USCG Exam PracticeTides and currents — predictions and corrections
A mariner needs to make good a track of 090°T through a tidal current setting 000°T at 3 knots. The vessel's speed through the water is 9 knots. Using the current vector triangle, the mariner must determine which of the following?
- ✓ The course to steer so that course steered plus the drift vector yields the desired course made good of 090°TCorrect
- B. The course to steer by subtracting the drift speed from the vessel's speed through the water
- C. The course to steer by applying the height difference from the tide tables to the reference station
- D. The course to steer by adding the set directly to the desired course made good
Why A is correct
Bowditch Ch. 24 §2402 states that to make a given track over the ground, the mariner inverts the vector triangle: from the desired course made good and the known drift vector, derive the course to steer such that course steered plus drift vector equals the desired course made good. Simply adding set to course made good or subtracting speeds does not satisfy the vector relationship.
Cited:Bowditch Ch. 24 §2402