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Recommend Redundant Air Supply Tank Size & Setup for Solo

Discussion in 'Solo Divers' started by SlugMug, May 23, 2021.

  1. SlugMug

    SlugMug Contributor

    # of Dives: I just don't log dives
    Location: Texas
    I'm currently looking into a Redundant Air Supply for recreational diving, and the only thing I'm unsure about is what size of tank to get. I've researched this enough to know to stick to 19cu or above.

    For Context:
    • Most of my ~35 dives are solo, and around 30-60ft. I'm comfortable at 100ft other than lack of redundant air, or reliable dive buddy. I've been to 130, but it's not currently my intent to go that deep solo. The short story with solo-dives is the visibility/murkiness frequently drops to 1ft visibility and my main "dive buddy" is impatient, so I dive solo or not at all.
    • Most of my current diving involves looting the floor of a murky lake-bed for sunglasses. I'll probably eventually get into technical diving, but that's probably 1.5+ years away. Travel isn't a primary concern at this time.
    • Each trip is usually 2x dives, 1-hour, on aluminum 80s. I'm not concerned about gas management, I always have plenty of air. I am mostly concerned about potential for tank-valve/hose/regulator failure.
    • Much of my diving is off a regular (non-dive) boat, with a small annoying ladder, which might make doubles difficult, but not impossible.
    Looking at my options:
    • 19 cu - would be the most streamlined, lightest, and least intrusive. The downside being I'd probably never use it for anything else.
    • 30 to 40 cu - would potentially have additional uses for short/shallow dives (with a 3cf spare-air I acquired) or for when I get into tech-diving. Would a tank this size be relatively out-of-the-way when front-mounted while sunglasses-hunting? Is the size/weight between 30cf and 40cf noticeable?
    • 80 cu (Doubles) - Double 80s, rear mounted, with independent regulators. I could refill both before each dive, and alternate regulators regularly, so each tank has similar PSI. My biggest concern is the weight and potential for back-injury, while climbing into or out of a boat on a small ladder a bunch of times.

    A few questions:
    • What are the pros and cons of front vs rear mount? Do people attach 30/40 cu bottles rear-mount?
    • When running front-mount with a 30 or 40 cu, do you usually detach your spare-tank before climbing into the boat?
    • Does anyone wear a back-brace (in addition to backplate) while scuba-diving with doubles? Or am I over-thinking it? I only just got a backplate this week, and I have twisted my back (lightly sore 1-2 days) while running a singles on a somewhat floppy BCD.
  2. Seaweed Doc

    Seaweed Doc MSDT ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: Seattle, Washington State, USA
    I dive with a 40 cf FWIW. It's definitely heavier, which I suppose makes me careful about my back.

    Can you ditch the rig on the surface and bring it on the boat in pieces? E.g, hand up or toss weight pockets, dismount pony and bring that aboard, then the main cylinder?
    SlugMug likes this.
  3. James79

    James79 Reinventor of Wheels ScubaBoard Supporter

    # of Dives: 50 - 99
    Location: Lower Alabama
    I use a 19 when solo, or diving single stage double hose regs. It also sees use as my shop tank when I'm working on regs (keeps me from having to lug a full size tank upstairs), and to fill tires (again, too lazy to drag around a full size tank).

    Regarding your small (non dive) boat conundrum, have you thought of putting a tag line with carabiners by the ladder? Then you can doff your whole rig, clip it off, climb in the boat and pull the rig in with the rope.


  4. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Philadelphia and Boynton Beach
    I'm with @James79

    I carry a slung 19 cu ft cylinder. A conservative rule of thumb is to calculate your gas use for a minute at the deepest depth you will use the cylinder, a normal ascent, and a safety stop, all at twice you normal RMV. For me, 19 cu ft is plenty for recreational depths.

    Of course, if push came to shove, for a no stop dive, you could press the ascent a bit and skip the safety stop
  5. SlugMug

    SlugMug Contributor

    # of Dives: I just don't log dives
    Location: Texas
    Normally, I place fins on the boat, then climb aboard with everything else. Nobody is usually assisting me, and time is usually not an issue. I usually carry 8lbs of weights on my jacket BC for a 5-mil wetsuit. I'd imagine I'll carry less with a steel backplate & redundant air-supply.

    I've never tried removing my BC before climbing on board. I'd have to ask my buddy (who owns the boat) about leaving a clip attached, but I could always just put the clip on my backplate & attach to the ladder before climbing aboard, then lift. First unclip and lift the 30/40cf, which negates the weight issue. Then lift the backplate with 80cf. I suppose I could even do something similar when entering the water. Clip the 19/30/40 cf to the ladder, jump in, then attach it to my BC. Front-mounted probably makes the most sense for clipping/unclipping in the water, since rear-mounts usually attach to the main tank.

    So, if above-water weight isn't an issue, would a 30cf or 40cf, front mounted, be in the way while grabbing small items off the bottom of a lake. It doesn't look in the way in videos, but I've never dove with a redundant bottle before.

    Based on my research, for recreational-depth emergencies 13 is risky, 19 is relatively safe, and 30 is a walk in the park. And skipping (or shortening) a safety stop is better than downing. If this was ONLY for emergencies, I'd probably just grab the 19. However, I'm considering possible dual use, which is why I'm also looking at 30 and 40 cf.

    For example (1) a if a tank valve has an issue, me or my buddy could still do a short/shallow dive. (2) I believe technical-divers often use 30s and 40s for a variety of things.

    Since unclipping before climbing aboard will probably work, it seems the main remaining issue is whether people do or don't find carrying 30s or 40s annoying during for recreational dives, due to drag, size, or being in the way.
  6. davecampbell

    davecampbell Contributor

    # of Dives: 50 - 99
    Location: Hamilton, Ontario, Canada
    everyone I've asked this question to always says to get the 40 if tech is ever in your future...
    sabbe likes this.
  7. OTF

    OTF Coney Island Whitefish Biologist ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: scubaboard
    I have a 19, a 40, and often sling 80s.

    First of all, slinging on the left side in a standard "stage bottle" style configuration is my preferred way to carry these things. You can remove it, pass it to others, reach the valve, and fix problems/entanglements much easier than if it's on your back. Rigged properly it has very little drag and is totally out of the way.

    The 19 is small, light, and plenty of air for shallow stuff like you're talking about. The 40 is good for deeper stuff but I rarely use it because at that point I'd usually just go to doubles or a slung 80. Slinging an 80 really isn't bad at all, once you're in the water it all but disappears.
    SlugMug likes this.
  8. SlugMug

    SlugMug Contributor

    # of Dives: I just don't log dives
    Location: Texas
    That's good to know. I'll add that as another point for 40cu (over 30cu).
    Since I already have several 80s, I might as well give slung-80 a try sometime. Might even be good for deeper dives, without going a full dual-back-mount setup.

    Based on your feedback a 40cu would be relatively unnoticeable and out of the way, which would fit what I'm looking for. I suspect a slung-80, pulling it in and out of the water, would annoy me enough for a casual-dive that I'd be tempted to skip it, but having to lug an extra 40cu out of the water would be nothing.
  9. runsongas

    runsongas Contributor

    # of Dives: 500 - 999
    Location: California - Bay Area
    40 if buying new, but a used 19 or 30 works if you find one cheap
    sabbe and Lostdiver71 like this.
  10. SlugMug

    SlugMug Contributor

    # of Dives: I just don't log dives
    Location: Texas
    Yes, buying new, a local dive-shop has a decent deal on tanks, which includes 10 "free" fills, and fills in my area are about $10. Looks like 40cu gets another point.

    I pretty much always snag cheap/used when they pop up, regardless of size. I have a 1.7 and 3.0 cu spare-air I bought super-cheap from some auction-sniping. Then I read that size is nearly useless ... haha ... guess I can keep them for shore-diving, retrieving an anchor, or a quick swim.

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