Technical diving with oc versus ccr gas requirements

[tbone1004]

Yeah, chasing 1.6 on your shallower stops is impossible. Super wasteful too. Since that's where most of your deco is, an OC diver has an advantage there since they can hit 1.6 on their 20ft stop and CCR will need to settle for 1.4. But the CCR diver can even it out on intermediate stops where the OC diver is working with a less optimal PO2. The real magic is on multilevel stuff. CCR will prevent a lot of deco from accumulating compared to OC by maintaining an ideal PO2 when away from the MOD. I did a 3 hour swim at Madison with some buddies on OC. They used 32% and ended up with 15 min of O2 time. I had no deco.

If you're doing multi-level or weird depth cave dives, particularly on a DPV or in high flow, you can also goose the ppO2's on the way out to start clearing deco earlier. I will typically go up to about 1.4 on the exit side if I'm not kicking and that helps to clear some of the deco a bit earlier.

 

[kensuf]

If I were on a cave dive, I’d really like to know if I had an oxygen leak so I could turn around and go home before it became a bailout situation.

I mean that’s pretty simple and a dang good reason to have a gauge.... mitigate the issue before it becomes a real problem.

Me too. I think SCR mode from 10k out is unrealistic. That's why I have a gauge and why I'll usually sling a 6ft3 of spare oxygen on big-boy dives.

 

[helodriver87]

Me too. I think SCR mode from 10k out is unrealistic. That's why I have a gauge and why I'll usually sling a 6ft3 of spare oxygen on big-boy dives.

How do you carry it? I keep inflation on my back, so I could probably just plate mount a 6 of O2 just like a drysuit bottle unless there's a better option.

 

[kensuf]

How do you carry it? I keep inflation on my back, so I could probably just plate mount a 6 of O2 just like a drysuit bottle unless there's a better option.

Butt clipped works really well. All it is is a drysuit bottle with a hose clamp and a clip. Actually, it's the same bottle I use for drysuits when I'm in need of a drysuit bottle.

 

[tbone1004]

How do you carry it? I keep inflation on my back, so I could probably just plate mount a 6 of O2 just like a drysuit bottle unless there's a better option.

KISS Sidekick with O2 sphere. I can swing it forward and see the SPG, but plugging in offboard O2 from a second O2 bottle is super sketchy with a CMF. Open needle valve isn't an issue since you can open it up all the way to clear it, but if you have a CMF I wouldn't attempt it, even with QC4's which have very small water ingress. If that was a "must" then I would put a second O2 MAV on there so you had a "dumb" mav on the spare bottle that doesn't have a leak on it.
If I was going to put redundant O2 on it, it would be a drysuit bottle that was plumbed in from the beginning of the dive but with the valve off and strapped to the CCR. With the Meg on a rack, since I use the 3l as inflation, a drysuit bottle rigged as normal would go into the O2 MAV on the lung.

 

[kensuf]

I've flooded a CMF once in the ocean, it wasn't pretty. However, if the choice is destroying an orifice, bailing out to OC, or possibly going hypoxic, I'll destroy the orifice as a first step every time.

 

[Manatee Diver]

...I'll usually sling a 6ft3 of spare oxygen on big-boy dives.

Finally found a use for those 6cuft spare air bottles?

 

[tbone1004]

I've flooded a CMF once in the ocean, it wasn't pretty. However, if the choice is destroying an orifice, bailing out to OC, or possibly going hypoxic, I'll destroy the orifice as a first step every time.

was thinking more about it clogging than destroying it. I don't mind killing it, but I'd rather not have it clog. I've been talking to @Bobby over the years about redundant O2 and since my primary CCR now is a CMF I'm tempted to leave an omni MAV on the spare bottle so I can plug that in since the unit doesn't have traditional lung configurations. On my Meg I just left a standard drysuit inflator on it and it wasn't an issue and I don't have a dil MAV on there to plug into since it only uses the ADV which is tied to the necklaced secondary which is probably not ideal. I may also just hard plumb it in ahead of the leaky valve and leave the valve off, but will check into that as this thing continues to evolve.

 

[rjack321]

Sorry I don't understand. Why would the same square profile have a longer deco time on ccr?

Below about 60-65m you will have more deco on CCR than a similar dive on OC. If you get to multilevel this difference can get negated, its most obvious on square profiles. Its a common misunderstanding that CCR has less deco.

 

[JonG1]

was thinking more about it clogging than destroying it. I don't mind killing it, but I'd rather not have it clog. I've been talking to @Bobby over the years about redundant O2 and since my primary CCR now is a CMF I'm tempted to leave an omni MAV on the spare bottle so I can plug that in since the unit doesn't have traditional lung configurations. On my Meg I just left a standard drysuit inflator on it and it wasn't an issue and I don't have a dil MAV on there to plug into since it only uses the ADV which is tied to the necklaced secondary which is probably not ideal. I may also just hard plumb it in ahead of the leaky valve and leave the valve off, but will check into that as this thing continues to evolve.

Could you link the 1st stages via HP ports, and then equalise if required, or connect the CMF to a manifold fed from 2 o2 cyls, 1 isolated until required.