Who should use a CCR?

[doctormike]

I've been doin some diving lately with guys on CCRs, and I've come to the conclusion that the "less deco time" thing is a myth. Never not ONCE has a CCR guy had less deco on his computer than I had. Same or similar gradient factors, same dives (obvi). At best they're equal.

As the OP, let me bring the discussion back to the original context. I know that some of you feel that a CCR should not be used for any sort of shallow, "easy" diving, so if that's the case, I guess you won't be interested in this. But I frequently dive in mixed groups, my three main dive buddies are excellent natural divers, but they are single tank, recreational divers. I'm writing right now from St. Croix, with them, where we are doing dives far less challenging than the ones being discussed here.

I have to say, I REALLY like diving the CCR here on the reefs. I just like the way it dives, I like the silence, I like the animal life interaction.

So getting to the point about a deco advantage - yes, if you are comparing a square profile deep dive to close to the MOD of the OC diver's back gas, then there wouldn't be much of a deco advantage. If anything, diving OC near the MOD would give you PO2 of 1.4, and the CCR diver would be ongassing more inert gas at 1.3.

But for example, I recently did a very nice shipwreck in 60 feet of water. At a PO2 of 1.3, that's the equivalent of me diving OC with a backgas of EAN 46. Say my OC buddy is diving EAN 32. According to MultiDeco (30/70), I can dive that wreck for 3 hours and end up with essentially no deco. My buddy (assuming that someone is bringing him over 400 CUF of nitrox!) would have about an hour of deco. More realistically, the PADI RDP for EAN 32 gives him an NDL of 90 minutes.

So there is some deco advantage for shallower dives where the CCR is mixing you a rich custom blend that wouldn't normally be available for an OC fill.

 

[kensuf]

I've been doin some diving lately with guys on CCRs, and I've come to the conclusion that the "less deco time" thing is a myth. Never not ONCE has a CCR guy had less deco on his computer than I had. Same or similar gradient factors, same dives (obvi). At best they're equal.

I tend to agree with this.

All these dives I'm talkin about are multi level. 210-290'.

Maybe the advantage is more pronounced when shallower?

Shallower/shorter. I think the advantage is legitimate where the inert gas loading results in less than 20 minutes of deco anyway. For anything more substantial, it doesn't matter that much.

 

[DA Aquamaster]

I tend to agree with this.

Shallower/shorter. I think the advantage is legitimate where the inert gas loading results in less than 20 minutes of deco anyway. For anything more substantial, it doesn't matter that much.

Deeper, multiple gas dives are where OC divers are using multiple deco gases, travel gas and bottom gas to keep the PPO2 near optimum for the dive, so naturally there will be less comparative deco advantage for a CCR diver. It isn't rocket science, nor any real surprise.

There are however still some logistical and cost advantages to CCR, given the need for fewer tanks and a lot smaller gas bill to get the same near optimum PPO2 results.

 

[LiteHedded]

Deeper, multiple gas dives are where OC divers are using multiple deco gases, travel gas and bottom gas to keep the PPO2 near optimum for the dive, so naturally there will be less comparative deco advantage for a CCR diver. It isn't rocket science, nor any real surprise.

There are however still some logistical and cost advantages to CCR, given the need for fewer tanks and a lot smaller gas bill to get the same near optimum PPO2 results.

keep in mind he's talking about an rb80 with a po2 drop. so it should be even worse than open circuit. but he still beats CCR divers to the surface everytime

my experience on rb80 mixed teams is the same

 

[Tassi Devil Diver]

In response to the OP anyone who has the aptitude to use a CCR (and not every one has).

I have been diving CCR for nearly 5 years and in that time I use CCR for around 90% of diving ranging from shallow pootle through to deeper longer decompression dives.

It’s the way diving should be!!! Before you ever learnt to dive you may have had some sort of “romantic” expectations of what it’s like the silent world and all that, then your do your OW course where you learn all about the limitations of OC, and it's not all that quiet with bubbles blasting past your ears after every breath scaring the fish away, a tank does not really last that long and there are decompression limitations etc…

Well diving a rebreather is what you always thought diving would be like before you did your open water course, quite (only the ticking of flapper valves as you breath in and out, the occasional firing of the solenoid), virtually unlimited gas supply, more relaxing not having to keep an eye on that SPG etc.

Whilst I got a rebreather to assist achieve my diving goals in the 50 plus meter range exploring deep reefs and wrecks, I also enjoy using my rebreather on the shallower dives, doing long dives where I can fully explore a site, taking my time much more relaxing than OC and feeling more at one with the environs. I always found on OC I always got to the best part of the dive just as it was time to think about ascending. Now on rebreather I can take all the time I need knowing I have plenty of gas to do what I want and any deco that might accrue.

 

[Gareth J]

I've posted once in this thread previously.
Dipping back in I noticed a post about which is the best unit.

This is an almost impossible question to answer. The best I can do is give the reasons I have my unit.

I dive an AP Inspiration Vision (although they have rebranded all the model names so don't ask me what they call it now).
Also, I started a long time ago, so there weren't that many units on the market.

I picked the inspiration vision because.

+ I live in the UK and its made in the UK, support both technical, spares and RTB is easy.
+ The units are well established, as is the manufacturer. So long term support is available.
+ The units are modifiable. Mine is not quite stock. All mine has is a backplate fitted in place of the standard harness.
+ When I stay stock, mine is an early version of the vision, so no bailout valve (very desirable), original handset (not the nice new colour one (which my eyes would prefer).
+ Running costs are low. Sensors are available from two sources (AP did have an issue when teledyne dropped out of the market). The current AP sensors are excellent, and this means AP are no longer reliant on a third party for there sensors.
+ The scrubber is do it your self, you buy the sofnalime and pack the scrubber yourself. Whilst there is a recommended grade, if forced to you can use an alternate - with the associated drop in run time.
+ The unit weight - was less than the twinset I was using. There are lighter units around now.
+ Scrubber duration. When I was first looking I had a number of choices. This had the longer scrubber running duration (note - scrubber runtime is depth dependent)
+ Cylinder size. Mine uses the 3 litre cylinders, You can now have 2 litre cylinders with the same scrubber (when I bought mine it was a 2 hour scrubber and 2 litre cylinders). The big advantage with the 3 litre cylinders, is that I can do a weekend of 'recreational' diving without refilling the cylinders. NOTE - the big issue is available bailout - so I either refill the DIL, or carry a bailout under this circumstance. In the early days, and even now, access to high pressure O2 can be an issue.
+ The units where tested to 100m+. And being dived in the UK to those depths.
+ The Inspiration is approved and tested for trimix use with thousands of trimix dives completed on it.
+ It does have full EU testing - which isn't really that important to most divers, but can impact legally on you in some places. Especially if you are commercial using the unit, instructing or diving. It can even impact on the ability to sell a unit in some places.

In truth I have been very happy with my unit. Other than the cell issue [1] that AP went through when Teledyne withdrew from the recreational market my unit has been very reliable. My handset died just before the new units where launched, so I have the original version. I do understand that there have been some problems with the newer handsets, but I would still have preferred the newer unit.

If I had the money to replace my unit I may well go for the JJ, but it would still be a bit of a toss up.

The main thing to consider is what do you want to use it for. How this impacts on the scrubber life. How easy is it to get the support if it goes wrong. What will you want to use it for in the future.

There are a lot of inspirations around, often, I can borrow, scrounge or beg for a spare, especially if on a trip.
Mine dropped off the harbour wall last year on to the boat, shattering part of the case. I was able to apply a few tie wraps to fix the problem - allowing me to finish the weeks diving.
There are after market travel frames that I could replace the case with - but I do quite like it. One day I might change.


Anyway, thats my reasoning.

Gareth


[1] I have to say AP where very good. There early attempt at mass produced sensors had early failures. I was back to back diving, they basically shipped me multiple sets of spares sensors. Strictly speaking if you returned a sensor under warranty they would ship you a replacement. In truth they shipped me half a dozen spare units, with me either returning defective sensors under warranty, sending back unused sensors, or paying for any i kept as spares. They had there problems - but they tried to support there users despite the technical problems they where experiencing.