Why have a rebreather?

[wedivebc]

I disagree with the third item. Think about it: A shark emits no bubbles (normally, at least), so if the theory of 'no bubbles=tame fishies', do you really think the fishies would still be there to look at? Fish don't survive by being friendly with a 6' long neoprene-covered object that's trying to get closer to them....

On my first ever rebreather dive I was playing with an octo at a site I had dove 100 times before and never seen an octo in the open. Believe me you bubble blowers are a noisy bunch

 

[teknitroxdiver]

I know. But the point still remains that if it isn't scared by a huge clumsy diver (and yes, we're all clumsy compared to underwater creatures...), it is in trouble, wouldn't you agree?

 

[BigJetDriver]

I disagree with the third item. Think about it: A shark emits no bubbles (normally, at least), so if the theory of 'no bubbles=tame fishies', do you really think the fishies would still be there to look at? Fish don't survive by being friendly with a 6' long neoprene-covered object that's trying to get closer to them....

Tek,

Well, sir, it sounds as if you should take a trial run on a re-breather!

I am here to tell you that they are less disturbed by a quiet RB diver, and sometimes downright friendly.

The pretty little neon fish that hide in the reef as you bubblers go by come out in clouds after you go away. I have watched that happen.

The Garden Eels that keep ducking down when you get close, come up right in front of my face mask!

The turtle that swam away when he saw you, spends his time eating a sponge in front of me and my student!

These are simple, but real-life, observations that I have made while diving my RB. Try it. You will like it!! :07:

 

[teknitroxdiver]

I'd like to take one on a trial. Must be one of those 'gotta see to believe' things....sounds like fun. Then I'd have another excuse to buy an Inspiration...

 

[silent running]

Hello av8er23 , all. I decided to buy a CCR mainly to increase the quantity/quality of my wildlife interactions. I have been amply rewarded. When I dove in Ambergris Key Belize where reef shark sightings are very rare, I saw several big ones every dive. Then there were the 2 100 plus year old turtles I saw. Going to to PNG, which has much better diving to begin with, the animals just got bigger and more numerous. On 1 dive at a place which is not known for having many big animals, I and other CCR divers saw many big reef sharks, 5 Hammerheads, several big Silvertips, a 12 ft Sand Tiger, and a giant Oceanic Manta in the space of about 10 minutes and most of them came around for several passes. There were at least 8 CCR divers in the water. Try that with 8 OC divers. Oh and then there was the 14 ft Bull shark I and 2 other CCR divers saw on the Papuan Barrier reef. It made 2 passes within 4 ft of us. They are not supposed to get that big. The point is, if it's out there you stand a much better chance of seeing it on CCR as you will blend in at worst and inspire curiousity in the animals at best. The other great thing about recreational CCR diving is that as long as the Capt. doesn't move the boat a whole lot, you can make your own dive schedule. I don't know anybody who likes the donning and doffing of gear and wet suits. I would much rather do 3 100 minute dives than 5 60 minute ones. And you will never have dry mouth and always be warmer and than on OC due to the scubber making heat and water as it reacts with your exhaled CO2. There are also of course, many dramatic benefits for tech diving, like cutting deco time to less than half, due to the fact that you're breathing the optimal mix for every depth. A CCR is basically a nitrox/trimx blending machine on your back. Oh, and I believe that with proper training they are safer too, as you have a much greater dive duration to work with and you have more than one way to solve problems. But they are not for everybody, especially lazy people or daredevils-Andy

 

[caveseeker7]

Found this on the internet:
Advantages of rebreathers include:

• Warm breathing air!—the chemical process of removing CO2 from recycled air heats the gas up to around 105° F.

That's correct, the scrubbing process generates heat and moisture (water).
Hence you breathe warm, moist gas (usually not air, though). That will reduce
'drymouth' and to some extend reduce dehydration. The warm gas will aid keep your
body temperature up, and temperature as well as hydration are factors in DCS.

• The high percent of O2 reduces post dive fatigue.

The O2 content depends on the type of rebreather you're using and the depth you're at.
SCRs use the same pre-mixed gases as OC does, so depending on the model and depth
nitrox and/or trimix are used.

CCRs use O2 and a diluent (air/heliox or trimix depending on depth) and mix it while you're diving.
You choose a setpoint, and the unit or the diver keep it there. The partial pressure of the O2 stays the same, the fraction (%) change.
In other words, you get the "ideal" mix for any given depth.

That can be a very high O2 content, or less than 21% depending on how deep you are.

• Your bottom time remains the same no matter how fast you breath, how hard you work underwater, or how deep you dive.

That is absolute nonsense.

Semi-closed rebreathers either have an active gas addition or passive gas addition.
Active the gas flow stays the same independent of depth (within MOD, anyway),
passive addition units are keyed to your respiratory minute volume (breathing rate).
Breathe faster and the gas gets added faster.

CCRs replace only the O2 that is metabolized. Metabolize more, more gets replaced.

In the scheme of things the biggest limitation for dive duration is the cannister duration.
The scrubber ability to remove CO2 from the loop. And that is influenced big time by both
breathing rate as well as depth.

The material itself has a finite capacity. The Inspiration for example around 288 liters of CO2 by CE test protocol. That's at 20 msw/65 fsw, where the scrubber is rated at 180 minutes. If you work hard you not only use more O2, but you generate more CO2.

As for depth, the same unit/scrubber is rated at 88 minutes at 100 msw/328 fsw.
So the material at increased depth but otherwise same conditions can only remove
141 liters of CO2.
Depth alone has cut the capacity in half.

For some more basic info on rebreathers have a look at Ron Micjan's article .
You'll find another one about Partial Pressure Math that'll go a long way in understanding CCRs.

 

[silent running]

Thanks caveseeker for taking the time to staighten out the lame layman expanation. I'm so used to that kind of sloppy thinking that it just washes over me now.-Andy

 

[MikeM_scuba]

Quick question.
How can you travel with Rebreather? Can you take on a plane?
If you have to disassemble it for flight how easy it is to assemble?
Thanks in advance for help.

 

[silent running]

Hi MikeM, people travel with RBs all the time. Some are easier to travel with than others. It takes about 5 minutes to take the cylinders and hoses/counterlungs off my Prism. I put everything but my cylinders and cowling(which go in the checked bag) in a small carry on bag and put it in the overhead compartment. No big deal. I've been to the Caribbean, Indonesia, Mexico and Papua New Guniea and never had any real trouble. The cylinders must be empty and the valves off when they are put in the checked bags. But many places have cylinders to rent, so you don't have to bring them. I usually bring my own absorbant in the checked bag, to keep the cost down. But most places will have this stuff if you are willing to pay for it. With the US luggage allowances I was been able to bring an entire month's worth of sorb to PNG without overweight charges. All I needed at the destination was O2.

 

[Diver0001]

I think the question should be why wouldn't you want a rebreather (other then price of course)

Failure modes. All your eggs are in one basket and some failures (whether diver error or apparatus error) will render you unconscious before you realize that there is a problem.... OC is much more forgiving in this respect.

R..