Some Thoughts on Independent Doubles

[MichaelMc]

Then along came side mount and now they are the darlings of the UW world. What exactly has changed other than position.

(Lower center of gravity, possibly more streamlined, no long metal object strapped to your back restricting spine flexibility and head tilt, and separate movement on land or water.)

I'm all for independent doubles via a closed manifold valve, though I'm already accustomed to sidemount gas management.

 

[Nemrod]

(Lower center of gravity, possibly more streamlined, no long metal object strapped to your back restricting spine flexibility and head tilt, and separate movement on land or water.)

I'm all for independent doubles via a closed manifold valve, though I'm already accustomed to sidemount gas management.

You have a closed manifold on your side mount independent doubles?

The prior objections had nothing to do with the things you mention. As to streamlining, prove it. Head tilt, drop the tanks lower, a lower center of gravity, it is a wash, movement on land, I guess I do not follow, individual carry I assume? Hey, I am not anti-side mount. I understand how it can be a useful rigging. That was not my point. I just bought an Oxy Travel Plate to use to rig a mini side mount system. Just for the fun of it. I promise to be conventional, wink, wink! Actually, my wife just grabbed it and ran off with it----hmmm.

James

 

[MichaelMc]

The prior objections had nothing to do with the things you mention

I was listing benefits that sidemount may add over (back mount) IDs. Things not relevant in the old back mount ID vs manifolded debates. Whose addition may tip the pro vs con.

You have a closed manifold on your side mount independent doubles?

My sidemount is just normal stuff.

In the back mount realm, I have a set of AL40 manifolded doubles that I run either closed or normal. So I can play with doubles valve things plus have a redundant, one unit, nothing strange here just a normal back mount tank(s) and BC system, . But the ID gas management is nothing new to me given my normal-stuff sidemount (aka IDs with bungees not steel). (Backmount) ID is fine, but I agree that creating it with a closed manifold gives you ID at minimal extra valve failure risk, plus has the benefits mentioned by others.

The rest has been well hashed before. But a rigid object strapped to your back feels significantly different from two half sized ones floating at your sides.

Yes, you can carry one at a time at half the weight. Like I did yesterday to get them back to the car, partly over soft sand, after being beat up and exhausted by a surf exit, fall, pancake slide, spin, pancake slide, and crawl out of Poseidon's grasp. After I shed my jacket at the car, I carried back my rig and one tank, then the other. I could have managed them as one unit, but sometimes them being split is handy. (We got caught by a bigger swell increase than expected, but crawling out is not unusual at Monastery beach.)

Half the weight is handy every time I put them in or out of my car trunk one at a time instead of two at a time, partly bent over reaching forward.

Do you mean mini as in 50s (that I dive) or even (super) smaller like LP27s? Either way, have fun. Which is something I think they add a bit more of than back mounted IDs, underwater.

 

[AfterDark]

(Lower center of gravity, possibly more streamlined, no long metal object strapped to your back restricting spine flexibility and head tilt, and separate movement on land or water.)

I'm all for independent doubles via a closed manifold valve, though I'm already accustomed to sidemount gas management.

You mean you are all for doubles with closed manifolds. Independent doubles are separate single tanks used BM. If your SM left tank fails, HP failure say. You'd do what? Close the valve and then what? Breathe from the right hand tank. With independent doubles if you can't reach valve the tank drains to empty while breathing is done from the other tank. So what is the problem again?

 

[Nemrod]

I

Do you mean mini as in 50s (that I dive) or even (super) smaller like LP27s? Either way, have fun. Which is something I think they add a bit more of than back mounted IDs, underwater.

I was thinking two aluminum 40s. I have two such tanks. Your mini-50 set, which tanks are you using for that?

You are right, it has all be hashed and rehashed . But I still do not see why I would want to manifold (with manifold closed) a back mount ID set vs a side mount system. It comes up in every rehashing of the hashed out and I do not understand why it even comes up-----.

My ID set is steel 72s with custom bands on a Hammerhead plate, I also have a set of ID on custom bands using aluminum 50s. I have a Dive Rite 40# wing but sometimes I use a SeaTec Sunfish horse collar BC with it. I run USD Conshelf XIV regulators. The LH regulator is on a long hose so that it can traverse the rig, go under and around as is Hog fashion and it is on a generous necklace. The RH is on a 22 inch hose and comes over my shoulder and when not in use clips off to my RH D-ring. I may change that yet again to a 36 inch hose under my right arm and still clip off to the RH D-ring because it sometimes falls off my shoulder and bugs me. The SPGs come down to D-rings on the waist strap on their respective sides.

A recent incident, not with IDs or SM, has me going back through all of my diving equipment with an open mind with Minimalism, Occam's Razor and Survivorship Bias in my mind. Not just equipment but also procedures and when and why I do what I do (or did). Concerning SM systems, what pegs my OCD meter is all of the bits and pieces and strings and bungees and clips and that to maintain (tank) trim adjustments may be needed during the dive. That results in task loading, which in my incident one thing initiated and piled on to a chain of events, a series of very simple and routine things became almost deadly taken together. So, this has put a screeching halt on my SM considerations for the moment while I mull it all over.

Back to thoughts on IDs and manifolds. If I wanted to dive a manifolded system, I have those. In an ID rig, a manifold is not needed and therefore is a complication. The key word is independent and IDs are by nature simple and minimal. All things are not equal however, thus the need for SMs and manifolded twins. When those things are needed, necessity (penetration and removing tanks to reduce profile or for portage for examples) overrides complexity yet we still endeavor to make such systems as robust and simple as possible. Nonetheless, a manifold set of twins is more complex (in system but not perhaps in use) than IDs and so is SM.

James

 

[Gareth J]

I dived independent twins (doubles) for a long period.

I finally switched to a manifolded set after a near miss on a deep wreck in the South of France.
As is usual, the issue wasn't a single problem, it was a series of issues.

1. We where diving a site where ascent via the shot was a requirement.
2. We where diving a wreck that is in two sections, which required a jump between the two sections.
3. There was a lot of current running across the site.

The first phases of the dive went well. We had made the jump to the second section of the wreck. Although we had made the jump belly to the sand to minimise the effect of the current.
I made a scheduled switch to the other regulator, and inhaled some water. It became apparent that I had damaged the diaphram (as it turned out it was gravel wedged under the diaphram).
This immediately meant I had lost access to 150bar of gas in the cylinder.

So I stayed on the cylinder, and we aborted, attempting to make the hop back to the main section of the wreck and the shot.

We then got swept further down the wreck missing the shot. In the end we had to release a DSMB, and make the ascent on the DSMB, and I finally exhausted my one remaining primary cylinder. I went onto the long hose for the ascent then switched to the travel and deco gas for the last phase of the dive. We where a long way from the cover boat when we finally surfaced because it was required to stay with the trapeze.

After that I switched to manifolded sets. Even if you dive with the manifold closed, and don't have the mobility to reach the isolator, your buddy can open the isolator in an event like mine. (or you can drag it over your back and open it yourself).
I subsequently did a lot of diving, with a buddy who dived manifolded twins with the isolator closed as if they where independents using this philosophy.

Independent sets are OK, but they do have their own limitations.

Gareth J

 

[AfterDark]

I dived independent twins (doubles) for a long period.

I finally switched to a manifolded set after a near miss on a deep wreck in the South of France.
As is usual, the issue wasn't a single problem, it was a series of issues.

1. We where diving a site where ascent via the shot was a requirement.
2. We where diving a wreck that is in two sections, which required a jump between the two sections.
3. There was a lot of current running across the site.

The first phases of the dive went well. We had made the jump to the second section of the wreck. Although we had made the jump belly to the sand to minimise the effect of the current.
I made a scheduled switch to the other regulator, and inhaled some water. It became apparent that I had damaged the diaphram (as it turned out it was gravel wedged under the diaphram).
This immediately meant I had lost access to 150bar of gas in the cylinder.

So I stayed on the cylinder, and we aborted, attempting to make the hop back to the main section of the wreck and the shot.

We then got swept further down the wreck missing the shot. In the end we had to release a DSMB, and make the ascent on the DSMB, and I finally exhausted my one remaining primary cylinder. I went onto the long hose for the ascent then switched to the travel and deco gas for the last phase of the dive. We where a long way from the cover boat when we finally surfaced because it was required to stay with the trapeze.

After that I switched to manifolded sets. Even if you dive with the manifold closed, and don't have the mobility to reach the isolator, your buddy can open the isolator in an event like mine. (or you can drag it over your back and open it yourself).
I subsequently did a lot of diving, with a buddy who dived manifolded twins with the isolator closed as if they where independents using this philosophy.

Independent sets are OK, but they do have their own limitations.

Gareth J

Glad everything turned out ok for you. Every set up known to diving have their own limitations it is up to the diver to dive within those limitations.

IDs for me have been more of a solo setup but I've done easy deep dives with buddies using them and have had no issues. Isolation manifolds came too late for me. Now the type of diving I do doesn't require them and I can't use them, 3 shoulder surgeries.

 

[Gareth J]

Glad everything turned out ok for you. Every set up known to diving have their own limitations it is up to the diver to dive within those limitations.

IDs for me have been more of a solo setup but I've done easy deep dives with buddies using them and have had no issues. Isolation manifolds came too late for me. Now the type of diving I do doesn't require them and I can't use them, 3 shoulder surgeries.

Even with limited mobility, you can open the manifold.
I don't dive twinsets much these days, I dive CCR. I have mobility issues in my shoulders. Although I probably could shutdown and open a manifold on my set. I tend to use a loan set of 10's when I do dive OC. In that case, I just loosen the waist and pull them up my back, easy then to open or close the manifold.

A lot of the guys I dive with who do dive OC, use inverted twins. Which actually is a far more sensible idea. Easy access to the cylinder valves, easy to untangle if you wrap a line around them. Zero roll off issues. No risk of smashing a valve against the wreck.

As I said, manifolded twinsets with the isolator closed, then dive them as independents is a really simple solution.

 

[MichaelMc]

I have a set of side Faber LP50s, side AL40s, and manifolded AL40s. I dive in cold open water, often solo. I like the LP50s best for the lead savings and that they do not start to float, so they are clip once and then do not move. And they have more gas.

I almost always dive sidemount, but back (tiny) doubles are still easier to strap on for me if on a bench or trunk, are far more similar to student's gear if helping a class, and if crawling out of surf they are likely in the air and so not tugged on by the waves. For a long surface swim, you can remove them and use them as a swim board to paddle along while being able to surface navigate easily, something I miss with my sidemount.

But I may have answered the wrong question. Above were some benefits of back mount ID vs sidemount.

I often dive solo so want redundancy. Between manifolded and ID, I like that ID does not need me to shut off the isolator to have gas to get to the OW surface. I find achieving that "ID" with a normally closed isolator gives more flexibility in how I use the doubles. They could be used normally, as progressive equalization, or as "ID".

Yes, independent of other factors, real ID are more robust for ID use than closed manifold. We could debate if the option to open the manifold after losing a side made up for the lower robustness, such as Gareth's case. I could also forget to close the valve predive. But I should notice that soon via the SPGs, and I can do a valve drill and would actually check the isolator in an emergency.

Also, there may be other factors, like fill cost for tiny true ID doubles, or wanting to try out 'ID' and normal manifolded diving procedures.

 

[Nemrod]

After that I switched to manifolded sets. Even if you dive with the manifold closed, and don't have the mobility to reach the isolator, your buddy can open the isolator in an event like mine. (or you can drag it over your back and open it yourself).
I subsequently did a lot of diving, with a buddy who dived manifolded twins with the isolator closed as if they where independents using this philosophy.

Thank you for the story, I always find such adventures interesting and worthy of thought. I am glad you were (are) okay.

This being the solo forum, I am diving my IDs solo. I do not have a buddy in such case. Given an incident which happened to me recently, while on a single tank with no pony, and unintentionally became solo, has me rethinking many things. When (intentionally) solo on a single tank I have generally carried a 19 cf bottle, sometimes a 30 cf bottle, depth dependent. I may add that to deeper solo dives with IDs. Not sure yet. Or plan my solo dives to be more shallow or shorter duration or both.

James