Some interesting thoughts on this thread!
If you’re diving sidemount it’s not as much of an issue to use the lean left, rich right approach as the long hose is harder to trap than in back mount, note harder, not can’t be trapped. This allows for the O2 bottle to be mounted on the right and the 50% on the left. I always mount decos on the bottom as I like to be breathing the top tank unless I’m on deco
If you’re using a travel gas I normally mount this on the top on the left side, them move it to trail or leash it once I’m finished breathing it. It can then be moved back at the end of the dive – if it’s still negatively buoyant (return gas supply due to the depth) then I probably wouldn’t be using a sidemount set-up anyway so having a it’s not been a problem for me. For the decos I generally trail or leach them once I’m done breathing them to keep things clean, if they are particularly heavy I keep them in place but this should only be the case if I’m using them on multiple dives so have them much fuller than I’d need.
Personally I like to use an Apeks XTX reg that can be switched so the hose feeds from the other side of the second stage, I can then use the same back of the neck routing with a 40” hose and avoid without crossing my chest with a deco hose, the new Hog second stages should also be great for this. I always route the hoses around the back of the neck as I find it much more comfortable, it also keeps the hoses much neater and tidier to avoid them flapping around in the current or getting snagged – this is even more important for sidemount as there’s also at least one other tank valve the hose can easily get caught up on if not routed behind the neck? I do all Deco while stationary so having the tanks mounted regularly under the sidemount tanks for hose deployment is no issue.
If the gas switch drills are done correctly, personally I can’t see a problem with running hoses behind the neck. It should still be obvious which hose is being used to other divers in the team and you should already know which one you are breathing. If divers are not stowing deco hoses that could be a problem but I’d say any diver capable of doing dives with two deco gases should be able to stow the hose of the first gas correctly, current, no current, one hand or two hands - if not it’s best to stick to a single gas for now.
The hardest gas switches to observe are normally those on a line with a current – it drifting isn’t an option routing the hose around the neck gives some idea to your buddies which hose you are breathing from (simple observation shows if it’s from the right or left tank?), routing it at the front leave them with no idea if you switch without telling them.
The ANDI tags are a good idea in principle but the positioning means the reg is harder to hold or stow it in the stage bottle - I find them more a hindrance than a help. It’s much easier to use some duct tape on the reg exhaust vale with the MOD written on it – the ANDI tags have too much going on in the background anyway in my opinion, all you need is one number – the MOD, no extra text – mark it on duct tape and stick it below the mouthpiece on the reg exhaust valve before the dive if you want the extra fail safe. If the tag is preferred use duct tape to make a tag, it’s much more manageable than a sharp plastic snag hazard with cable ties all over it. The main worry for me is that the reg can easily be switched between tanks and it is hard to spot (some boat crews don’t know better, especially if they take your gear back to ‘clean’ and reassemble without your knowledge), tank marking are easier to spot if the label has been tampered with or the pressure has changed overnight.
The wrong switch kills a lot of people and is a real issue, that’s why using the same config in the team and using the same config on every dive makes so much sense. Tags, hoses etc are just a back up for days your brain isn’t in gear and no one else is on the ball either. It would be interesting to know statistically how many accidents involving wrong switches were down to incorrect marking and how many were due to wrong switches with the correct marking? I had a good friend who almost lest their life in a wrong switch due to incorrect markings but everything else, including ANDI style markers, were in place. His fault was he didn’t label tanks right away, he analyzed them then went to get tape but it seems someone had moved around the tanks or he got them mixed up – I’d expect that kind of incident could be the biggest killer out there? We permanently mark our tanks as 50% or O2 now and only verify the contents with the top label (initials, mix and MOD), if it’s out we reject it and get it refilled.
