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doubles diving, allys or steel?

Discussion in 'Technical Diving Specialties' started by Nitro91, Apr 6, 2012.

  1. Nitro91

    Nitro91 Barracuda

    # of Dives: 50 - 99
    Location: Sydney, Australia
    285
    10
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    just wondering, i am considering going into tec diving sooner or later this year. and i am looking into getting some tanks.
    i know most tec diving is with double tanks, so is it better to go with steel or ally with doubles? or does it not matter
     
  2. Dive Bug Bit Me

    Dive Bug Bit Me Solo Diver

    # of Dives: 200 - 499
    Location: Cape Town
    406
    170
    43
    Ally wet, steel dry.

    Most tech divers I know dive dry suit so steel more common. Only place I have seen double ally tanks has been the Carribean.

    I would suggest getting a copy of the GUE guide "Dress for Success". It tells you what to look for in tanks, tank valves and isolator valves. To my astonishment not all steel double tanks are equal.

    I would also chat to an instructor in the area that you expect to dive to see what set up works best.

    And, welcome to the world of tech. It's totally worth it.
     
    Last edited: Apr 6, 2012
  3. spectrum

    spectrum Dive Bum Wannabe ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: The Atlantic Northeast (Maine)
    11,362
    806
    113
    There are a number of considerations that go into this.

    1) Will this be the end of single cylinder diving for you? That's not likely. In most cases going tech means MORE gear, no re-purposing what you have.

    2) Aluminum doubles are generally associated with wetsuits. Double steel will have considerable negative buoyancy and lacking the redundant lift of a drysuit a wing failure can put you in a bad place. There are dual bladder wings, lift bags and such but you get the gist.

    I think the suggestion of getting some training under your belt is a good one. Try others/rental gear, learn all you can and then make your purchase. This may be a lot like a drysuit course where a lot of the material is how to buy the drysuit you just bought, duhhh.

    Pete
     
  4. Jim Lapenta

    Jim Lapenta Dive Shop

    # of Dives: 500 - 999
    Location: Canonsburg, Pa
    16,265
    7,657
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    I use steel doubles for wet and dry diving. I have a set of aluminums that I am going to put together this season for student use in my new intro to tech class. My current doubles are LP72's, which are great little tanks and work well with my 3mm and 5mm suits, and LP 85's which I use when diving dry. I have a pair of LP95's and have the manifold and bands for them but have been using them as singles for students on the deep dive of my AOW class. Not doing enough boat diving for deep wrecks to yet justify putting them together since they are beasts when doubled up. They are the kind of tanks I want to put on, stand up, and fall off the boat with. Not walk 50 - 100 yds with for shore diving. And for the shore dives I do that much gas is really not necessary at this time.

    There is more than weighting to consider when selecting doubles. Since some steels can be used diving wet. My 72's and twin 50's can be used quite easily wet and with a lift bag or smb for redundant buoyancy they give the benefits of redundant gas and more of it. What kind of dives are you doing and what is the length of them now? Thing is that once you go this route it is unlikely you will have only one set of doubles for very long. Many divers I know have several sets of different capacity and use them as dictated by the dive profile, needs of the team, and even planned mix. Right now my 85's are O2 clean for anything up to trimix. My 72's are air only since they primarily get used for OW dives under 130 feet and not worth using nitrox on. Heck most of time they are what I'm doing OW checkouts in or the shallow dives for AOW.

    This is something that I and many other instructors cover in our Intro to Tech classes: cylinder selection. DO you really need double 120's or 130's to begin with? Most likely not. Will al 80's or Lp72's work to start out. Could very well be the best choice but only you and your instructor can make that call based on your dive needs, gasses you'll be using, the environment (I understand some cavers don't care much for al mains because they are floaty once the gas gets used), and bottom line how much you have to spend initially.

    Tech is not cheap. But you don't need to mortage the house to get started. However once you do and your diving skill, training, and experience progress you need to be able/ready to spend more on tanks, regs, mixed gas computers, dry suits, etc. If that is going to be a hardship then you may want to rethink the whole tech route. It's not like recreational stuff where you can rent 90% of the stuff you need to dive. Going beyond recreational means all the gear gets much more personal and it pretty much needs to be yours.
     
  5. PfcAJ

    PfcAJ Orca

    # of Dives:
    Location: St Petersburg, Fl
    5,504
    3,041
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    I don't buy for a second that a lift bag or smb is 'redundent' buoyancy. Imagine fumbling with a lift bag as you lawn dart into the ocean depths. Veto.

    With a drysuit, you must mash the inflator and get yourself situated.
     
    JamesK and Dive Bug Bit Me like this.
  6. RTee

    RTee Divemaster

    # of Dives: 500 - 999
    Location: Ottawa, ON
    1,249
    153
    63
    If money was no object than you could easily have an assortment of tanks (single and double) in your basement, closet or garage and pick and choose the ideal one for the job you are contemplating. I think very few of us can afford that. Therefore my recommandation would be to pick whatever will suit the type of diving you will do the most in terms of alloy and size.

    My own preference is steel (for singles and doubles). I own a set of twin HP 120 and four AL tanks (two of which use as stage bottles). My intent is to trade two AL 80 tanks this upcoming summer for probably two HP 120s that I will use as singles. With steel, the extra weight you are carrying on your back (check the specs of the tank, more specifically empty buoyancy) is no longer require around your waist...be it for single or doubles. In fact, I wear no weights in fresh water when diving my doubles and I know that I am quite overweighted at the start of the dive, therefore, I carry redundancy and normally more than one. Even though I dive mostly dry (first redundancy) in doubles, I have also installed a second independent bladder (second redundancy) on my BP that I can easily remove or add and I will carry a 50 lbs lift bag (third redundancy) in a technical pouch.

    I am quite certain that when diving AL doubles, not only would you have more weight on your back (that I am certain), but you would also require more weight on your belt to offset the positive buoyancy of two tanks (minus the weight of the manifold, bands and an additional set of reg) at the near empty level.

    As for size...considerations would be your SAC/RMV, the type of diving you intend to do (rec vs tech) how deep do you intend to dive with that set-up, how many consecutive dives, etc.

    FYI, last summer, I did dive my doubles wearing a 7mm full length wetsuit only. While I did not have my drysuit anymore as redundancy, I still had two others at my disposal to handle the possibility of a Wg failure.
     
  7. Nitro91

    Nitro91 Barracuda

    # of Dives: 50 - 99
    Location: Sydney, Australia
    285
    10
    0
    well at the moment with a 80 CUFT/10 litre steel tank i can get about 30 minutes with safety stop, at 30metres max depth.

    considering getting 2x 12.2/100cuft steels

    I much prefer steels to allys anyway as i can use 0-3lbs with a steel and 5mm suit, but with al80 i have to use 9lbs or so.
     
  8. Dive Bug Bit Me

    Dive Bug Bit Me Solo Diver

    # of Dives: 200 - 499
    Location: Cape Town
    406
    170
    43

    Agree. If you can't swim a rig up with no air in the wing, then it's too negatively buoyant. I've dropped to the 30ft grid and dumped all air. Swimming a set of double 120s up was surprisingly easy, wouldn't want to do that wet though.
     
  9. mathauck0814

    mathauck0814 Assistant Instructor

    # of Dives:
    Location: Killington, VT & San Diego, CA
    2,034
    760
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    It's more a question of how much gas you need to do the types of diving you want to do. If you can get away with 160 cubic feet (keeping reserves in mind) then you can have an aluminum v. steel discussion. I've found, personally, that volume of gas to be insufficient for the dives that I enjoy and so AL tanks came off the table by necessity.
     
    Colliam7 and waterpirate like this.
  10. Colliam7

    Colliam7 Tech Instructor Staff Member

    # of Dives: 1,000 - 2,499
    Location: Hillsborough, NC
    3,599
    1,150
    113
    As several have suggested, it 'depends' - on how much gas you need, for the type of diving you like / intend to do.
    It does not sound like you are an air hog. But, what do you want to do with doubles diving? Go (much) deeper, stay longer, use one set of doubles for two boat dives (instead of having to change tanks), or simply have the training / experience for those times when you want to do a longer, leisurely deco dive?
    I presume you are referring to a SINGLE AL80 and a SINGLE steel tank. Results with doubles may vary.
    A very popular rig. I have a set of double PST HP100s, and dive them wet and dry. I do NOT use them for serious deep (>200 ft) or long dives, they simply don't provide the gas supply I want for the dive, and reserves. In those cases I use a set of double HP130s. But, I love the weight of the 100s. Having said this, I will also say that my favorite rig for coastal recreational diving is a set of double AL80s, from the perspective of trim characteristics.
     
    mathauck0814 likes this.

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