Tank configuration

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So, right now I only know singles. I dive with 1/3 going, 1/3 coming, and 1/3 for emergency. I have always dove that way, even prior to cavern course.

As I understood it, diving SM, 1/6 in, 1/6 out, 1/6 for emergency. That mean you come out with roughly 1/2 of your gas you started with, if both tanks are full.

Now, here is where I get confused: On your second dive with those tanks, is it still 1/6, or is it 1/3?

your 2d dive should be planned based on 1/3rd or (1/6th for doubles) of your new total capacity. So you start out each dive with a new plan and turn pressure.

This is primarily to limit your penetreation distance.. if your diving doubles, you are really not adding penetration, just reserve gas.
-** and the 1/6 or 1/3 rules are a starting point. Being more conservative is always better.

The interest in SM or doubles was purely because it was made out that everyone who dives in an overhead environment, which even cavern diving is, should have redundancies.

Cavern does NOT require a totally redundant reg, with a separate 1st stage and isolated gas. *although I don't think it's a bad idea.

Although you can get a Y or H valve that will allow for that in singles.

As far as who gets what, when we go through the pre dive checks, if someone of a higher certification tells me that they do it one way or another, I follow that. I know for SM, you give them your long hose, and you take your short hose.

It's good to talk through the share Air protocol pre-dive. You need to be prepared that a panicking OOA diver is not going to wait for you to remember which reg is in your mouth. Or try to sort out which hose to grab. If you see them coming at you, follow your training!! Pull the working reg from your mouth and hand it too them right side up and mouth piece first. You might be the only one thinking clearly at this point!. ..once stabilized, you can switch to long hose donate and exit the OH or trouble shoot the problem etc.

You need to lead this dance if at all possible.
 
I am of the attitude that I should be diving similar equipment as those I am diving with. For instance, we all are diving dry, or we all have the same tank configuration. While there, I noticed others diving with SM. So, my logic tells me that maybe I should dive SM too.

But my guess is that those SM people you saw in Mexico were cave divers. That is, people with a higher level of training than what you received from your cavern course, who are diving beyond the cavern zone. You won't be diving with them if you're doing guided cavern dives. Am I wrong again?

Enjoy the cavern zone the way just about everyone else does: a single tank with a guide who supposedly is qualified to take single-tank divers around the cavern line. It's a lot of fun. Why complicate things if all you want to see is the cavern zone?

As for SM, if that's what you're aiming for, why not learn to dive SM at home, but when you're next in Mexico just continue to do the guided cenote dives, single-tank style like everyone else, until such time as you may decide to take a cave course?
 
But my guess is that those SM people you saw in Mexico were cave divers. That is, people with a higher level of training than what you received from your cavern course, who are diving beyond the cavern zone. You won't be diving with them if you're doing guided cavern dives. Am I wrong again?

Enjoy the cavern zone the way just about everyone else does: a single tank with a guide who supposedly is qualified to take single-tank divers around the cavern line. It's a lot of fun. Why complicate things if all you want to see is the cavern zone?

As for SM, if that's what you're aiming for, why not learn to dive SM at home, but when you're next in Mexico just continue to do the guided cenote dives, single-tank style like everyone else, until such time as you may decide to take a cave course?

What is the furthest you can be trained to that does not include tight spaces?

I do plan to enjoy the range I have qualified for. When I first got my OW, I dove to that level and enjoyed it. When I qualified AOW, I dove to those limits too. II did an ice diver course, and am hoping to do more of that diving. Now that I am cavern qualified, I plan to dive that more.

I was under the understanding that it would be better. However, if there is no need to, then I likely won't worry about it.

I did not think SM diving would be the best idea for around here.
 
Even through full cave there is no requirement to go into tight spaces.

However, I can say from experience that as I've gained experience and time in the water, passages that once seemed small have gotten much larger.

I once thought 30 feet was deep. Then I dove to 90 feet with almost clear visibility to the surface.

I get what you mean, and one day I might get there.
 
Even through full cave there is no requirement to go into tight spaces.

However, I can say from experience that as I've gained experience and time in the water, passages that once seemed small have gotten much larger.

Very true. The first time I saw video of Blue Hole/Jug, I thought anyone doing that dive was nuts.. now it's one of my favorite dives. ...but I worked towards that very slowly, and made sure I was with divers that were all 100% ok with turning the dive at any point if things didn't feel "right".

Not much really freaks me out, but I get more "butterflies" when in super large wide open caves, where you can't see the far wall, or the floor.
 
Not much really freaks me out, but I get more "butterflies" when in super large wide open caves, where you can't see the far wall, or the floor.

Black Abyss, Wakulla Room, Mother of all Great Waters if the viz isn't perfect...yup... Know what you mean
 
I am of the attitude that I should be diving similar equipment as those I am diving with. For instance, we all are diving dry, or we all have the same tank configuration. While there, I noticed others diving with SM. So, my logic tells me that maybe I should dive SM too.

There is a dive that is near Kingston/Cornwall ON which I have been suggested to dive doubles. So, I am considering doubles.

Air consumption is not the issue. I could be on a rebreather and still suck it back faster than many. That will get better the more I dive.

I want to dive with a guide as I do not know the cave systems. If a friend of mine knew them and invited me to dive with them, then I like would, but they are still a guide.

Other dives likely do not need doubles/SM.
Be careful not to get pulled into ‘trust me’ dives by other divers who should know better. Looking the part of a tech diver doesn’t mean you should do those dives until you have been properly trained.

Rebreathers don’t work like that, the actual amount of O2 used by divers doesn’t vary that much. However rapid breathing on rebreathers is bad for other reasons.
 
Be careful not to get pulled into ‘trust me’ dives by other divers who should know better. Looking the part of a tech diver doesn’t mean you should do those dives until you have been properly trained.

Rebreathers don’t work like that, the actual amount of O2 used by divers doesn’t vary that much. However rapid breathing on rebreathers is bad for other reasons.

The comment about using a rebreather was more sarcasm than actual thought.
 
I am Cavern certified with TDI. I did it because I wanted to dive the cenotes. I did that last year. Due to life, I am not able to go again for a year or so.

When I did it, I did it on a single tank, back mounted.

I want to go longer, and to the maximum depth and penetration. I also want to limit the time spent fumbling with gear on land. I also want some redundancy.

So, the next time I go cenote diving, I want to have 2 tanks.

So, which is better - doubles or sidemount?

Which is "idiot resistant"? (I don't use idiot proof, as things I thought were idiot proof, the idiots went against it.)

The problem with simple questions is they attract difficult answers :)

First, at word on backmount. Then sidemount. Then my view on what I choose to dive, and why.
I hope it might help stimulate consideration that helps you in your search for answers and a decision.

Backmount
I'll say the "standard" of backmount is the Hogarthian setup, with the isolatable manifold between the tanks. It's clever.
It's clever because for almost all of the critical failures, there is a redundancy.

The exception is the manifold. Roughly put, if you damage the manifold connection, you may lose your system and all your gas.
Most other cases, you swap to a backup and keep all of your gas.

The tanks are manifolded on the high-pressure side. This means that you won't be able to swap tanks around inside the system (there's no working up against a 200bar connection), but it doesn't matter - the tanks are bolted down on your back anyway, so they're staying put. The positive in this is, you don't have to manage opening and shutting valves or swapping regulators around. The gas will balance itself across the two tanks automatically. As I wrote above, it also means that you can reach all your gas from an alternate source, if the other fails (true for first- and second stages along with tank valves, not anything related to the manifold).

Now, you can also set up a single-tank to have the same touchpoints as the twinset in backmount. Your regs will be the same places, your inflators work the same way, the SPG is in the same place. Consistent.
This helps you in your development from one tank to two, and it helps you work together with other divers who have the other amount of tanks on their back.

This, however, is where the limitations begin to kick in. Of course, swapping from one tank to two means pretty much a whole new rig, but what's more, by the time you've got two tanks on your back, that system won't hold any more.
You can bring a third, fourth and tenth tank for that matter, but they'll be separate from the original system.

That's not necessarily a problem, but it does mean there are some limitations, and it does mean that as we progress deeper down or into an overhead, a decreasing portion of the dive is actually carried out on the clever base that we like. There are also some limitations to how much gas we can use from the individual tanks, but that's for another day.

Consider a 75m dive - we'd be on the backmounted rig only around 25% of the dive, and spend around 75% of the dive on individual tanks that are completely separate.

But, the general gist of it is, it's rather standardized - and it's rather simple.

Sidemount
It's complicated.
The reason I say it's complicated is because there isn't a "gold standard" in the dive industry, in the way that one might fairly say that the Hogarthian rig is in backmount. There are quite a few different takes on sidemount out there.

The original reason for going from backmount to sidemount, was to go through narrow constrictions.

To form a narrative, it'd be two divers going cave diving in their Hogarthian rig because it's clever, and they get to a narrowing. One says "oh well, end of cave" and the other says "oh well, end of backmount".

The bulk of sidemount divers use individual singles, which is to say completely separated tanks that have separate outputs (regulators, inflator hoses, SPGs).

The advantage to sidemount, regardless how you do it, is of course it's possible to penetrate narrow constrictions (sidemount or no-mount). But in almost all cases, the consistency from the traditional backmounted doubles, is lost - that is to say, you'll need to apply a different reaction pattern to diving in general, and specific scenarios (read: emergency protocol).
For many, this is the reason not to make the transition ("oh well, end of cave").
Others really don't like having to swap regulators to balance the tanks.

As for myself...
I dive mostly oceanic dives - what that mainly says, is vertical. The implication is that for most of the longer dives, there's a correlation, in my case, to different gases needed, for decompression.

Personally, I like the double-backmount. It's consistent and well thought out. But it has limitations.
Sure, I don't like dragging it around, but most importantly, I don't like that it's really only [dare I say] "perfect" (in my subjective view) for one particular thing:
Recreational diving between 18m and 30m.
Anything shallower, one tank is enough. Pretty much anything deeper, I want or need at least one more tank.

That's me.

That's why I swapped to the Z-system, which - yes, yes - can do narrow constrictions (sidemount/no-mount), but is:
1) Consistent, and
2) Scalable

I can whack one tank into it, two tanks, three, four or a hundred for that matter, and it'll always work exactly the same way - and procedures will be interoperable with the Hogarthian rig so I can mix up the team or easily swap between sets if I need to (I only have my Z-system at this point, as I've sold everything else by now).

I can even add an additional layer by putting a rebreather on it. Same base.


So, the simple answer?

There is no simple answer, but I will advocate to assume and maintain an attitude that no equipment in the world is even a little bit fool-resistant. Good rig makes it easier for you to use your skills, but it willl never improve them.
So, the best investment you can make, is in you. Your skills, your training and your diving.

If you're lucky enough to end up with a solution that takes you everywhere, from the start, you're one of few.
That said, if I could go back to my own Day 1 and choose, I'd pick Z-system, hands down.

That's my take on it, hope it's spurred on thought :)

Happy diving!
 
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