Tiny Doubles

Nothing makes me cringe more than watching a diver enter a wreck utilizing a single tank with a K-valve and a single regulator. With this configuration, in the event of a regulator failure, it may be possible to go to an octopus, but you do not have a redundant first stage regulator. You cannot shut down a regulator with a freeflow. Penetrating a wreck or entering into an overhead environment with a single regulator requires that you rely heavily on luck, and I don't like to dive that way; in spite of the fact that I am very lucky.

The vast majority of divers are single tank divers, and single tank diving totally works for them. They have their setup, they know their equipment, and they know their limitations. However, some of you may want to extend those single tank limitations, but are just not interested in a big, heavy, twin set of killer LP130's!!! Or even a twin set of aluminum 80's for that matter??

Image from Andrea Doria video footage

Image from Andrea Doria video footage

On my back, I love steel tanks. I always have. My first set of doubles was a mismatched pair of steel 72's, of course with a single outlet manifold. I replaced them with a very pretty set of galvanized steel Healthways 80's with an original hydro stamp of 1969!! They were just like the steel 72's, but longer. They fit me, they held lots of air (relatively speaking), and they were 2400 psi cylinders, so on occasion I accidentally overfilled them a little on purpose. They were great tanks for my early years of deep air diving, however with the single outlet manifolds, and thereby a single regulator, we carried 20, 30, or even 40 cf pony bottles for bailout. In a primary regulator failure, you could not access your primary back gas, so your pony bottle could not be big enough. Regardless of how much air we had, penetrating the Doria relying on a single regulator was obviously foolish.

For me, aluminum cylinders are okay for side slung, or stage bottles, but I really don't like them on my back because they do not have that much gas, I don't like the way they feel, and I have to wear more lead on my waist. The only advantage to aluminum cylinders is that they are cheap. Aside from that, I once had a set of twin aluminum 50's with an original hydro date of 1972. Because of industry warnings, and for good reason, no one would fill them because they were too old. 🙁  I sold them to the scrap guy for $23. I now have one set of aluminum 80 Doubles, but I really don't prefer to use them.

Left to right: double HP120's, LP108's, HP100's, AL80's, LP72's, LP50's, LP45's

"If I am diving deep on open circuit, I will match my doubles to the dive..."

For the sake of argument, let's forget about rebreathers right now. If I am diving deep on open circuit, I will match my doubles to the dive, which usually means a big set of steel, HP 120's (3,500psi). They are big and heavy, but I like having all the gas, and I am 6'1" so the tanks fit me well both on the bench and in the water. I could dive steel HP 100's, but the tanks are shorter and for the difference in weight, I personally prefer the 120's.

However, I am not always diving deep, and I am not a big fan of the H or Y valves. For regular old recreational dives, my favorite tank(s) of all time are…..(drum roll please)…..my little twin LP steel 50's (2400psi)!!!!! They rock!

The center of gravity for these 5.5" diameter tanks is closer to my back, so they don't move around as much, which gives them a more natural feel. The buoyancy characteristics of the steel tanks mean I need little or no lead. I prefer this, but some divers might need the additional security of big lead weights they can ditch? The dual outlet manifold means I can utilize a primary and secondary regulator, and even an isolation valve if I want? Regardless, in the event of a regulator failure, I have some excellent options. In addition, the dry weight is pretty user friendly, and they provide lots of gas for most all recreational dives. Aside from all that, I use the same backplate and harness for pretty much all of my diving.

But wait, I also have a couple of 45cf double sets. These are even smaller and lighter than the 50's, but still 5.5" diameter. Because I am tall, I prefer the 50's when I am suiting up on the bench, but for divers shorter than me, the 45's are a very comfortable set of cylinders.

AL80's and Steel 50's from above

"I am a big fan of the dual outlet manifold for safety reasons, regardless of cylinder size, or severity of the dive."

The dual outlet manifold, where two independent regulators can be utilized, was a huge development in diving equipment. It meant that the primary bottom gas supply can be accessed, even after a regulator failure and shutdown. So, I am a big fan of the dual outlet manifold for safety reasons, regardless of cylinder size, or severity of the dive. Divers using a Side Mount system cannot do this, and I see this as a weakness in their setup. Personally, I think Side Mount is great for certain mission specific applications, like in cave diving, but in general it has more disadvantages than advantages to me. So, I avoid Side Mount, but diving is about having fun and that does not mean someone else should not enjoy that setup if it makes them somehow happy.

JC with his collection of Tiny Doubles

Me with my collection of Tiny Doubles...and my HP120's

I always choose utility over fashion, but IMHO the twin set 5.5" cylinders provide both for recreational divers. If you come down to Pompano, and see a guy a guy on the boat with Tiny Doubles, it is most likely me (or Megan). But maybe..... some day in the future (when we are disembodied heads in jars?)..... everyone will be diving them??? Then again, probably not as they are not for everyone, and it would be boring if we all dived the same.

Notice that I did not even mention how they make me more... self reliant. 🙂


everyone sing along now...

Cheers,

43 Responses

  1. Skip
    Great article - I dive double 95's - heavy as the dickens - plenty of air though - maybe one day soon I will steal my wife's double 72's and go for a ride!!
    • John Chatterton
      Jajajajajaja Okay, maybe you buy her a set of 50's before you pirate her 72's??? :)
  2. Yvan
    Diving double should be the only way to dive. Since I've started to dive them I really feel uncomfortable on single tank dive. People learn to stay blind with risks and when you open your eyes, crap, did I do that? Thanks for your article John.
  3. Rich Hanner
    John- What are your feelings on a single 130 with an "H" valve vs. the double 50? It's still got the redundant 1st stages, but with more gas and without the bulk of doubles (my thoughts, anyway)
    • John Chatterton
      There is no single setup that works for everyone. A lot of this is personal preference. If you like a single 130 with an H-Valve (or Y-Valve), then don't let me talk you out of it, because it is a solid setup. You have both primary and secondary regulators on the bottom gas supply, and a whole lot of cubic feet of gas, so you are good to go for pretty much any recreational dive. For me, I notice that the center of gravity is further away from my back with a single. That makes the tank move around more, especially if I roll onto my side. If I am in the wreck, I have a lower profile with the doubles, and can fit more easily into places that are more problematic with a single. At the same time, the end valves on the manifold are easier for me to reach in case of an emergency. The Tiny Doubles seem to fit me better, or seem to be more a part of me, than a big single. Tiny Doubles are another option, and one that works well enough for me that I felt I should blog about it. Thanks for the input. Cheers
    • Brian Bordieri
      I like that setup too for long, but not deep dives. Never considered tiny doubles before, but I can see the advantage of the low profile. Nice development.
  4. As always, a very informative and cool article! I know when I first saw all of you at Fill-Express getting these tanks filled that it was the perfect solution for me. Now I have a really nice redundant setup whether I am doing a deep wreck on my HP100 doubles, or shallower wreck/reef, on my double 50's. The day on the boat is also much simpler as there is no gear reconfiguration switching from technical to recreational dives. I have built a few sets of the double 50's based on your advice, and I absolutely love them. If anyone needs any help putting together a set I am more than happy to provide the information I have on how to obtain some tiny doubles!
  5. I love my tiny doubles! If I didn't already dive double steel 70s (a little taller and skinnier than 72s) at home, I would have bought the LP50s I rented in Florida last summer. I loved them so much, I didn't want to let them go: http://www.ashleyhauck.com/blog/wp-content/uploads/2012/09/Ginnie-Springs-12.jpg I just can't think of any reason to dive a big single tank over smaller doubles for recreational dives. Doubles sit better on my back, trim out better in the water, offer some redundancy, and don't weigh significantly more than a big single tank and a weight belt--and as a bonus, I can generally skip the weightbelt when I wear little doubles! I am also tall, and for bigger dives, vastly prefer the HP120s to the HP100s as well. Nice post!
  6. Gordon Johnson
    I almost always have to take the airlines when I dive. So, I usually rent a 100 cu. - 120 cu.ft. HP steel tank and bring my own 30. cu.ft pony bottle, in case I have a problem. It's hard to tell from your pictures, but I'm wondering if I could throw those little 50's into a checked bag and quit renting tanks and scrap the pony. Any idea what the 2 50's weigh? (over 50 lbs and the airlines jack the fees way up). I try to keep two checked bags under 51 pounds each. I've actually never seen little ones like that. What a great idea for recreational diving, especially for dives like the Spiegal Grove, Vandenberg, etc. Sometimes I never know who I will be diving with, and it sounds to me that the two little 50's and the systems redundancy definitely increases the safety margin and reduces the amount of risk. I'll have to check in to getting me some of those!
    • John Chatterton
      G, The beloved TSA will not allow you to carry any cylinders on a plane with the valves in, so you need to carry them disassembled, which you could do if you wanted? At the same time, you could ground ship them ahead of time to the dive shop or hotel, and not even have to bleed the tanks down? :) CHeers JC
    • Allen Sanderson
      I just threw a set of doubled 45s in my luggage and flew with them. I had a few other things in my bag so the bag weighed a total of 56 pounds. I have status on that airline so it was no big deal. Without the extra the bag would have been 50 punds.  Also as said you will want to dismantle them not just for the TSA goons (which inspected mine) but also for the baggage handler who will toss them around. Finailly, do not tell the airlines what is in your bag as like to charge extra for scuba cylinders.
      • Gordon johnson
        Thanks for the info. Do you recommend any particular product with the mini ( tanks and regs)?
  7. Thomas A Burke
    My first doubles were when I put my 80's together with a single manifold and a old O2 bottle as a pony. I bought a set of steel 72's at the Scuba flea market in Toms River. The 72's were nicer to dive with than the 80's. they had better balance than the 80's and they fit my size better. (5' 5") https://sphotos-b.xx.fbcdn.net/hphotos-snc6/230742_1044316354045_5167_n.jpg
    • Thomas A Burke
      Double 80's, old O2 pony, Jersey up line, and a horse collar BC.
      • John Chatterton
        No doubt, you are still having fun with it, and that is what counts. You rock on, Thomas.
  8. Jane S
    Hey John: I remember your "tiny doubles" well. I was happy to take advantage of them in the DR. Looking forward to diving with you again soon, Great blog, BTW, it has become a must read. Cheers...Jane S
  9. FS
    You mentioned that in sidemount, the "primary bottom gas supply" can not be accessed given a regulator failure. At least that is what is implied. Could you elaborate on this and why you believe this is to be true ? I dive both backmount doubles and sidemount and maybe I misunderstood or am missing something but I don't see the same issue. thanks.
    • John Chatterton
      I meant the entire primary bottom gas supply. If you have two cylinders, each with an independent regulator, and one regulator has a catastrophic failure, you have the redundant regulator, with your redundant bottom gas supply (on the other side). However, you don't have access to the gas in the cylinder with the failed regulator. So, you still have bottom gas, but not access to the entire bottom gas supply, or the same volume of bottom gas that you would have access to if you were diving doubles with a manifold, where you could just shut down the single offending regulator by closing the valve. Cheers
  10. [...] Have you ever considered using small twin tanks for a recreational dive? Check out John Chatterton's latest blog on using tiny doubles instead of a single tank...interesting. Tiny Doubles | Shadow Diver | John Chatterton [...]
  11. Double dives in Bali
    Am kind of envious reading this. The choice of tanks isn't that great where I live. No steel tanks, s80 & s40 are almost all that's around. You might 100cf if you're lucky and can pay twice their worth... Only way to get twins was to import all gear from back home. S80's it has to be. Add a stage if you need mor gas. Not ideal but not much of a chance really! Having tons of fun with doubles though, both backmount & sidemount...
    • John Chatterton
      The late Bill Hamilton was fond of saying, "What works, works."
  12. Kurt Ahlstrom
    I've got a set of steel 45s that suit me just fine.  Those tanks, with a harness and an OLD but well maintained Aquamaster double hose reg get some strange looks on the beech or on the boat.  Having said that, for a shallow dive or for any photography dives they allow a freedom of movement that an Al80 or even a steel 72 can't come close to.
  13. Andrew Pitman
    Tiny doubles, in a set Makes me happy... Makes me wanna get wet!
  14. Adam
    John, I noticed you didn't have an isolator valve on your two smaller sets of doubles. I suppose it's not as critical for the types of dives you are using them for but I would think independent doubles would be safer than diving no isolator. Your thoughts? Great blog BTW.
    • John Chatterton
      When OMS first offered these tanks, it was with a proprietary short manifold bar with no isolator. That was all they offered, so that is what I have. Now, Blue Steel has modified the bands to accept any standard manifold, so an isolator is possible and would be my choice. For me, i would rather not use twin K valves, and stick with the manifold with no isolator for my existing setup. JC
  15. Tim Hogan
    Great information. I am about your height and build. For some time I've planned to double a set of older OMS 45's together. I'm going to use it with my double hose US Divers aqua lung (vintage-looking, but completely new parts and modern build)…this ideally would get mounted to a port in the center of the crossbar of the manifold. I have a bunch of old and new manifolds to do this but, so far I haven't found a way to isolate the center port while still getting gas to another post for a redundant regulator-(except by using an old Sherwood Selpac manifold..too bad the center-to-center distance is a bit wider than i'd like at 7.25"). I may have to have a crossbar machined to get what I prefer. Cheers, Tim
    • John Chatterton
      Tim, It sounds like you are looking to have some fun tinkering with old school concepts. Diving is supposed to be about having fun, so you are probably doing it right?? CHeers JC
  16. […] few months ago, I read John Chatterton’s blog article, Tiny Doubles. (BTW, John, if you happen to read this, I enjoy reading your blog. Please write more.) In it, he […]
  17. Hope you (all you tiny doubles divers) don't mind a comparatively beginner budgetary question: I am looking at my first cylinder (s) purchase and have yet to figure if I end up going with two larger singles and a pony (for two dive boat "rides") - or if I should just go from singles rental straight to doubles. I think I understand the pros and cons and like that I may not need the pony with the right doubles setup, but I also see advantages in being abble to fly with the (dismantled) pony. What I am wondering is: How do you get charged in various places for refilling doubles and especially tiny doubles? Same as for a similar volume single? Or same as for two singles?
    • John Chatterton
      IMHO, if you think you are going to end up in doubles, don't invest much in singles. It is common for divers to get large cylinders for singles diving, that simply do not convert well to the kind of doubles they want to put together later. I like the Faber LP85, and HP120 cylinders because of the buoyancy characteristics, but also because of the relatively small cylinder diameter, 7-1/4". Large diameter cylinders, like the 8" dia cylinders, place the center of gravity of the cylinders further from your body's CG. I know the difference between 7.25" and 8" may not seem like much, but you definitely notice it. As far as fills, that is something you need to figure out with your local shops. I hope this helps.
      • I know this is a year old post, but I thought I'd add this anyway. In addition to the difference in CG, 8" cylinders place the valves farther away from your back. I've seen divers that have no problem with valve shutdowns in 7.25" cylinders have an impossibly difficult time with 8" doubles. This is especially true in a stiff drysuit like the Viking.
        • John Chatterton
          Yes, the valves are further away, and hard to reach. IMHO, having the cylinders center of gravity farther away, is even more uncomfortable. JC
  18. I have three questions regarding tiny doubles. 1. Tiny doubles filled up to 3000 psi gives you approximately 130 cu ft. of gas. Do you get two dives on the tiny doubles at recreational depths, less than 100ft? 2. Are you trans-filling the set after the each dive? 3. If you transfill your tanks, what size tank are you transfixing from? 120hp 130hp? If so how many cu ft. of gas will you have for the second dive.
    • John Chatterton
      Hey Charlie, The Tiny Doubles are 50 cf each, for 100 cf total when filled to 2640. At 3000 psi, they would be roughly 113 cf, and I would typically take two sets of doubles for two dives. I may also carry a side slung cylinder for deco, or just as a contingency, depending. I use a transfill on occasion, and pretty much always have one on the boat with me, however I can't recall the last time I transfilled a set of Tiny Doubles? Cheers JC
  19. I'm currently looking to setup some tiny doubles. I'll be diving off a jetski, which means wearing my equipment to and from the dive site. Additionally, I'm only 5'3", so I want my air source to be as small and light as possible while still providing for an adequate air supply. I plan to use a pony bottle to supply air for both my drysuit and BCD. Currently I'm looking at combining my 40's, possibly twin 63's, or HP steel tanks.
    • John Chatterton
      Personally, I love the Faber steel 50's, but you can certainly try to see what will work best for you and the way you want to dive.
  20. John, thank you for the great post and information. I mainly dive in the Pacific NW and I have been diving with a steel HP80 + a 19CF pony. While this has worked for me, and it has provided the redundancy I need... I have been thinking there has to be a better alternative w/o having to jump to a set of twin 80's or 100's and the above water weight that comes along with that setup. Since most of my dives are above 110' that seems like overkill. Reading about the twin LP 50's has me wondering that it might be the perfect alternative. Thank you, Ignacio
    • John Chatterton
      IMHO, you will find the Tiny Double 50's much more comfortable to dive than what you are currently using. Side from that, you will have redundancy on your main gas supply as well as more gas overall. Please let me know how you make out. JC
  21. what harness do you suggest for the twin 50s? should i find an old yoke? what about a back plate and a wing? pat
    • John Chatterton
      On the Tiny Doubles, I use the same harness and backplate that I use for all my doubles diving. I have an Apeks aluminum backplate, with Apeks straps, a variety of hardware for those straps, and a Dive Rite Rec Wing with a dual bladder in 45# of lift. The Old Style OMS bands required the use of a short manifold crossbar. The New tank bands are made for the full size manifold, they are even more comfortable, and are available through Blue Steel here in the US.
  22. John, Where do you get training for diving doubles recreational? Seems most Padi shops are pushing sidemount regardless of application. The impression I get is that many feel doubles are "outdated". Thanks
    • John Chatterton
      There are advantages to Sidemount over Manifolded Doubles, and the reverse is true as well. One size does not fit all. Anyone who gives you the impression that Doubles are "outdated" probably is not familiar with doubles, does not understand doubles, or has some sort of agenda. What works best for you depends on what kind of diving you are doing, as well as your personal preferences? For recreational divers that want to learn to use Manifolded Doubles, you have a few training options. Since I am a TDI Instructor, I will use the TDI terminology, but all the training agencies are similar. Intro To Tech is a 3 dive class that will introduce you to Doubles. Advanced Wreck/Decompression Procedures is 6 dives of entry level Deco training for divers who are new to Doubles and the Soft Overheard Environment. Advanced Wreck is 6 dives of wreck training including wreck penetration, for divers new to doubles and the Hard Overhead Environment. Setting up your rig is where new divers need the most help, IMHO. Regardless, my Advanced Wreck and Deco classes are suitable for divers new to doubles. I hope this helps. Cheers JC
  23. I didn't see anything about the USD twin 30's that came out, plastic coated, in differnt colors, during the 70's with a "unitized" black anodized bronze manifold made specifically for this duel set-up. I drilled and taped the manifold mid-section up between the tanks, to install a mini gauge,,,SS banded an Ameron commercial divers harness on and drilled and taped the reg connection port to fit on a posiden 1st stage which screwed directly into the DIN port I taped in. This was my bail out rig,,,small and tight to the body,,,worn maniflod down. This I connected to a quick connect, with a locking ring, on the block of my Aquadyne DM-7 with a SS small diameter hose. Used this rig for 15 years mostly overseas. Sold it to a German last year,,,,,,,,,,,,,the guy was thrilled with it,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,I think he's using it for his commercial diving. Thanks Rick

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