Each of the posts can be independently shut down, but the cylinders cannot be isolated on my manifolds. Yes, experttechnical divers sometimes experience freezing but with free flows, but that simply doesn’t happen with double hose regulators.
SeaRat
Twinsets, redundancy, and what problem are we solving...
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SeaRat
Unfortunately today's diver can't swim, they don't have the agility to move around underwater like the Causteau team. They can't swim to the bottom or more importantly swim to the surface. So there always looking for a gear solution which further limits the agility to move in the water. The surface was always the natural bailout when available but not anymore. There carrying so much gear they can't swim to the surface.Guys, you are way overthinking this. You are planning as if you are solo diving and tech diving at the same time, which is not necessarily the case. You talk about redundancy as if your wonderful, shiny new regulators are going to conk out on you at any time. Is that a remote possibility? Now, maybe, as these regulators have gotten very, very complex compared to the regulators of old. If you haven’t seen it, your should watch the Cousteau video about finding the Britannic. Yes, they used some rather advanced techniques and weren’t solo diving; they were tech diving with a triple tank system at 300 plus feet though. Why could they accomplish that? Well, they Mistral double hose regulator they used had six moving parts—that’s all. Take a look at the video:
Now, if you are diving solo using recreational rules (no decompression diving, no overhead environment, to caves, etc.), there is no reason for this redundancy, You can just swim to the surface. I have been diving this way for over 50, mostly solo. I usually have some redundancy, sometimes using double tanks, but not always. I have a Sherwood manifold that has twin posts, and a newer Scubapro manifold with twin posts. But this is so I can used my vintage double hose regulators with a single hose regulator that has LP and HP ports. But there are numerous times that I dive a small twin set with only a Mistral or Healthways Scuba regulator (both basically the same single stage design, with six moving parts). I have never had a failure. On several of my twin tank sets, I have a J-valve that I use with these regulators, just as I was taught to do in the U.S. Naval School for Underwater Swimmers in 1967.
Whenever you load up your gear with redundant gear, you are compromising your swimming ability. You have much more resistance to swimming in the water, which leads to more redundancy and a dive scooter (or two or three, according to the above photos).
I have made a study of underwater swimming techniques, and those skills have deteriorated over the last two or three decades amongst most divers. Why? Well, the so-called “frog kick” is one reason, but the other is loading one’s self up with redundant, but very in streamlined, gear. Dry suits also have contributed to the loss of swimming ability of divers, again due to their excess drag.
Just a few things to think about.
SeaRat
Subtidal Clambed Survey006 by John Ratliff, on Flickr
How I dove in the 1970s, with a BCD built into the back of my wetsuit, and a CO2 vest for surface emergencies. I also used a full-face mask at times with my double hose reguator (one only). The weights are built into the Mar-Vel backpack. (Note also that I had hair on top back then.
John Photos003 by John Ratliff, on Flickr
Diving solo in Alexander Springs State Park, Florida in 1970, with only our PJ jump tanks and a Mistral regulator with a J-reserve.
JCR & Aqueon by John Ratliff, on Flickr
Studying swimming techniques and ability with the Aqueon in Lake Chalan, Washington, 1972. Note how streamlined I am.
fullsizeoutput_29b4 by John Ratliff, on Flickr
This is perhaps the most advanced scuba unit I own, which has a Scubapro twin post manifold, a Mk V/A.I.R. I regulator and a Mk VII/Pilot regulator. Talk about redundancy; but they are not isolated. And, I have about a 350 psig sonic reserve on the Mk VII. I also use this combo with a Mistral double hose regulator on the center post.
This level of the “today’s diver” is rather scary to me. I remember starting diving out of the YMCA swim team, first snorkeling, then scuba, all the while continuing my swim team participation. Along the way, early, I earned first the Junior lifeguard, then lifeguard through the YMCA program, and finally the WSI (water safety instructor). We at that time (early 1960s) would not envision anyone taking up scuba without being able to swim.
SeaRat
I was snorkeling and spearfishing for years, in my early teens, before borrowing a spiro72 and reg. All shore diving at first. When the tank was empty we'd leave it on the beach and stay snorkeling. My brother and I shared it. I'd use the reserve one day and he the next.
The excitement to be able to breathe underwater was something else.
The excitement to be able to breathe underwater was something else.
Not fully, especially if you are on low on gas when a failure occurs. That is why I keep my isolation valve shut and follow the Progressive Equalization procedure.
That is why I dive valve-down doubles with a protector in a drysuit. I can easily reach all the valves on valve-up doubles in a 3 mm wetsuit.
Here is another image of getting a little obsessives:
Or a tanker truck.What's diving if you're not a neutrally buoyant M1 Abrams underwater?
Ok, I'll bite.
I've heard this pony argument before but I think it depends on how you're diving.
I used to sling a 7L instead of a 3L pony because a friend talked me into it when I started solo. Better to have more air than you need right?
Better still is to dive twins but for a long walk to the beach for a not crazy dive it's a killer and the 7L sling is a pain in the culo too.
(You're British so you'll prob know Chesil Beach/Cove for example)
So I ditched my 7L (which is sort of too much or not enough air for how I dive) and got a 3L pony to use on chilled dives with tricky access. (I mostly beach dive these days)
In fact I got sick of the sling so I used to twin the 7 and 12L.
Indi-twins lets you do that sort of thing.
Anyway I keep posting this for different reasons but as it's very relevant here, I dive a single 12L down to 10m max. 12 and a 3 down to 20m. Twins past that. I don't fancy trying to race up to the surface on 3L of gas from 40m but from 20m is doable for sure. It's a quarter of my 12L when its full. It doesn't take me a full 50 bar to swim up, do a little stop, then go roll a smoke.
Also...why would I...or anyone... dive with a redundant supply switched off? Genuine question.
The challenge with "the classic" large single with attached 3 litre pony is remembering to turn both on. It *is* possible to have a separate SPG that's visible and your pony's regulator necklaced; your checklist on the boat will be to breathe from the pony reg and watch the gauge, then breathe from the main tank and watch that gauge. There's also the third "alternate air source" coming off your main cylinder.
One of the great things about twinsets and sidemount is you've just two regulators to worry about.
My personal system of choice for solo diving off the beach is sidemount every time. You don't need massive cylinders, those 8.5 litre long tins are sublime - 17 litres at 240bar is loads of gas. This means you've a single smaller tin to carry to the beach and go back for the other. You've then got full redundancy, ease of access to the valves, everything's in front of you and it dives amazingly well.
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