Independent Doubles

[-JD-]

Interesting

Thank you @jd. I don't want to go the route of adding mounting. We will be out for three dives. There is no room on the boat. I had thought about bands but it's to complex. Having the tanks shift was one of my main concerns.

Good to know you emptied an entire tank and did not experience any issues hopefully that is understood as well.

Your thinking on the redundant air source is exactly what I was trying to convey. Maybe you can articulate it better.

As far as the back plate or set up in general, there is a guy on YouTube that put a rig together. Its 4 cam straps on a BP/Wing

To be clear:
Left tank (with one 2nd stage) was breathed down (with occasional switches to the right (with primary and safe 2nds) for validation) to near min-safe ascent pressure.
Then I switched to the right tank for the relatively brief remainder of bottom time.
For ascent I switched back to the left tank.
The donatable, right tank retained maximal available gas.
I did not have significant roll issues.
Renting one additional AL80 tank for a 2-tank trip was les than upgrading to 2 100s amd gve me built in redundancy AND more usable gas on both dives.


Normally in a travel situation, I'd dive with a BM AL80 and sling my personal AL27 pony. For the Coz invasion trip we were doing a cenote "cavern" (effectively cave) dive on the last day and I could not get a pony rental nor a fill on my own bottle. By going BM ID, I simply used my 2 tanks simultanously for both dives in the cenote and could maintain my personal redundancy - a deal-breaker for me where I was on a trust-me dive with unknown guides and unknown "buddies". That led to using BM ID for the Coz dives prior. Good practice and good for thise dives as well.

Mounting was a customised backplate with 2 pairs of cambands instead of BM ID adapters. The way my rig is set up the 2 tanks are super tight, separated only by the camband webbing.

 

[Clernix]

To be clear:
Left tank (with one 2nd stage) was breathed down (with occasional switches to the right (with primary and safe 2nds) for validation) to near min-safe ascent pressure.
Then I switched to the right tank for the relatively brief remainder of bottom time.
For ascent I switched back to the left tank.
The donatable, right tank retained maximal available gas.
I did not have significant roll issues.
Renting one additional AL80 tank for a 2-tank trip was les than upgrading to 2 100s amd gve me built in redundancy AND more usable gas on both dives.


Normally in a travel situation, I'd dive with a BM AL80 and sling my personal AL27 pony. For the Coz invasion trip we were doing a cenote "cavern" (effectively cave) dive on the last day and I could not get a pony rental nor a fill on my own bottle. By going BM ID, I simply used my 2 tanks simultanously for both dives in the cenote and could maintain my personal redundancy - a deal-breaker for me where I was on a trust-me dive with unknown guides and unknown "buddies". That led to using BM ID for the Coz dives prior. Good practice and good for thise dives as well.

Mounting was a customised backplate with 2 pairs of cambands instead of BM ID adapters. The way my rig is set up the 2 tanks are super tight, separated only by the camband webbing.

So it sounds like my concerns about additional banding is overkill. I'm not too concerned about switching the regulators I have a bungee so no issues.

My plan was to take an extra tank each dive, breathing the tanks evenly would force this since neither tank would be useable for the next dive. With your method I could get away with two tanks for three dives.

@tmassey the valve stem is turned around so it faces out. I only know that from the YouTube video LOL

 

[MarkA]

Independent twinsets are still reasonably common in the UK. It was the most common way to dive a twinset here really up until the DIR movement gained popularity and there are still plenty of people who use indies. AP do (or at least did) a set of soft twinset bands. I think other companies do them as well. Basically a pair of plastic spacers that go between the cylinders with standard cam bands to hold them. You either strap the set to whatever backplate/BCD you are using or you can buy adapters if you want to bolt them on. I can't recall who makes the adapters, might be Custom Divers.

View attachment 921624

I've never heard of anyone using an octopus with this kind of set up. One 2nd stage, one SPG and an inflator for either BCD or drysuit on each cylinder. There is no need for an octopus.

That is similar to mine on a buddy commando. As you say, pre DIR. Kent tooling make stuff to fit on a backplate, and adaptors for the AP bands.

Independent Twinset Adapter to suit 10-15ltr Cylinders

www.divingproducts.co.uk

 

[lizardland]

I use a very similar style of bands for independent doubles. I used a single tank adapter instead of those plastic pieces, but the configuration is largely the same.

I used to use a single tank adapter for travel when I used indies. If you flip the STA the opposite way round then the concave side nests against the ridge on the backplate. It forms a wedge between the cylinders which stabilises the cylinders when you tighten the cam straps. Excuse the crayon drawing (wing omitted for clarity and mainly because I forgot to draw it on):

It's maybe not as stable as permanently banding and bolting them on but it works good enough.

 

[paddydiver]

Not obvious why. Their website is not inspiring. They offer NO courses beyond AOW. They appear VERY inexperienced.

I'd say they're very experienced......in exactly one type of diving. That is diving with a single 12l tank using a standard reg and bcd set up. My gut feeling is you'll turn up, they'll see this mess and say no way, sorry, here's you're tank. These are diving by numbers resort shops and don't want anything out of the ordinary. If you really want to try this set up do multiple shallow dives at home, fix your weighting, figure out how much you're going to roll or how stable the tanks are. Then, when you have a perfect usuable set up, take it on holidays with you. You're going to try this out with a guide you don't know, with an insta buddy in an area that can have strong currents and deep water. If you're already a heavy breather think about how this is going to work out swimming against current with the drag of 2 potentially wobbly tanks and too much weight!
A lot of people giving advice here are seasoned UK or US divers. They're used to diving independently with a buddy, in control of their own dive, not following a DM. I'd imagine a lot are also using drysuits which gives you a back up buoyancy if something goes wrong with your BCD, a legit concern if you're carrying two tanks on a 30m dive.
It sounds like a disaster. They have 10l tanks. Get one and sling it.

 

[-JD-]

So it sounds like my concerns about additional banding is overkill. I'm not too concerned about switching the regulators I have a bungee so no issues.

My plan was to take an extra tank each dive, breathing the tanks evenly would force this since neither tank would be useable for the next dive. With your method I could get away with two tanks for three dives.

@tmassey the valve stem is turned around so it faces out. I only know that from the YouTube video LOL

Mine were held quite firmly. You will need to evaluate your assemblage of components ...

Your air consumption in the environment and dive profile will dictate if it would work for you. I am normally OK using an AL80 and surfacing "a little low" since my AL27 gives me a ⅓ equvalent reserve for SHTF. So the use of the 2nd bottle with AL80 ID was pretty minimal.

I do have to echo the others and suggest some practice, and a commtment to extra discipline on your field dives, especially if you know you tend to distraction by environment and camera. Some of my past training in other diciplines built scanning habits and I have AI pressure for both tanks on my computer.

I would try NOT turning the cylinder around, but maybe at a slight angle. At least for my bio-mechanics, it is actually easier to reach the left-cylinder knob which is behind my neck than the right valve which is behind my right shoulder. Flipping the left tank puts the reg in a position where it is more exposed to damage.

ETA @paddydiver brings up some good points about experience, support, environment, others in the dive, bouyancy loss, etc. I had worked out the "other stuff" (including bouyancy loss) and had experience diving manifolded BM doubles in cold and near zero viz. BM ID was a relatively minor change for me and I obsessed over the plannig for months in advance ...

 

[divezonescuba]

You can make your own double tank adapter (DTA) from two single tank adapters and a 1 x 1 x 12 inch section of square aluminum tubing and four normal tank bands. All of these are readily available components. Some people don't want to make their own, so we occasional make them for divers.

This allows you to readily switch between single tanks and independent backmount doubles. I have on occasion done a deep technical dive with manifolded trimix doubles, a shallower afternoon technical dive with air, and a night dive with a single tank. So, it allows a lot of flexibility.

I reverse the left hand tank. So the valve drills are the same.

The DTA will work with any plate. However, there is one plate on the market which has four extra sets of slots that enable two tank bands to be threaded on each side of the plate. It is less convenient always threading and rethreading the tank bands thru the plate, but you don't have to use the DTA. It is sold by xsscuba.

There are actually a number of nuances to using independent backmount doubles with regular AL80 right hand tank valves. These are covered on a number of videos on our channel. We have dove in Egypt and most of the Caribbean using this approach when manifolded twinsets are not available (less developed dive destinations), too expensive to rent (technical diving locations), or are too inconvenient to refill (Bonaire).

 

[Nick_Radov]

You can make your own double tank adapter (DTA) from two single tank adapters and a 1 x 1 x 12 inch section of square aluminum tubing and four normal tank bands. All of these are readily available components. Some people don't want to make their own, so we occasional make them for divers.

This allows you to readily switch between single tanks and independent backmount doubles

I reverse the left hand tank.

What a mess. Instead of just buying and using the correct gear in the first place you guys create all sorts of problems for yourselves with unnecessary convolutions. The sad part is that you're apparently teaching this stuff when you're not even clear on the basics.

 

[Nick_Radov]

Hola~ I am heading to out in a couple weeks. The shop I am using only has 80's but I will burn that in about 30mins. I am an older bigger guy so air consumption is higher.

Work on your gas consumption. Age and size aren't a major causative factor. I am a large man and not exactly young, and I don't have this problem. It helps to relax and stay in good trim. Apparently you're planning to take pictures so maybe leave the camera behind until you get everything else squared away; I find that my gas consumption goes up significantly on photo dives. A good pair of running shoes also helps: I can personally recommend the Saucony ISO line for long runs and Nike Vaporfly for fast interval workouts, but other brands also work.

If I can get a 100 or even better a 120 then I am gtg.

Anyway, I would really like to use this shop. I was watching a YouTube video where a tech puts together set of 80's as Independent Doubles on a backplate/wing. So two complete regulator set ups. The local dive shop did insist on a octo on each regulator.

Has anyone ever set something like this up?

Yes, I've seen something like this. Total CF. If you actually need double tanks at your destination then do it properly, and bring an isolation manifold plus tank bands in your checked luggage. Assemble the doubles at the local shop. You'll need to coordinate this with them in advance.

 

[divezonescuba]

What a mess.

That's your argument? It would be more constructive to explain why it is a mess or a total CF?

When I first starting discussing this several years ago, a number of people said things like I was going to die or kill someone diving independent backmount doubles. I even got comments that people would get bent using the system. Well, that has yet to happened. It is interesting to hear that independent backmount doubles have been used more extensively in other countries than in the US.

The use of Independent backmount doubles is approved for instruction by TDI for any level of technical diving and PADI approves it up to TEC 40. So, the use of independent backmount doubles is accepted for instruction by at least two major certification agencies. I have used independent double successfully on dives over 250 feet without incident. I have also certified a number of technical divers who appreciate the advantages that independent backmount doubles offer and are currently using a DTA. Those include when manifolded twinsets are not available, are too costly to rent, or cannot be conveniently filled.

Many shops will not want to be bothered disassembling their tanks and putting your manifold and modular valves on their tanks. The diver or people doing so, may not assemble the twinset properly. That would be a concern. How would the shop know how to do correctly that if they did not have twinsets to start with. How would the shop know that the diver knew how to properly assemble a twinset. We once had a diver attempt to assemble a twinset by watching videos on youtube. His twinset was not assembled correctly. He thought there was something wrong with the bands.

I have actually tried to do take a manifold and modular valves on an overseas trip myself, for real and have been told that it would not be allowed due to liability reasons by the shop manager.

While I will acknowledge that the initial setup years ago was less than optimal, the process has evolved making the whole setup as streamlined as any manifolded twinset. The same regulators are used. The right post is exactly the same as a twinset. The only difference is that the left post is reversed. To keep everything streamlined, you can use transmitters or put a transmitter on the left post and the analog gauge on the right side. I normally dive twinsets with an analog gauge on the left and a transmitter on the right, so no extra gear is required.