Double Tank Manifolds, Bad Idea!

[ianr33]

I don't need that with ID's. I also like the fact that I can carry them one at a time until I make them doubles. For me ID's are the way to go, Thanks much.

Just trying to be helpful

 

[RJP]

If you add another "old school" idea to the mix you could easily set up doubles using two single rental tanks. All you need to bring is a set of double tank bands and a harness that connects directly to the bands without a backpack.

Especially great in places like Bonaire resorts where you have unlimited access to AL80's. Nothing like a nice relaxing 3hr shore dive...

 

[mathauck0814]

So far this looks like an ID vs MD battle with MD's winning for tech diving, but I really see an ID vs MD vs RB debate with RB's being the better all around choice. Deeper, longer, in a far smaller package. It seems the most advanced dives are being done on RB these days so a tech diver, beginning with the end in mind, should skip OC MD's all together and choose RB. Yet many MD divers might vehemently oppose such a suggestion. How would those self limiting arguments (excuses) be any different from the current ID vs MD discussion. In the end, an inferior system is chosen, be it for safety, familiarity or personal preference reasons.

There's a world of grey area in between the point where the volume of bottom gas exceeds a single tank becomes and the most advanced dives being done.

I do think that there is little that is directly transferrable from MB doubles/OC tech diving to CCR from a "bottom gas" perspective. There are other skills that you learn in your OC training on your way up to those big dives that is highly transferrable (gas switches, communications, etc).

For mid-range dives (~150-200fsw) open circuit can be simpler. For deep dives (~200fsw+) the CCR gives you a number of advantages. I think most people don't live in a place where they have the ability to do deep dives with regularity (let's go with bi-weekly) and therefore can get by with a set of doubles (in whatever configuration).

There's also an economic aspect to the CCR. We have a few folks that dive with us out here who are doing the "deep dives" on OC because they're unwilling to lay out the $$ for the CCR. They're laying out a ton of cash in gas instead (pay now v. pay later). I see that as the decision to use an inferior system.

So perhaps a range of:

0-100 feet: Single Tank OC is sufficient, other systems are viable but probably overkill
100-150 feet: Redundant gas becomes necessary, multi-gas diving becomes more relevant, a decision can be made of ID/MD. Rebreather is a more efficient tool for this dive but the risks may not outweigh the benefits.
150-200 feet: Multi-gas diving becomes the norm. Decision is between OC and CC, not necessarily the OC configuration.
200+ feet: OC in any configuration becomes disadvantageous to the CCR solution

Since most people don't go straight from 100 feet to 200+ I think skipping OC diving in that range is a mistake (or frankly, skipping steps in an attempt to economize and potentially introducing unnecessary risk on dives where it is not warranted).

---------- Post added September 21st, 2013 at 09:03 AM ----------

Especially great in places like Bonaire resorts where you have unlimited access to AL80's. Nothing like a nice relaxing 3hr shore dive...

I've enjoyed several dives in places like Bonaire/Curacao with a BM single AL80 and two slung AL80s. No good reason not to do long and shallow with gear like that. I'd not (personally) be doing deep and long with that config, but I'd much rather do one long shallow dive than muck around with entries and exits on several.

 

[DaleC]

My point with the ID/MD/RB comparison is that the same sorts of arguments an ID user might make are the same a MD user would make.

Andy sort of touched on an interesting point of progression. New technology usually solves some problem associated with past technology. For penetrations the isolation manifold allowed more gas to be used and thus the envelope to be pushed. Sidemount allows valves to be accessed easier when that is needed. Rebreathers allow for more efficient use of gas when that is needed. But the question is, does a diver need to follow each progression like a dog following his master or can they pick which stage of development suits them and simply have the balls to say so? If you are not pushing the envelope you may not need every new advancement that comes down the pike - which always comes at a cost, either financial or training-wise.

I can do my dives at the BM ID level. Why should I switch - because others think so? Am I doing my dives or theirs. Are they all running out and switching to RB's?
For me to move into the type of diving which would necessitate MD's I would need to shell out for bigger tanks and Adv.N/Deco and H training, because I solo and won't go much deeper that 130 for very long on 72's filled with air. Until I come up with that dough MD's represent a want - not a need.

This may be a point where solo personalities differ from the norm. Team divers may engage in a form of group think and will go with what their peers suggest but individualist personalities tend to pick what they know they need, regardless of popular opinion.

As to SM over BM.
First they will tell you to dive independents it's needed.
Then they will tell you taking a course is needed.
Then they will tell you a store bought rig is needed.
Then they will tell you which store bought rig is needed...

If you can't think for yourself it never stops.

 

[Akimbo]

After 20 plus years of abuse lugging doubles around, my T3/T4 vertebra are damaged and I have been advised not too. This conveniently coincided with a decision to dive sidemount when the task at hand called for an open-circuit solution.

I have slung bottles but never used any of the new side-mount rigs. I don’t understand the mechanics of how the weight distribution to the shoulders using a side-mount is different than back-mount. I understand the lower center of gravity on deck, but the weight transfer to the shoulders and spine look the same. Am I missing something?

No expert here, but I can see an advantage for a lot of divers with spine-related limitations if all or part of the weight could be transferred to the hips and legs. This is easier said than done with a disappearing-butt male geezer like me, but it looks doable for divers with more pronounced hips. This would not necessarily be a tech-rig but more likely side-mounting independent 30s or 40s. Leg straps for weight transfer and stabilizing might work well on the some amputees and paraplegics.

 

[tskovan]

Yes, any of those failures "can loose you all your back gas" if you don't do anything about it. My mistake, I thought we were talking about scenarios where the diver actually had some influence on their equipment.

So in summary, I totally agree with you; you shouldn't dive manifolded doubles if you're incapable of closing the isolation valve/posts since that defeats the purpose of having a manual valve anyway.

I have come to that conclusion because the only other scenario that makes sense is that you don't actually know how an isolation manifold works

You still don't get it?.......OK, Let's play your game

Name me three failures that "can loose you all your back gas" using IDs

Here I'll Start you off:

1. Double Malfunction of two COMPLETLY INDEPENDENT Scuba systems in the same dive.
2. ???????
3. ????????

I have come to this conclusion because the only other scenario that makes sense is that you don't actually know how Independant doubles work.

 

[AfterDark]

I have slung bottles but never used any of the new side-mount rigs. I don’t understand the mechanics of how the weight distribution to the shoulders using a side-mount is different than back-mount. I understand the lower center of gravity on deck, but the weight transfer to the shoulders and spine look the same. Am I missing something?

No expert here, but I can see an advantage for a lot of divers with spine-related limitations if all or part of the weight could be transferred to the hips and legs. This is easier said than done with a disappearing-butt male geezer like me, but it looks doable for divers with more pronounced hips. This would not necessarily be a tech-rig but more likely side-mounting independent 30s or 40s. Leg straps for weight transfer and stabilizing might work well on the some amputees and paraplegics.

From my very limited use of sidemount I'd say the fact that on a shore dive for example the tanks can be carried into the water by hand and attached to the harness in chest deep water thus eliminating back strain carrying the entire load into the water. From a boat one can also put the tanks on in the water, calm water, I don't think I'd like to try a rough water sidemount donning. Like I posted limited use.

Slung bottles to me are a curse. I loath them. I recently made the switch to a slung pony for buddy dive so I could stop transferring my octo to my 2nd reg when solo diving with my IDs. I'm not sure now which is more trouble that damn bottle or switching the 2nd stage. From the start of the dive to the end of the dive that bottle is in the way, from putting my fins on to inflating my BC that bottle is in the way. I may ask my buddy to carry it!

 

[DevonDiver]

Slung bottles to me are a curse. I loath them.

Well, talking of 'evolution', I had my last tech student add a sidemount bungee to his back-mount wing. He was diving MD with 1-2 decos. The deco cylinders were clipped on as per normal, but the bungee was then wrapped on the neck to bring the deco cylinder up tight and trimmed. It worked well - an amalgam of two approaches.

 

[ajduplessis]

You still don't get it?.......OK, Let's play your game

Name me three failures that "can loose you all your back gas" using IDs

Here I'll Start you off:

1. Double Malfunction of two COMPLETLY INDEPENDENT Scuba systems in the same dive.
2. ???????
3. ????????

I have come to this conclusion because the only other scenario that makes sense is that you don't actually know how Independant doubles work.

Let me coreect you here. You don't know anything related to diving and your "broad" understanding of basic gas planning, dive planning and equipment is well documented here within your posts.

You start off by vomiting up a lot of junk on something you clearly don't understand, make comments around cave diving not understanding it and expect not to get any negative feedback. The only thing that comes to mind is a doornail.

 

[AfterDark]

Let me coreect you here. You don't know anything related to diving and your "broad" understanding of basic gas planning, dive planning and equipment is well documented here within your posts.

You start off by vomiting up a lot of junk on something you clearly don't understand, make comments around cave diving not understanding it and expect not to get any negative feedback. The only thing that comes to mind is a doornail.

He is correct the only way to lose all the back gas with IDs is a Malfunction of two COMPLETLY INDEPENDENT Scuba systems during the same dive. The OP apologized for the attitude in his 1st post. Are you looking for a argument?