Tiny Doubles, I Second That

Joe's Double Scuba Tanks

Double OMS 112’s, OMS 85’s and ScubaPro 38’s in Front

My first set of scuba tanks was a pair of “tiny doubles” (1800psi 38’s, or so I’m told). I suspect they are actually 45’s, and, when filled 10% over, 50’s. They were manufactured by ScubaPro in 1972, but I got them used about 10 years after that. I was really excited to get them because they not only looked cool, but fit me much better than an AL80, or a steel 72. The tanks had a single outlet manifold with a J-valve, which were still common at the time. Today, they call that a suicide manifold because of the lack of redundancy.

Sometime in the early 90’s I decided to up the volume a bit by replacing those trusty steel 38’s with aluminum 50’s, which were much more common by then. Trouble is, double AL50’s are a completely different animal underwater (they suck, actually). And, within months of making the switch, Sherwood introduced the Genesis line of high pressure DIN tanks. Since then, those have been replaced in the market with 3442psi cylinders, but you can still find 3500psi Genesis tanks pretty easily.

I still have a bunch of  Genesis cylinders, all of which I continue to dive. They are heavenly in the water. Meanwhile, my lowly 1800psi 38’s (?) have been just sitting for decades. I used them individually in the pool for teaching Open Water classes for a long time, but even that stopped when I picked up a couple Genesis 65’s, which are easily 6 inches shorter.

Tiny Doubles (ala John Chatterton)

These days, unless I’m teaching or flying on vacation, I rarely dive singles. Mostly, that’s because the majority of my dives are technical dives. However, in cold water like we have here (Lake Tahoe and surrounding mountain lakes), once you start getting around 3-4 ATA, the rapid gas expansion can cause a first stage to freeze with very little warning.

Early in a dive a free flow at 100 feet plus is annoying. Late in the dive, it can be very dangerous. I dealt with that just a few nights ago. I decided to dive a single HP80. Sure enough, 7 minutes into the dive at 103 feet, it started with a trickle. At a normal ascent rate (30 FPM), I went from 3200psi to 1550psi in just over 3 minutes. Had that happened later in the dive, things could’ve gotten very uncomfortable.

A 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 makes a great case for small sets of doubles. He matches his tanks to the type of dive, which often means double 45’s or 50’s. In doing so, he never sacrifices redundancy. It also means he is able to dive the exact same configuration for every dive.

A new life for my steel 38’s

Thus inspired (get it? inspired?), I re-banded by 38’s (?), this time with an isolator manifold, and ignored the odd stares I got from my tech diving buddies. In addition to the nostalgic rush I get from being able to dive my very first set of cylinders, they make a very practical kit. One might argue that the capacity is basically the same as an 80, so why bother? The answer is obvious if you recall my anecdote above. Safety.

In diving, safety almost always takes the form of redundancy. Recreational divers carry octopuses or safe second stages, but only rarely pony bottles. On my recent dive, I had an octopus. So what? My first stage was frozen. There was nothing I could do but surface and/or share air and surface.

Capacity isn’t the issue at all. I have a SAC rate that averages .35 to .42, so I am rarely the first to run low on gas anyway. Like John, I have larger doubles, but for recreational dives, it isn’t always practical, comfortable or necessary to lug around 170 or even 224 cubic feet of gas.

To sum up, I agree with Chatterton all the way around. Doubles feel better in the water and provide redundancy that isn’t possible when diving with single tank. I had been thinking of re-doubling those 38’s for a long time but, it wasn’t until I read his blog that I went ahead and did it. Now, I’m seriously considering a pair of those LP50’s. Then, except when I teach Open Water classes, I’ll probably stop diving with singles except on warm water vacations.

7 thoughts on “Tiny Doubles, I Second That

  1. I just came across your blog about small twins, and I do in fact have a set of Scubapro (PST) steel, round bottom. 1800 PSI, twin 38s, complete with the “suicide manifold”. I bought the set in 1974 along with a used Aqua Master twin hose, and still have both! In 1975 my two hose was put aside for a Scubapro Mark 5, and that same year I acquired a hose collar BC with an LP inflator. That was progress!

    It wasn’t until 1982 that an octopus 2d stage appeared on my rig, and the horse collar gave way to the ‘Stabilizer Jacket”, the forerunner of our modern BC’s. My 38’s were replaced by 45’s, then a set of 72’s (71.2). In 1982 I had the opportunity of a lifetime, when I was sent with the 82d Airborne Division as the battalion Physician Assistant, to the MFO Mission in the Sinai. I had become a NAUI instructor the year before, and we set up the army’s first recreational diving school in South Camp at Sharem. I spent three tours with the MFO between Egypt and Israel, seeing patients during sick call and teaching young paratroopers to dive in the Red Sea. We were exposed to European gear and methods, and made friends lasting to this day. One night we life-flighted a young French diver to Israel, after his Fenzy vest inflated during his first deco stop on a night dive on the “Towers”. He blew past the next three stops to find himself paralyzed from the waist down. We had several Huey helicopters on station and flew him north, into Israel. A hour later he was standing and waiving to me through the port window of the recompression chamber in Eliat. A week later a bottle of good French wine found it’s way to my clinic in South Camp as a thank you for our intervention. These days there is a robust recompression facility, fully staffed in Sharem, but in 1982 there was little development there to speak of, and the place was a protected marine sanctuary void of modern medical assets. Nostalgia …
    As for the 38’s, I think I’ll have them hydro’d, slap on my 1st edition mark 5, and take them into our local quarry for a dive …
    Jack Cheasty
    NAUI 6171

    • Jack, thanks so much for reaching out! That must have been a magical time. Scuba diving was so different back then. To be able to live and work where you did is just amazing. I hope you’ll stay in touch. If you happen to have any pictures, I’d love to see them. If you get your rig into the water, I’d love to see that too! – Joe

  2. I too have just purchased a set of 50’s. Waiting for them to arrive. I second the redundancy of safety. Same for me, love my double 120’s. But no need for them on a shallow rec dive. Other then teaching, and vacation, it’s going to be all doubles for me!!!! Thank you for another vote in the right direction!

  3. Really funny as I’ve read John’s blog too and am doing the same with little doubles. I don’t need more tanks but this I could not resist.

Leave a Reply

Your email address will not be published. Required fields are marked *