CCR max depth?

[Rhone Man]

I remember reading an article written by somebody who seemed well placed to know, and he was talking about military rebreather use, and he implied that although much of it was classified in terms of maximum depths etc., nobody in the USN seemed to have any problem admitting that they conducted missions on rebreathers in the 1,000 - 2,000 foot range. He also implied that the rebreathers they were using were not the sort of thing you could buy as a civilian. That was about 5 years ago, so Lord knows how deep they go now.

 

[down4fun]

Many CCR divers whose intention is to go "deep" (and I have never been close to the depths David achieved so deep in this case is anything between 60 and 120 metres), take greater than normal care when packing sofnolime into their scrubber canister. They will attempt to remove all dust and be anal about settling the lime as much as possible. I am in the school who believe that "really" tamping the scrubber so that you can get an extra few dozen grams into it, is counter-productive. What little benefit is derived from more media for CO2 to bond to is negated by an increase in Work of Breathing. This school of thought feels that even an extra joule per litre added to the WOB is potentially dangerous... let me rephrase that... challenging.

However, it is NOT uncommon for a CCR diver to cram a little more lime in for a deep dive. "We all do it," and I am sure that if David were here, he would be amply able to present very good reasons for the way he packed his that day.

I hadn't heard this before about overpacking the scrubber. But it seems pretty silly. Certainly you want to make sure there is no channeling, but to try to cram a few more granules in seems pointless. First off, how long a scrubber will best is a best guess scenario. And a gram more of sofnolime in a 8# scrubber is negligible.

I'm not claiming to be anywhere near Dave Shaw, but for my deep dive I didn't want anything new or changed. No new variables.

 

[Superlyte27]

1000ft for ccr is very very deep. Divers typically switch to OC deeper that 300ft, I see this a lot. That said Don Shirley used to dive dual and modified inspos to 600ft. I dont know ccr but was under the impression most factory units have max depth of 300ft??

It's my opinion that CCR's really begin to shine at 250+. I've had mine to 300' and it was perfect. I'm hoping to hit 400' in the near future. I'll never do deep again on OC, so much easier/safer/cheaper (IMHO) on CCR.

 

[Akimbo]

Is it possible for them to deploy out of the sub at around 1000ft and make a rapid ascent to their target? I would imagine automatic deco, but for how long?

For all practical purposes, no. Hyperbaric physiology is not that different between recreational divers and athletes like SEALs. Maybe this link will help explain.

http://www.scubaboard.com/forums/commercial-divers/467739-what-saturation-diving.html

It is difficult to envision a scenario where you would want to make a lockout like this. Covert military deep lockouts are for doing work on the bottom like object recovery, cable tapping, time-delayed destruction (demolition or otherwise) or misinformation — basically espionage. There really isn’t any reason for combat swimmers to surface from great depths to avoid detection; it can be done from much shallower depths.

 

[sunkmail]

Just thinking out loud here for a moment ...

Is it possible that the 1000 ft was referring to distance rather than depth?? (Remember, "20,000 Leagues Under the Sea" didn't refer to depth.)



I know that isn't a super far distance, but navigating in the dark in open water can be tricky. Any little error in the compass and they could go really off course from the desired landing point.
I'd imagine that a small, stealthy, boat 100 ft from shore, on a dark night, would be pretty easy to miss, but make the navigating significantly easier on the divers.

 

[Akimbo]

Just thinking out loud here for a moment ...

Is it possible that the 1000 ft was referring to distance rather than depth?? (Remember, "20,000 Leagues Under the Sea" didn't refer to depth.)...

Interesting thought, but 1000' horizontally is nothing for combat swimmers. They travel many miles by swimming and even farther using SDVs (Swimmer Delivery Vehicles). 1000' deep is not unreasonable at all with the support of a nuclear submarine equipped with a saturation diving system, which is known to have existed as early as the 1970s.

The most difficult part of a rebreather operating at 1000' is to carry enough diluent gas to inflate the bags and lower the percentage of oxygen to maintain a reasonable PPO2. The diluent supply problem is not an issue if the dive starts near 1000' in a chamber and the mix in the rig is already appropriate for the depth, between 1 and 2½% O2 or 0.3 to 0.8 PPO2.

Also remember that going on an open circuit bailout in case of a rebreather failure is not an option because you couldn’t carry enough gas at 1000' for more than a few minutes and the bubbles would give away your position.

The electronics and sensors have no problem controlling such low oxygen levels because they operate on partial pressure, not percentage. The absorbent is only marginally effected because the amount of CO2 produced by the body is virtually the same.

The biggest practical impediment is thermal. That problem is solved by open circuit hot-water heated wetsuits that also heats the absorbent canister and breathing gas. If I had to “guess” I would say that the divers would be using a push-pull rig — basically a rebreather on the sub itself. Their umbilicals would have supply and return hoses along with their hot water, depth sensing, hard-wire communications, video, and lighting. A rebreather on their back would be for bailout.

You can’t expect any reasonable task to be accomplished in the few minutes of bottom time that a surface dive to 1000' on a rebreather allows; therefore a submarine platform makes sense. You can’t use an acoustic locating device for untethered divers to find their way back since it would reveal the sub’s presence; therefore umbilicals make sense. If divers are tethered they may as well have hot water and all the rest. At that point bottom times can be measured in days, not minutes.