Doubles etc.

[PerroneFord]

I don't do decompression diving, and may never do any...

But so far, I've been diving two years, and have only made one trip to a place where it was an issue, so that's not a powerful driving force.

Someone write these words down! LOL!

Borg Queen, when the world beyond the sign opens to you, you'll be asking about staging and rebreathers.

 

[Hammerhead]

I have been happily diving a single 95 with a 30cuft pony. Most of the time it is filled with 28%, and most of the time I don't get to reap the benefits of the oxygen rich (and expensive) gas, as I run low on air before getting close to my NDLs.

The next logical step then, would be to move on to doubles. With the right Nitrox Mix and an inshore location I could easily streatch my NDLs to my little hearts desire and spend a greater amount of time on the whatever it is I'm diving. This is all well and good for a site less than 100 ft, but then arises the question of the deeper wrecks. At 130 feet, with 28% you get 13 minutes of NDL....that isn't very long. So what's next....decompression diving.

I'm a little apprehensive to venture into this type of diving, particularly because I only have a neophytes understanding of the techniques and equipment involved in its application.

I understand there are a few schools of thought in diving doubles period. The manifold setup is one I see most often, but some also dive independent doubles. What are your thoughts on this?

When applying double tanks to decompression diving what is really involved? Sling bottles of greater O2 mixes for decreased hangs? Advanced computers for gas switching? More advanced dive planning? A fat wallet?

Bottom line is I'm trying to extend the time I get to spend underwater.

Gills would obviously be the best solution, and I've got a few geneticist friends trying to figure that one out Wink. Until then though I'll just have to stick to current technologies.

Would appreciate any feedback

I may come across as argumentative, but if you might be asking a bit much here...

Do you want advice on deeper?

Do you want advice on longer?

Do you want advice on doubles?

Do you want advice on independent doubles?

Do you want advice on manifolds?

Do you want advice on nitrox mixes?

Do you want advice on wreck diving?

Do you want advice on air management?

Do you want advice on slung tanks?

Do you want advice on the benefits (or otherwise) of pony bottles?

Do you want advice on O2 mixes?

Do you want advice on what all of the above cost?


Edit. whatever the answer(s), don't ask me.

 

[CompuDude]

Rec diving, I can get a weekend out my 104's. (3-4 dives)

I'd say build one set of proper doubles. Try them, see if you like them and they'll work for you.

I'll third this advice. Makes the most sense. Take two of your 4 tanks and double them all proper-like, with bands and manifold. That gives you, in essence, 3 tanks: 1 big one (the doubles) and you'll still have the two singles.

If you're trying to get four dives in a day from a boat, you're really not in any different situation from where you are now... you still have four tanks to take, you'll just go down in one set twice. For shorter trips you can bring doubles or two singles or whatever the situation calls for.

Meanwhile, with a good set of doubles, properly configured, you can start the learning process and get comfortable. Assuming you like it, only then should you need to decide if you want to double the other pair or invest in new tanks for another set.

Note: It's easy to pick up used or otherwise inexpensive, yet good quality, bands. Check out Salvo's 300 bar manifold for an excellent manifold at a WAY better price than DiveRite, Halcyon, or any of the other usual suspects. They're pretty much all made by the same factory in Italy anyway... my Salvo manifold gets mistaken for a DiveRite all the time.

 

[jeckyll]

... and don't forget to check to ensure that the boats you normally get out on can handle doubles.

Some are set up for it, but some smaller ones may not be or won't be able to take as many divers if a bunch take doubles.

YMMV.

Bjorn

 

[Drewski]

To answer a recent poster's question, I think the discussion the OP is looking for is probably NOT sarcastic discussion!

So, here's my shot. NJScubaDoc, I'd ask that you think about this line from your previous post:

if i'm on a boat, its for at least 2 dives.

Does this mean you would be using one set of doubles for two dives? If this is the case, it means that on the second dive, you have no real "gas advantage" compared to the first. It also means that if you are diving paired singles, you would need to use a thirds planning rule (or something similar) on each tank to manage your gas, meaning a "switch" partway through each dive. Again, no gas advantage on the second dive. Alternatively, if you’re planning to use 2 sets of doubles for 2 dives, then what I said is not an issue.

I’d also suggest you ask the question "am I in good enough shape to use doubles when boat diving?" Doubles TAKE strength AND endurance. Both the weight of the kit and the increased profile create issues both in and out of the water. Sure, putting them on at the car then walking 30 yards to a beach might be OK, but try climbing a steep ladder on a dive boat in 6 FT seas after making a 100 FT surface swim back to the boat because you missed the tag line in the current. It becomes difficult.

Your information also indicated you were using LP steels. That's good, because LP steels when jam filled can give you a bunch more gas. Assuming your 10% overfill is 2640 PSI, a fill to 3200 will give you 115 CFT of gas. That gives you almost 80 CFT of useable gas following a simple rule of thirds with no other adjustments. For most experienced divers, I'd say such an amount of gas should get you "in the ballpark" for a turn pressure near the EAN NDL down to about 140 FT assuming an EAN mix between 28% and 32%. Doubles might be “sexier” for the type diving you are doing, but ask yourself, “do I REALLY need them?”

OK, so you want to do deco too. For depth ranges to around 140 FT (with planned BTs beyond EAN NDLs), I'd recommend switching to "H" valves on your 95s and using a 40 CFT 50/50 mix stage. Sling the stage. It's small, fairly unobtrusive, and easy to dive with. The "H" valve provides you with good redundancy for your bottom gas in the event of regulator failure, assuming you can cut off quickly. Personally, I'd always use an "H" if I did the type of diving you described earlier. Using the 50/50 mix for deco really decreases hang time, so even if you do EAN BTs close to 60 minutes for 100+ FT dives, deco stops are often short, generally 20 minutes or less. From a safety standpoint, the "goal" of this type diving is to minimize nitrogen exposure, stay below a 1.4 PO2 "ceiling" and minimize deco hang time. For beginning deep diving, in my opinion, this is exactly where you need to be going. Save the higher exposures and more complicated stuff for trimix, if you ever want to do it. Save the doubles for below 140 FT, or use them on specific dives where LONG BT on the first dive (or only ONE dive) is important to you.

Finally, and needless to say, get some training! Learning gas management, deco theory and the other stuff often isn't the hard part. Instead, handling the equipment while underwater, especially if you get stressed, is the challenge. Learning gas switching on a computer AND knowing how to use back-up tables while underwater takes some getting used to. Getting the "feel" of stage bottles, understanding how to handle "emergencies" with other divers, overcoming equipment problems and getting used to hanging on a line while bouncing up and down in rough water while doing nothing for 20 minutes are all part of the process. Hooking up with a GOOD mentor and "seeing" how it's done completes the training process.

Good Luck!

 

[AquaW]

I have been happily diving a single 95 with a 30cuft pony. Most of the time it is filled with 28%, and most of the time I don't get to reap the benefits of the oxygen rich (and expensive) gas, as I run low on air before getting close to my NDLs.

The next logical step then, would be to move on to doubles. With the right Nitrox Mix and an inshore location I could easily streatch my NDLs to my little hearts desire and spend a greater amount of time on the whatever it is I'm diving. This is all well and good for a site less than 100 ft, but then arises the question of the deeper wrecks. At 130 feet, with 28% you get 13 minutes of NDL....that isn't very long. So what's next....decompression diving.

I'm a little apprehensive to venture into this type of diving, particularly because I only have a neophytes understanding of the techniques and equipment involved in its application.

I understand there are a few schools of thought in diving doubles period. The manifold setup is one I see most often, but some also dive independent doubles. What are your thoughts on this?

When applying double tanks to decompression diving what is really involved? Sling bottles of greater O2 mixes for decreased hangs? Advanced computers for gas switching? More advanced dive planning? A fat wallet?

Bottom line is I'm trying to extend the time I get to spend underwater.

Would appreciate any feedback

A few notes, suggestions, opinions etc.
Your statement,” I don't get to reap the benefits of the oxygen rich (and expensive) gas,..." concerns me a little. How much do you pay for fills? a 28% fill shouldn't be all that expensive. Going doubles and learning decompression diving will be extremely expensive to you if the fills in your pony are worrying you.

I see you are from New Jersey. NY & NJ share many of the same wrecks and conditions of course. If you want to be a North east wreck diver you haven't scratched the surface (perhaps I should say bottom?) until you get into decompression diving here. There are many wrecks in your waters that are fantastic but deep enough that to get the most out of your dive you need to be equipped, trained, and prepared for decompression. That said, if you want to do it, it will cost you money. You won't be in Kansas anymore Toto. Only you can decide if it's worth the time money and effort to get trained and equipped for it. It sounds like you love diving wrecks in the Northeast so I think you want to do it, you just don't know how to go about starting. My advice may be different than others here. That doesn't necessarily make them wrong and me right. There’s more than 1 way to skin a cat. My opinion is based on my experience as a technical instructor and an avid Northeast wreck diver.
You stated,” I’m a little apprehensive to venture into this type of diving, particularly because I only have a neophytes understanding of the techniques and equipment involved in its application." It's good that you want to learn. I'd suggest finding a good local instructor. I wouldn't buy new gear until I learned what options I had. A good instructor will explain the different configurations, pros and cons of each and their suggestions. In the long run you'll save lots of time and money because you'll only have to buy gear once.
You must dive on local boats. Talk to the crew. They're out every weekend and have tons of experience. Ask them to recommend a good instructor. They see who's good and who isn't. Talk to other divers about their gear but don't just get the gear that someone else uses because he's the "best" diver you know. Find out WHY they like a certain configuration.
To give you my opinion to your questions, "what is really involved? Sling bottles of greater O2 mixes for decreased hangs? Advanced computers for gas switching? More advanced dive planning? A fat wallet?" Yes, all those things. Although, you don't need an "Advanced Computer" you can use a bottom timer and slates with your deco on them (your instructor will teach you how to plan the dives safely) but it is going to cost you some money. I think it's worth it. To me it is anyway. Only you can decide if it is to you.
Some answers (my opinions) to your other questions. Get isolation manifold. I don't like independents. Do they work? Sure they do. That’s how I started. A manifolfd is better. The only benefits to independents are cost, and you can disband the tanks to use as singles. Also, Aqua explorers makes a band system where you can kind of snap the tanks together on the boat so it’s easier to carry.
Stay away from those very large cylinders. To dive safely with them you need H valves, which cost almost as much as a manifold. I disagree with anyone that says a 140 cf single tank is as stable on your back as doubles. Think center of gravity. Well, that's my 2 cents. Good luck and I hope with all the info people have given you it will help you make an informed decision on how to proceed.

 

[String]

I understand there are a few schools of thought in diving doubles period. The manifold setup is one I see most often, but some also dive independent doubles. What are your thoughts on this?

I've used both manifold and independent twinsets. Both do a job and depend on circumstances. Abroad where people rent manifold twins i use them. I like manifold, gas planning is a little easier and provided you can do valve drills have more options in terms of recovering from a failiure.

However in the UK i use independents. A lot of my club diving is single tank, we have small boats sometimes only 1 tank each. Occasionally we do dives that allow for twins. Instead of owning a twinset AND single tanks and only using the former occasionally its easier to get the cam straps out and just twin up the singles as and when needed. That way i have the benefit of owning singles setups for normal diving but can twin up for the small number of dives that use it without having to spend money on a full manifold system to get used 2-3 times per year. Cost effective solution for me at least, especially when diving off small RIBs where you cant always take 2 tanks each.

When applying double tanks to decompression diving what is really involved? Sling bottles of greater O2 mixes for decreased hangs? Advanced computers for gas switching? More advanced dive planning? A fat wallet?

Far more understanding of deco theories and methods around (TABLES, few will use a computer at this level), gas planning, contingency planning, equipment setup and importantly it demands a FAR higher level of dive skill and task loading than normal diving. Skills and buoyancy have to be spot-on, you need to be able to deal with potentially multiple failiures at once without losing buoyancy and surfacing is now an option. These are situations that recreational training doesn't begin to get you used to. In recreational, you get a problem, you surface. In mandatory deco you dont have that luxury. Recreational diving, out of air, just ascend to surface. Decompression diving you cant. You have to share air with a buddy for a long time or if you lose deco gas have to have planned enough backgas to deco on that, cope with buddy having same thing and so on. Everything is far more involved with far less room for error. Forget the bent can be fixed myth - it cant always be fixed and can sometimes be fatal.

Id suggest training such as TDIs Advanced Nitrox and Decompression Procedures, the IANTD or other agency equivalents. Its not something you should attempt without a proper course. You dont know what you dont know at this point. A good course will also let you use and talk about the pros and cons of manifold vs independent twins so you can get an idea of what you want before having to buy.

Fat wallet. Yes....Even more than normal diving sadly. A fat wallet soon becomes a thin wallet.

 

[DeepBound]

i'm not ignoring advice, i'm simply offering counterpoints in an effort to continue brainstorming.

Sorry if you feel that way.

Independent doubles are a good setup for solo diving, but they might make it hard to do buddy diving for these reasons:

1. People will say you're some kind of crazy rebel
2. You'll have to keep switching between regulators. Which regulator are you going to tell your buddy to take if they are OOA? Most doubles divers have one short hose and a long hose, but you'll be switching back and forth. Could cause some confusion.

 

[String]

Not a big issue on indies if you use surgical tubing style holders on shoulder D-ring. Just tell them to grab the reg on the tubing.

 

[NJScubaDoc]

These past few responses have been stellar. Thanks for the thoughts.

As AquaW mentioned, you really can't begin to scratch the bottom? of NJ wreck diving without getting into decompression. Many of the larger wrecks lie in deeper water, and to spend some worthwhile time on these you have to start thinking about decompression. Which is what I'm doing. I deal with a great shop (Divers Two in Avon-By-The-Sea, NJ) and they employ some of the most talented instructors around, especially when it coms to technical diving. I like getting opinions and feelings from various sources though, hence the reason for this thread.

Onto some questions posed, and my feelings...

The boat(s) I dive off are well equipped to handle doubles, so that won't be an issue. I'm still young (22) and in pretty good shape. The extra weight is something I can handle at this point. As for shore diving with doubles, perhaps I mislead, most of the shore dives are done in water that is 20fsw deep or less. Using double 95s for that is something I just would rather not do.

If there is one key point that I take from all the posts thus far is that decompression diving requires proper training, equipment, and a certain mentality. When the time comes that I want to get into decompression diving I certainly have a good sense of what to expect and how to go about it. Thanks.

In the meantime (read while I amass more funding) I need to increase my gas volume allow me to reach the maximum limits of my NDLs as provided by the Nitrox I'm diving ($15 a fill). The best way I can figure to do that is to take my four tanks and dive them as 3 sets of independent doubles (for potentially 3 boat dives). In practice, I would take 2 full 95s on my first dive, breathe them down in increments of 500 psi. At the end of dive number one I would have one tank with 1500 psi and one with 500 psi (i'd breathe the last 1000 psi off a single 95). For dive two I would take a fresh tank and the 1500 psi tank from dive one and breathe the full tank down to 1500, then switch off to the half full (always an optimist) tank from the first dive, and breathe the final 1000 off that. For dive numero tre I would simply repeat the same procedure as with dive #1.

The first thought is probably, my that's an awfully complicated amount of gas management. I don't think it is though, and I think the same level of competency in gas management and ability would be required for decompression/technical diving anyway. I think I'd also sling my 30cft which I'm currently using as a pony. Aside from it offering me another redundant air source, I think it'll get me used to diving with bottles in that configuration.

The whole thing seems like it could work, and would allow me to accomplish my immediate goals without a huge investment, while also not limiting me in my variability when it comes to gear configuration (I.e. single tank shore diving).

Any thoughts, are as always, welcome.