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Purchasing Doubles and need some advice from DIR'ers

Discussion in 'DIR' started by jgoodstein, May 20, 2011.

  1. limeyx

    limeyx Guest

    3,054
    46
    Yeah, i treat the PST and worthington 3442 tanks as essentially identical, with at least 2 pounds per tank needed for the Faber LPs
     
  2. lv2dive

    lv2dive Formerly known as KatePNAtl

    # of Dives: I'm a Fish!
    Location: Lake City, FL
    2,795
    2,086
    You've gotten some great advice on this thread. The main thing I'd add to it, is to try the tanks you are considering - dive them. I'm getting ready to sell my shiny new LP95's - fabulous tanks - for the following reasons:
    • Would have to wear a ridiculous amount of fluffy undergarments for them to be anywhere near a balanced rig
    • Difficult to trim out
    • Plain old heavy to carry around for me - a pain to get them to the dive sites

    I've tried several other types of tanks trying to figure out what I'm going to replace them with. AL80's, LP85's, 104's, 12 litre's, etc. And here's the thing... the only way I KNOW what a balanced rig is for me, is to test it. I could do the calculations on paper until the cows come home, but there's no substitute for getting in the water, "failing" the wing, then seeing how much it takes to swim up from depth simulating minimum deco. I can do it with the smaller tanks, I can't with the 95's and the 104's. Not to mention, I find the longer thinner tanks much easier to trim out. But if I hadn't gotten in water with them, I wouldn't know any of this. To reiterate - there is no substitute for trying the tanks you are considering.




    I laughed out loud when I read this. Since just this weekend I accidentally bought a full singles BP/W setup as well as a new doubles wing.... yeah, slippery slope.

    HA! Very valuable advice. Re: cambands, completely agreed!! See above accidental purchase reference.
     
  3. elan

    elan Contributor

    # of Dives: 200 - 499
    Location: Toronto, Ontario, Canada
    3,381
    429
    You cannot go wrong with AL80, even if you get another set later those would become your stage bottles. Luxfers work great for that purpose although they are a bit tail light so they might require tail weight when set up as doubles.
     
    Last edited: May 23, 2011
  4. kanonfodr

    kanonfodr Contributor

    # of Dives: 100 - 199
    Location: Seattle, Wa
    1,486
    104
    For warm-water diving, regular Luxfer AL80s work fine. I hear the Catalinas are a bit better for backgas, but that they aren't as nice for stage bottles. I'd say go with whichever set you get cheaper and be happy, you can always sell AL80s, singled or doubled.

    Peace,
    Greg
     
  5. Howdy Doody

    Howdy Doody Contributor

    # of Dives: I just don't log dives
    Location: Northeast.
    72
    0
    over the last few years, I have dove; LP 108's (most commonly), HP 100's (for a while), LP 85's (quite a bit, fresh and salt), HP 130's, and LP 121's.
    I must say, that personally, even as early as 6 months ago, I prob. would never had pictured myself saying this, but double AL80's are probably my favorite of the entire bunch.
    They are easy to maintain/build/service, etc., cheap and as some of the above listed users have mentioned, balance out very well.
    There is very little "swing" in the buoyancy with the 80's, even once a V-weight is added (11-14 lb.) when compared to some of the above listed tanks.
    I love the 80's and highly recommend them, but must agree as well that LP 85's are probably the best "all around" bet. The Faber version are very light weight and balance well, while the
    Worthington version are a bit more negative, but still balance well, and with a nice "cave fill," (as mentioned,) we're talking well over the 100 cu/ft. range of gas, while still maintaining a safe balance.
     
  6. TSandM

    TSandM Missed and loved by many. Rest in Peace ScubaBoard Supporter

    36,349
    13,629
    Just wanted to observe, again, that swing is a function of gas you use out of tanks, and is utterly independent of the material from which the tank is made, and the size of the tank. Use 130 cubic feet of air or Nitrox out of ANY set, and you will swing 10 lbs.

    Total land weight, buoyancy characteristics, and balance differ among sets of doubles, and should be things you take into account in selecting what you use. I don't like Al80s because they get butt-light as they empty, and because, when I dive in cold water, I have to wear more weight with them. Someone diving in water water, with minimal exposure protection, might not like my negative Worthington 85s, because they're too overweighted with them. You have to fit the tanks to the purpose, and sometimes to the person, too.
     
    Compressor likes this.
  7. James R

    James R PADI Pro

    # of Dives: I'm a Fish!
    Location: Austin, TX USA
    2,721
    1,134
    1. Why can't you dive with your friends and buddies in doubles? Tons of people do it around here all the time, myself included! You don't have to be on a technical dive to dive them! It's nice to end dive 1 and not have to change tanks out for any subsequent dives. If I'm working a charter and have an insta-buddy, it's a 20 second "here's how you will get air from me should you find yourself out of air" briefing and off we go...no biggie.

    2) What do you mean by "a bit more technical?" Do you know the difference between rec & tec? I hope you aren't planning on doing any technical diving without proper instruction.

    3) You will have double the capacity, and basically double the equipment & tasks to use it safely. I highly suggest finding an instructor/mentor to help you out, at least at first.

    One thing I didn't see, and maybe I missed it, if you end up buying and diving doubles (especially steel) and you have a wing failure at depth what will you do? I hope you have a redundant buoyancy device & plan. I have personally seen two separate instances of this happen.

    Have to agree with TSandM - assemble/disassemble doubles to go from singles and back to doubles etc etc is not a realistic or viable solution.

    I don't even use the same regs for my doubles and single tank diving. It's much easier, and better in my opinion, to have doubles regs, deco regs, and recreational regs and not have to constantly mess with moving stuff around to make a dive. Sucks to see someone come all the way out for a charter only to realize he forgot to move his SPG from his doubles reg to his recreational reg and not be able to dive.
     
  8. Gilldiver

    Gilldiver Contributor

    # of Dives: 500 - 999
    Location: Northeast US
    1,770
    139
    First, I am not DIR, but I do understand some/most of the DIR philosophies. I would consider these points:
    1 – If you are doing Scientific Diving for a University or Gov/Semi-Governmental organization like NOAA or NURC you will be diving under a Scientific Diving program and will need to conform to that programs standards which may not be DIR. Make sure that you check with your Diving Safety Officer on any tanks/tank configuration prior to purchase.
    2- Much Archeological diving involves staying in one place and taking notes & measurements, doing counts, or making drawings. Trim may not be a major consideration as you will in all likelihood dump your BC in order to get heavy and stay in one place laying on the bottom. Don’t be surprised if your entire dive consists of 30+ minutes in one place.
    3- Aluminums can be used as stage bottles if you go further into diving. They can also be bought cheaply on the used market.
    4-Vintage steel 72’s make fine doubles and have a nicely controlled swing and buoyancy characteristic. Doubled up with a modern isolator manifold are DIR compliant but are very cheap. A set of 72’s with bands and manifold can be put together for the cost one newer steel tank, sometimes for a good bit less.
    5- 300 BAR Din manifolds are great if you need tanks with service pressure up to 4,300PSI, for all other tanks, with the exception of 3,500 PSI steels, 230 BAR manifolds will do just fine.
    6- A lot will depend on the temp of water you will be diving in. Cold water up in the Northeast or Northwest will require a dry suit especially if you stay in one place for a half hour and are not making a lot of heat moving the big leg muscles. If you will be working in the Southern waters or other warm water areas, a 3 mil or skin may be all you need. The range of ballast requirements between these two extremes will play a large role in the tank vs. weight calculation.
     

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