USCG Exam PracticeRunning fix from a single object
You are approaching a rocky shoal and have only one charted lighthouse visible. You take a bearing of 035°T on the lighthouse at 1430 while on course 090°T at 8 knots. At 1445 the bearing to the same lighthouse is 355°T. After advancing the 1430 LOP by 2.0 nautical miles along the DR track and plotting the running fix, you find the fix places your vessel inside a charted danger circle. Which statement BEST describes the limitation that may have caused this discrepancy?
- A. The running fix is more accurate than a simultaneous fix because two bearings were used
- ✓ The running fix assumes exact course and speed were maintained, and any deviation between observations introduces positional errorCorrect
- C. The advanced LOP should have been corrected for set and drift before intersection with the second bearing
- D. The cocked hat formed by the two LOPs should have been resolved by taking its corner nearest the danger
Why B is correct
Bowditch Ch. 7 §708 explicitly states the running fix is less reliable than a simultaneous two-object fix because it assumes course and speed were held exactly between observations. Option C describes the EP procedure (Bowditch Ch. 8 §803), which applies to DR correction, not to advancing an LOP for a running fix. Option D applies to a three-bearing fix cocked hat (Bowditch Ch. 7 §705), not a running fix from a single object.