USCG Exam PracticeRunning fix from a single object
A vessel is transiting a channel on course 000°T at 6 knots. Only one charted object is visible. The navigator takes a relative bearing of 045° on the object at 1100, then a relative bearing of 090° on the same object at 1118. Using the doubling-the-angle technique, what is the vessel's distance off the object at 1118, and what additional navigational tool should be used to ensure the vessel remains clear of a charted hazard lying to starboard of the track between fixes?
- ✓ Distance off is 1.8 nm at 1118; use a danger bearing labelled NLT on the charted object to keep the vessel in safe waterCorrect
- B. Distance off is 3.6 nm at 1118; use a three-bearing fix cocked hat to resolve the vessel's position
- C. Distance off is 1.8 nm at 1118; advance the DR position by the current set and drift to obtain an estimated position
- D. Distance off is 0.9 nm at 1118; use a danger bearing labelled NMT on the charted object to keep the vessel in safe water
Why A is correct
By the doubling-the-angle technique (Bowditch Ch. 7 §703), the distance run between the first and second bearings equals the distance off at the second bearing. Elapsed time is 18 minutes; at 6 knots, distance run = (6 × 18) / 60 = 1.8 nm, so distance off at 1118 is 1.8 nm. To remain clear of a hazard to starboard, a danger bearing labelled NLT (not less than) is drawn from the charted object so the vessel stays on the safe side — per Bowditch Ch. 7 §706.