Twinsets, redundancy, and what problem are we solving...

[Cthippo]

Now yer just wanking.........................grasshopper

Perhaps, but it has answered my question. I now understand why twinsets are considered to be redundant despite potentially having a human failure point, so for that I appreciate the responses.

 

[-JD-]

Perhaps, but it has answered my question. I now understand why twinsets are considered to be redundant despite potentially having a human failure point, so for that I appreciate the responses.

There are always potential human failure points. Different configurations, make different tradeoffs, shifting the relative likelihoods, at different costs.

Something that has always intrigued me ...
With respect to manifolded doubles: one option is to run them with the isolator valve closed. You can then use them:

• Like independent doubles - switching regulators
• with progressive equalization - periodically opening the isolator for a bit to let the tanks re-balance

In the event of a reg problem, once the problem reg is shut down, the balance of the gas can be accessed through the good reg by opening the isolator.

Uncommon, and requiring a different "manual of arms", but interesting.

 

[Wibble]

The point about twinsets, rebreathers, accelerated decompression, gas limits, reserves, etc…. It is wholly the responsibility of the diver to get the right training and constantly practice. Someone who’s incapable — for any reason — of following the very simple rules should not be diving.

We’ve all heard stories of so called experienced people dying in benign circumstances — Blue Hole depths, ignoring gas limits, expecting others to provide gas, diving solo without adequate skills, etc. — much of which their demise was thoroughly predictable through their atrocious attitude. Their death isn’t anyone else’s concern, as sad as it may be for the bereaved family.

When diving a twinset you must know your depth and remaining gas. You must be able to use the equipment you’re using. Full stop/period.

 

[rx7diver]

So, are twinsets considered redundant enough because the mitigate the possibility of mechanical failure alone?

This is the "Solo Divers" forum. Independent back mount doubles was mentioned above as a solution for divers diving back mount. All other things being equal, I completely agree. I especially like the fact that the diver is continually "cycling" his/her two regulators, which provides less of a chance that he will discover too late that something is wrong with one of his two independent systems. And the diver never has to be concerned with the state of an isolator valve.

rx7diver

 

[rob.mwpropane]

So, if I'm understanding this right, you are saying that that a large enough amount of gas is adequate to mitigate the possibility of an OOA situation and that no further steps are necessary? Or, to put it another way, taking enough gas means you don't need a second source of gas?

Is that correct?

No... that's fixing a skills problem with more gear. Eventually that line of thought will fail.

But is a twinset redundant if the isolation valve is open? I understand the need for redundancy in hardware but does that redundancy still exist if we are creating essentially a single air source?

I guess what I'm really getting at is does the redundancy afforded by doubles do anything to mitigate user error? Does gear configuration reduce the chances, or in this case the consequences of a diver using up all their air because they are task saturated, narced, exerting themselves harder than they expected, or just not paying attention?

You can still royally f**k up in a set of doubles. All the things you mentioned tell me that someone was diving outside of their skill set. Sure you can find yourself in that situation, but I'd venture to say there was a lot of signs that you ignored along the way.

I like doubles. They work for every bit of diving I do. I am 100% self sufficient, and most of the time ready for dive 2 without changing anything over. If shtf I can close the isolator and end the dive and still have plenty of gas left. I do reg switches on every dive because I should. I do valve drills on every dive because I want it to be 2nd nature. I do not "throw on a bunch of gas and hope for the best".

 

[blatter]

Independent doubles or sidemount: if you run them properly it takes 2 major mechanical failures or a major mechanical failure and a major brain failure before you are out of gas. With normal doubles with manifold a single (unlikely) mechanical failure or failure to monitor contents can result in not enough gas to surface safely. I use independent doubles a lot (and ccr with bailout). Independent doubles are great for solo deco dives especially if you take some O2 or rich nitrox.

 

[sourdough]

Dudes you can never be too redundant, which is why I always play it safe on my recreational dives and carry some extras. fish are hypnotic, what if a turtle appears and you have to chase it for an unknown amount of time before getting that selfie?

 

[rob.mwpropane]

Dudes you can never be too redundant, which is why I always play it safe on my recreational dives and carry some extras. fish are hypnotic, what if a turtle appears and you have to chase it for an unknown amount of time before getting that selfie?

Was time for a RB 6 or 7 tanks ago

 

[John C. Ratliff]

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.

 

[Alaskan Scuba Dude]

If you're unable to shutdown the valve on your manifold, then maybe you should take a pony when diving intermediate depths with a negligible amount of decompression. I've heard of expert technical divers freezing up when a freeflow blows.