Thinking about doubles....

[cstreu1026]

OK, so the thought ran through my mind that maybe I might want a set of doubles. However I am not really sure they are for me. I was thinking of a set of steel hp 80's. I am thinking though that they will be too much for diving wet. I have also been thinking about all the extra equipment needed. Speaking of equipment, besides tanks, valves, manifold, and tank bands what would I need ...specifically concerning regs and such.

The more I think about it I am probably going to be better off with a single large steel tank, but what does everyone else think. BTW , I am just looking to extend my bottom time since my air usually seems to run out before my computer or tables do.

 

[Boogie711]

If you don't think you need doubles or are going in that direction, I would advise you to not do it. You can get into a whole lot of trouble with all that air.

In terms of regulators, you're going to need a second seperate first and second stage. You probably have a first and two second stages on a singles reg. At a bare minimum, you're going to need a second first stage.

You're also going to want to review your bouyancy needs. If you're diving a plain old BC, you might need a new one for doubles, or some sort of modified bands set up. Even then it's not ideal for doubles. If you've got a BP and Wings, then you probably just need a new wing.

And yes, if you're diving wet, I'd avoid steel tanks regardless. Think about putting together a set of AL80's if you insist on going ahead with this. They swing positive as they empty, meaning you won't be in a death spiral or pinned to the bottom if your BC craps out on you.

 

[ninjamuzo]

Diving doubles is not quite as simple as getting two tanks strapping them together, strapping them on and going down.

There are two schools of thought on doubles. If you talk to the cave divers in Oz they will tell you never to dive manifolded doubles. If you talk to Americans most of them say diving manifolded is the only way to dive.

I dived both and each system has its advantages and disadvantages. If you are trained with independants than you can take along a doubles attachment and strap on two tanks just about anywhere.

I like a backplate but you don't have to use one. Tank bands are a must for manifolded doubles but they are heavy to carry and move around that way. I use this system when diving on Trimix in in Open water and in wrecks. I use independents when cave diving and you have no manifold option at when you are diving sidemounts for example.

Manifold out of air drills are more complex and if something critical happens you can lose a lot more air with manifolds than independants.

I've dived both Al and Steel. Typically your wings will have a dual bladder setup and worst case you can use your lift bag for an ascent assist so the steel tank's floating issue is a bit of a red herring, full Al. tanks are negatively bouyant. I've found steels easier to use on deco stops for example because they tend to be neutral or slightly negative.

If you can, try a couple of different systems and find the one you are comfortable with. Depending on yor experience level get some training in emergency drills, equipment configurations etc. Just like you did when you learned to dive with singles

 

[Boogie711]

Manifold out of air drills are more complex and if something critical happens you can lose a lot more air with manifolds than independants.

Not to hark on a point, but if my reg craps out on independents, I've just lost half my air. If my reg craps out on manifolded doubles, I've lost none of my air (minus the time it takes to shut down the post.)

So your statement about you can lose a lot more air with manifolds than independents isn't entirely accurate.

 

[JeffG]

Not to hark on a point, but if my reg craps out on independents, I've just lost half my air. If my reg craps out on manifolded doubles, I've lost none of my air (minus the time it takes to shut down the post.)

So your statement about you can lose a lot more air with manifolds than independents isn't entirely accurate.

If one has a total CF...they (independents) can only lose 1/2 of their gas....manifolded doubles could lose 100%

If your reg craps out you lose none of your air (not 100%) (minus the time it takes to shut down the offending post.)

 

[Boogie711]

If manifolded doubles could lose 100% of their air (how???) then so could independents, using your logic.

Worst case scenario (blown O-Ring, maybe?) I still have 50% of my air, thanks to the beauty of an isolation valve.

 

[JeffG]

If manifolded doubles could lose 100% of their air (how???) then so could independents, using your logic.

Worst case scenario (blown O-Ring, maybe?) I still have 50% of my air, thanks to the beauty of an isolation valve.

how --- Not being able to manipulate the isolation valve. (not saying this would happen...just worst case)

Independents are "Independent"...so you could only lose 1 of the two tanks. (are you thinking of manifolded tanks without an Isolation valve?)

 

[Boogie711]

I'm trying to understand you here - you feel that manifolded doubles are unsafe because if you blow an O-ring or something, and then you can't isolate, then you would lose all of your air???

Well - I'm sorry, but my stock response is - take training, and don't dive if you can't reach your valves. That's valid for singles, doubles, independent doubles... everything.

I feel they're safer for exactly this reason. With a minor failure (reg uncontrollably won't stop freeflowing, broken knob, whatever) then I still have 100% of my air. With a minor failure with independents, I only have 50% of my air - and if that happens at max penetration, I've put myself and my team at risk.

If I suffer a major failure (which I've never seen happen, by the way. I know it happens, I've just never seen it) such as a blown O-Ring, I STILL have 50% of my air, so in a worst case scenario, I'm at least as 'good' as having independent doubles.

 

[Ber Rabbit]

Cstreu, when my husband was doing lots of check out dives as an AI with the university years ago he said he used double 60's and loved them. They gave him enough air to complete a whole day of check out dives (the classes were large so staff did several dives) and they were small enough to manage with a wetsuit.
Ber

 

[matt_unique]

I'm trying to understand you here - you feel that manifolded doubles are unsafe because if you blow an O-ring or something, and then you can't isolate, then you would lose all of your air???

Well - I'm sorry, but my stock response is - take training, and don't dive if you can't reach your valves. That's valid for singles, doubles, independent doubles... everything.

I feel they're safer for exactly this reason. With a minor failure (reg uncontrollably won't stop freeflowing, broken knob, whatever) then I still have 100% of my air. With a minor failure with independents, I only have 50% of my air - and if that happens at max penetration, I've put myself and my team at risk.

If I suffer a major failure (which I've never seen happen, by the way. I know it happens, I've just never seen it) such as a blown O-Ring, I STILL have 50% of my air, so in a worst case scenario, I'm at least as 'good' as having independent doubles.

I thought a lot about independent's vs. manifolded doubles with isolation. I went with the manifold/isolator but I understand the benefit of the independent's. Worst case scenario - you hear a boom and air is whizzing away - you can do nothing with independents and *still* have half your remaining air (assuming you used them properly - switching every so often, etc). With a manifold/isolator if you do nothing you *will* loose 100% of your air. So looking at the lowest common denominator, independents will ensure half remaining air even if you do nothing whearas manifold/isolator can loose 100% if you do nothing.

Of course - you would not just sit there and do nothing - you would most likely freeze for a few seconds with shock then reach for your isolator to shut it down. Then of course grab the offending post if you know which one it is. If not, cycle through both to find the offending post. Open isolator once offending post is found assuming the loss has stopped. If not isolator remains closed as you head to the surface/first stop.

--Matt