Cold water, heavy current and CCR's...do they mix?

[Gill Envy]

this is especially for the cold water divers who dive rebreathers under current or other work loads. the more I read about breakthrough and the inability as of yet to detect breakthrough CO2, the more I wonder if strong current and cold water are appropriate applications of CCR diving.
Like a moth to the flame, i am drawn to the current swept passes here in WA and the nothern gulf islands of British Columbia because that is where healthy, vibrant inverts and fishes still remain. The added range in depth and time that CCR’s have to offer will undoubtedly tempt me to start my dives earlier before slack and push the envelope a bit after slack ends, in both cases exposing me to moderate, sometimes even strong current. I wonder if the added respiration rate from the added kicking amounts to an appreciable hazard, especially when taking into account the effect that cold water/air has on the rate of reaction in the scrubber.
I’m drawn to RB’s in part because I hate worrying about how fast my gas is being used up when I’m in a current on OC…there are plenty of times when I would just assume kick harder, stay warmer and extend the dive…if only I had more gas. Most of my dives are kayak dives/effectively shore dives and thus I must return to the entry point by the end of the dive…I drift with the ebb and flood as efficiently as possible but it doesn’t always work that way in these waters… micro currents and reverse eddies sometimes cause ebbs and floods to go in the same direction, and sometimes you see something really cool and you want to work against the current to maintain your vantage point. I’m very attracted to the idea that I will be able to kick harder, stay warmer and extend my time at the precious reefey areas with a rebreather without being so limited by my air supply. Would this be considered a heavy work load? Too heavy to be safe? Are their cold water current CCR divers out there that care to share their tolerations? Is there any one who knows how the testing of the scrubber units of the various CCR’s compares to diving against, say a ¾ knot current in 45 F water? In your oppinion does a particular unit hold up to higher respiration rates in cold water better than another?

[jradomski]

this is especially for the cold water divers who dive rebreathers under current or other work loads. the more I read about breakthrough and the inability as of yet to detect breakthrough CO2, the more I wonder if strong current and cold water are appropriate applications of CCR diving.
Like a moth to the flame, i am drawn to the current swept passes here in WA and the nothern gulf islands of British Columbia because that is where healthy, vibrant inverts and fishes still remain. The added range in depth and time that CCR’s have to offer will undoubtedly tempt me to start my dives earlier before slack and push the envelope a bit after slack ends, in both cases exposing me to moderate, sometimes even strong current. I wonder if the added respiration rate from the added kicking amounts to an appreciable hazard, especially when taking into account the effect that cold water/air has on the rate of reaction in the scrubber.
I’m drawn to RB’s in part because I hate worrying about how fast my gas is being used up when I’m in a current…there are plenty of times when I would just assume kick harder, stay warmer and extend the dive…if only I had more gas. Most of my dives are kayak dives/effectively shore dives and thus I must return to the entry point by the end of the dive…I drift with the ebb and flood as efficiently as possible but it doesn’t always work that way in these waters… micro currents and reverse eddies sometimes cause ebbs and floods to go in the same direction, and sometimes you see something really cool and you want to work against the current to maintain your vantage point. I’m very attracted to the idea that I will be able to kick harder, stay warmer and extend my time at the precious reefey areas with a rebreather without being so limited by my air supply. Would this be considered a heavy work load? Too heavy to be safe? Are their cold water current CCR divers out there that care to share their tolerations? Is there any one who knows how the testing of the scrubber units of the various CCR’s compares to diving against, say a ¾ knot current in 45 F water? In your oppinion does a particular unit hold up to higher respiration rates in cold water better than another?

Units that have undergone CE testing regure 1.6lpm co2 production and 4c as the test parameters.. The US navy uses 1.35lpm co2 production and slightly warmer water...

I can tell you that I have been in currents on my CCR that I was able to swim against and My oc buddies couldnt.. I am talking about going all out for several minutes (I felt like a sprinter afterwards)..

For CCRs the Inspiration and Ouroboris have undergone CE testing, and the Prism has gone through the US navy protocols..

When you compare test results take this into consideration, you cant directly compare performance numbers for those choosing different methods.. a unit rated for 3hrs at 1.6 a reasonable expectation would be to last approximately 4 hours at 1.35.. BUT another caveat.. You also need to know the test depth.. CE units are usually tested for endurance at 20m



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[Mark Chase]

I finned and draged my self over a reef against a strong current as we decended to 90m. Andy P and I were working so hard thaught my heart would pack in. We sat at 90 panting like dogs and then decended to 105m for about 5mins on the wreck it took 20mins to get there and out dive was well and truley blown when a seel failed on a canister torch. It rates as the madist dive i have ever done but after a full three hours on the scrubber by the end of deco I had no indication of C02 hit on my classic.

However the water wasent cold it was about 15c at max depth 20 on deco

ATB

Mark Chase

[wizbang]

Hi Gillenvy, I moved to CCR for more gas especially in currents etc.
I breathe deep and hard when working hard and OC is just useless for me. (I can watch the needle moving).

Let me state the caveat up front, I believe there is alot of difference between people for DCS, O2 sensitivity but also their CO2 sensitivity.
YMMV.
Also 45 F is about 7C, colder than I have experienced (yet ;) )
10 (50F) is my coldest and I have had a few heavy current dives at about 13 (55F).

I have completed more than a few dives where other OC and CCR divers could not get down or were not comfortable to continue. On more than half of these occasions I had to stop and catch my breathe on the bottom.

My rebreather performed flawlessly to my knowledge. It only took upto 10 second or so to bring the breathing under full control and ready to go again.

I don't muck around with extending the limits of the Dolphin scrubber or using a partially used scrubber or sorb. Especially not for deep dives. I change it happily as cheap insurance. I also have a 3mm neoprene cover that goes over my scrubber as well as loop covers.

My advice would be to start with fresh sorb for the cold current dives, and to pre-breath it at least 10 mins. I also think some Sorb work better than others, efficency wise.

Hope that helps. Wiz

[mattmexico]

Yo there

I think that these are exactly the conditions where a breather either keeps you alive or enables you in the first place to do the dive. I would never dream to go under a iceberg, into a cave with a very strong current unless on a CCR, period.

Matt

[E-man]

I would find out your personal RMV and CO2 (VO2) at different workloads and compare them to released test data on rebreathers to see how long they will work for you. Remember cold, high breathing rate, high CO2, and depth all cause lower scrubber durations.

Most (infact almost all i've seen) rebreather scrubber duration data is done at a set depth, work rate, and co2 production...all of which will vary throughout the dive.

[Deepwreck]

I have done dives in 39 degree water with a current. I use a Classic, and I try not to go beyond 3 to 4 hours on the sorb. With that say Ill open myself up for some flaming.
On one cold A-- dive(water around 41 degrees all the way up) the current at the surface was just cooking, and it was all I could do to get to the down line, and stay on that line. My heart felt like it was going to explode, and my lungs, well my lungs were burning. Once down to around 70 or 80 feet the current let off and my hand over hand desent with full kicking to aid ended and I had a chance to catch my breath. The Wreck was 200 feet and bottom time was about 25 min. The ascent went fine other than having to hang on for dear life. This was the Second dive of the day and all total with the two dives I had just over 5hrs on the scubber. (not recomembed) Both dives were in the same water with depths of 200' to 220'. The water was scheduled to be around 70 degrees for deco above 40', but all that warm water was blown south, and all be got was 41 degrees from surface to depth.
So I would have to say that Im happy with the way my unit works and functions under workload, and cold water. However you may want to talk to others who have overworked there units, and under what conditions they overworked them. I know of some who have overbreathed the units, and its not pretty or fun. So one must always take care to watch just how hard we are breathing.
Just my 2cents.

[Gill Envy]

I also think some Sorb work better than others, efficency wise.

Hope that helps. Wiz

which sorb do you recomend?

[wizbang]

Each RB manufacturer recommends a specific sorb with their unit as that is what their scrubber rating will be matched to.
That being said, some of us are penny pinching tight wads and have tried several brands.

I regularly use Medisorb, but I have also used Sofnolime (both sizes) and Drager sorb. (thats it I think)
IMHO both Drager and Sofnolime are more efficient and less dusty.
My preference is for the large Sofnolime.

Hope that helps.

[Deep Thought]

[quote=GillenvyI’m drawn to RB’s in part because I hate worrying about how fast my gas is being used up when I’m in a current on OC…there are plenty of times when I would just assume kick harder, stay warmer and extend the dive…if only I had more gas.

In your oppinion does a particular unit hold up to higher respiration rates in cold water better than another?[/quote]

That just about sums up why I love my rebreathers so much, huff and puff against a current in a cave or swimming to a ascent / descent line….just keep breathing and enjoy the dive.

Regarding CO2 and breakthrough, I have had experiences in cold and warm water on the inspiration and I have read that over-breathing this unit is not possible. Well I would put the person who stated this in my fins when the feeling hits you and the only resolve is numerous flushes. I have never experienced the same feeling of over-breathing or CO2 excess in the Meg, and I have not had my KISS units in heavy current situation yet. I have only had the Optima in the Devils system a couple times in good current, but warm water and it seems to breath quite nicely – not enough time to make good comments yet.