DOUBLING ANGLE

DOUBLING THE ANGLE ON THE BOW

    Object is to determine how far your vessel is offshore.
  • Relative bearings are measured from the vessel’s bow clockwise; dead ahead = 000°R or 360°R; dead astern = 180°R.
  • Relative bearing can be eyeballed by ADDING the desired bearing (say 45°R) to the vessel’s compass course ( say 105°C) and sight over the vessel’s compass for an object at 150°C.
  • Note the time the object is sighted at the relative bearing.
  • When the same object is sighted at twice the relative bearing (say 90°R) or 195° Compass, note the time.
  • Calculate Speed-Distance-Time problem: (See Speed/Distance/Time page)
    • Speed = boat speed, known (example=12kts)
    • Time = difference between first and second bearings (example: Time1=0900; Time2=0915)
    • Distance: will equal the distance off the object when you arrive at second bearing