Chart Navigation & Plotting · Set & Drift — Speed of Advance
In the previous problem (steer ≈079°T at 10 kn to make good 090°T against a 2.0 kn current setting 180°T), what is your approximate speed of advance along the 090° track?
- A12.0 knots
- B8.0 knots
- C9.8 knots✓ Correct
- D10.0 knots
Explanation
The along-track (eastward) component of boat speed is 10 × cos(11.5°) ≈ 9.8 kn. The current is purely north-south, so it adds nothing eastward. Speed of advance along the 090° track is about 9.8 knots.
Authority: Bowditch (Pub. No. 9), current sailing; speed of advance
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