USCG Exam PracticeThree-bearing fix and cocked-hat triangle
A vessel is on a steady course and speed. At 1000, the navigator takes a visual bearing of 045°T to a lighthouse and plots the LOP. At 1020, the navigator takes a second bearing of 090°T to the same lighthouse and plots that LOP. The vessel's 1000 LOP is then advanced 20 minutes along the DR track. The resulting position is BEST described as:
- A. A fix, because two LOPs to the same object were used
- ✓ A running fix, less accurate than a fix from simultaneous LOPsCorrect
- C. A dead reckoning position, because only one object was observed
- D. A direct fix, because the bearing change was greater than 30 degrees
Why B is correct
Bowditch Ch. 7 §702 defines a running fix as one obtained when LOPs cannot be taken simultaneously — the earlier LOP is advanced along the DR track. Bowditch Ch. 7 §703 confirms that bearings to a single object with substantial bearing change can produce a running fix. It is inherently less accurate than a simultaneous fix because DR errors accumulate during the interval.