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Tech divers...We need to reenergize this forum


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#1 techintime

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Posted 21 May 2008 - 11:57 PM

Fellow tech divers, I'm a fairly new tech diver and I've read every post on this entire forum and have learned a lot from it. Many thanks to those who have posted here, but I'm hungry for more and the posts have kind of dried up lately. You all are probably too busy diving, but I'd like to stir up some discussion so that I can learn from those with more experience than I. Here is a topic:

Independent doubles versus manifolded doubles: I've dived both setups and have heard the argument about the difficulty in balancing the gas remaining in each tank, but what I'm finding is that even if I run the first tank down to 500 psi (with the other still full) before changing tanks I get no noticable trim/roll problems. Concerning the benefits of independent doubles, it is far easier to rent single tanks and much easier to change them out for consecutive dives. And as long as I keep my BC connected to my second planned tank, I run no risk of inadvertently running out of gas for my BC. I also find it easy enough to monitor two SPGs (one as an air-integrated computer and the other as a standard SPG with each clipped to the appropriate side of my setup. All it takes as far as equipment goes is a set of double-bands and an extra SPG which is much cheaper than maintaining dedicated manifolded, banded doubles. I can use the tanks I own as independent doubles for a tech dive and then use them as single tanks for recreational dives the next day, or even the same day with no modification to the tanks and a simple wrench removes the double band setup from my standard BC or from my tech wing/backplate setup. I understand that sharing gas with an OOA diver will be a little more complex, but still doable. But very few divers use independent doubles. So am I missing anything here?
Hope I haven't made the DIR folks out there cringe too much and please don't call me the S-word. I can (and have gone) full DIR, but am not convinced that it is the only way to go. Hey I'm still learning (always will be) and am inviting constructive input.
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#2 netmage

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Posted 22 May 2008 - 06:59 AM

Independent doubles versus manifolded doubles: I've dived both setups and have heard the argument about the difficulty in balancing the gas remaining in each tank, but what I'm finding is that even if I run the first tank down to 500 psi (with the other still full) before changing tanks I get no noticable trim/roll problems. Concerning the benefits of independent doubles, it is far easier to rent single tanks and much easier to change them out for consecutive dives. And as long as I keep my BC connected to my second planned tank, I run no risk of inadvertently running out of gas for my BC. I also find it easy enough to monitor two SPGs (one as an air-integrated computer and the other as a standard SPG with each clipped to the appropriate side of my setup. All it takes as far as equipment goes is a set of double-bands and an extra SPG which is much cheaper than maintaining dedicated manifolded, banded doubles. I can use the tanks I own as independent doubles for a tech dive and then use them as single tanks for recreational dives the next day, or even the same day with no modification to the tanks and a simple wrench removes the double band setup from my standard BC or from my tech wing/backplate setup. I understand that sharing gas with an OOA diver will be a little more complex, but still doable. But very few divers use independent doubles. So am I missing anything here?
Hope I haven't made the DIR folks out there cringe too much and please don't call me the S-word. I can (and have gone) full DIR, but am not convinced that it is the only way to go. Hey I'm still learning (always will be) and am inviting constructive input.


I dunno if I can still claim being DIR now that I'm on a meg... but, the mindset still applies...

A tech diver renting tanks/swapping tanks between dives...? surely you jest....

If your going to travel someplace w/ a tech destination; they will have doubles, or pack your bands and manifold. Having just traveled w/ the equivilent of a tech rig (rebreather), I can tell you its do-able, and in the grand scheme of things, very easy compared to compromising your safety or introducing a deviation from normal.

One of the key lessons of DIR, is to dive the rig you dive all the time. Muscle memory, patterns, routines... these help form the basis of survival instincts. If your constantly changing, switching, moving from one setup to the other, you are introducing change and risk to these memories. In practice w/ a clear head, it may be easy, however when it hits the fan, you revert to what you use. So commit one way or the other..., embrace the BP/W setup and eBay the jacket BC... doubles on a Jacket may fit, but not very well...

An air integrated computer? Surely you jest......

Whats to stop you from diving the AL80 doubles on a recreational dive - nothing.... I used to do it all the time.

AL80's are cheap. Stinking cheap. Tech diving ain't cheap, and I can appreciate maneuvering ways to incrementally get into it. But, making the case for independant doubles as cost savings I think is just an answer looking for an excuse.

I don't do this, a few friends do... take those independants and sling them on the side... you may have something there... with Sidemounting the regs are right there in front of you, If you have an issue you can deal with it; independant doubles; all you can do is shut it down, hope for the best, maybe get a buddies eyes on it, assuming you can communicate effectively.
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#3 diverdeb

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Posted 22 May 2008 - 07:22 AM

Is your only reason for diving doubles to have a lot gas available? What about redundancy - if you have a problem with your reg and say you just switched to that tank, now you have to switch back to the other tank with less available gas. Now you have a tank that is completely unavailable to you? My thought is I can shut down the valve but still have access to the gas with a manifold set up.

I probably could have said that better, but I'm at work and well, really should be working . . . :cool1:
As for me, I'm feeling pretty scubalicious. 

#4 peterbj7

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Posted 22 May 2008 - 07:25 AM

I don't go with the idea that if you change your setup you may die! I actually don't go with a lot that DIR preaches, but this thread's not about DIR, it's about doubles. The problem with using single tanks is that if there's a problem with one of them you may lose access to that gas, and if you've planned to have it available that may be inconvenient to say the least! Always dive your doubles manifolded if you can (and of course keep your valve shutdown skills well honed), but if you're travelling and it isn't practicable then use singles and plan your dives more conservatively. Take the possible loss of gas into consideration when you're planning your gas consumption and reserve. I've often done this, on liveaboards for example, where they don't take kindly to people messing around with their tanks.

I actually believe that you SHOULD experiment with different gear and different setups, for two reasons. One, to encourage you to think about what you're doing and not function as an automaton. And two, you may find something you prefer.

#5 running_diver

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Posted 22 May 2008 - 08:27 AM

The problem with using single tanks is that if there's a problem with one of them you may lose access to that gas, and if you've planned to have it available that may be inconvenient to say the least!


I think this needs to be clarified. When I first read it, I thought that it was clearly wrong since if you lose a single, you only lose that gas, and if you are using doubles, you could possibly lose them both.

I think what Peter is trying to say is that when you are using two singles, you are only breathing off of one of them. Should there be something wrong with the other one, you will not know it and will be SOL when it comes time to switch to it. That's why you need the complicated switching patterns to make sure that if you lose either cylinder at any time, you can still make it safely to the surface.

There's an axiom when doing anything that requires high reliability. Anything not currently being used doesn't work. You need to take that into account when diving and have a viable bail out plan in case you switch to something and discover it's not working.

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#6 netmage

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Posted 22 May 2008 - 09:39 AM

The problem with using single tanks is that if there's a problem with one of them you may lose access to that gas, and if you've planned to have it available that may be inconvenient to say the least!


I think this needs to be clarified. When I first read it, I thought that it was clearly wrong since if you lose a single, you only lose that gas, and if you are using doubles, you could possibly lose them both.

I think what Peter is trying to say is that when you are using two singles, you are only breathing off of one of them. Should there be something wrong with the other one, you will not know it and will be SOL when it comes time to switch to it. That's why you need the complicated switching patterns to make sure that if you lose either cylinder at any time, you can still make it safely to the surface.

There's an axiom when doing anything that requires high reliability. Anything not currently being used doesn't work. You need to take that into account when diving and have a viable bail out plan in case you switch to something and discover it's not working.

Ross


Well, breathing tank one to 500psi then switching isn't exactly following tech best practices. Depending on tanks, you could be talk a wide swing in weighting, balance, trim. In addition, you arn't really maintaining thirds are you?

Take a note from the side mounters... 1/3rd, switch, 1/3rd turn,switch, 1/3rd, switch, 1/3rd, surface and you still have a 3rd in each tank (and total gas) for contingency.
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#7 ScubaDadMiami

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Posted 22 May 2008 - 10:16 AM

Either way works. It's just that manifolded doubles allow you to access all of the gas in both tanks should there be a problem with one of the regulators. You won't be able to do this with independent tanks. On the other hand, managed properly (by switching at the proper times), independent tanks should still work just fine.
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#8 peterbj7

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Posted 22 May 2008 - 10:24 AM

When I'm using non-manifolded doubles I change each 15 bar, around 300 psi. I don't want to wait until I've used a whole 1/3.

I didn't realise that what I said earlier was unclear, and to be honest I still don't think it was. What I said and meant was that if there is a failure with either tank or something attached to it, such as a burst LP hose or a reg freezing up and freeflowing, you'll lose simple access to whatever gas remains in that tank, and if you don't act fast you'll lose the gas anyway. Regardless which tank you're breathing at the time - such a failure is actually far more likely with the tank you're using than with the other.

Going beyond the point, the sensible thing to do is shut that tank down and switch to the other. If it was a freeze-up it may well thaw out while you're not using it, and if it was something more catastrophic such as a ruptured LP hose (the most common reg failure is the primary 2nd stage hose failing near the ferrule at the tank end, especially if hose protectors aren't used) then you can take the rig off, put it on your front, and then turn the "broken" reg on whenever you need to sip air from the hole in the hose. But that's a lot less convenient than simply shutting down the failed reg and breathing the air in that tank from the other 2nd stage via the manifold.

#9 techintime

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Posted 22 May 2008 - 11:00 PM

Awesome input folks. This is exactly why I threw the question out there. I figured that there were some issues that I wasn't thinking through completely. As a new tech diver I know that I have a lot to learn. I'm making the transition and can't help comparing the procedures and equipment from my new tech training to the advanced recreational diving that makes up the bulk of my experience and asking "why"...and I have garnered a number of gold nuggets from this discussion. You folks are also reading me like a book. I am probably guilty of "incrementally getting into tech diving" in terms of the equipment expenses and I ought to just take the plunge. But I'll admit that it's hard to shelve those expensive recreational components. So far Ive got all of the proper tech equipment except the manifolded steel tanks, the HID light, and the gas switching wrist computer.

I do have a couple of more questions though:

Netmage,
1. Please elaborate on why renting/swapping tanks is a no-no. We are all products of our experience and my introduction to tech diving (actually more of a tech-lite diving) was in Truk and it was prior to my tech training. All that was available were basic, yoke, AL 80s. At least at our resort they didn't do manifolds...period. The options were either independent doubles (AL 80s) or a single AL 80. On a single AL 80, you could not follow the rule of thirds and penetrate the wrecks or even do justice to surveying the outside. So our entire group of 16 divers employed independent doubles that were owned by the dive operator and we swapped them out between dives. There really wasn't any other option. The dive planning (elaborated below) seemed to work just fine. Here is what we did and I invite your (or anyone elses) input.
For most dives, the extra gas provided by the independent double AL 80s (air or basic EAN32/36) was for the wreck penetration "thirds" calculations which we followed closely. The dive guides slung backup AL 80s to donate in case of a reg failure and we also hung EAN 50 at 20-30 ft in case anyone bafooned their bottom time. We often flirted into deco, but just barely and our dive planning considered this and ensured that our back gas was adequate to accomplish the deco stops. We only had one honest tech dive (the San Francisco sitting at 180 ft). This trip is where I caught the tech bug and what prompted me to seek the proper training.

2. Why is using an air-integrated computer a no-no? This is an honest question, because I really dont see a life-or-death reason. Perhaps there is one and hence I invite input. I've read some DIR/GUE stuff on line, and what I have garnered is that wrist computers are the DIR standard in order to have quick access to depth and elapsed time. I have taken to wearing a backup wrist computer for that very reason. The rest of the data on that clipped-off air-integrated computer does not seem as time-critical. Again, it's all about asking "why" of people with more tech experience than I.
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#10 netmage

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Posted 22 May 2008 - 11:37 PM

Awesome input folks. This is exactly why I threw the question out there. I figured that there were some issues that I wasn't thinking through completely. As a new tech diver I know that I have a lot to learn. I'm making the transition and can't help comparing the procedures and equipment from my new tech training to the advanced recreational diving that makes up the bulk of my experience and asking "why"...and I have garnered a number of gold nuggets from this discussion. You folks are also reading me like a book. I am probably guilty of "incrementally getting into tech diving" in terms of the equipment expenses and I ought to just take the plunge. But I'll admit that it's hard to shelve those expensive recreational components. So far Ive got all of the proper tech equipment except the manifolded steel tanks, the HID light, and the gas switching wrist computer.

I do have a couple of more questions though:

Netmage,
1. Please elaborate on why renting/swapping tanks is a no-no. We are all products of our experience and my introduction to tech diving (actually more of a tech-lite diving) was in Truk and it was prior to my tech training. All that was available were basic, yoke, AL 80s. At least at our resort they didn't do manifolds...period. The options were either independent doubles (AL 80s) or a single AL 80. On a single AL 80, you could not follow the rule of thirds and penetrate the wrecks or even do justice to surveying the outside. So our entire group of 16 divers employed independent doubles that were owned by the dive operator and we swapped them out between dives. There really wasn't any other option. The dive planning (elaborated below) seemed to work just fine. Here is what we did and I invite your (or anyone elses) input.
For most dives, the extra gas provided by the independent double AL 80s (air or basic EAN32/36) was for the wreck penetration "thirds" calculations which we followed closely. The dive guides slung backup AL 80s to donate in case of a reg failure and we also hung EAN 50 at 20-30 ft in case anyone bafooned their bottom time. We often flirted into deco, but just barely and our dive planning considered this and ensured that our back gas was adequate to accomplish the deco stops. We only had one honest tech dive (the San Francisco sitting at 180 ft). This trip is where I caught the tech bug and what prompted me to seek the proper training.

2. Why is using an air-integrated computer a no-no? This is an honest question, because I really dont see a life-or-death reason. Perhaps there is one and hence I invite input. I've read some DIR/GUE stuff on line, and what I have garnered is that wrist computers are the DIR standard in order to have quick access to depth and elapsed time. I have taken to wearing a backup wrist computer for that very reason. The rest of the data on that clipped-off air-integrated computer does not seem as time-critical. Again, it's all about asking "why" of people with more tech experience than I.


Taking extreme examples like Truk, and applying back home isn't a fair argument... you might at well stack the deck against me.. :thankyou: Next your going to slam me for diving deep air in Bikini...! <g>

Who says you need steel doubles for tech dives...? Your not jumping to 300' in your first year - i certainly hope not... AL80's can take you quite a few places, assuming you have decent cardiovascular fitness. Deco on the Duane, Speigel Grove, Hydro Atlantic, and tons of recreational in AL80's... they work just fine, perfect when wet...

The general mindset in tech diving is planning. How does an air integrated computer help you plan? It dosn't. It's quite a crutch, I've been there... I had a AirZ, and I checked my brain at the door. Dive until one of the two numbers says go up.... deco or mins remaining of gas. DIR actually says ditch the computer all together, use a simple SPG and plan everything w/ tables and write down a schedule on wetnotes and use a simple bottom timer... Personally I used a simple SPG and a computer. Tech dives we plan a schedule ahead of time for contingency, and I deco out on the computer. Part of my personal reasoning is that I've had a few undeserved hits, so I slant quite conservatively (long story; do a search for PFO...)

Traditional air integrateds either come w/ absurdly long hoses, or wireless... neither of which can stand up to the streamlining, effeciency, reliability, and lack of expense of a clean brass spg (no boot).
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#11 techintime

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Posted 23 May 2008 - 12:25 AM

Taking extreme examples like Truk, and applying back home isn't a fair argument... you might at well stack the deck against me.. :thankyou: Next your going to slam me for diving deep air in Bikini...! <g>

Who says you need steel doubles for tech dives...? Your not jumping to 300' in your first year - i certainly hope not... AL80's can take you quite a few places, assuming you have decent cardiovascular fitness. Deco on the Duane, Speigel Grove, Hydro Atlantic, and tons of recreational in AL80's... they work just fine, perfect when wet...

The general mindset in tech diving is planning. How does an air integrated computer help you plan? It dosn't. It's quite a crutch, I've been there... I had a AirZ, and I checked my brain at the door. Dive until one of the two numbers says go up.... deco or mins remaining of gas. DIR actually says ditch the computer all together, use a simple SPG and plan everything w/ tables and write down a schedule on wetnotes and use a simple bottom timer... Personally I used a simple SPG and a computer. Tech dives we plan a schedule ahead of time for contingency, and I deco out on the computer. Part of my personal reasoning is that I've had a few undeserved hits, so I slant quite conservatively (long story; do a search for PFO...)

Traditional air integrateds either come w/ absurdly long hoses, or wireless... neither of which can stand up to the streamlining, effeciency, reliability, and lack of expense of a clean brass spg (no boot).


I'm the same as you on using the computer for deco. I understand the simplicity of just using tables and an SPG, but I like having a computer as a backup guide for deco to confirm that I planned it right and as a backup in case I made a mistake reading my bottom timer. I take comfort in having the computer also tell me that I'm cleaned out and safe to surface. And I like using a conservation factor of extra deco at 20 feet until I'm a couple of extra pixels into the green and I'll breath well into that last third to do it to. In Truk we had a guy stay a few extra minutes on the San Francisco and it cost him 45 extra minutes deco time. For me ditching the computer seems similar to removing the gas gage from your car. You could calculate your gas mileage and then read your odometer to figure out when to go to the gas station, but why not have the gas gage? I'll take the crutch, especially while I'm a greenhorn at tech diving. Trimix is next on my training list. Having lost someone else's camera on a probable Narcosis hit I'm not planning on diving below the Oriskany hanger deck until I get some experience under my belt and get the trimix course done. Deep air is still a mystery to me. Did you really go to Bikini? That's on my bucket list. New tech subject coming up on a separate thread.
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#12 peterbj7

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Posted 23 May 2008 - 08:29 AM

When I'm deep diving (helium depths) I always use tables and a timing device, with a computer (if I have one suitable) as backup. My dive plans are printed on a slate, and I usually construct three to cover whatever eventualities I anticipate. I NEVER go outside these plans. If I'm using a suitable computer then as I get shallower (and off helium) I follow the more conservative of dive plan and computer. I don't bend the computer on these dives.

When I say "timing device" that's usually a rec computer in gauge mode, and I always have at least two of them.

I build my dive plans on a PC using suitable software. I'm not going to say which as there are several good ones, and more important than which one you choose is how you configure it. Over years of experience I've learned what configuration suits me best - you'll need advice on how to do it. There is no absolute right or wrong answer, but there will be answers that work better for you than others.

I long since stopped using air-integrated and/or console-mounted computers. I agree with the GUI/DIR philosophy (though from them it's an instruction) that the best place for a computer is on the wrist. Glancing occasionally at an SPG is no hardship, and of course once you have multiple tanks you need to be very sure that the SPG you're looking at is the right one. I know there are wireless-integrated computers out there that can read gas pressures from several tanks, but I equally know people using them who got hopelessly confused. With an SPG on each tank all you have to do is trace the hose back to the reg to be absolutely certain which one you're looking at.

You only have to try once making a series of accurate deco stops on a helium dive (where precision is of the essence) using a hose-mounted computer to be cured of ever wanting to use it again. Trust me - you'll want a wrist mount.

#13 Geek

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Posted 27 May 2008 - 08:03 PM

Fellow tech divers, I'm a fairly new tech diver and I've read every post on this entire forum and have learned a lot from it. Many thanks to those who have posted here, but I'm hungry for more and the posts have kind of dried up lately. You all are probably too busy diving, but I'd like to stir up some discussion so that I can learn from those with more experience than I. Here is a topic:

Independent doubles versus manifolded doubles: I've dived both setups and have heard the argument about the difficulty in balancing the gas remaining in each tank, but what I'm finding is that even if I run the first tank down to 500 psi (with the other still full) before changing tanks I get no noticable trim/roll problems. Concerning the benefits of independent doubles, it is far easier to rent single tanks and much easier to change them out for consecutive dives. And as long as I keep my BC connected to my second planned tank, I run no risk of inadvertently running out of gas for my BC. I also find it easy enough to monitor two SPGs (one as an air-integrated computer and the other as a standard SPG with each clipped to the appropriate side of my setup. All it takes as far as equipment goes is a set of double-bands and an extra SPG which is much cheaper than maintaining dedicated manifolded, banded doubles. I can use the tanks I own as independent doubles for a tech dive and then use them as single tanks for recreational dives the next day, or even the same day with no modification to the tanks and a simple wrench removes the double band setup from my standard BC or from my tech wing/backplate setup. I understand that sharing gas with an OOA diver will be a little more complex, but still doable. But very few divers use independent doubles. So am I missing anything here?
Hope I haven't made the DIR folks out there cringe too much and please don't call me the S-word. I can (and have gone) full DIR, but am not convinced that it is the only way to go. Hey I'm still learning (always will be) and am inviting constructive input.


The purpose of doubles is redundancy, so if you run down to 500psi in one tank, but lose the full one, you've defeated the purpose of doubles. If you just wanted a lot of gas, use a larger single tank and get rid of all the extra stuff.

Independent doubles were common years ago, but manifolds are pretty cheap compared to a lot of the other stuff tech divers buy and they eliminate the switching back and forth issues, so they've become the norm. A nice new set of steel doubles can set you back $1000, but you'll only save about $100 by going with independent doubles rather than a manifold. There are still people who go the independent route though, so if you prefer independent doubles you won't be alone.

Most of the folks who want to switch tanks around like you are talking about, or who aren't ready to spend the bucks on a set of steel doubles, go the pony tank route. This works as you are moving through the transition from recreational to tech diving and once you move to doubles the pony can be used as a deco bottle so the money isn't wasted.




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