How to progress to twin tanks?

[DevonDiver]

It's important to understand how a manifold works, and how the gas routes through it, because it impacts how you solve problems.

If a diver were to teach themselves doubles, for the purposes of recreational diving, there's little overwhelming initial need to complicate the transition by covering shut-downs and manifold drills.

Whilst shut-down/manifold drills provide redundancy, which is optimal, it is okay to get initial equipment familiarity by diving the rig as a 'singe, large tank'. Do that until the rig is properly adjusted and core skills (buoyancy, trim, propulsion, situational awareness etc) are dialed down in it.

Once the task-loading of initial equipment familiarity is overcome, then isolate the doubles. Consider doing some dives as per independents. That'll also improve your regulator skills, gas awareness and the need to plan your dive. After you get comfortable over a few dives, start using the isolation valve to balance the tanks as your dive progresses.

Lastly, once everything else is ingrained, start practicing shut-down drills and dive with the isolation valve open.

Proper training fast-tracks this process - and gets you started with full manifold/shut-down capability from the offset. Without that, IMHO, a graduated progression in complexity is a better (and safer) option. I've seen novices screw-up shut-down drills before (leaving themselves OOA)... it's not something to be taken lightly or without dedicated support/supervision.

 

[00wabbit]

I actually did my first doubles dive today. Most of the people I dive around dive doubles so I was able to get good advice before hand. I have been diving with my current buddy quite a few times and we have a similar style and trust each other. I finally reached a very comfortable level with singles and wanted to give doubles a try. I read a lot on here and past threads and watched a lot of YouTube and talked to a lot of Facebook scuba friends.

I got got my doubles together and calculated my weighting and did it today.

It went very well. I was
only a couple pounds negative at 500psi so my calculation were pretty close. The doubles were ver stable and fortunately I didn't have any major trim issues. Underwater they dive just like singles but if you roll left or right you can feel them a little. You also have to get used to a different placement of the dump valve from the singles wing and make sure to roll a little to move air towards the dump if needed.
I tried reaching my valves while on a platform and had some trouble. I could reach one but not the other or the isolator. I will work on this.

I think its important to have a very good understanding of the mechanics of the manifold and the nine failures. If you can't work the valves then it's just a big tank on your back and not redundant.

The only things that were really different were on the surface. You have more weight up high in your back now. You have to be careful about falling and getting the tanks in and out of your car etc you need to develop a technique so you don't hurt yourself.

Other than that it went well and if you have good mentors seems fairly straightforward
to get into.

 

[rongoodman]

Once again, Lynn beat me to it--I was just about to enter something about the counterintuitive things they can do to your trim. If we knew where the OP was located, we might be able to point out a good local mentor. Anywhere in central Mass. or Conn., Ed Hayes at Scuba Shack is the guy to see.

 

[Searcaigh]

I had 4 AL50s and decided to double up a pair of them, and whilst my local tech friendly dive shop was trying to obtain bands for them I as offered a pair of O2 clean HP Australian 7.9L Luxfers as singles, that I subsequently set up as doubles, bought a wing and after some mentoring plus some pool work learning valve shutdown I decided to try them out in 3M of water with one of my irregular buddies resulting in me wondering why I was going down this road, my trim was really way out and felt I was really top heavy and that was without carrying my usual couple of kilos of photographic gear.

After a few dives it all worked pretty good and frequently use them for two dives depending on the dive sites planned as my SAC rate is pretty low. I also have the AL50s set up too and use them for specific dive sites, but they are lighter and shorter than the Ozzie Luxfers and trim differently and work great with a side slung stage or deco bottle.

 

[Michael Guerrero]

I just bought some doubles and threw'em on.

Same, didn't bother with a class. You can see all the drills on youtube videos and other websites. Just do the drills in shallow water, and practice when you do your dives and you should be good to go.

This assumes of course you have the requisite gear (double regs & BP/W--recommended). I found the transition to doubles to be no more than a checkout dive (solo) with valve drills.

EDIT:

And yes, your trim will likely be affected. I ended up a little head heavy so I moved my weight belt a little lower and no issues. As always, you need to sort out your trim when you change something.

 

[DevonDiver]

Same, didn't bother with a class. You can see all the drills on youtube videos and other websites. Just do the drills in shallow water, and practice when you do your dives and you should be good to go.

As mentioned, there is some danger in this. A mistake made with the order of a valve shut-down drills can leave you without gas. Even in very shallow water, the weight of technical diving equipment can mean standing/surfacing quickly is difficult.

If you are going to learn/practice this by yourself, then make some arrangement for supervision. An instructor/mentor is best, but any trusted and competent diver is better than nothing. They should be close at hand, to observe you and be ready to donate air immediately if the need arises.

You should also spend some significant time ingraining muscle memory for the drills on dry land. Just sit in your rig and go through the drills until your arms burn and your brain reaches its boredom threshold. When you can do the drills without thinking about them, you are ready to try them in the water.

 

[TSandM]

Totally agree that if you are going to practice shutdown drills, you need a buddy who understands what you are doing and is very prepared to donate if you turn off all your gas. ALL of us have done it. I had an interesting experience with a buddy I didn't know, who, when I turned off all my gas, was looking at some kind of critter and facing away from me. Not a good feeling, but I learned I could turn my gas back on faster than I could get my buddy's attention . . .

 

[rjack321]

Totally agree that if you are going to practice shutdown drills, you need a buddy who understands what you are doing and is very prepared to donate if you turn off all your gas. ALL of us have done it. I had an interesting experience with a buddy I didn't know, who, when I turned off all my gas, was looking at some kind of critter and facing away from me. Not a good feeling, but I learned I could turn my gas back on faster than I could get my buddy's attention . . .

Strong motivation not to repeat that mistake too!

 

[Bob DBF]

I just bought some doubles and threw'em on.

I did that in the late '60's, however it was a couple of 72's on a J valve manifold and isolation was not available nor were two posts. I still dive it when I need a 130 because I have the gear lying around and I'm too cheap to buy a 130. Never had a problem trimming them out.

If I needed more air or went back to aggressive and/or deco diving, I would strap on the new gear and sort it out. However, I wouldn't necessarily recommend that course of action to anyone else.



Bob
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I think that advocating unsafe and dangerous practices is both stupid and foolish. That is why I don't tell people to do what I do. Dsix36