Some Thoughts on Independent Doubles

[rx7diver]

All,

I just sent this via PM to another member here. I though I would share it with more of you.

rx7diver

"[Addressee],

"When I returned to central MO (after having lived in SE Michigan and learning to extended range dive on Great Lakes shipwrecks), I had no one down here to do advanced diving with. So, I thought long and hard about how I could do it solo safely.

"I settled on independent doubles and sixths--which required only two changes to my kit: delete the isolator section of my manifold, and add a second SPG. That's it! So, my solution is exactly the ID's that you, by your own posts, have been diving for many, many years.

"It's the (nearly) perfect, simplest solution, IMHO. It seems to me that anything else necessarily will be more complicated and maybe introduce more risk.

" 'Nearly perfect,' rather than 'perfect,' because ID's involve a standby system of sorts, and standby systems always give me pause: While you're breathing down a 500 (say) psig amount of gas before you do the next regulator switch, the other cylinder and reg constitute, essentially, a standby system that you're betting will work if you *need* to go to it right NOW (!!), which means there is a bit of risk that it will NOT work if you need it right NOW. However, this ID standby system is "tested" frequently during a dive (every 500 psig, or so)--which IMHO is a much better system than a large single cylinder and a pony/bailout bottle, a system in which the standby pony bottle is most often left untested during a dive unless it is needed in an emergency.

"[Addressee], I am almost certain that if I could not easily reach my valves on an ID setup, I would simply try inverting the tanks as a very natural solution, unless some other simpler solution wouldn't work. (I switched from using isolation-manifolded HP 100's to using the four inches taller isolation-manifolded HP 120's in order to more easily reach my valves--a solution that worked marvelously! However, double 120's are way overkill for recreation dives, and, besides, my senior citizen back absolutely doesn't need the corresponding punishment!)

"Anyway, good luck with your experimenting. Be safe.

"rx7diver"

 

[Bigbella]

I have used any number of arrangements, over the years, while diving solo, including independent doubles; or, else, simply generous-sized pony bottles.

I don’t quite understand your respondent’s “pause” when it comes to redundant systems. I have always ensured that everything was fully functional from the get-go; that the regulators were also those that I commonly used and frequently swapped — not some occasionally-used eBay throwaway from the back of a garage, that should pose any doubt, at depth.

A close friend of mine, who was cursed with spectacular back problems and all-too recent surgery, took it upon herself to take up diving(!), some years back, and opted for a side-mount arrangement — two separate, well-maintained, identical systems, that she swaps-out, mid-dive, without so much as a hitch or a second thought . . .

 

[Thrutch]

I solo with sidemounted HP100s, switching to keep a sub-500 psi difference between the tanks, mostly shore dives. One of the big reasons I switched from manifolded, backmount doubles was having to drag myself out of the water with 100+ lbs of steel, brass, and lead on my back, a rig that I can't just put down and throw back on from the ground, meaning I have to go from the water to the parked car directly, even if that's a schlepp. Right after a dive, that much effort seemed like playing Russian roulette with DCS. Now, I doff my tanks before I get out of the water, go change, and grab them a few minutes later. It's also far easier to see and manipulate all of the valves in case something goes wrong. I was a little worried about not liking the switch from doubles, but I enjoy sidemount so much that I actually sold my doubles wing!

 

[Angelo Farina]

"I settled on independent doubles and sixths--which required only two changes to my kit: delete the isolator section of my manifold, and add a second SPG.

I agree that keeping the two tanks separated adds some safety, at the price of more complex management.
However I do not see the reason for removing the isolation manifold.
Better to leave it there, with the valve closed.
In case one of the two regs fail, you loose access to the air trapped in that tank if there is no manifold.
Instead with the manifold you can open the isolation valve, in such a case, regaining access to all the gas.

 

[rx7diver]

... One of the big reasons I switched from manifolded, backmount doubles was having to drag myself out of the water with 100+ lbs of steel, brass, and lead on my back. ...

Yes, ID's comprised of OMS/Faber LP 46/50's are much lighter, much easier on old backs, than ID's comprised of HP 100/120's--well, on my old back, at least! They seem a perfect solution for moderate- to deeper-depth recreational dives (yielding two-thirds of 105/115 cu ft gas to use, leaving sufficient reserves).

For those of us diving three seasons in MO/AR, who prefer back-mounted scuba.

rx7diver

 

[AfterDark]

I agree that keeping the two tanks separated adds some safety, at the price of more complex management.
However I do not see the reason for removing the isolation manifold.
Better to leave it there, with the valve closed.
In case one of the two regs fail, you loose access to the air trapped in that tank if there is no manifold.
Instead with the manifold you can open the isolation valve, in such a case, regaining access to all the gas.

Isolations valves are great. Wish they had been around when I started diving doubles but all there were was non-isolation manifolds which I used many times during the 70's with both double hose and single hose regulators.

Then in the 80's I read about IDs and thought even with more gear it's still safer and better than the non-isolations I'd been diving. So that was my choice when I used doubles and did use them quite a bit at 1st but over time I used doubles less and then a long time during the 90's that I didn't use doubles at all or maybe 1 or 2 times. The diving I was doing did not require doubles.

Then the rotator cuff surgeries 1 in 99 and in 2010 (after NC thank God!) Then the last one 2012.
this makes isolation valve use for me impossible.

Then in 2010 NC wreck diving became possible for me to do financially and I broke out the ID setup and went diving after probably a 10 year lapse from diving doubles. Now I use them on and off more since I got the 2 50's makes shore diving doubles easier. I just manage my air and dive so that no matter when during the dive I can abort and do a safe ascent with the air in 1 tank.

 

[happy-diver]

" 'Nearly perfect,' rather than 'perfect,' because ID's involve a standby system of sorts, and standby systems always give me pause:

Is this standby system similar to the standby system that every diver uses whereby there is a pause
between the first and second stages opening and closing

which IMHO is a much better system than a large single cylinder and a pony/bailout bottle, a system in which the standby pony bottle is most often left untested during a dive unless it is needed in an emergency.

It's not a diver that would permit their gear to deteriorate to u/s and then continue to carry it

, I am almost certain that if I could not easily reach my valves on an ID setup, I would simply try inverting the tanks as a very natural solution

More ridiculousness

(I switched from using isolation-manifolded HP 100's to using the four inches taller isolation-manifolded HP 120's in order to more easily reach my valves

This doesn't physically work no matter how one convinces themselves



Well this member I wouldn't send to check the letterbox let alone discuss gear options for diving

Zero experience outside their own body and mind


Build the gear put it on and dive it that's it!

 

[AfterDark]

I am still trying to understand the fixation on being able to reach the valves with an ID system.
So what if the valve could be reached? What does it matter? If there is an issue that causes an air loss with an ID system that air is lost to the diver regardless whether the air is in the tank or escaped out the OVR. There is no transferring it the other tank, the air in the failed side is inaccessible.

So the diver using an ID system must understand that their gas must be managed and the dive planned and conducted so that the gas remaining in one tank is always enough to end the dive and safely surface. IMO anyone with OW training should be capable of doing that. As they say it ain't rocket science.

 

[Wstern5]

I am still trying to understand the fixation on being able to reach the valves with an ID system.
So what if the valve could be reached? What does it matter? If there is an issue that causes an air loss with an ID system that air is lost to the diver regardless whether the air is in the tank or escaped out the OVR. There is no transferring it the other tank, the air in the failed side is inaccessible.

So the diver using an ID system must understand that their gas must be managed and the dive planned and conducted so that the gas remaining in one tank is always enough to end the dive and safely surface. IMO anyone with OW training should be capable of doing that. As they say it ain't rocket science.

The main reason divers should be able to reach their valves- doubles, single, side mount, rebreather or any other configuration is in case they jump into deep water with them accidentally turned off.

 

[Nemrod]

I am still trying to understand the fixation on being able to reach the valves with an ID system.
So what if the valve could be reached? What does it matter? If there is an issue that causes an air loss with an ID system that air is lost to the diver regardless whether the air is in the tank or escaped out the OVR. There is no transferring it the other tank, the air in the failed side is inaccessible.

So the diver using an ID system must understand that their gas must be managed and the dive planned and conducted so that the gas remaining in one tank is always enough to end the dive and safely surface. IMO anyone with OW training should be capable of doing that. As they say it ain't rocket science.

Me too. Sorta. And the same with a single, much less two singles. Why again do we need to reach the valve? Well, I do know of at least one fatality reported on the forum where an overweighted diver went in with the air valve shut off. I read the report and frankly was a little amazed, the diver as I recall did not have ditch-able weight sufficient to establish positive buoyancy, at least to the extent the diver could swim back up. Yes, the valve being off initiated the event but it was the inability to establish positive buoyancy by ditching weight that was the cause of the fatality, not the valve being off upon entry.

There is no reason to shut the air valve on a single tank or a double set of single tanks. Whatever has failed, breath it until it quits and then go to your buddy and if solo ID then it is time to go to the other tank or if single tank, solo standards do required a redundant air source!

But, I can reach my valve/valves, I may have to unsnap my crotch strap (mine all have a quick clip), just depends. In over 50 years of SCUBA diving I cannot recall needing to reach my valve/valves. And I am aware of Survivor Bias. One of the last things I do before going in is to take a few puffs off my regulator while viewing my SPG. If the SPG drops then I better get the mate to turn the valves on for me or wait until I am in the water and with the weight now off the rig open the valve myself. Yeah, it could be a surprise, we get forgetful when rushed (or get older, lol). On my manifolded set, I do want to reach my valves easily but it is a completely different rig for completely different intent than my single rig or my ID rig. And, I do not wear so much non-ditchable weight that swimming up is impossible.

This board, not that many years ago, was of the cumulative position that ID rigs were suicide machines. Then along came side mount and now they are the darlings of the UW world. What exactly has changed other than position. If reaching the valves is really that important to a diver, then set your back mount ID rig up so that you can reach the darn valves.

N