Recommend Redundant Air Supply Tank Size & Setup for Solo

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Capt. T. Goetz

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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.
I love my twinset bp/w setup, It is really secure and stable (AL80s/122s on Zeagle 911). When you dive doubles there is a cross bar between both tanks, no need to switch regs. I have one spg, one/sometimes two primary 2nd stages, an octo, and two LPIs great for redundancy. Entire setup weights 60-70 lbs w/o weights, I usually dive off a 27' Grady and I don't have huge problems. If i were to dive w/ a pony bottle then I would sling it or side mount it.... But since you are diving solo I'd go doubles, and have a wing with 50+ lbs of lift....
<TG>
 

Bowers

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I would recommend the 19 for recreational just because it transports to the dive site easily. If tech is in the future then the 40 will serve you now and still be useful for tech.

You mentioned doubles... have you looked into sidemount? If you used your existing 80s, you would;
-have complete redundancy,
-would not need to buy another tank,
-would be preparing yourself for a setup that is widely used in technical diving.
-could still use the tanks independently if the need arises (whereas manifolded doubles are stuck together unless drained and reconfigured)

for what it’s worth, when recreational solo diving, i sling a 19 when backmount, or i sidemount my small lp50s.
 

Seaweed Doc

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My back mounted pony has pins you can pull to easily release it. That said, in your situation I'd go with a slung bottle. Pass it on to the boat and then climb out as usual.
 

Lostdiver71

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Since you are buying new, I would go ahead and get the 40. If slung properly you will barely notice it is there. I do not recommend doubles on a boat that is not set up for diving, especially if you do not have help getting back into the boat.
 

SlugMug

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My backplate wing has 94lb of lift. (edit: 85lbs, not 94)

After some advice and thought, doubles would be pointless for my use-cases. They would be heavy, clumsy, and a pain climbing in/out of a boat. I also already have 3 sets of regs (lucky craigslist find) and would like completely independent air-systems.

I just looked into side-mount more, and I think I'm sold even for my main-tank. I always find the stuffing tanks in/out of the back of a BCD straps while on a boat kind of annoying too. The ability to clip tanks and go, or unclip and climb in the boat without straining my back could be useful.

I'll still go with a 19, 30, or 40 for my spare, just to reduce how much I have to lug in/out of the water and to/from the boat. I think I'll stop by the dive-store tomorrow, check out the tank-sizes in person, and pick one up.
 

johndiver999

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Your depth is 30 to 60 feet, you are diving in terrible vis and you are never getting low on air. For diving in 60 feet of water, you can probably make it to the surface with a 3 cu-ft spare air if you have a scuba failure.

If it were me, I would be most worried about a really bad entanglement issue in the terrible vis rather than a scuba failure.

If I got tangled badly, I would want to be very comfortable in removing the tank and harness/bc from my body, so I could work on the problem. In those types of conditions, I think a front mounted and easily detachable pony bottle would be advantageous, because even if your tank and BC were really tangled up - if you got out of the unit, got you body clear, it should be reasonable to be able to detach the side slung bottle and come up with just that in your hands.

Most back mounted pony rigs are not so easily detached.

A 13 cu-ft probably has way more capacity than you need to come up from 60 feet, but a 19 is a little longer and I bet will ride nicer on your rig, so the 19 sounds reasonable. Anything larger is not really necessary.

If you wanted to go cheap, buy a 6 cu-ft pony bottle, slap the spare air reg on that and clip it off securely to the front of your BC.

And 94 lbs of lift in a bc for diving with a single 80 aluminum is something I would be moving away from ASAP.
 

Divin'Papaw

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My wing has 94lb of lift.

After some advice and thought, doubles would be pointless for my use-cases. They would be heavy, clumsy, and a pain climbing in/out of a boat. I also already have 3 sets of regs (lucky craigslist find) and would like completely independent air-systems.

I just looked into side-mount more, and I think I'm sold even for my main-tank. I always find the stuffing tanks in/

94# of lift and you’re not diving doubles? That is a TON of lift. I didn’t even know they made wings with that much lift. That seems completely out of balance to what you really need. More isn’t always better when it comes to wings. The right lift is what’s important.
 

SlugMug

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The main reason I stick to 60ft or less, is because I haven't had a redundant air-source, and dive solo. I'm comfortable at 100ft, but mostly avoid it due to lack of redundant air-source.

I haven't practiced harness removal since my intro dive-class, I'll add that to my TODO list. I haven't had entanglement issues yet, but some problems aren't problems until they're problems. :wink: I have a knife, but was thinking of adding scissors.

I'm fairly sold on doing a side-mount setup.

re: 94lb Wing. (edit: It's actually 85lbs, still a lot) It's just what I happened to get with that craigslist lot. Should I get a smaller wing? If I don't put much air in the wing, it shouldn't have much lift. Or is the problem more related to air getting pooled? Or difficulty dumping air? I haven't used the wing yet, and was planning on diving with it soon.
 

Divin'Papaw

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re: 94lb Wing. (edit: It's actually 85lbs, still a lot) It's just what I happened to get with that craigslist lot. Should I get a smaller wing? If I don't put much air in the wing, it shouldn't have much lift. Or is the problem more related to air getting pooled? Or difficulty dumping air? I haven't used the wing yet, and was planning on diving with it soon.

Yes, you need a smaller wing IMO. Too much wing leads to issues like tacoing, air trapping, and lack of streamlining moving through the water. You need the right lift not the most lift.
 

Bowers

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The wing i use with steel doubles is #60, and thats mostly because it needs to be big enough around to not be pinched under the tanks. For singles a 20-35 lbs wing is perfect. My sidemount wing is #32 lift and does fine with 2 lp85 steel tanks. Excessive wing space means more difficulty in controlling the bubble, especially in an emergency when you have other things to task load yourself with.
If you go sidemount there are a lot of good options. I would recommend a wing that holds the air low on your back. There are wings and/or adapters to put on your existing bp/w or you can get a dedicated sidemount rig which will ultimately be better.
Im fortunate enough to have numerous rigs for backmount and sidemount that i switch between weather im teaching, working, tec diving or having my own fun in the shallows.. But ultimately my favorite is sidemount. With a preference toward loop bungees and a streamlined harness. Xdeep is a great option but I’ve dove several rigs that perform well.
 
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