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Compass Navigation run on obtuse triangle

Discussion in 'Advanced Scuba' started by DiveLvr, Apr 10, 2015.

  1. DiveLvr

    DiveLvr Contributor

    # of Dives: 500 - 999
    Location: Mobile AL
    128
    23
    I am looking at running a underwater compass course involving an obtuse angle. I know all the particulars (side lengths, angles) but I am trying to figure out how I would execute this course without all the knowns, a real live situation.

    Assuming I can accurately measure my swim distances and there isn't any current:

    Starting at a point, say a boat anchor, swimming due North on a 0 deg heading for 57 ft.
    I vector left and swim 30 ft on a 315 deg heading.

    Beside surfacing and looking to see where the start point at the beach or boat is, how would I determine what my return vector is to get back to my start point?

    Doug
     
  2. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    11,180
    17,456
    Off the top of my head, I'd head back about 85' on 165 heading, and look for the boat. I'd be closer to the boat when I surfaced than out at the other end of the dive. All that being said, my dives are usually not so precise that I need to bring a set of trig tables with me.


    Bob
    ---------------------
    I may be old, but I'm not dead yet

    ---------- Post added April 11th, 2015 at 08:38 AM ----------

    If my trig skills haven't completely gone, by my calculations it is 78' on a heading of 170. Of course by the time I figured that out I would have been OOA, and have to come up at the wrong end of my dive anyway.

    If you are that particular, look around for a PADI Nav-Finder, it is a circular slide rule that lets you track headings and distance and will calculate a heading and distance to your start point. Mine is for display purposes only, but it does work if used properly.



    Bob
    ----------------------
    My hero is "Wrong Way" Corrigan.
     
    Last edited: Apr 11, 2015
    oldschoolto, DiveLvr and Jax like this.
  3. Hatul

    Hatul Solo Diver

    # of Dives: 500 - 999
    Location: Tustin, California, United States
    4,237
    651
    Good luck measuring distances under water and working this out there. Be sure to take your trig tables and pencil and paper.
     
  4. g1138

    g1138 Marine Scientist

    # of Dives: 500 - 999
    Location: Charleston, SC
    3,068
    809
    I'd head back somewhere between 180 & 135 with some Kentucky windage.
    Note some landmarks off the left peripheral on my way out on the 0 heading and try to spot them on my way in.

    Navigation is an art form. Some art looks like sh-t.

    Similar swim pace and use time as a measure of distance. Assuming no current.

    Realistically, unless you're trying to hit a knife stuck in the sand at your starting point, getting within 100ft of the starting point is pretty stellar by me.
     
  5. Jax

    Jax Deplorable American ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: AZ TX
    26,682
    8,880
  6. waterpirate

    waterpirate Solo Diver

    # of Dives:
    Location: Delmarva peninsula
    1,393
    418
    Can you execute this drill walking in unknown terrain? Basic orienteering. I would practice on land before a "wet" run.
    YMMV
    Eric
     
  7. Charles2

    Charles2 Contributor

    # of Dives: I just don't log dives
    Location: Montgomery, Texas
    528
    322
    I get 81 ft at 165°. YMMV Too bad that road flares don't work underwater.
     
  8. Jax

    Jax Deplorable American ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: AZ TX
    26,682
    8,880
    Blinking lights hung on the anchor line do work underwater.
     
    AfterDark and Charles2 like this.
  9. Necklinsberg

    Necklinsberg Divemaster Candidate

    # of Dives: 500 - 999
    Location: Lancaster County, PA
    94
    15
    Check out 'navfinders' as used in PADI's underwater navigation specialty course. Use that tool to track your kick-cycles and directions.
     
  10. radtype

    radtype PADI Pro

    # of Dives: 200 - 499
    Location: Kentucky
    92
    26
    I'd cheat and go 30 feet on a heading 135 degrees and south for 57 feet. If you have decent visibility, head south for about 80 feet.
     

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