Question Bailout gas configs for tech/deep chestmount rebreathers

[Wibble]

Could someone confirm this viewpoint please:

A drawback of ChestMount vs. Backmount CCR is that Backmount tends to have larger scrubbers available which is important for deeper diving (both dive length and additional scrubber for the wider active front). AIUI ChestMount tends to have small scrubbers as there's limited space. Similarly, chestmount has smaller O2 cylinder as it's transverse below the unit.

Also scooters: isn't the DPV tow line going to be caught around the chestmount unit+O2 bottle?

 

[justinthedeeps]

Could someone confirm this viewpoint please:

A drawback of ChestMount vs. Backmount CCR is that Backmount tends to have larger scrubbers available which is important for deeper diving (both dive length and additional scrubber for the wider active front). AIUI ChestMount tends to have small scrubbers as there's limited space. Similarly, chestmount has smaller O2 cylinder as it's transverse below the unit.

Also scooters: isn't the DPV tow line going to be caught around the chestmount unit+O2 bottle?

There are some videos out of Bali recently of some quite highly trained fellows scootering around at 180 metres with a backmount primary rebreather, plus a chestmount bailout rebreather, AND bailout cylinders.

Probably no more encumbered than the deep OC twinset plus chestmount config that inspired this thread.

How many bar-litres oxygen is enough? A 2L at 200 bar has 400 bar-litres, you could be on the loop for a 200 minute dive at a consumption of 1 bar-litre per minute and still have half remaining for accelerated deco.

 

[lostsheep]

You're just moving all this stuff from your back to your front and/or sides, and you can't drop any of the bottles and you need 4+ if you want redundant dil. And creating a ton of conflicts with suit gases, suit heaters, and canister lights. For what? Why? What exactly are you gaining here?

Just use a dang BM unit, there are tons out there moving everything off your back accomplishes nothing except to make everywhere else crowded.

To be clear, I am not advocating wasting the real estate on your back or running a single deep dilout.

That out of the way, the alleged conflicts just aren’t the problem you think they are when using the standard OC DIR configuration with a CM, I.e., BM doubles , slung deco bottles, suit gas on the backplate, and canister on the right hip.

I’m not sure what your point is about bottle count; how many does a heavy configuration BM unit have? By my count they are the same.

Why can’t you drop bottles? Slung bottles are slung bottles, and no one is taking their backgas off…right? Related, a CM itself can be staged / swapped easily, remove and replace was part of the 1st class.

What are you gaining? Familiarity and standardization with OC gear because IT IS your OC gear. There’s value in modularity.

I would happily run a BM unit but for now the CM is what I have. I’m not claiming it’s the best at anything I just object to the inaccurate claims against it.

 

[Rayk]

While I am reading this thread, I really get to more and more appreciate my instructor and training I have received. It is one hundred percent true that one must seek for quality education and learn right procedures. There are some wild stuff out there.

 

[justinthedeeps]

While I am reading this thread, I really get to more and more appreciate my instructor and training I have received. It is one hundred percent true that one must seek for quality education and learn right procedures. There are some wild stuff out there.

I think I would add to this a willingness and capability to carefully reason through scenarios, seeing the risks or drawbacks of each approach, including our own. Debate is great. Think about what people said. There might something to it that you hadn't considered. Valuable and quite interesting as a learning experience.

 

[Dsix36]

@Cio interesting point on an H valve. Does in theory address the loss of gas issue from a single cylinder. Is anyone doing that?

Still only 1 o-ring from total gas loss.

 

[mr_v]

While I am reading this thread, I really get to more and more appreciate my instructor and training I have received. It is one hundred percent true that one must seek for quality education and learn right procedures. There are some wild stuff out there.

Have you ever considered that your instructor may not be correct or know everything? Just a thought.

 

[Dsix36]

I moved to a CM from a BM unit. I did it primarily for for 2 reasons. I moved to cave country and no longer do ocean dives so caves are now all I dive. I wanted something easy to remove, clip to the line, and continue in SM to get some places that BM never used to let me get AND I was getting sick and tired of so much weight on my back when climbing out of the water after a dive. My CM has been remarkable at doing everything that I am currently doing. I have to admit that the concept of dilout was a bit of a concern after all my years of having planned dives much differently. I now must accept that my 2 dilout tanks have much less capacity for bailing out than previously and the configuring for deeper and/or longer dives is more complicated and difficult than previously too. I doubt that I will ever do anything deeper than 300ish foot again but I am beginning to to longish dives again and getting 3 stages clipped on is a PITA considering I used to be able to clip on 4 stages pretty easily. I really just hope that people are honest with themselves in regard to the amount of gas needed if a bad day comes their way

 

[kensuf]

They aren't honest with themselves.

 

[J-Vo]

I see a lot of strait up stupid CCR gas planning. Primary gas aside, why is everyone in cave country afraid to take an 80 of O2. I see CCR divers planning an hour of deco with just a 40 for bailout, and probably not even a full one.