Okay, I'm confused. I use a silicone (or some similar rubbery material)
regulator necklace (not bungee cord) for my secondary with the idea that I would donate this secondary to the OOA diver and keep the reg I'm using in my mouth. ~
How long is your secondary hose? If it is 40in then I would imagine that is a pretty big bow of hose hanging off your profile. If it is the short 22-26in hose then it is too shore to be an ideal share air option. Adding an angle adapter+40in hose will create a floppy connection and also isn't ideal.
The ideal configuration for ease of use and ergonomics (lesser wake profile) would be using a short 22-24in hose and utilizing the bungee backup as your personal backup. This means donating a primary that's long enough, my preference being 40in or more (usual increments being 40in, 44in, 5ft, 6ft, 7ft).
I'll never understand (or agree) with what is done in that picture. Why would a person secure the bungee using the same zip tie that is securing the mouthpiece? First of all, a properly done bungee necklace is just as effective AND you can take the bungee off quickly without tearing off the mouthpiece if required for any reason. The method of securing the bungee in that picture also guarantees that there is uneven pressure holding your mouthpiece on.....could possibly lead to issues. Who can explain why this picture is a good solution because I am missing the pro points?
By quickly, we're talking about matter of a second, adding a bit more finesse required for the zip-tied bungee side.
Remember bungee is compressible, the uneven pressure you're talking about is so minuscule it really doesn't have an effect. With this method you're assured that your reg will never come undone. There still is pressure all around the mouthpiece, with a slight heavier pressure where the bungee sits, but the mouthpiece will not come undone anymore than a mouthpiece ziptied on normally.
With the blood knot method (removable way) there still is a chance of the reg coming undone, especially in high energy surf entries. Maybe not specific to your local but certainly there is at least one beach in my area where this is a strong possibility.
The tradeoff is having a 100% sure way your reg is not coming out of the bungee unless you want it to, at the cost of being easily removable. (easy being a word of opinion)
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When it comes down to it I side with bungee regs being truly useful serving as the personal backup role. For donating it is better to use a primary or a secondary that's located on your chest. True donating a reg out of a necklace would be simple, but on the flip side someone grabbing a reg off your neck is going to cause some unneeded neck pain. There's also the hose routing issue.