Why recreational backmount doubles

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I went from a single steel 72 to Aluminum Twin 50's in 1976. I loved the extra air, especially for long shallow beach dives, plus they balanced just right on me. When I use short doubles these days they are either my steel 38's or 45's. Back in the day I tried twin steel 72's a few times but they never felt right, hard to swim with, were too heavy, hurt my back and I never needed that much air. I did use back-mount dual 80's cave diving for 20 years but for some reason they felt fine (modern back-plate maybe and not the blow-molded Cam-packs we used to use). Here is a photo a friend took of me in 1977 with my old twin 50's (yes the 'bad' alloy). Please note that I was properly protecting my snorkel in my mouth during my entrance and wholly disregarding where the 2nd stage of my Calypso IV was. :) Who knows what I was thinking at the time - back then I would assume my air was on until proven otherwise a few feet down. :) These days I'm a tad more cautious on the pre-dive planning aspect of things. :) M

gcV0J1.jpg
 
Redundancy, like what? I have a buddy, that is my redundancy
Depends where you dive and how attached you are to your buddy. Cold tidal wrecks in poor visibility isn’t a place to need the redundancy but it’s cleared off in the opposite direction.
 
I remember :wink: my instructor said:wink: that it was impossible to go into deco with a steel 72 because that is why that capacity was developed. Huh! An aluminum 64 is all I need to bust deco at anything over 60 feet or so. And when I dive tables or square profiles I use the old Navy Tables because I know them even for multilevel dives by heart and can compute on the fly. But then I got me some new fangled 'puters so with some evasive (of deco) planning I could exhaust an 80 and not go into deco I suppose, if I went deep and then came up shallow and strung the dive out. I just do not need doubles for any sort of non-deco recreational dives unless we are doing the Spiegel or something like that and staying at 130 feet for the duration. And even then I do okay with an aluminum 80.

James
James you my hero! ! :) I wouldn't even attempt a bounce dive to 100fsw with a AL80!
I might have to CESA the last 20' on ascent!
 
I went from a single steel 72 to Aluminum Twin 50's in 1976.

gcV0J1.jpg

That is a cool picture. And a nice suit too!

That sort of doubles set, I have one just like it (mine has a Sherwood double post manifold), does not offer redundancy, it is no different from a single tank of similar capacity in that regard. I think I do not see any means of shutting off or isolating the tanks? I think I see an Aquamaster there and a Conshelf for octopus. But that rig is not the self redundancy this thread was created to promote or question by the OP.

The OPs premise is confused or confusing. He says "recreational" but then goes off into a discussion of recreational divers not having deco training. Yeah, is this news to him? I can fully understand a solo diver or a diver like @Wibble who is diving technical or very advanced recreational profile (where is the cross over for that depends) who therefore needs redundancy in addition to his team support.

Regardless, I do not think the OP was addressing vintage twinsets which are for all intent and purpose a single tank as there is not a means to isolate or provide real redundancy. My twin 50s plus manifold do not weigh any different from a single HP100, not much of a difference anyways. Comfort is a wash (for me) and I would like to see any hard data demonstrating a difference in so called streamlining or drag reduction aside from anecdotal-isms.

James
 
A few people I dive with in SE FL dive small doubles, twin 50s, to satisfy the redundancy for solo. They switch over at the SI, just like the rest of us do. They just take up more room :)
 
I only dive in tech equipment, even so for recreational sportsdiving. The reason: I refer it and it means you can do 3 dives on a twin12 sometimes, but I can also stay under longer en with a ccr you can see some fish better because of no bubbles.
 
Infomercial designed to sell more useless gear to divers with a lot of disposable income.
Thank you for this useful contribution.
 
Couple years ago I was doing a cattle boat to the U352. There was a guy running doubles. Had a little talk with him. Can't say it was strange as I was the only one on the boat with a rebreather as well. His comment for doing recreational dives with doubles, that is what he normally (tech) dives with and is what he is most comfortable with. Doesn't have to change tanks between dives. Has a whole extra bottle of reserve gas on the first dive. Whatever gas was left over from the first dive gets added to the reserve on the second dive. Sounds like good planning to me. I was just there to put hours on the rebreather and be comfortable with it. Between dives all he did was set the doubles down and was ready to go when we got to the second site. Everyone else was taking everything apart and changing tanks and having to rebuild everything on the moving boat.
 
Couple years ago I was doing a cattle boat to the U352. There was a guy running doubles. Had a little talk with him. Can't say it was strange as I was the only one on the boat with a rebreather as well. His comment for doing recreational dives with doubles, that is what he normally (tech) dives with and is what he is most comfortable with. Doesn't have to change tanks between dives. Has a whole extra bottle of reserve gas on the first dive. Whatever gas was left over from the first dive gets added to the reserve on the second dive. Sounds like good planning to me. I was just there to put hours on the rebreather and be comfortable with it. Between dives all he did was set the doubles down and was ready to go when we got to the second site. Everyone else was taking everything apart and changing tanks and having to rebuild everything on the moving boat.
What sort of depth?

Completely with him though: I don't have nor would ever use a single: it's either sidemount, backmount twinset or rebreather for whatever depth we're doing.
 
https://www.shearwater.com/products/peregrine/

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