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Average Depth Diving?

Discussion in 'Basic Scuba Discussions' started by recdiver, Apr 11, 2005.

  1. recdiver

    recdiver Angel Fish

    As a back-up to using a computer and/or using tables while planning a dive does considering average depth work as well?

    For example if while diving I figure that my average depth has been around 60 fsw and I've been down for less than 60 minutes then I should know that I haven't exceeded the NDL for the dive as a whole. Correct?

    I could have exceeded 40 minutes at 70 fsw but if I balanced out the dive at 20 fsw for 19 minutes then for the dive as a whole I've met any obligations and could do a free ascent?

    I'm just asking if using average depths on the fly while diving is a useful way to double check the computer or to dive without a computer just using a timer and depth gauge plus having knowledge of the tables in your head.
  2. Travis*N

    Travis*N Angel Fish


    I'm not sure, but my gut feeling would be that its not ok. I think you saturate yourself exponetially quicker (with nitrogen) the deeper you go, so when you start guesstimating, it could lead to trouble, especially on deeper dives like around 100 fsw
  3. lamont

    lamont Orca Staff Member

    # of Dives:
    Location: Seattle, WA
    spend 45 mins at 30 fsw and then 15 mins at 130 fsw and if don't have this wrong, it averages out to 60 mins at 55 fsw...
  4. To_Narced

    To_Narced Angel Fish


    Im thinking this isnt a great idea. First of all if you dive at 70ft for 40 minutes you are at your NDL max. However if you already spent time at a shallower depth, then hit 70 ft where you spent 40 minutes, you would have a decompression obligation and unless you know your exact depth and times for the entire dive and can calculate your deco obligations on the fly you better have your computer. Personally i dive with my computer in gauge mode because I always plan the dive and dive the plan. In my opinion this makes you a more disciplined diver. However if im at a new site and just want to check it all out i will use my computer so that I dont have to stay on a strict profile.
  5. ScubaDadMiami

    ScubaDadMiami CCR Instructor

    A lot of people I know use the average depth method. However, they do so within reason and not using far-fetched methods.

    For example, you are diving a wreck. The top of it is at 100 and the bottom is at 130. You enter, and you spend almost all time at 120. You see something interesting on the floor, and you briefly descend to check it out. It now turns out that you hit the 126 mark for about 30 seconds. In that case, many would just go with the 120 max depth.

    If there is a large spread between the top and bottom of your dive, I wouldn't use this method.
  6. TimMorrison

    TimMorrison Guest

    So in your plan here do you take the deepest point dived, or are you trying to say the average between 100ft and 50ft is 75ft? If you do this will likley end up in a deco chamber soon. The biggest issue is that you absorb gasses at different rates depending on the depth. If the rate of absorption and offgassing was the same at all depths (which it is not) then you could use your new method. But until the laws of physics change be prepred to be crippled or dead.

    But hey, if it works out for you I would love to hear about it.
  7. miketsp

    miketsp Solo Diver

    # of Dives: 500 - 999
    Location: São Paulo, Brazil
    If you can work out a way to average half a dozen exponential functions in your head, one for each compartment, I'd say you're a genius.
  8. boomx5

    boomx5 DIR Practitioner

    We average our depth all the time, but we know how to do it. Becareful what you say here because there are people who have a lot more experience than you and who are doing successfully the things that you say will get someone bent.
  9. Walter

    Walter Instructor, Scuba

    The concept violates the basic rules of table use. The deepest point of the dive is the depth of the dive. The dive is treated as if the entire time of the dive was spent at the deepest depth. Your average depth method is a good way to get bent.
  10. H2Andy

    H2Andy Blue Whale

    # of Dives: 200 - 499
    Location: NE Florida
    average depth is an advanced technique, and it is done succesfully by advanced
    divers all the time, who don't get bent.

    you just need to know how to do it right.

    (i am neither (a) an advanced diver; nor (b) know how to do it right.... i'm just saying)

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