I passed my RB80 course back in February and since I got back I’ve been hitting the quarries and building up some hours. Along the way the biggest issues I’ve had have been around the lack of standardised kit. Sounds rather odd but given the small number of units in existence it’s not that odd!
First off I’ve struggled with backgas cylinder size. In Florida we rented twin 85cf bottles in a steel rack. This was great for the course as we spent quite a lot of time OC during drills and emergencies so the cylinder size made a lot of sense. Equally if you are cave diving having bigger backgas is very sensible as you’ll typically be scootering in which case reserves are very important. However for UK ocean diving I don’t need as much. Minimum gas in the RB is that you plan to have enough to get just yourself up to your next breathable source of gas. If you actually had an RB failure and a complete loss of backgas then you’ve had two critical failures (very unlikely) and you’ve still got your buddies reserve as you’d assume their RB was still working. For this strategy to still lead to problems you’d have to have three critical failures in the team. If you put that in OC terms and you’d need to lose all three twinsets in a team of three!
Florida rack
So initially I rig twin 12’s as backgas. I’ve got them and for quarry days it’s fine. But for an ocean dive its overkill. It’s also damn heavy! For the UK ocean diving I need to stand up wearing all the kit, pick a scooter and leap into the water. With the short slack water windows we have you have to up and go and you can’t stage kit in the water.
The solution has turned out to be is 8.5 litre cylinders. These are almost impossible to find but John Grogan had a contact in Holland who sold his own set to Clare on the basis he has more coming at the end of April. I’m still struggling on with the 12’s and praying he does get some more. Twin 8.5’s are perfect size being tall enough to ensure the scrubber is not hitting the ground when I sit down. I really don’t want the scrubber supporting all the weight when the kits rigged. They are the same height as 12’s but very narrow and give enough gas to do most Ocean dives.
Next up we had frames, it’s not like getting bands for a twinset you need a special frame. We used the Halcyon travel frame initially which uses cam bands and is a pain in the arse! It didn’t provide enough rigidity. We also had the wrong manifold extension so we had to route it badly – so badly that I couldn’t reach the isolator. It also didn’t provide any negative buoyancy so we had p-weights and big weightbelts to let us sink.
Rigged with travel frame- to keep the cylinder rigid I had to keep the scrubbers in the frame when transporting them around (PITA).
We’ve now got a solid frame (not the one we rented in Florida, but one from Graham HK) and life is much better. I can reach my valves and it adds some negative buoyancy into the proceedings. Graham’s clearly put a lot of thought into the design and it has numerous very clever little tweaks. It’s beautifully made and we’ve already ordered two more. However I still need to find ways of getting lead into the set as v-chunks don’t work. Just like a RB diver – I keep needing to fettle kit, very sad 
Twin 8.5’s in Graham’s frame
After that the next purchase was a new big P-weight and a heavy backplate. I’m now perfectly weighted with just the heavy backplate and the frame. Clare’s stolen my big p-weight and is also chuffed. I’m now contemplating how to get lead blocks into the frame in some of the gaps as when I move away from the 12’s I’ll need more negative buoyancy.
We also ordered some different manifold extensions from Halcyon to give us some more flexibility in positioning the cylinders. This has brought the manifold into more a straight line and made the different in terms of me reaching. The trouble was we didn’t know what we needed.
With 12’s and curly manifold.
Next up was argon bottle rigging – I was struggling with the bottle digging in to my back as with essentially 3 x 12L cylinders on my back it feels crowded. I’ve had to re-rig it in an attempt to make it more comfortable. I tried wreck mount and didn’t get on with it, so I’ve gone for a custom backplate mount. It’s working OK at the moment.
Next problem on the horizon was manipulating the switch block. Initially we were diving back gas only so this wasn’t cropping up. Now we are adding stages the issue is getting a good contact and plugging in the hose. It is a bit tricky with dry gloves and a little less dexterity. Casey’s recommendation was hose protectors; we’ve now found that the scubapro ones are bloody marvellous. They give you a good handhold to let you plug in the cheater. Needless to say I threw all the ones I had away years ago as I didn’t think I needed them 
I also had to track down coarse grade lime. A lot of the UK CCR’s using a fine grade lime which isn’t ideal as it would increase work of breathing (WOB). Mike’s dive shop in Reading supplies it, as do molecular products. I’ve been pointed at AP valves as well but have yet to try them.
Most of the diving elements are OK. The kit is all in the same place as OC but I do feel more cluttered. The gas is warmer and it has let us do some long shallow dives in the 6 degree water beyond what we could mange OC from a warmth perspective. Gas extension is working OK and apparently will improve. I’m getting about a 5-1 gas extension ratio at the moment so my twin 12’s are currently acting like twin 60’s which will eventually open up some different diving opportunities.
I got asked the other day if I would recommend it and the person asking seemed very surprised when I didn’t wax lyrical about it. In practise it is a lot of extra hassle and additional risk. Unless you’ve really exhausted OC then it’s hard to justify. One of the interesting slides in the course was that as you build experience on OC you typically become safer. As you build experience on the RB you become complacent and it becomes more dangerous.
I switched back to OC to video on a fundies class two weeks ago and it was absolute bliss to just have the old twinset on. Anyway hope this has been interesting.
