Your vessel has changed course and is heading 285°T, you are on the charted range and it appears as in illustration D048NG below. After several minutes the range appears as in illustration D047NG below and your heading is still 285°T. What does this indicate?
• Range markers: When you are exactly on the range line, the front and rear markers appear vertically aligned; if they separate left/right, you are off the range. • Relative motion of range marks: Think about what it means when the rear mark appears to move left or right relative to the front mark as time passes. • Set vs. leeway and course made good: Understand the difference between the heading you steer, the course made good, and how current or wind can push you off your intended track.
• From your position looking forward, if your vessel is being pushed to the right of the range line, which way will the rear mark appear to move relative to the front mark? What if you are being pushed to the left? • Compare your fixed heading of 285°T with the change in how the range looks. Does this change suggest that your course made good is left or right of the intended track? • For a NE’ly wind, which way would leeway push your vessel (toward which cardinal direction), and would that be consistent with the way the range picture changes? What about a north‑setting or south‑setting current?
• Identify clearly which side of the range line you must now be on (left or right) based on the second illustration, using the apparent shift of the rear mark relative to the front mark. • Determine whether that side-of-track error could be caused by a north-setting current, a south-setting current, or leeway from a NE’ly wind, given your westerly heading of 285°T. • Confirm whether the situation described is talking about the actual track over the ground (course made good) versus the dead-reckoned (DR) track you intended to follow.
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