q's about dept and longevity

imwax3

Silly q's but I was wondering exactly how deep and how long one can stay underwater using a ccr. Is there any publications I can get to start to study for my course certificate on rebreathers? Very new to this sight and read were cedric went down I believe 636 ft. Which is nuts. But hope to reach that level of comfidence one day.

Scuba_Vixen

"Nuts" is a very relative point of view. There are folks I'd consider safer at 600' on their RBs, than others in a half full bathtub at home.

When you get to expedition/exploration level diving, you usually have in place support operations that you don't have otherwise. Habitats for deco on those 20 hr dives, for example.

To give a relatively meaningfull answer to how deep/how long, Very experienced divers seem to see 400 to 450' as a practical limit with overall runtimes exceeding 4, 5, maybe 6 hrs as getting into the uncomfortably long zone, and about as far as you'd want to push most of the better scrubbers.

RonMicjan

there are several answers to how deep and how long

How Long?
duration of the scrubber canister used, there are more than one version for many rebreathers, 2 hours up to over 10
duration of your oxygen and diluent supply, a 13 cf cylinder can last me for 3-4 hours.
bottom time based on decompression status, how much Nitrogen and or HE your body has absorbed, before you have to make stops on the way up, or how long of stops if you continue into planned deco diving. An 80 foot dive for 120 minutes at 1.2 setpoint will obligate you to 10 minutes of decompression. Most folks will not be able to get an alum 80 to last that long at depth.
thermal considerations, in warm water a person can stay under for many hours, in cold water, it is based on how cold and what kind of thermal protection you have. My longest cold water dive is around 2 hours, warm water dives have run into 3, by then Im hungry...

How deep is mostly based on your level of training and comfort. different machines are rated to different depths. Cedric did his 600+ on a meg (my chosen weapon), his partner was on an ouroboros, AP machines are rated by CE to 300ish, the manufacturer now says 500, CK is 250ish and the SK is 165. What kind of diving do you wish to do? Pick the correct machine now and it can take you a lifetime to outgrow it, or pick the wrong one and outgrow it in 6 months.

Advantages over normal open circuit scuba are relative, gas efficiency can be as high as 100 times greater, depending on the depth you compare at, cost is significantly higher to get into the game, (unit + training = 5500-15,000)but savings while diving using helium based mixtures can pay for your CCR eventually. Instructional costs are higher, consumables (scrubber material) can cost more than gas fills for OC, but one can run to 10+ hours on a $20 scrubber fill.

you are in the right place, keep reading and learning. Hit some of the articles, but remember, what someone's opinion is, may not match what you want to do. most everyone will swear that what they dive is the best and all the rest are cattle patties. This is especially true for someone who is selling brand X, but not brand Y, consider the source. Advanced diver magazine occasionally sets up Rebreather tryout days in a pool, check into one and good luck.

__________________
Ron
"Life is pain princess, anyone who tells you different, is selling something", The Dread Pirate Wesley.


www.tmishop.com Diving bits etc.

fubari

For reading material, this thread, while inspiration-centric, has some good general references:http://www.rebreatherworld.com/inspi...ion-diver.html

For additional reading, operational theory and practice isn't enough. You'll find it helpful to know how things can go wrong. Spend some time reading through the incident-writeups. Not all of these stories have happy endings... thankfully, many do. It is very much worth while to learn from them. Here are some I've found interesting:

• http://www.rebreatherworld.com/rebre...ents-incidents
• http://thedecostop.com/forums/forumdisplay.php?f=36
• http://www.btinternet.com/~madmole/DiverMole/DMDanger.htm

I wouldn't say "how deep? how long?" are silly questions... though I would rephrase them in terms of goals, e.g.

• What do you want to see?
• What kind of bottom times do you want to have?
• How much are you willing to spend to reach those goals? (by spend, I mean time, energy, training, & practice in addition to mere money).

The more you learn, the more you'll appreciate the cost of your choices. Everything has tradeoffs:
longer bottom times = longer deco.
Deeper dives = more planning & support.

I can give you my goals for "how deep? how long?": I'm interested in reaching some wrecks that are beyond recreational limits, not in setting new world records. While I'm amazed at some of the profiles that people have achieved, I'm also pretty happy with where I'm at skill-wise. I have: plenty of time to learn, lots of new stuff to see, and no rush to reach any goals.

So... I suspect you'll find your answer to "how deep?" will be "deep enough." Seriously , how deep do you want to go? Eventually diminishing returns start to kick in, and you reach a point where it isn't worth it.

Sorry - I know this doesn't tell you what you wanted to know
about depth limits. I do hope the reading material is helpful.
Good luck with your research!