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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
    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?

  2. Bob DBF

    Bob DBF Contributor

    # of Dives: I just don't log dives
    Location: NorCal
    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.

    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.

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

    Hatul Contributor

    # of Dives: 500 - 999
    Location: Tustin, California, United States
    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 Contributor

    # of Dives: 500 - 999
    Location: Charleston, SC
    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
  6. waterpirate

    waterpirate Contributor

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

    Charles2 Contributor

    # of Dives: I just don't log dives
    Location: Montgomery, Texas
    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
    Blinking lights hung on the anchor line do work underwater.
    AfterDark and Charles2 like this.
  9. Necklinsberg

    Necklinsberg Contributor

    # of Dives: 500 - 999
    Location: Lancaster County, PA
    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 Instructor, Scuba

    # of Dives: 200 - 499
    Location: Kentucky
    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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