Closed manifold, most of the time

[divad]

I may well be overthinking this, sorry, but that's because I'm always thinking about scuba diving when I'm not diving.

It's a debilitating sickness. All you can do is try to work around it. We all have it..............Welcome aboard........................................................................................................................................................
........BWAAAAAAAHAHAHAHAHAHA

 

[beester]

How important is 10 seconds when you are near your planned "leave bottom" point and an O-Ring or blow-out plug fails?

I'm sorry didn't follow up that much been busy with life.

Not important at all if you plan adequate gas reserves (min gas). I once had a freeflow on a 80m dive, which amounts to the same thing. I switched to backup reg and closed the main reg valve. Took 10 secs didn't put a dent in my gas reserves at all. If you take 2 minutes yes your tank will be empty. But what are you doing diving solo if you can't close a manifold in 10 seconds. Certainly at 20 m depth it takes a while before you empty a tank caused by valve failure or freeflow.

Your solution instead introduces a lot of unnecessary complexity for no real benefit. At least with sidemount you have in circumstances some benefit (smaller profile).

 

[RyanT]

I think if none of this were the case I would be very inclined towards a bailout/pony for solo.

I would agree. I dive doubles as my standard rig. For most dives I do, they aren't necessary, but I like to keep my gear consistent for familiarity. They are ridiculously heavy and so aren't so great for recreational dives.

If I were planning the kind of dives you're talking about, I would get a big single tank (maybe a steel 117 or even 133) and then sling a 30 cf pony. That will give you lots of gas and redundancy for long shallow dives and be way simpler than dealing with a set of doubles.

 

[Akimbo]

Not important at all if you plan adequate gas reserves (min gas). I once had a freeflow on a 80m dive, which amounts to the same thing.

True, but what about one of your two regulators blowing an HP DIN O-ring near the end of your planned bottom time? That is first thing that goes wrong, Now let's say you are in the North Atlantic, miles offshore. The current is high, visibility is 15' and no other divers are in sight when you look up from your valve shut-down... not planned but but it happens. That is the second thing that went wrong. After studying accidents over the years it is not unusual to see a cascade of three or more problems that contributes to a diver's death. What else would you like to add? During a wreck penetration perhaps? How important is that 10 seconds of lost gas from both cylinders now?

On the other hand, what is so onerous about reaching back and cycling the isolation valve? It takes about a second to crack it open on valve-down doubles.

(Reprinted by permission)
This table appeared in Life Ending Seconds, 3000 to Zero in 72 Seconds, Advanced Diver Magazine by Curt Bowen​

​

 

[beester]

Hi Akimbo. I'm not disputing that it could happen. I'm saying that 10 seconds of breathing gas in most scenarios is not relevant. On the other hand complicating your dive procedures with isolated tanks (manifolded) has in my book a much higher chance of fack ups than 10 secs less gas.

You don't need a lot of imagination to find some scenarios where the additional taskload of isolated tanks causes issues. In fact I'm sure that we can find more incidents related to this than to open manifold not closed in time?!

In any case the OP is talking about solo dives to 20 m max... our discussion is not really relevant to that scenario.

 

[Akimbo]

... On the other hand complicating your dive procedures with isolated tanks (manifolded) has in my book a much higher chance of fack ups...

I think that is the part that is over-weighted in your analysis. I haven't found it to be as bothersome as being more obsessive about checking available gas. I normally equalize before sucking the online bottle near zero, but I am reminded when I misjudge. For me, having a virtually hard reserve all the time without carrying a dedicated bailout bottle too is well worth the procedure involved.

I'm not trying to sell the idea as much as helping people to understand what it is really like to use Progressive Equalization. I was a little hesitant when I first heard about it too.

 

[Dave Bevan]

For the type of diving you are doing (20m depth and no overhead) I would suggest going with a normal single tank perhaps something like a steel 16l if you want to maximise your bottom time and just sling a small 40cu ft bailout bottle as a stage. I think you will have a lot less faff than and you wouldn't need to change you equipment or training too much. Just practice opening the stage and getting the regulator in your mouth after a failure.

Working on the KISS principle this would be my ideal suggestion. As it's basically just diving what you already dive and adding the bail out for redundancy. No need to buy lots of gear. Just another stage regulator and stage kit. You could also have spare bands so that if you travel you can bring it woth you and just rent an extra tank.

 

[shoredivr]

Even though I am at least a hundred of dives away from solo diving, I have been thinking about solo configurations recently. I'm mostly interested in solo diving up to 60ft (20m) in warm or almost warm water (with a wetsuit), with a light nitrox gas (32 or 36) and no decompression stops, for dives up to 2 hours.

This is what I came up with :
- steel twin tanks, with a closed manifold and a suitable wing

I was taught that in general, steel tanks and a wetsuit are not the best combination, because you have no redundant buoyancy like you do with a drysuit.

Of course, the worst combo is a thick wetsuit and heavy steels where the wetsuit crushes at depth and loses buoyancy.

Of course, some steel tanks are pretty close to neural. You don't say what kind of tanks you are thinking of.

Of course, you can get a redundant bladder wing, too.

Of course, some plan to use a lift bag for redundant buoyancy, though the time it takes to deploy it may be too long.

And of course, you're talking about shallowish solo dives.

Just thought I'd throw in a Scubaboard tangent type of post.

I'd chose sidemount or a slung tank. But you may be planning to go tech, in which case doubles are reasonable to get used to. Decisions, decisions.

 

[shoredivr]

True, but what about one of your two regulators blowing an HP DIN O-ring near the end of your planned bottom time? That is first thing that goes wrong, Now let's say you are in the North Atlantic, miles offshore. The current is high, visibility is 15' and no other divers are in sight when you look up from your valve shut-down... not planned but but it happens. That is the second thing that went wrong. After studying accidents over the years it is not unusual to see a cascade of three or more problems that contributes to a diver's death. What else would you like to add? During a wreck penetration perhaps? How important is that 10 seconds of lost gas from both cylinders now?

On the other hand, what is so onerous about reaching back and cycling the isolation valve? It takes about a second to crack it open on valve-down doubles.

View attachment 432343
(Reprinted by permission)
This table appeared in Life Ending Seconds, 3000 to Zero in 72 Seconds, Advanced Diver Magazine by Curt Bowen​

​

View attachment 432344​

Akimbo, how do you reach the isolator with the valve protectors? Is there a space behind it?

 

[Akimbo]

Akimbo, how do you reach the isolator with the valve protectors? Is there a space behind it?

That problem nearly changed the design of my first prototype while the concept was still in my imagination. In fact, it is a little embarrassing given that I had been thinking about them for years and looked at plenty of related designs. The post valves are easy to reach, just like many rebreathers and most SCBA rigs (used by firefighters and in mine safety). It was access to the isolation valve the perplexed me and probably prompted your "first glance" question. My "lightbulb" moment came when I realized that the tank swings away from my butt when I bend my spine forward. The valve stem of the isolation valve is rotated so the stem points toward me instead of down.

In practice I found that it works great and protects the manifold and regulators even in the most hostile environments.