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View Full Version : Unit choice, and 2L versus 3L DIL/O2 onboard



MattD
01-09-2015, 12:12 PM
Hi,

I briefly dived CCR in 2006 with mod 1 on a Classic and a dozen dives. Then baby #2 came along and I sold the unit focusing on OC diving.

I'm considering getting back into re-breather diving, probably in 2016, but have a few questions...

I have followed the Hogathian style of OC diving, and GUE training for cave diving. My T2 buddies are buying JJ's and running them in the GUE configuration. This is extremely heavy and as a lot of my diving is shore based I would prefer to have offboard bailout that I can take down to the water with my scooter, rather than have D18 worth of weight on my back. This is a bit of a show stopper for me.

1.) What is the disadvantage to having Bailout gases staged, compared to on the unit? I can imagine that having backmounted 2x7 allows you to only need an intermediate deco gas and oxygen staged, so you save on one stage cylinder & also it would potentially allow a long hose to be availble for primary donate? Anything else? What do people think about this? I have discussed with many people and I tend to get two main answers: "GUE don't think like a eCCR diver" or the other side "We like lots of bailout, and we believe in the primary donate system"

This is an important question, as I really don't think a GUE style rig is something I can crawl over boulders with. In the exact opposite fashion to my OC DIR rig.

2.) What are the major differences between a JJ and Vision, assuming:

JJ: Has Golem Gear BOV & Nerd HUD
Vision: 2020 Display, AP BOV & HUS, Back Mounted counter lungs, Temp Stick & CO2 sensor

I'd appreciate comments on: Design differences, Quality issues known on both, Service Turnaround etc. My impression is that the JJ allows mounting of cylinders directly onto the unit, but a Vision would need a GBOX or similar?

3.) Why choose 2L cylinders?

I am struggling with this one. What is the main advantage of 2L tanks? I appreciate that you don't use much DIL/O2 on a dive, and have bailout available, but for several dives or where one can't get 200Bar of Oxygen, isn't a 3L cylinder preferable? Or I suppose you could have two 2L sets for a dive trip.

4.) How do they trim out?
Having good trim is very important for my comfort on a dive, and especially when inside wrecks, how do these units trim? The JJ seems very easy to trim out, how about the vision (2L/3L versions)

5.) How much customisation is needed?
I am not an engineer. It was a freaking nightmare diving trimix in the 90s where you had to fettle and machine your own clips and parts and harness etc. I know some divers (and explorers!) excel at this shit, but not me. I love the hogathian rig as the only thing I had to learn was what size inner tubes to cut up for snooopy loops on my harness and stages... I want to keep the simplicity of my harness and hope to be able to use the same. How much work is needed? Can I use my backplate on the vision? It seems easy enough on the JJ.

PS: For info the Meg looks great, but I can't afford one. I have friends diving on JJ, MEG and Vision, so have a community for help/tips after training.

notdeadyet
01-09-2015, 12:41 PM
I really do not understand the point of trying to turn a rebreather into a twinset. I think the GUE config is a pretty sloppy way of rigging a unit based more on history and dogma rather than practicality.

The disadvantages of offboard bailout? Possibly that it is very slightly less streamlined? I dont know. Carrying any bailout is an inconvenience but carrying it on your back with a convoluted donation drill is the last place I'd put it. Dive a rebreather like a rebreather, not some half hearted non-committal, let's pretend we're still on oc set up.

Disadvantages of 2's? Less gas. For uppy downy dives this can be a consideration. You'll be refilling more often. The weight and size difference is minimal. Bare 3's are piss cheap.

There have been a few bargain priced Megs knocking around.

jturner
01-09-2015, 01:01 PM
Here's a few thoughts from a relative noob to this:


1.) What is the disadvantage to having Bailout gases staged, compared to on the unit? I can imagine that having backmounted 2x7 allows you to only need an intermediate deco gas and oxygen staged, so you save on one stage cylinder & also it would potentially allow a long hose to be availble for primary donate? Anything else? What do people think about this? I have discussed with many people and I tend to get two main answers: "GUE don't think like a eCCR diver" or the other side "We like lots of bailout, and we believe in the primary donate system"

This is an important question, as I really don't think a GUE style rig is something I can crawl over boulders with. In the exact opposite fashion to my OC DIR rig.

For me, it's having to muck around with the large cylinders and the fact that it means I'll away have to carry at least one stage unless I'm going alpinst... but I'd rather have to do that, than having them on the unit. That way, when the CCR goes wrong, I need have nothing more to do with it - it is simply a method of attaching the wing and various other bits to me (plus a load of expensive stuff I'm no longer using because it's broken). CCR is the CCR; bailout is entirely separate.



3.) Why choose 2L cylinders?

I am struggling with this one. What is the main advantage of 2L tanks? I appreciate that you don't use much DIL/O2 on a dive, and have bailout available, but for several dives or where one can't get 200Bar of Oxygen, isn't a 3L cylinder preferable? Or I suppose you could have two 2L sets for a dive trip.

They're small and you can use one pair for each dive. You then just swap them out rather than trying to eek out a second on them. If I'd wanted to do 2 long or deep dives, I'd have needed larger than a 3L anyway to give me a little extra reserve, so why not just use 2x2L and swap them? There's a chap near our place who's just ordered 2 x 4L cylinders and they are obscenely long and just downright weird...


4.) How do they trim out?
Having good trim is very important for my comfort on a dive, and especially when inside wrecks, how do these units trim? The JJ seems very easy to trim out, how about the vision (2L/3L versions)

The APD's trim out fine especially if you put a lump weight on the top or on the top of the head.


5.) How much customisation is needed?
I am not an engineer. It was a freaking nightmare diving trimix in the 90s where you had to fettle and machine your own clips and parts and harness etc. I know some divers (and explorers!) excel at this shit, but not me. I love the hogathian rig as the only thing I had to learn was what size inner tubes to cut up for snooopy loops on my harness and stages... I want to keep the simplicity of my harness and hope to be able to use the same. How much work is needed? Can I use my backplate on the vision? It seems easy enough on the JJ.

Probably a lot for the APD units but most of the stuff is available, as people have been making custom frames and harnesses for them for years. No need to re-invent the wheel.

YMMV on all this of course!

nickb
01-09-2015, 01:13 PM
They're small and you can use one pair for each dive. You then just swap them out rather than trying to eek out a second on them. If I'd wanted to do 2 long or deep dives, I'd have needed larger than a 3L anyway to give me a little extra reserve, so why not just use 2x2L and swap them?3l tins are small too. Additionally, they are far more available. So, the argument should really be: "why not just use 2x3L and swap them?"

The length of a dive (on a square profile, at least) makes little or no difference to the amount of diluent used. It makes very little difference to the amount of O2 used too. In my experience, most is used on the ascent. An extra hour in the water will mean an extra 50l (ish) of O2.

nigel hewitt
01-09-2015, 01:24 PM
If you learnt back in the early 2000s then you probably didn't get the 'bailout bailout bailout' style training that effectively negates all the advantages of a rebreather. Go back to that.

I dive an Inspo with two 3Ls to do gas and a 2L suit inflater to save blowing conductive mix onto my sensitive bits.
Yes, if the loop dismantles itself, I only have my DIL to breathe but virtually all the faults I have hit have been manageable with that.
I take the view that adding extra cylinders adds weight, size, entanglement hazards, reduces the fun of a dive and probably increases the risk of the dive going south.

If you're shore diving beware of a rig you can't sit down in.
When you put your bottom on a convenient wall/rock you want the rig to touch down too so the weight comes off.

gobfish1
01-09-2015, 01:25 PM
on a 3hr dive i use 50/70 bar of 02 depending how often i flush at 6m , (3l in boards)
i all ways dive with in board and off board o2 , 5l max 3l in board and 2l off board so if i run out of inboard o2 or have a 02 solenoid problem i can use back and mav,
dill is not a problem as my deep bail out will be much the same as my on board dill ,

i like having the o2 back up and 5l to play with , and for a lot of my diving the o2 can be used for bailout , last stop 6m
just need two hump two bail outs, deep and mid water , the mid water will see me home but i can all ways use the o2 backup if needed or wanted out a bit faster ,

problem for me with the big back mounts is your ok at depth but you end up having the wrong gas mid water / ie shitty ppo2

that,s open water , cave maybe ok as i would dump a shit load of gas going in , lol tho im no cave diver ,

PeterL
01-09-2015, 01:28 PM
The older I get the more I realise that having all your weight strapped together is a dumb dumb dumb idea...........................

Fine, dive to 200m, dive for 5H, but on and off the boat never more than 20KG per arm load or 35KG on your back. Anything else is a disk herniation waiting to say hello.

nickb
01-09-2015, 01:28 PM
problem for me with the big back mounts is your ok at depth but you end up having the wrong gas mid water / ie shitty ppo2All the GUE JJ guys I've seen have taken off board intermediate gas like 32% or 35/25 etc. They really do take shitloads of gas into the water. It boggles the mind!

gobfish1
01-09-2015, 01:58 PM
All the GUE JJ guys I've seen have taken off board intermediate gas like 32% or 35/25 etc. They really do take shitloads of gas into the water. It boggles the mind!

so what do they use at depth and what is used at 6m ppo2 on that 35/25 is shite at 6m
35/25 is only good at 24m if you want to say in the gue ppo2 numbers , (or your having a co2 problem ) i have two depth,s for using my 50% ie 21m norm bail and and what ever depth my bottom bail runs out if co2 problem , bottom bail has to be able to get me back to 1.2ppo2 or less

tho im happy to hit 1.6pp2 for a norm bail out ,

what sort of depth and run time are we talking about ,

nickb
01-09-2015, 02:20 PM
so what do they use at depth and what is used at 6m ppo2 on that 35/25 is shite at 6m At depth, they'll have OC access to the 14-17 litres of gas on their back. Both 7l or 8.5l tins are manifolded and contain their diluent.

At 6m they'll use their O2 (I assume)

The intermediate gas would be appropriate to the bottom gas. They may have more than one.

gobfish1
01-09-2015, 02:37 PM
At depth, they'll have OC access to the 14-17 litres of gas on their back. Both 7l or 8.5l tins are manifolded and contain their diluent.

At 6m they'll use their O2 (I assume)

The intermediate gas would be appropriate to the bottom gas. They may have more than one.

so 14l on your back and two cans on side , i take it they wont be ponys thats a lot of shite to hump for a 45m dive lol
all dressed up and no place to go ,

no a 75m dive id need 3 gas.s about 1000l of each , cant think what id use 3400l+ of the same gas for , blowing lift bags maybe

dont get me wrong im humping 10l fixed to the unit but thats made up of 3 dif gas,s
so not far short of a set of back mount 7s , gas choice to me is better that having lots of the same gas ,

cave it could be ok , wreck i think not ,

jturner
01-09-2015, 03:08 PM
3l tins are small too. Additionally, they are far more available. So, the argument should really be: "why not just use 2x3L and swap them?"

The length of a dive (on a square profile, at least) makes little or no difference to the amount of diluent used. It makes very little difference to the amount of O2 used too. In my experience, most is used on the ascent. An extra hour in the water will mean an extra 50l (ish) of O2.

3Ls or 2Ls work for me in principle (well they wouldn't really as I have an Evolution so the 3s won't fit but you get the idea!)... it's the 4Ls, 5Ls, 7Ls or bigger cylinders I don't get!

nickb
01-09-2015, 03:39 PM
3Ls or 2Ls work for me in principle (well they wouldn't really as I have an Evolution so the 3s won't fit but you get the idea!)... it's the 4Ls, 5Ls, 7Ls or bigger cylinders I don't get!To be fair, 7s work nicely on a JJ as long as you get the hose routing right. Used valves-up, you can remove the stand and the unit will stand up like a twin set. Good for a long weekend's diving where gas logistics are poor or to go a bit lighter on deep off board bailout.

Just don't manifold the things together ;)

gobfish1
01-09-2015, 03:46 PM
To be fair, 7s work nicely on a JJ as long as you get the hose routing right. Used valves-up, you can remove the stand and the unit will stand up like a twin set. Good for a long weekend's diving where gas logistics are poor or to go a bit lighter on deep off board bailout.

Just don't manifold the things together ;)
and take cylinder o2 to drive the unit, best not manifold as you need the deep bail in one and your 35/25 in the other lol

dont forget to stick a nice nitrox mix in that suit cylinder ,

MikeF
01-09-2015, 03:55 PM
personally I dive 3L of air dil on the unit that doubles as suit gas and a 3L of O2. anything where I need more bailout or anything other than air as dil I just carry a bigger sideslung dil/bailout cylinder and plug the unit into that rather than the 3L leaving the onboard air 3L as suit feed only.

climbing over rocks I'd rather carry the dil/bailout to the water then come back with the unit and hook up to the dil at the water's edge than stagger over rocks carrying loads of heavy cylinders.

Gareth J
01-09-2015, 04:27 PM
Hi Matt

I may not be the best person to ask, because most of my deeper diving stopped shortly after I got my rebreather due to work pressure and lack of funds. i.e. when I've got money I haven't got the time, when I've got the time I haven't got the money.

1. Off board bailout.
Its easier to have sets of tin's for different bailouts at different depths.
Its easier to carry the kit in relay i.e. move the bailouts, move the rebreather. Than carry all the weight in one go. If your diving off a boat all the time perhaps not so important, but shore dives or carrying the kit any distance its an advantage.
You can off load your bailout before leaving the water, either climbing onto a boat (ladder), hanging on a lift, walking out after shore diving, etc.
You can share bailout with the team if its off board (if plumbed in then no, unless you can un-plumb it in water).
If you do have a buddy with OOG you can potentially give him the bail out and let him get on with it. (I was taught to exchange bailout when team diving, i.e. if you have to bailout, breath your bailout down to half, then off load it to a buddy and take on new gas - only required if you are sharing bailout on long/deep dives.)
If you have a buddy on OC and they loose their deco mix, you can hand off your rich mix.

2. Can't answer that. I have no knowledge of the JJ. I have been very happy with the Inspiration vision. The new HUDC and colour display have definitely updated the vision. The service I have had and the reliability has been very good.
The advantages of a locally made unit (in the UK), is lost a little with you being in Norway.

3. I have friends on Sentinels, they have modified their units from 2l to 3l cylinders. They where feed up having to refill them so often especially over a weekends diving.
For 'club' diving, 3l's allow a weekends diving without the irritation of getting refills.
Although on club diving trips, I will often fill the dil' if refills are easily available and I'm only using air. That often means I don't need any (off board) bailout.
3's for simple dives do mean you normally have enough onboard bailout - although CO2 hits and high breathing rates make this questionable.

If you have a BOV, and its plumbed into the DIL, then I reckon you need at least 3l DIL for the sanity breath (and that's just 'club diving'). Ideally be able to plumb in the off board gas to the DIL otherwise your DIL will disappear and you will still have to bailout before your breathing is under control.
(In fairness I still don't have a BOV so I'm not doing what I preach).


4. The Inspiration seems to trim out quite well. No knowledge of the JJ.

5. My unit is still pretty stock, except for the crap AP harness. I fitted my standard backplate, which I can switch back and forth to my OC rig.
In an ideal world I would add the BOV, with a switching block to allow plumbing in the off board bailout.

The vision has been around a while and is basically the original unit with better electronics. So there is a lot of kit around for customising the APD units. So you don't have to reinvent the wheel.
I do know a few people have gone back to the original AP case because access to 3l compatible cylinders when travelling is a lot easier these days. So the need for the travel frame has diminished.

It has got a lot easier to travel with rebreathers. The smaller vision (with the 2l tins) was designed as a travelling unit being a little lighter. You need to understand that it has a smaller scrubber, so this reduces dive time.
The Inspiration is quite a heavy unit to travel with, some of the other units are a lot easier to pack and are a lot lighter.

Gareth

Major Clanger
02-09-2015, 07:16 AM
Why limit yourself in choice? The ISC Pathfinder is awesome for sports diving.


The ultra light PATHFINDER rebreather system is used primarily with one oxygen cylinder mounted on the unit. The diluent cylinder is mounted as a stage bottle to supple diluent, BCD operation and bailout. This eases weight and complexity, as the diver does not need two cylinders mounted on the back of the CCR to operate the PATHFINDER (although that is an available option)





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notdeadyet
02-09-2015, 09:02 AM
personally I dive 3L of air dil on the unit that doubles as suit gas and a 3L of O2. anything where I need more bailout or anything other than air as dil I just carry a bigger sideslung dil/bailout cylinder and plug the unit into that rather than the 3L leaving the onboard air 3L as suit feed only.

climbing over rocks I'd rather carry the dil/bailout to the water then come back with the unit and hook up to the dil at the water's edge than stagger over rocks carrying loads of heavy cylinders.
Must admit for typical west coast Scottish shore diving I find staged bailout a bit of a ballache. Having to get fins and a stage on in a couple of feet of water. I tend to just plumb my 3l air suit bottle into my BOV now and not take any BO bottles.

Or just dive a 12 and a pony :)

MattD
02-09-2015, 10:09 AM
Sorry, when I said shore diving, I didn't mean shallow stuff. (I do enjoy a 30m ramble) but I'm looking at CCR for trimix diving 70-80m and over here our shore dives can be quite deep.

For example: DS Oldenburg the prop starts at 70m:

http://www.dykkepedia.com/wiki/Oldenburg

http://www.dykkepedia.com/images/5/5f/FSC_1146.jpg

I couldn't understand the choice of 2L onboard, but have now got some good feedback on that. For myself I think 3L will be fine.

I think my plan is for getting a stock Vision or JJ, diving it with 3L Dil and offboard bailout for 100 hours & then looking at the bailout strategy when I do MOD2/3. I believe that having MOD1 from before and Advanced Trimix, I might be able to do some kind of Mod1/Normoxic course, because I do want to build experience around 40m and would prefer not to have the extra burden of Narcosis and thick gas. I'll leave that discussion for the instructor.

If I was diving from a hardboat all the time, (With a lift) I wouldn't be worried about the backmounted double 7's, but we do a lot of squidgy and RIB diving and to be perfectly honest as a young 40 year old I don't think my back will survive sitting on a RIB tube with D18 of weight. I do train reguarly and have a good BMI, but still get some issues with the back and weight. D12 weight is fine.

I have a drop line I like to use, and just load the cylinders and scooter down to the waters edge. I think the same would be nice with CCR.

notdeadyet
02-09-2015, 10:41 AM
I did a bit of shore diving with a club from Stavanger. Slightly different to Loch Fyne :) I remember most of the places we went were a ton or more straight down off the kerb of the road.

I think I'd struggle getting and out the water with backmounted bail out. Cant remember if I was using 15's or 20's but it was a fight getting out and up on the shore again.

I'd definitely go for sideslung bailout and a line to clip it to.

OutOfTest
02-09-2015, 03:24 PM
I'm on a project at the moment with a JJ diver diving GUE style.

He's using two 12L onboards of 10/70, a 5L onboard of O2, a 5L suit bottle (big cave) and then a multitude of more stages for the intermediate stops etc.

His unit is MASSIVE.

However, at this level of diving, the unit makes sense as he has less stages to manage and he can run "alpinist" with just the onboard gas once he hits the deep section. The other divers still have tonnes of stages for bottom bailout and look a clusterfuck.

Apart from one guy, he runs a KISS and a sidemounted, self contained KISS as bailout. He's slick as.

So, if you want to dive super deep and long in caves and mixed team, the GUE config makes sense.

If you want to dive super deep and long solo/all RB divers, small onboards and BOB.

If you're just cocking about at 50/60m, get yourself whatever you want, small onboards, and a few stages to bailout.


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