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Deep Diving 108 feet w/ a single AL 80 (Air.) No redundancy.

Discussion in 'Advanced Scuba' started by Boston Breakwater, Oct 16, 2020.

  1. rick00001967

    rick00001967 Tech Instructor

    # of Dives: 500 - 999
    Location: canada
    1,729
    680
    thats ok. i am used to looking foolish. :)
     
    BurhanMuntasser and Storker like this.
  2. Diver-Drex

    Diver-Drex Contributor

    # of Dives: 1,000 - 2,499
    Location: US east coast
    288
    147
    I’ve been diving NJ wrecks since 1984. Redundancy is required, steels and pony bottles or twins are standard. I guess you could argue that we are not doing ‘normal recreational’ dives here.

    I can’t speak to other agencies but PADI does not tell new OW divers they can go to 130fsw.

    From what I’ve seen, you are correct about students being taught using al80s. They are cheap and easy to maintain and for diving wet within rec limits, they are good tanks. They are also what most people are going to find available at dive vacation locations. The Caribbean, Mexico, the Keys, the Red Sea, Fiji.... al80s. So it makes sense to use al80s for OW classes.
     
  3. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
    2,928
    1,578
    I'm kinda getting a kick out of reading all these posts. Why? Well, my first dive set was a 38 cubic foot tank and a Healthways Scuba double hose regulator, with a restrictor orifice reserve. I'm pretty sure I took that unit to greater than 40 feet as a young teen, and no formal training (1959-63). I then switched to a single steel 72 (which held about 65 cubic feet at 2250 psi). That unit probably saw 75-100 foot dives on occasion, but usually in the 25-55 foot region; no SPG, only a Healthways Scuba Star regulator, again with a restrictor orifice reserve. It was commonly thought that getting into decompression difficulty was difficult on a single steel 72, so normally we just surfaced when breathing got difficult (restrictir oriface reserves become noticeable at about 500 psi when diving). We normally did not have deep dives in the Pacific Northwest with shore dives, so most of our dives were in the 35-55 foot range. We did dive some deep, clear lakes, and by that time were looking at the Cross Altitude Diving Tables. We had to do some calculations before the dives for the 4000 foot altitude, and in this scenario we could get into decompression problems on a single steel 72.

    SeaRat
     
    scubadada likes this.
  4. Darnold9999

    Darnold9999 Solo Diver

    # of Dives: 500 - 999
    Location: Victoria BC Canada
    2,564
    790
    Also somewhat amused as my first dive after certification was beyond 110 feet on a steel 72. Was diving with one of the assistant instructors for the course on a university club dive. I say beyond 110 as my depth gauge was a capillary gauge so of iffy accuracy so depth is more from charts of the bottom than the gauge. JValve and no SPG. The memorable part of the dive was seeing a salmon flash by on the blue water ascent. At no time did we consider this dive to be “risky”. Today, I would do the same dive using a steel HP 100 because that is what I have, and I would stay longer than the couple of minutes we stayed back then.
     
    John C. Ratliff likes this.
  5. Dan

    Dan ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: Lake Jackson, Texas
    7,003
    4,549
    Just dove Blue Hole in Belize to 138’ with AL80 on air last week.

    CDA5D39B-C8B7-4EA1-A11D-6A3205FB9902.jpeg 8D45FCA7-A081-4558-8AA5-F58E07CF1A52.png
     
    ChuckP likes this.
  6. Eric Sedletzky

    Eric Sedletzky Contributor

    # of Dives: 500 - 999
    Location: Santa Rosa, CA
    4,419
    4,779
    My first dive after OW (dive number five) was off a charter boat in Monterey and I took an aluminum 80 to 95’ on tables.
    You don’t want to know what I did after that on some of my dives off the North Coast, children might be reading.
    Now according to some you can’t dive with anything less than 32% for anything up to 100’,
    and beyond 100’ you need mix, and you have to do it using a Shearwater.

    Outa here again
     
    keyshunter likes this.
  7. Storker

    Storker ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
    17,017
    13,437
    • What was your proper min gas reserve?
    • At which bottom time did you pass that reserve?
    • How did that bottom time square with your NDL?
    • Did you overstay your proper min gas time, or did you leave the bottom when you reached your proper min gas reserve?
    • If there was a mismatch between your min gas time and your NDL, did you have sufficient reserves and a redundant gas supply in case you had to do deco time?
    Curious minds would like to know.
     
    Wibble and OTF like this.
  8. oly5050user

    oly5050user Dive Travel Professional

    # of Dives: 5,000 - ∞
    Location: Westchester NY
    4,108
    873
    Can do no problem
     
  9. kelemvor

    kelemvor Big Fleshy Monster ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Largo, FL USA
    6,960
    4,058
    I'd prefer nitrox, but 108feet is well within normal recreational range on an al80. Seems odd that you would be so worried about such an innocuous dive to me. Maybe diving just isn't for you?
     
    ChuckP and oly5050user like this.
  10. Dan

    Dan ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: Lake Jackson, Texas
    7,003
    4,549
    It'll take me about 5 minutes to get to 130 ft and 5 minutes NDL bottom time. My SAC would be about 0.5 cfm. So at 5 atmospheres, it would be about 2.5 cfm x 5 minutes = 12.5 cubic feet (cf). Let's triple that volume to account for 5 minutes descending and 5 minutes ascending, 12.5 x 3 = 37.5 cf. So, I would have more than half of air capacity left in the tank when I get back. At that depth, the time to surface is about 10 minutes x 2.5 cfm = 25 cf x 3000 psi / 80 cf = 938 psi. So, when my tank pressure reaches 1500 psi, it's time to get the hell up.

    I never passed the bottom time for the reserve pressure of 1500 psi. I started with 3048 psi in the tank and came back with 1696 psi left in the tank at the surface. It looks like my gas planning estimate is conservative.

    I still have 2 minute NDL when I ascent from 138 feet depth. I carried a 3cf Spare Air too as a back up.
     
    Lostdiver71 and happy-diver like this.

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