR dive. The only people doing 100m dives with air, 32% and 80% BO are fools on the internet - that went out of fashion for good reason 20 years ago.

I've done the drills plugging in 80%, it's not really THAT bad... 50% definitely not as fun, nearly pointless when you could just bail out.

32/00 yeah that sounds a little foolish. But 32/20, 35/25 etc are indeed legit deep deco.

 

[Learner Diver]

On the last trip the other two divers AP and rEvo agreed after seeing the configuration and the ease of being more self reliant that it just works better.

Is too much redundancy a concern? Just curious... 5 cylinders + CCR + scooter for a 12 to 13 ata dive. Were currents the main factor for your configuration? Was a shot line and support divers part of the group?

 

[PfcAJ]

I know better than to jump into this thread because I know too well how the discussion goes, but oh well, here we go…

I’ve said it many times, if you are using a single deep bailout as your dil, you are effectively diving without deep bailout, just a big dil bottle, and is an example of trying to jam a square peg (sidemount or chest mount rebreathers) into a round hole (deep diving). 5 or 6 years ago, we wouldn’t have been having this discussion, because everyone knew it was dumb. Now with the explosion of sidemount and chestmount units… we’re forgetting the basics because we’re trying to sell these units as the best thing ever.“Oh but I can just race up quick and switch to my next gas” is a horrible mindset. You never really know how long it will take you to ascend when dealing with a failure. Team separation, buoyancy issues, etc aside, what if you’re inside a wreck or should really make it back to the up line before ascending?

Carry sufficient bailout gas to get yourself from max depth to the next gas. Drive the unit with a SEPARATE gas source.

Good lord finally someone sensible in this thread.

Took far too long to get here.

 

[PfcAJ]

Most folks diving the JJ this way have multiple sets of lp50s (eg a 21/35 and a 15/55 set). Its just the cost of diving this way and not really any different than me having 8 different 80s of BO in the garage.

This. I have 3 sets of RB configured manifolded doubles with 18/45 (lp50), 15/55 (lp85s) and 10/85 (lp120s) pick the tanks I need for the dive. Often the deeper the dive, the higher the BO requirement so this fits really well.

In the off chance I need a different gas in a different BO volume I’ll adjust the rack as needed. Not common, but sometimes it be like that.