Two dives in Stoney Cove today to try out the Back Mounted Counter Lungs on the JJ-CCR. Firstly my thanks to Zoe who buddied me on the two dives and kept an eye on the two new-ish PADI divers we had with us. Zoe is a self proclaimed 'blond' and a recreational diver, who makes a habit of rescuing technical divers in Stoney, so I was in very safe company...
The strip down of the BMCL's is on the next post, so I won't go into that here in too much detail. Suffice it to say, they are of the 'Plastic Bag in Nylon' construction, very tough and sturdy and come as a single 'panel' to attach between your wing and your backplate. The actual 'bag' bit of the lungs sits outside the backplate wings and so isn't compressed and is free to work.
I was quite nervous about these dives as I had never dived with BMCL's before. Itís funny really, I had no trouble jumping straight in with the OTS lungs, but I was very cautious with the BMCL's, I guess itís what you are used to..
If you have been following this thread, you will know that I have had some discomfort with the ADV not pumping enough gas into the loop on descent. To try and make that better, I cranked up the IP from 9 bar to 11 bar, which caused me my only problem of the day. Every time I looked down, the BOV free flowed, so I had to do the whole first dive staring straight ahead.
Dive 1, Max 21m, 36 minutes, ppO2 1.2, 20/30
This was a dive in off the bus stop, then over to the Stanegarth, tried to find the APC, back to the 6m shelf and out. I had the BOV trouble at the beginning, but the rest of the dive went smoothly. The BMCL's do not have a sensitive OP valve in the same way as the OTS lungs do. You have to be very aware of your loop volume and adjusting it through your mouth regularly. This took some getting used to, and I did bob up and down a bit, but never by more than a metre and it was quickly sorted. For me, this was not as comfortable a dive as OTS lungs but it was my first one, so I was fairly happy. The BMCL's certainly make it a lot easier to get into and out of the unit, and that was something that I did appreciate.
Dive 2, Max 26m, 40 minutes, ppO2 1.2, 20/30
Before this dive I tweaked the IP down to 10 bar, this seems to be a good number for it. The ADV worked well, with only an occasional need for injection and the BOV was fine. I think that this is where I will leave it for the moment, if I need more gas I will work on the ADV next.
From the bus stop, down the road, followed the wall around at about 25m, over the pit and onto the plateau on the other side. Was a bit more used to the BMCL's now so this dive was a bit easier. I just felt that I had to be a little bit more aware, actively ensuring that I was maintaining MLV, which is something I can do almost unconsciously on the OTS lungs. I nailed my weighting on this dive as well, with 20 bar in my dil bottle and 30 bar of O2, I was perfectly weighted in fresh water with just the backplate and nothing else. I am using 5l steel cylinders for both dil and O2 and carrying a 7l stage with air at 200 bar. I guess this means I will have to lose the KT reel, itís just too heavy and I am starting to notice it now.
I must also confess to getting a bit of a spank from Dave. I mentioned in a previous post that I was using the HUD as my primary display, this is very bad practice, the Pursuit set point controller is always primary, the HUD is a secondary and that is the proper way to dive this unit. I'm very sorry Dave, I will look at my Pursuit from now on...
All in all, no huge problems diving the BMCL's, I wasn't as comfortable on them as I was on the OTS lungs, but that is probably just familiarity. I will be taking both to Scapa with me at the end of the week. I certainly felt I had to be more aware to maintain MLV on the BMCL's and my buoyancy was occasionally ropey, but never anything dangerous. There was certainly no noticeable difference in WOB, at one point I was swimming quite hard and I had no problems getting the gas I needed through the loop. On the second dive I tried the BMCL's in different positions, level, head up and head down, didn't seem to make a whole lot of difference, but when I rolled over onto my back, I did get a bit of 'chipmunk' cheeks, nothing uncomfortable, but a very slight pressure on my cheeks. If I blew off gas here, then when I rolled back over, I had a small hit on the ADV as you would expect, so really, everything worked normally.
I was under the impression that the BMCL's would dive very differently to the OTS lungs, they do not, and this is a good thing, though you need to be a little more aware at the beginning. I know some people obsess about a clear chest area etc., personally, I don't give a toss, I just want to dive with the safest lungs that give me the lowest WOB. Given this, I would be happy diving either the BMCL's, with more practice, or the OTS lungs right now. The OTS lungs lie flat against your chest so they don't get in your way, the BMCL's are totally out of the way and apart from the O2 injector will leave your chest completely clear. They seem to breathe as well as the OTS lungs and thus will be a good choice if this is important to you. Providing the WOB is the same on both BMCL and OTS lungs, then this is a choice you can make entirely on personal preference, with no need to make any compromises, and that is a very good thing. I enjoyed diving them and they make getting into and out of the unit a lot easier, so I will report back on my progress with them next week.