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New divers with question on calculating min sufrace intervals!

Discussion in 'Basic Scuba Discussions' started by ricster80, Nov 10, 2009.

  1. ricster80

    ricster80 Angel Fish

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    Hi All,

    My Girlfriend and I are currently nose deep in learning to dive and have managed to get stuck on using the RDP card to calculate minimum surface intervals.

    In particular there is one example we can't understand; it's question 7 on the chapter 5 knoledge review in the open water diver manual. The example results in a pre second dive PG of M and a post dive PG of P. These two letters don't match up in table 3.

    Should you assume that this means the min surface interval between dives is zero? Surley that can't be right?

    Can anyone help?

    Thanks,

    Ric n Ros. :idk:
     
  2. jasoninbtr

    jasoninbtr Angel Fish

    # of Dives: 0 - 24
    Location: Baton Rouge, LA
    54
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    Without knowing the entire question it is hard to tell. I remember one "trick" question we had in our OW class that resulted in a SI less than 10 minutes. In this case the second dive is considered a continuation of the first.

    HTH,

    Jason
     
  3. RikRaeder

    RikRaeder Photographer

    # of Dives: 200 - 499
    Location: Oakland, Ca
    744
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    I got in trouble on that translating 1:20 as 120 minutes rather than on HOUR and twenty minutes.
    Not those numbers, exactly, but that type of error. Double check your numbers. Maybe not the problem, but that was a mistake I made...good luck!
     
  4. ricster80

    ricster80 Angel Fish

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    Ok guys,

    Here's the full question:

    'What is the minumum surface interval required between the following dives: first dive to 20m/70ft for 29 mins then to 14m/50ft for 39mins?'

    The result is pressure group M at the end of the first dive and you must be at at lease group P before the second dive begins. These two letters don't match up on table 3 so no min surface interval can be determined.

    Does that mean that you could theoretically dive to 20m for half an hour, surface, then dive straight back down to 14m for 40 mins without taking a break in between to allow Nitrogen to disperse?

    Doesn't seem right to me; is there a minimum surface interval between all dives that should be observed whatever depth you go to (above 40m obviously)?

    The problem is not isolated to these particular dives as above. I just can't get my head around what happens if your two PG's don't match up...

    Thanks for your help.

    Ric.
     
  5. jasoninbtr

    jasoninbtr Angel Fish

    # of Dives: 0 - 24
    Location: Baton Rouge, LA
    54
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    What tables are you using?

    According to NAUI tables you would be at group F after the first dive. In order to do a 50/39 you would need a min 0:46 to put you at a new group of E.

    Jason
     
  6. ricster80

    ricster80 Angel Fish

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    I guess my table must be different.

    I'm using the RDP by 'Diving Science & Technology Corp' which is distributed by PADI in their OW Crew Pack. It has Product No. 66055 Ver 1.2 (02/03) stamped on it.
     
  7. jasoninbtr

    jasoninbtr Angel Fish

    # of Dives: 0 - 24
    Location: Baton Rouge, LA
    54
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    Found it:

    http://www.scubadiverinfo.com/images/dive_tables_PADI_front.jpg

    It looks like according to the PADI tables no SI is required for this repetitive dive. Not sure how you are supposed to be "at least group P" unless you stay in the water for 33 min on the first dive.

    I would ask your instructor for clarification.

    Jason
     
  8. RikRaeder

    RikRaeder Photographer

    # of Dives: 200 - 499
    Location: Oakland, Ca
    744
    13
    0
    I see what you mean. Group P or lower allows the dive, and you finish at M, so....
    no SI is indicated. I always try to take a one hour SI, at least. I just browsed and didn't see a recommended mandatory SI in PADI OW. It sounds like you're working the table correctly, so check with your instructor, or I'm sure a certified instructor will be along presently to answer about agency recommendations.
     
  9. 300bar

    300bar ScubaBoard Supporter ScubaBoard Supporter

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    ** MOD POST: **

    Moved to basicScuba
     
  10. rwgodfrey

    rwgodfrey Solo Diver

    # of Dives: 0 - 24
    Location: Boiling Springs, SC
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    ??

    70ft for 29 mins puts you in "N" according to the above linked table.

    50ft for 39 mins requires "M" according to the same table.

    "M" intersects "N" with a minimum surface interval of 4 minutes.
     

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