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Off the chart on the dive tables

Discussion in 'Basic Scuba' started by Alligood, Aug 9, 2017.

  1. gfaith

    gfaith Solo Diver

    # of Dives: 100 - 199
    Location: Desert SE of NM
    444
    169
  2. blac86

    blac86 Banned

    # of Dives: 500 - 999
    Location: Sarasota, Florida
    241
    90
    Ok, lets play good news bad news:
    Bad news - your dives are wildly off tables
    Good news - I ran them through my decompression planning software (using zhlc16 70/90)
    Good news - your Nitrox dive was well within limits.
    Bad news - your second dive already had you with a non negligible deco obligation.
    Bad News - your third dive called for 30 minutes of decompression, which you did not do and are lucky you did not get hurt.
    Good news - you survived
     
  3. flymolo

    flymolo DIR Practitioner

    401
    177

    Do you have logs? Can you post them?
     
  4. Neilwood

    Neilwood Contributor

    # of Dives: 50 - 99
    Location: Scotland
    2,558
    1,678
    Agreed - without the logs, we know nothing of how the dive was carried out so impossible to know how near to NDL the OP was. Tables work on absolute worst case scenario - descend to max depth immediately, stay there for the whole length of the dive and ascend to the surface (at a safe rate). As such, when faced with real world multi level dives tables become really restrictive.

    If it was a bounce to 50ft, then the nitrogen uptake would indeed be minimal. I can only assume (as you did) that the computer was set correctly in the nitrox course for the mix. If that was done and the OP followed the computer and stayed within NDL on each dive, I don't see it being unsafe as such.

    Personally I would prefer to see a lot longer surface intervals (30mins really is cutting things very fine).

    To the OP, if you can post logs of the dives, it would help a lot in understanding the profiles involved.
     
    KeithG likes this.
  5. Neilwood

    Neilwood Contributor

    # of Dives: 50 - 99
    Location: Scotland
    2,558
    1,678
    Not sure how you can know these as facts unless you know the profiles. Ran on tables with no allowance for multilevel diving, they may be beyond deco planning software or table NDLs but going by a computer they may have been within NDL by a long way.
     
  6. blac86

    blac86 Banned

    # of Dives: 500 - 999
    Location: Sarasota, Florida
    241
    90
    I mean I can only work with the data that's given, and using that data constructed a four dive profile. If the data is bad of course the result is bad.
     
  7. Neilwood

    Neilwood Contributor

    # of Dives: 50 - 99
    Location: Scotland
    2,558
    1,678
    I know what you mean and do not doubt the good intention but, given the forum we are in, it is better to give try to give a more balanced point of view than to jump to conclusions. Without logs or an idea of the profile, we are really in the dark.

    I would agree though that those dives might not constitute the best series of dives (SI is way too short for my liking with any profile of dive - I try to go for 1hr as a minimum).
     
  8. sea_ledford

    sea_ledford Captain

    # of Dives: 2,500 - 4,999
    Location: Galveston, TX
    691
    508
    I think he gave a perfectly well balanced point of view. The OP was diving tables because he didn't know how to use a brand new computer. The primary issue was a complete lack of planning of the dives. It sounds like this was more of the inst/DM than the OP, and likely the plan was "my boss told me I had to get all three of these dives done today, and I have nitrox class to teach this afternoon."

    I don't think there was any jumping to conclusions, the dive times, depth and SI were provided. Sure we are in the dark about the actual profile, but that is true about every table dive. This is a perfect example of plan your dive and dive your plan not being followed.

    Thanks to the OP for sharing this, I'm not meaning to dig on him at all! These posts are great to have in the Basic Scuba Diving forum. Just because you are diving with a "professional" it doesn't mean that they have your best interest in mind.

    -Chris
     
  9. doctormike

    doctormike Medical Moderator Staff Member

    # of Dives: 1,000 - 2,499
    Location: New York City
    6,875
    6,990
    I think that's sort of the point - if you don't have a logged profile, if you are doing table dives, you have to assume square profiles. All the people who come here and say that they don't need computers, and that they just dive tables, need to do calculations as if their maximum depth was their depth all through their bottom time (or that dive segment, if they are doing multi level). In fact, the main advantage of a dive computer is that it gives you credit for time above maximum depth.

    If those were his dives, then he blew off deco. Now, he might have been physiologically safe because he really didn't spend much time at maximum depth, but there is no way of knowing that. From a dive planning and post dive analysis point of view, he blew off a lot of deco (I ran this through multi-deco as well, see below). That should be the take home message, and there is no need to sugar coat that just because we are in a green zone.


    DIVE PLAN #1
    Surface interval = 5 day 0 hr 0 min.
    Elevation = 0ft
    Conservatism = GF 30/70

    Dec to 50ft (0) Air 60ft/min descent.
    Level 50ft 29:10 (30) Air 0.53 ppO2, 50ft ead
    Asc to 20ft (31) Air -30ft/min ascent.
    Stop at 20ft 1:00 (32) Air 0.34 ppO2, 20ft ead
    Stop at 10ft 1:00 (33) Air 0.27 ppO2, 10ft ead
    Surface (33) Air -30ft/min ascent.

    DIVE PLAN #2
    Surface interval = 0 day 0 hr 30 min.
    Elevation = 0ft
    Conservatism = GF 30/70

    Dec to 60ft (1) Air 60ft/min descent.
    Level 60ft 29:00 (30) Air 0.59 ppO2, 60ft ead
    Asc to 20ft (31) Air -30ft/min ascent.
    Stop at 20ft 0:40 (32) Air 0.34 ppO2, 20ft ead
    Stop at 10ft 3:00 (35) Air 0.27 ppO2, 10ft ead
    Surface (35) Air -30ft/min ascent.


    DIVE PLAN #3
    Surface interval = 0 day 0 hr 30 min.
    Elevation = 0ft
    Conservatism = GF 30/70

    Dec to 90ft (1) Air 60ft/min descent.
    Level 90ft 28:30 (30) Air 0.78 ppO2, 90ft ead
    Asc to 40ft (31) Air -30ft/min ascent.
    Stop at 40ft 0:20 (32) Air 0.46 ppO2, 40ft ead
    Stop at 30ft 3:00 (35) Air 0.40 ppO2, 30ft ead
    Stop at 20ft 12:00 (47) Air 0.34 ppO2, 20ft ead
    Stop at 10ft 37:00 (84) Air 0.27 ppO2, 10ft ead
    Surface (84) Air -30ft/min ascent.

    DIVE PLAN #4
    Surface interval = 0 day 2 hr 30 min.
    Elevation = 0ft
    Conservatism = GF 30/70

    Dec to 90ft (1) Nitrox 32 60ft/min descent.
    Level 90ft 28:30 (30) Nitrox 32 1.19 ppO2, 73ft ead
    Asc to 30ft (32) Nitrox 32 -30ft/min ascent.
    Stop at 30ft 1:00 (33) Nitrox 32 0.61 ppO2, 21ft ead
    Stop at 20ft 1:00 (34) Nitrox 32 0.51 ppO2, 13ft ead
    Stop at 10ft 4:00 (38) Nitrox 32 0.42 ppO2, 4ft ead
    Surface (38) Nitrox 32 -30ft/min ascent.
     
    sea_ledford likes this.
  10. KeithG

    KeithG Guest

    I do not think the OP was diving tables. They are asking how to back track their dives to the tables. And the the posted profiles obviously exceed normal tables (and hence a pile of outraged peeps have their panty's in a knot).

    As a computer diver, the profiles look fine to me - if I assume a conservative multi level dive profile. These were training dives after all. Has everyone assumed the instructor is a moron?

    I believe the OP was naively doing "trust me" training dives while wearing a unfamiliar computer thingy and is now trying desperately to get some feedback on why they are not badly bent after radically exceeding their knowledge of the tables.

    I could be wrong. The only way to discover the truth and provide sane feedback is for the OP to provide some clarification regarding their interpretation of the dives. Hopefully we have not scared the OP away.

    If we have, I am happy to provide an alternate non square profile interpretation of the dives that makes the OPs day totally safe.
     
    Neilwood likes this.

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