Hello and welcome to our community! Is this your first visit?
Register
Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 26
  1. #11
    Established TDF Member
    Join Date
    Jul 2017
    Location
    South East
    Posts
    583
    Likes (Given)
    343
    Likes (Received)
    352
    Quote Originally Posted by Wardy_uk View Post
    this question has puzzled me for a while... I'd assumed that because of the phrase "use the tables" - you needed to use the PP table for the ppO2 - not calculate it. As you have to round up (well, technically down) to 42m, that gives a ppO2 of 1.4

    28 mins @ 1.4 gives CNS after dive 1 of 18.76, down to 2.345 after the SI... bl00dy annoying, as that way doesn't match up with any answer!

    the joys of BSAC exams...
    You have to add the CNS load for the stops on Dive 1 too... I missed that bit when I first tried to work it out on paper. While you can work out the figures mathematically the question specifies using the tables, so yeah, have to round up to that 1.4 ppo2 @ 42m

    This is the full working out with the correct numbers in case it helps someone in the future:
    Dive 1: 40m, 25 minute bottom time, 3 minutes ascent, 1min@9m, 6min@6m, on Nitrox27
    Surface interval: 6 hours
    Dive 2: 21m, 40 minutes, no stops, Nitrox36

    I need to calculate the CNS% at the end of the 2nd dive so:
    Dive 1: 28mins@40m + 1min@9m + 6mins@6m
    28mins@ 1.4ppo2 + 1min@ 0.51ppo2 + 6mins@ 0.43ppo2
    28mins@ 0.67CNS + 1min@ 0.16CNS + 6mins@ 0.16CNS
    18.76 + 0.16 + 0.96
    19.88

    Reduce CNS by 50% every 2 hours:
    CNS+2 hours | CNS+4 hours | CNS+6 hours
    9.94 |4.97 | 2.485

    Dive 2: 40mins@21m
    40mins@ 1.12ppo2
    40mins@ 0.44CNS
    17.6

    So at the end of dive2 the %CNS is 17.6+2.485 = 20.085
    Which rounded to 1dp matches the BSAC answer of 20.1

    If anyone has any easy to understand further reading about CNS% load and dissipation I'm open to reading it. I'm not chained to the BSAC doctrine, if there is new or further discoveries that contradict this i'm all for taking it onboard. I'll probably stick with he more conservative method, but either way it would be good to know.
    Last edited by ManualOverride; 10-08-2018 at 09:32 AM.

  2. #12
    Established TDF Member Wardy_uk's Avatar
    Join Date
    Jan 2016
    Location
    NW Leicestershire
    Posts
    561
    Likes (Given)
    524
    Likes (Received)
    94
    I was only doing the first step at this point - but wasnt including the stops in the calc.. theres no CNS loading of consequence there... by 9 m your ppO2 is below the 0.65 on the table

    Gah!!!

  3. #13
    Established TDF Member Wardy_uk's Avatar
    Join Date
    Jan 2016
    Location
    NW Leicestershire
    Posts
    561
    Likes (Given)
    524
    Likes (Received)
    94
    Quote Originally Posted by ManualOverride View Post
    You have to add the CNS load for the stops on Dive 1 too... I missed that bit when I first tried to work it out on paper. While you can work out the figures mathematically the question specifies using the tables, so yeah, have to round up to that 1.4 ppo2 @ 42m

    This is the full working out with the correct numbers in case it helps someone in the future:
    Dive 1: 40m, 25 minute bottom time, 3 minutes ascent, 1min@9m, 6min@6m, on Nitrox27
    Surface interval: 6 hours
    Dive 2: 21m, 40 minutes, no stops, Nitrox36

    I need to calculate the CNS% at the end of the 2nd dive so:
    Dive 1: 28mins@40m + 1min@9m + 6mins@6m
    28mins@ 1.4ppo2 + 1min@ 0.51ppo2 + 6mins@ 0.43ppo2
    28mins@ 0.67CNS + 1min@ 0.16CNS + 6mins@ 0.16CNS
    18.76 + 0.16 + 0.96
    19.88

    Reduce CNS by 50% every 2 hours:
    CNS+2 hours | CNS+4 hours | CNS+6 hours
    9.94 |4.97 | 2.485

    Dive 2: 40mins@21m
    40mins@ 1.12ppo2
    40mins@ 0.44CNS
    17.6

    So at the end of dive2 the %CNS is 17.6+2.485 = 20.085
    Which rounded to 1dp matches the BSAC answer of 20.1

    If anyone has any easy to understand further reading about CNS% load and dissipation I'm open to reading it. I'm not chained to the BSAC doctrine, if there is new or further discoveries that contradict this i'm all for taking it onboard. I'll probably stick with he more conservative method, but either way it would be good to know.
    and why isnt the 1 min to surface at the end of the dive included in the calcs?

    I say again. Bl00dy BSAC!
    Last edited by Wardy_uk; 10-08-2018 at 09:39 AM.

  4. #14
    Established TDF Member
    Join Date
    Jul 2017
    Location
    South East
    Posts
    583
    Likes (Given)
    343
    Likes (Received)
    352
    Quote Originally Posted by Wardy_uk View Post
    I was only doing the first step at this point - but wasnt including the stops in the calc.. theres no CNS loading of consequence there... by 9 m your ppO2 is below the 0.65 on the table

    Gah!!!
    Ah but of course without them it all adds up to 19.9 which is close to one of the other possible answers on the exam.
    Gah! indeed

  5. #15
    Established TDF Member
    Join Date
    Jul 2017
    Location
    South East
    Posts
    583
    Likes (Given)
    343
    Likes (Received)
    352
    Quote Originally Posted by Wardy_uk View Post
    and why isnt the 1 min to surface at the end of the dive included in the calcs?

    I say again. Bl00dy BSAC!
    Ha! maybe it is! That would make the total 20.105

  6. #16
    Established TDF Member Wardy_uk's Avatar
    Join Date
    Jan 2016
    Location
    NW Leicestershire
    Posts
    561
    Likes (Given)
    524
    Likes (Received)
    94
    Quote Originally Posted by ManualOverride View Post
    Ah but of course without them it all adds up to 19.9 which is close to one of the other possible answers on the exam.
    Gah! indeed
    yeah - thats the answer I gave

  7. #17
    TDF Member
    Join Date
    Oct 2015
    Location
    United Kingdom
    Posts
    409
    Likes (Given)
    16
    Likes (Received)
    190
    Where are all the new instructors going to come from to teach this over complicated bollocks?

  8. #18
    Established TDF Member Energy58's Avatar
    Join Date
    Jun 2014
    Location
    Oman
    Posts
    1,538
    Likes (Given)
    248
    Likes (Received)
    395
    Quote Originally Posted by NWdiver View Post
    Where are all the new instructors going to come from to teach this over complicated bollocks?
    It's not over complicated bollox its holy writ handed down in tablets of stone...

    I tell my students "this is how you do the exam questions" and go through the various forms over and over again. I don't think I have ever had anyone fail on the tables questions but it has the square root of bog-all to do with any actual diving. I did a dive today during which my computer - set to its least conservative setting - threw 25 minutes of deco at me; the same dive on the 88s has a grand total of 7 minutes!

  9. #19
    Established TDF Member
    Join Date
    Jul 2017
    Location
    South East
    Posts
    583
    Likes (Given)
    343
    Likes (Received)
    352
    Quote Originally Posted by Energy58 View Post
    It's not over complicated bollox its holy writ handed down in tablets of stone...
    Tablets of stone? My Holy writs (tables) are on 12 sheets of wetnote with a very chincy plastic binder. (think if an enterprising 8-year-old made them during his juice break with spare school supplies)
    Plus they are 20+3 P&P, and you have to buy 3 of them! (88, Nitrox, and Ox-Stop)
    Still I suppose 69 is cheap in comparison to doing just about anything with PADI

    Edit: Slight correction... Ox-Stop is 32 so 81 for the lot... or 109 for non BSAC.
    Last edited by ManualOverride; 10-08-2018 at 10:20 PM.

  10. #20
    Last of the Mohicans gobfish1's Avatar
    Join Date
    Jan 2013
    Location
    the grassy knoll
    Posts
    3,423
    Likes (Given)
    3915
    Likes (Received)
    2159
    No comment
    None diver as of 2018.


 
Page 2 of 3 FirstFirst 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •