What is the best way to start diving doubles?

Sometime in the spring, I want to start to dive doubles and am wondering what the best way to start is. Should I beg/borrow/steel a set of doubles and head out to the quarry or is there a course that teaches the finer points of weighting, trim, gas management, etc?

I already have a back plate and single tank wing. Aside from tanks, I would need a bigger wing and extra reg set-up. What else should I consider?

There are some courses that use doubles, or allow the use of doubles as the case may be. The IANTD Deep Diver/Adv. Nitrox is setup for doubles and staged deco to 130'.
I don't know of a course that just teaches doubles and equipment configuration. Some would say a DirF, but you have to know everything before you take the course to have a snowball's chance to pass it.

Doubles diving is also expensive. If you don't have a real reason other than you wanna see what they're like, I would suggest the beg/borrow route.

Diving doubles entails a never-ending stream of needed equipment. It never stops

Oh, and doubles diving should NOT be under Basic Scuba Discussions because it's not. Don't be in a hurry to get beyond yourself if that's the case.

MD

If you have two matching tanks at home already, then take them in and have them banded and manifolded together. You will need another 1st stage. If you are diving with an economical octo, then you will need another 2nd stage as well. And both your 1st stages will normally need to be converted to DIN.

The twins should fit onto your backplate. The hardware should come with the bands. If not, you can get stainless steel nuts and bolts at any marine hardware store.

That is the cheapest way.

The next cheapest way is to buy two LP steel 72s and match them to bands and a manifold. That assumes that you are already diving with steel and a drysuit, rather than with a wetsuit.

If you are a wetsuit diver, then twin aluminum 80s (used) may be the next cheapest way to go. Or even twin aluminum 65s.

You should practice with your new twins at the pool before going to the open water. Sit on your rump in 4 ft of water and practice reaching back and isolating each tank and the manifold. If anything goes wrong, just stand up.

If you have a friend who is a tech diver, he(she) can show you how to do all this. It is simple enough.

When you do go diving with your new twins, mind your NDL times.

Those are the main caveats, if this is how you really want to do it.

I do not recommend it however. I recommend that you sign up with a tech store and learn the proper procedures correctly from the start. Additionally, some tech stores will want you use specific gear, and avoid other types of gear. So in the long term, by buying the right equipment first, you may be saving yourself money.

Best is to have or make a friend who dives doubles. Dive with him (you in single, him in doubles) and observe and ask questions. If and when he observes that you are a good diver, he may allow you to try a dive or 2 in his rig under his observation.

Did I leave out that you must already have mastered diving in a single tank with buoyancy control and buddy awareness before anyone is going to want to give you a chance in doubles?

If not in a pool, make your first dive in a simple open water environment with a solid bottom at a known depth. With the dude who loaned you his doubles at your side to assist if needed. Expect some balance and buoyancy challenges, and remain calm. And don't throw in the towel if your first dive isn't a stellar experience.

Safe diving to you, within your comfort & skill limits,
theskull

Hi mwilding,

I'd recommend signing up for a technical course or two, for example, I signed up for the TDI Advanced Nitrox/Deco Procedures class (6 dives over 3 days in twin LP 98's)...that was my 1st exposure to doubles. I'd never even tried them on until my 1st dive in 80 ft of water.......but it didn't turn out to be as hard as I'd feared.

I dove 'wet' in 60 degree water, which was by far the coldest water I'd ever dove......each dive averaged 45 min, and I'd say the cold at the end of the dives was a much bigger factor than mastering doubles.

My main issue was LP 95's are short --only 24 inches long-- so valve drills were difficult, as the tanks were too short to easily reach the manifolds.

The other issue was topside weight......I only weigh 140 lbs, so twin LP 98's were HEAVY......not something I'd want to dive regularly.

Among other things, my 85's and 76's are 2 inches longer, making valve drills much easier for me, and their 6.75 and 7 inch diameters make for a more compact package, easier for me to handle than the 8 inch diameter LP 98's.

Twins, especially new ones, are expensive.....I'd definitely rent/borrow a set and experiment with them in a controlled class setting first. You need to experience the weight/balance before making a decision.....I discovered twin LP 85's or twin LP 76's were about as big as I want to handle...although I might dive twin LP 98's for a cave/deep dive course.

I enjoy my 'petite' doubles (have a LP steel 85 twinset and a LP 76 twinset) but I'd never have bought them without some professional instruction/experience 1st.

There are a lot of factors you won't appreciate until you get hands on experience...only then can you begin to make intelligent choices about what you prefer.

Ok, I'm gonna be the stick in the mud here, but its well-known around here what I think of most of the classes and agencies.

Doubles. First question is why do you want to dive them? If you're diving in the range of > 60 < 130 or so, and are carrying a pony, and would like something a bit more secure, then you have a reason to dive doubles.

If you're doing it as a means to get familiar with them before undertaking serious technical diving, then there's a good reason to dive doubles.

If you're doing it because you are ALREADY doing deco dives on a single, and you've had a few too many thoughts go through your head of bending the bejeezus out of yourself due to a problem with a reg or similar event, you have a good reason.

Otherwise, think long and hard about it. Doubles are heavy, for one. My sets of Double 72s weigh 65 lbs empty, and 75 lbs full of Nitrox. My Double HP100s weigh 90 lbs full. They are a pain in the butt to move around on dry land and ALWAYS WILL BE. In fact, I have a hand truck at my house that I use to move them around my fillstation area!

OK, you've decided you're going to do it anyway.

First things first. A set of Doubles can be very negative. Choose carefully based on your exposure suit and plans. Remember, the deal is that you have to be able to swim up the kit from the bottom, with a full load of gas, and a dead wing.

The usual limit for most people on this is somewhere around -20lbs or so. Beyond that you WILL SINK UNCONTROLLABLY, and if in a place without a bottom, that would be bad!

The usual "DIR parrot line" is "never dive steel doubles in a wetsuit." I will tell you right now that this is absolute, complete, unadultered crap. I do this all the time without violating the above rule and there is ABSOLUTELY NOTHING WRONG WITH IT. In fact, there is plenty wrong with double AL80s, not the least of which is that they are VERY butt-light and can make trim a real nightmare.

Do the math. An HP100 is about -1 empty. Double HP100s are -2 for the tanks, and another -3 for the bands and manifolds, or a total of about -5. Double AL80s are about +5 empty, all in the butt, which can be extremely uncomfortable.

Assuming you're diving a 3mil wetsuit, and are an average size man, the suit + booties are probably +7 or thereabouts. An AL plate is -2 Double HP100s are -5. Guess what - that's a balanced rig. It will be -20 or so at the bottom full, as the wetsuit will lose most of its buoyancy and double HP100s hold 15lbs of Nitrox (less if they're full of Trimix.) If you can't swim up -20, you can't carry 15lbs of gas and you need smaller tanks. If you can, then the suit you wear is not relavent.

Having done this computation (and you NEED TO COMPUTE IT for your combination - get a fish scale if you need and weigh the freaking tanks in the water!) the other "big deal" is valve skills.

The reason you dive manifolded doubles is to have redundancy. You only have that if you can shut down a leak before a significant amount of your gas bleeds out into the water. If you cannot do this, then the doubles are useless and a big single is a better choice.

OK, what does "reasonably quickly" mean? It means that within 15-30 seconds you must be able to stop ALL loss of gas, and ideally, within 5-10 seconds you should be able to isolate. Why? Because the worst-case scenario is a blown LP hose that will dump your tank at your first stage's "open flow" rate - which is stupid high. If you cannot protect at least half your gas in that scenario, you die anyway, doubles or no doubles!

I've given this a LOT of thought. In the event of a MAJOR leak the first priority is to close the isolator unless you are CERTAIN that (1) which side the leak is on, and (2) that its NOT coming from the tank O-ring or manifold itself. If in doubt, close the isolator first!

I KNOW there will be people who will argue this, but consider the facts. Most leaks are small. In that case, which you close first doesn't matter, as the gas loss rate is not all that high. So whether you turn one valve or two doesn't make a bit of difference to the outcome. If I lose an extra couple of cubic feet, its no big deal.

But consider the worst case scenario - a catastrophic failure of the crossbar O-rings, or a total tank O-ring failure (extrusion, etc). Or, for that matter, a blown LP section on your reg (e.g. hose fails at the swege, turret blows off, etc.)

In the case of a tank or crossbar O-ring, only shutting down the isolator protects any of your gas. Closing a post does nothing, except waste time, and time you ain't got.

If you lose a turret or LP hose at the swege, you can dump a tank - a full tank - inside of one minute. Don't believe me? Try it sometime; remove a hose, jack the reg to a tank, put on some hearing protection, make sure the tank is secure so it doesn't fall over from jet effect and turn it on with your stopwatch. Be ready to be amazed.

Now given the chaos you're going to be experiencing right about then with the gas flow involved and the huge bubble clouds and noise everything; if you get it wrong as to which post is blown you may be screwed. Your immediate priority is to insure that you have something to breathe. The only way to KNOW that this will be the case is to close the isolator. Having done that, you then close what you THINK is the bad post. If the leak stops, you're right. If it stops and so does your breathing gas, you switch to the other side. If it DOESN'T stop you guessed wrong; turn back on the good one and shut the other one off! In any event you know that you protected at least half of your remaining gas immediately, so you're not screwed even if by the time you get it shut down the dead post has bled off everything underneath it.

Now the usual drill for "practice purposes" is to (1) close the right (main) post and breathe down the reg, (2) switch to backup, (3) open the right post and purge the reg to make sure its really on, (4) close the left post and breathe it down, (5) switch back to main, (6) open the left post and purge the reg to make sure its really on, and (7) close and open the isolator. The usual claimed "metric" for being able to do all this is 2 minutes; in a real "oh no" situation the real time to actually close that isolator is more like 10 seconds, and then another 10 to close the offending post. Unless the leak is small, I argue that you close the isolator first in a real emergency.

You need to make VERY sure that you can reach the valves and do all this, in "fighting trim" (with all your gear on, in the water) almost instantly if necessary. Practice, practice, practice, and do it in a pool that's shallow enough that if there's a problem you can just stand up! If you can't reach and manipulate your valves with reasonable efficiency, you have ZERO redundancy and in fact have ADDED risk, as there are more places you can get a leak with a doubles rig than a singles one!

Don't be surprised if it takes you a while to get the trim and feel down and be comfortable. It did take me a while.

ordered the doubles and wing which should be in a week or so. I plan on doing many many pool dives before hitting the open water. Genesis: Great advice. I made the decision to dive doubles based on the deeper wrecks I plan on doing here off the coast of New York and New Jersey and also to not have to deal with the PITA of switching tanks on two tank dives

that is not often understood but is very, very real when using them this way.

You have more actual, usable gas.

Here's why.

Let's say you double two HP100s, and would normally dive a single HP100 with an emergency bail-out bottle (say, an AL19) slung like a stage.

Ok, the doubles are heavier. Quite a bit heavier, in fact, probably by 20-25lbs or so all-up in dry weight.

BUT, while you start with 200cf of gas, you get to use more of it.

Here's why.

First dive. You start with 3500 psi. If you had a single, you'd plan for either thirds or rock bottom; in the latter case, for example, you might plan to be back on the boat with 500 psi. Let's say you actually do a bit better, and get back on the boat and the gauge reads 700. That's 1/5th of your gas, or 20cf. You had that specifically for an "oh @hit" which didn't happen.

Now in the single, that gas is wasted. You can't get to it for your next dive.

But in doubles, it doesn't work that way. On your first dive, you can go "halves" and go all the way to the wall, because you know you still have half left! So you can breathe the entire 100cf, or 1750 psi on the first dive.

On the second dive you must leave the same "rock bottom" reserve, of course. But that reserve is 250 psi on the boat, not 500 psi, since what you really are protecting is 20cf - not 40.

The result is that you actually have 20cf more breathing medium to use than you do with two singles of equivalent size!

It gets even better if you want to do one deco or other "overhead" (e.g. penetration) dive and one NDL one in a given day. Assuming you do thirds, you might turn at 2330 on the first dive. Let's say that you are nice and relaxed, and actually consume LESS than a third getting back. Its not implausible. You might get back on the boat burning only through to 1700 or so. Aha! You now did a "thirds" dive, and yet have a full 100cf in the can for the second! If you end up with only 80cf in the can, you're still in good shape, as the other guys on the boat probalby have AL80s. Cool eh?

Where this really comes into its own is if your gas consumption is such that the OTHER GUY you're diving with turns the dive first due to pressure. Then you REALLY win, because you might get THREE dives off one set of tanks. Now you only hump two tanks instead of three, because once again, you would not have enough gas in a single to complete the second dive. This often happens with me when I dive doubles and my buddies are on singles - my gas consumption is usually lower than theirs, so I frequently can do three dives to their two because I "waste" very little, while they all have partially-full tanks littering the boat deck.

dabigcat once bubbled... ordered the doubles and wing which should be in a week or so. I plan on doing many many pool dives before hitting the open water. Genesis: Great advice. I made the decision to dive doubles based on the deeper wrecks I plan on doing here off the coast of New York and New Jersey and also to not have to deal with the PITA of switching tanks on two tank dives

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I've found the double 72s to be much less hassle than a big single with a pony. Your mileage may vary.

The thing about "no steel tanks with a wetsuit" is only rough guidance. Even the most outspoken DIR advocate I know realizes there are exceptions. Personally, I dive steel whenever I can do it safely.

I do have a set of double 80s and dive them when the situation calls for it. They weigh more than the 72s and require 12 pounds more weight, making me twenty-something pounds heavier on the boat. That difference is literally impossible to take lightly.

Many make two dives on one set of doubles. I just bring two sets of small tanks. It is quite a bit easier on the back and I think it is safer.

Knowing where you are going with all of this is the key. If you are smart enough to realize that you need doubles for wreck penetration and staged decompression diving, you are also smart enough to know that you need training to go with the equipment. I dove doubles before I took any deco training because I didn't see any point in taking the training if I couldn't handle doubles. In fact, I find double 72s easier to deal with than a single 125.

Small doubles make a pretty good setup with nitrox within the NDLs. I've terminated dives because I was getting hungry and thirsty.

Be careful and watch your time. You can screw yourself up pretty badly with a lot of gas whether it is in two tanks or one big one.

Be careful and watch your time. You can screw yourself up pretty badly with a lot of gas whether it is in two tanks or one big one.

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Double 72s are more than enough gas to get you WELL into deco, and if you don't have the gas to complete it.......

PAY ATTENTION!