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Underwater Navigation

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  1. Underwater Navigation

  2. Contents • Why use a compass ? • Cardinal Points / Compass Bearings. • Divers Compass. • Using the Bezel. • Using Compass Bearings. • Turning/Using Multiple Bearings.

  3. Contents • Reciprocal Bearings. • Other Considerations. • Examples.

  4. Why use a Compass? • To help you get where you want to go ! • Limited field and range of vision => impossible to orient yourself underwater • Safety • Get you to shore • To keep you out of a run/current/deep water • To avoid surfacing in the “Wash”

  5. Cardinal Points / Compass Bearings • North (N) - 0 ° or 360 ° • East (E) - 90 ° • South (S) - 180 ° • West (W) - 270 ° • NE - 45 ° • SW - 225 ° • SSE - 158 ° approx • WNW - 293 ° approx

  6. Rotating Bezel Lubber Line Markings North of Needle Direction of Travel Line Diving Compass

  7. Using Compass Bearings

  8. Using Compass Bearings • Rotate compass until chosen bearing is in the viewing window • E.g. want to go NE => 45° • Keep chosen heading in the window and proceed in direction of lubber line

  9. Using the Bezel

  10. Using the Bezel • Point lubber line in desired direction. • Wait for compass to settle. • Align bezel markings with ‘N’ arrow on compass needle. • Reciprocal will be opposite compass marking. • Do not move bezel during the dive. • Set up bezel/get bearings before submerging.

  11. Reciprocal Bearings • Reciprocal bearing is the opposite bearing of a given bearing i.e. return bearing. • Allows you to return to where you started. • !NB you must allow for drift & “Kick”. • To calculate a reciprocal bearing: • Add 180 to outward bearing • If the result is >360, then subtract 360

  12. Reciprocal Bearings • Out on 90º(E) • 90 + 180 = 270 • =>return on 270º(W) Out on 90º N Back on 270º

  13. Out on 225º N Back on 45º Reciprocal Bearings • Out on 225º(SW) • 225 + 180 =405 (NB > 360) • 405 - 360 = 45 • =>return on 45º(NE)

  14. Turning/Using Multiple Bearings • Use rule of thumb: • “left is less” • To make a 90º left turn. • => subtract 90 - “left is less” • To make a 90º right turn. • => add 90 - “right is more”

  15. Turning/Using Multiple Bearings • Example 1 (turn left) • going west, turn left will point you south • 270º (W) - 90 = 180º (S) • Example 2 (turn right) • going north, turn right will point you east • 0º (N) + 90 = 90º (E)

  16. Considerations • Trust the compass - It doesn’t lie ! • Hold compass level. • Plan the dive: winds, currents, deep water • Local features e.g. sand ripples, buoy & line • Remember your bearings! • Night use - Luminous markings. • Magnetic interference.

  17. Examples • Shore Diving. • Diving an Island. • Wall Diving. • Diving a Sea Stack.

  18. Shore Dive

  19. Shore Dive

  20. Island

  21. Wall Dive

  22. Sea Stack

  23. Summary • Why, how and when to use a compass. • Cardinal Points / Compass Bearings. • Multiple bearings. • Reciprocal bearings. • Considerations. • Examples.

  24. Questions?