USCG Exam PracticeEstimated position from current set & drift
A vessel's DR position at 1200 is determined after steaming C 045 T, S 10 kts for two hours from a 1000 fix. The navigator estimates a current setting 090 T at 2 kts. How is the estimated position (EP) constructed from the 1200 DR position?
- ✓ Apply the current vector (set 090 T, 4 nm for two hours) from the 1200 DR position; the end of that vector is the EPCorrect
- B. Apply the current vector (set 090 T, 2 nm for one hour) from the 1000 fix; the end of that vector is the EP
- C. Average the DR position and the fix to obtain the EP
- D. Plot the EP halfway between the 1000 fix and the 1200 DR position along the course line
Why A is correct
Bowditch Ch. 8 §803 directs the navigator to lay off the current's set and drift for the elapsed time from the DR position. Two hours at 2 kts drift equals 4 nm in the direction of set (090 T). The end of that vector, plotted as a dot inside a square, is the EP.
Cited:Bowditch Ch. 8 §803