Doubles

Could i get some help on doubles? I would like to start using doubles but i am not sure really where to start. Is there any Class on using doubles or is this somthing i can do on my own? I am trying to avoid Techincal Diving until later. I am thinking double because i beleive in redundancy. and i would like to gain some good bottom time in my deeper dives that i do. 80 to 100ft. Any info would be great. Also i know a guys who really like independent doubles is that a good idea or no or go with the manifold.

Well to get a good bottom time on a 100ft dive (pst 22 minutes acording to NAUI) would take you into decomp. Do you not consider deco tech? I have never dove doubles but from what I've read independant doubles would give you the most redundancy but its a fair amount of work load. Changing regs every so often so you dont lean to one side or the other, keep an eye on 2 spg. Do you know anyone who dives doubles personally? If so give them a call and talk to them. Go diving with them, see if theyll become a mentor. Kind of an unpaid instructor.

Even if you buy doubles without the intent of doing deco diving - I bet deco diving isn't far behind. When you start surfacing with 2000 PSI in each tank your going to start thinking - hmmmm wonder if I should stay longer and burn that extra guess. So just take the deco class which will most likely cover/require doubles and be down with it

I would NOT advise independant doubles, aka twins, because you have to switch back and forth every few hundred psi to ensure that you have a sufficient amount of gas in each tank to be a backup. With manifolded doubles the manifold takes care of equalizing the pressure, so you stay on the primary reg for the whole dive, assuming all goes as planned.

Going ahead and doing non-deco diving with doubles is a very good idea. That way, when you do a deco class, you'll be comfy diving doubles and will only have to worry about learning deco, not learning doubles and deco at the same time.

I've been diving doubles about 90% of my dives for the past decade. I strongly urge you to use a isolation manifold. The greatest risk of any gear malfunction or failure is a freeflowing reg. With an isolated manifold you can close off that reg and still have access to all your gas. If you were diving independent doubles you would have just lost half your gas right then. You also only need one spg, eliminating two possible O-ring failures and an extra hose.
I have my spg, drysuit inflator hose and backup reg on my left post, with my primary reg(seven foot hose) and BC/wing inflator on the right. My backup reg is necklaced under my chin so I can get to it quickly and I know it hasn't come out of some plastic holder and dragged across the bottom. I try to keep my diving as simple and uncomplicated as possible. Having to switch regs every third of the volume with independents takes away from the fun for me.

teknitroxdiver:

I would NOT advise independant doubles, aka twins, because you have to switch back and forth every few hundred psi to ensure that you have a sufficient amount of gas in each tank to be a backup.

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That's not the case. You need to switch regs after burning 1/3 from the first tank (at 2000 psi if you are using 3000 psi tanks) and then switch back to the first tank after using 2/3 of the the second tank (ie. switch at 1000 psi).

This results in you reaching your turn point with 2000 psi and 2/3rds capacity in each tank and results in you ending the dive with 1000 psi and 1/3 reserve left in each tank. Two regs switches over the course of the dive is not quite the same as switching every few hundred psi. This approach combined with proper gas planning this will ensure you have enough air to reach the surface and/or reach your first deco stop and deco gas switch in the event you lose the entire contents of either tank.

The advantage then is that, unlike isolator manifolded doubles, no action is required to close the valve to an offending regulator or to close the isolator valve in an emergency as even if you do not close a valve you will not lose all your gas - something that will occur with manifolded doubles unless some action is taken. It is still desirable to close the valve and save the gas, but your life does not depend on it.

Independent duobles are not DIR and in most circles are not even politically correct, but they are very flexible and very redundant and are well suited to cold water diving where the most likely failure is a first stage freeze up. And in that case, you can turn the valve back on and access the remaining gas after the frozen reg thaws out in a minute or two.

MaxBottomtime:

The greatest risk of any gear malfunction or failure is a freeflowing reg. With an isolated manifold you can close off that reg and still have access to all your gas. If you were diving independent doubles you would have just lost half your gas right then. You also only need one spg, eliminating two possible O-ring failures and an extra hose.

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The most likely cause of a violently free flowing reg is a frozen first stage. If your gear is well maintained, any other failure resulting in a violent freeflow is virtually unheard of. As indicated above, if the reg does freeze, in a few minutes, you can turn it back on and access the remaining gas.

So admittely with independent doubles you are potentially giving up half your remaining gas (which is not a problem anyway with proper gas planning and management) in a small minority of freeflow situations. But on the other hand you are gaining the safety advantage of never being at risk of losing all your gas if you have a freeflow in a restriction or other situation that prevents you from immediately closing the required valve(s). It's a wash in my opinion and my preference is to stay with the greater operational flexibility allowed with independent doubles.

A minor freeflow is another story. In that case with manifolded doubles you could turn off the offending primary reg and use the backup and access all of your gas. On the other hand having to shut off a reg due to mechanical problem should be cause to abort the dive. In the case of independent doubles you'd abort and stay on the slightly freeflowing reg and breathe the tank down before shutting it off and then finish the small remaining portion of the dive (if any) on the other tank. Again it is pretty much a wash either way.

DudleyNMU:

Could i get some help on boubles. I would like to start using doubles but i am not sure really where to start. Is there any Class on using doubles or is this somthing i can do on my own. I am trying to avoid Techincal Diving until later. I am thinking double because i beleive in redundancy. and i would like to gain some good bottom time in my deeper dives that i do. 80 to 100ft. Any info would be great. Also i know a guys who really like independent doubles is that a good idea or no or go with the manifold.

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Just a couple of general thoughts.

- if you want doubles for redundancy then you must become proficient at valve shut downs & isolating. If you don't then all that redundancy buys you nothing when you need it.

- Your costs will go up. You need at least one new regulator, you may need to convert your existing regulator to DIN and you may need to change a number of hose lengths etc. Also, an extra regulator and an extra tank translates into more maintenance costs and the double set may translate into higher costs for fills. Additionally, a traditional BCD isn't really suited to holding doubles so you may need a new BCD.

- They weigh a lot. This could become an issue with shore diving depending on how your shoreline looks.

R..

Doubles provide excellent redundancy for recreational dives in the 50-100 range for divers WITH PROPER TRAINING, EXPERIENCE, AND EQUIPMENT SETUP. Like many things in this sport, without proper training and experience the equipment can get you into trouble.

I loved my GUE triox class, which gives you a great education in diving doubles, but you gotta make it through GUE-fundamentals first.

Do find an instructor in your area who dives doubles and can, in person, walk you through whether independant, manifolded, or isolator manifolded is the right choice for you and WHY? Learn how to plan your gas, weight yourself properly, and handle failures. Your buddies also need to understand doubles, even if they are diving singles.

Do not learn how to dive doubles on the internet, and please make sure you can reach your valves.

Good luck.

My doubles rig (in case it mattered): Halcyon 300bar Isolation Manifold (w/ double barrel o-rings), 2x Apeks Atx50/DS4 regs in DIN, Hogarthian configuration, 55# wing with steels, 40# wing with Al80s

Long before there the multitude of dual outlet manifolds on the market we dived with independant doubles. The days when the US Navy tables were what we used for no stop and possibly 1 or 2 levels of deco stops. Pretty benign dives compared to todays diving but a great place to start.

If your plan is to stay within the no-stop limits and possibly a little longer flying independant doubles is fine. I have more than 3000 dives on doubles and my first thousand were on independant rigs.

The method:

1. make sure they mount to your BC ( a plate harness is best) but it can be done with Scuba Pro classic jacket and Seaquest Black Diamond BCs

2. chose permanent bands or "travel bands" Travel bands lets you carry three tanks on a trip and swap them out. Dive Rite, OMS, etc make them.

3. You will need two regulators and two SPGs -- you will need to mark them carefully. So you know which reg matches which gauge.

4. Using the system is easy. Assuming you start with 3000 PSI

Tank 1 2500 switch
Tank 2 2500 switch
Tank 1 2000 switch
Tank 2 2000 switch
Tank 1 1500 ...and out

You are left with Tank 2 at 2000 and Tank one at about 1000 when you are back on the surface.

Next -- take out Tank 1 and replace with new tank. Dive 2 is shorter than dive 1

Tank 1 2000 switch
Tank 2 1500 switch
Tank 1 1500 ... out ...

The key here is to always have more than 1/3 of your total gas available distributed between the 2 cylinders. Never take Tank 1 to 500 and then switch - bad thing. Take a little at a time in 500 psi increments.

While some may not like this approach it is a very valid method of extending some time. It's not any different than when cavers "side mount" and use two seperate bottles or when one dives with a single and a single stage. Or when they dive with doubles and use a single stage for bottom gas. Get comfortable with the gas managment and it works well.

I can't tell you how many times i am in the Caribbean on a weenie trip and decide to extend my bottom time on 100 fsw dives and carry a second cylinder stage style. It's all part of gas managment.

Regards,

JS1, you had me confused for a little while, but after rereading your post, I think I understand. Interesting.....