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1st time past 100ft for a big guy, Advice needed!

Discussion in 'Basic Scuba' started by toshman001, Sep 30, 2010.

  1. toshman001

    toshman001 New

    # of Dives: 0 - 24
    Location: Hoboken, NJ
    4
    0
    Background: I'm going to Roatan in December:D and the first dive each day is to 90-110ft. My dive buddy is a 5'3" 120lbs female AOW (15 dives), I am 6'7" 230 lbs male AOW (25 dives up to 75ft). Her SAC rate is about half of mine (.45 vs .9) and the dive operator does not have any tanks bigger than Al80s. I dive a Deep Sea Supply SS BP/W and have a 19cf bailout slung for the deeper stuff.

    My Question: Is this smart for me to go past 100 (probably on EA32) on a single Al80 + 19cf bailout (not part of my gas plan) at my size and experience level, it just doesn't seem like enough gas to me? I have considered getting training on independent twins for safety and to even up dive times, but this seems like a huge hassle and too much to worry about for my first major dive trip...Yet I don't want to skip the morning dives.

    Thank you everyone, just trying to dive smart...
     
  2. rongoodman

    rongoodman ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Albany, NY
    5,395
    2,112
    You should take at look at this article regarding Rock Bottom. The important thing to keep in mind is how much gas you will need to get yourself and your buddy safely to the surface, from whatever depth you're at. That being said, if you're uncomfortable about the depth of the morning dives, sleep late--they'll still be there when you have some more experience.
     
  3. herbdb

    herbdb Contributor Rest in Peace

    # of Dives: 200 - 499
    Location: Allentown, PA
    1,241
    284
    I too am going to Roatan for the first time in Dec. My previous deep diving experience is in Cozumel. The first dive of the day there would be deep, but really just for a short time. After an initial descent to 80-100 feet, the DM would lead the group to an area in the 40-60 foot range. This multilevel dive profile is not uncomfortable and no one complained about their computer giving them a NDT warnings. I am a real air hog and most of my deep dives were in the 30-40 minute range.

    I am expecting something similar in Roatan. It they are just deep, they will be very short for me.
     
  4. dumpsterDiver

    dumpsterDiver Banned

    # of Dives: 2,500 - 4,999
    Location:
    9,003
    4,674
    You should be able to do about 15 minutes, give or take. If you can get your SAC down a little maybe more.

    I think if you have the 19 cu-ft filled and you leave the bottom with 1,000 psi, you should have no problems with gas supply. Other people may give you a ton of calcualtions to do (which you should learn yourself) but 15 minutes and a little less than 1000 psi will be in the ballpark, based on my estimates in my head.

    depth 99 feet
    pressure 4 atmosphere
    SAC = 1 cu-ft /min
    breathing rate at depth 4 * 1 = 4 cu-ft per minute
    15 minutes times 4 is 60 cu-ft of gas used.
    Which leaves 20 out of 80 cu-ft which is 25% of your air.
    25% of 3000 psi is 750 psi.
    In 15 minutes you will be around 750 psi.

    Do your own calcs and see if 750 psi will get you to the surface.
     
  5. sam1

    sam1 Contributor

    # of Dives: 500 - 999
    Location: Jupiter, FL and Cape Cod, MA
    138
    9
    FWIW, I was in Roatan 1.5 years ago and did 16 dives, below are my max and average depths for each of the dives.

    Max Ave
    67 29
    54 36
    58 29
    68 43
    57 35
    75 44
    62 39
    47 33
    108 38
    44 35
    60 28
    96 41
    78 37
    68 43
    95 49
    52 30

    So, as was said above, the time at (max) depth may be short, and the average depth (for me) averaged about 55% of the max depth.
     
  6. Michael Kazma

    Michael Kazma Contributor

    # of Dives:
    Location: Carlsbad, California
    332
    12
    Im sorry but you probably wont like my opinion but I do not think it is a good idea for anyone to dive below 100 with just an al.80 whatever their SAC is.
     
  7. Kilili

    Kilili Contributor

    # of Dives:
    Location: SF Bay Area
    623
    97
    Approaching it somewhat differently, I suggest you look into doing meditation and yoga. Also controlled breathing exercises.
    Though I'm not as tall, I weigh more, and when I started I was always the first person up from a dive, by a lot. Now, I'm one of the last. My air consumption has been reduced by about 50%.
     
  8. dumpsterDiver

    dumpsterDiver Banned

    # of Dives: 2,500 - 4,999
    Location:
    9,003
    4,674
    You didn't read the part about him bringing a 19 cu-ft pony bottle as a bail out? He never asked if he should dive with just an 80 cu-ft tank...:shakehead::shakehead:
     
  9. aquaregia

    aquaregia NAUI Instructor

    # of Dives: 500 - 999
    Location: Santa Cruz, CA
    1,969
    191
    I did some 100' dives with an instabuddy who was cool with starting our ascent at 1500psi (AL80, no pony). They ended up being shortish dives and I was back on the boat with 1100psi, but it was about aggressive as I wanted to be with a guy I'd never met before.
     
  10. OneRestlessNative

    OneRestlessNative Contributor

    # of Dives: 100 - 199
    Location: East Coast Central Florida
    269
    1
    Just because the dive site is a 100ft doesn't mean you have to visit the bottom or stay there. Sometimes its nice to get in close and see all the little stuff, sometimes its cool to hoover a little higher off the reef and get a bigger picture of whats going on. Maybe drop in to 100 get a feel for it then chill in the 80ft zone for the remainder of the dive if you and buddy feel at ease with the situation. I'd probably set my limit to 100 and only briefly, monitor gas frequently. Remember you need to plan enough reserve to get 2 divers to the surface also. The pony "should" be plenty for one diver in a "moderate" frame of mind.

    NDL on 32% @100 is 29min
    NDL on 32% @80ft is 43min
    Anything past 110 puts you into the 1.4 ppO2 zone (PADI)
    That's 14 more minutes of bottom time if you can make the gas last.

    If I have the choice (conditions permitting) I usually opt for the longer/shallower dive versus the deeper/shorter as described above. It also helps the surface intervals and subsequent dive times too.:D
     

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