For my own convenience only (to make room), I would like to go to a 22" octo hose and necklace. If needed, I'd donate the primary and go myself to octo. I dive with insta -buddies often. In this case are there any cons?
I see virtually no 'cons', albeit with certain caveats. In fact, I see many, many pros. The primary caveats relate to hose length, second stage purge cover color, and communication.
The 'pros' are obvious:
1. In the unlikely event of an OOA situation, you are donating a second stage that you know is working - you have been breathing from it.
2. In the unlikely event of an OOA situation, the OOA diver does not have to search for the octo / alternate somewhere in the Bermuda Triangle, I mean the triangle created by your chin and the costal margins - you are in a position to actively donate a functioning second stage to them, instead of passively going into the 'hold up' position' and waiting for them to find the octo (if they are lucky).
3. In the unlikely event of an OOA situation, where the OOA diver does what some people might expect a stressed diver to do - grabs the second stage out of your mouth - you know exactly where your back-up second stage is, and you can quickly put that in your mouth.
The 'cons' are less challenging:
1. You are employing an approach that is not necessarily entirely consistent with how many OW student divers are taught to use an Alternate Second Stage. Therefore, a thorough pre-dive discussion, as part of the Pre-dive Safety Check with your buddy, is advisable.
2. You need to be sure that the length of the hose on the second stage that you donate is sufficient to allow for comfortable Alternate Air Source breathing.
3. You need to be sure that the length of the hose on the second stage that you place on a bungee necklace is sufficient to allow you to breath from it comfortably.
4. You need to dive with second stages that are both properly tuned, fully functional, and of comparable performance quality - i.e. no cheap, low performance, needlessly 'de-tuned', second stages on either hose.
I ordinarily dive with a 7 ft hose as my 'primary' - with a yellow purge cover on the second stage - and a 34" hose for my 'alternate', which is on a bungee necklace. I donate what is in my mouth in an OOA situation - which I have never experienced in 'real life' - and go to the second stage hanging on the bungee necklace.
I also have one reg set up with the 'standard' hose lengths - a 40" octo / alternate hose, and a 34" primary hose. I have put a bungee necklace on the primary, and I breath from the second stage on the longer hose - the second stage that is also on the yellow hose, and which has the yellow purge cover. That hose is a bit long, but it is not a problem (I can route it under my arm to decrease the entanglement /drag issues). The primary (on the bungee necklace) is on a hose that is long enough for me to easily put it in my mouth and breath. For a single cylinder reg configuration, 22" would be a bit short for me. It may not be for you, though. Bottom line, make sure the hose lengths are right for you.
I now demonstrate this configuration to OW students during their training course - as an example of something they may see - and I require my DM candidates to be actively familiar with it. Several university-based programs use this approach, and I think it makes a lot of sense. While I'm personally prefer a long hose for donation of the second stage to an OOA diver, the general principle is easily accommodated with 'standard' lengths.
Good for you.
