On 25 April your 0930 zone time position is LAT 28° 35' S, LONG 82° 30' W. Your vessel is on course 300° T at a speed of 20.0 knots. Determine the zone time of LAN.
• Local Apparent Noon (LAN) occurs when the Sun is on your meridian (same longitude as you) • Relationship between longitude and time: 15° of longitude = 1 hour of time • How your change in longitude between 0930 and LAN (while steaming on course 300°T at 20 knots) affects the time of meridian passage
• From 0930 until LAN, are you moving toward or away from the Sun’s meridian if the Sun’s GHA is increasing? Think about whether that makes LAN earlier or later in zone time. • First, ignore the ship’s movement: based only on your starting longitude, about what time (zone time) would LAN be if you stayed put? Then adjust that time for the longitude you will actually be at when LAN occurs. • How many minutes of time do you gain or lose for each degree (and each minute) of longitude you change while steaming between 0930 and LAN?
• Be sure you use the correct sign and direction for your change in longitude when converting to time (E vs W and whether GHA is increasing). • Confirm your zone description (ZD) from 82° 30' W and use it consistently when converting between GMT and zone time. • After you estimate a LAN time, check that your assumed steaming time from 0930 to LAN, at 20 knots, gives a distance run that matches the change in longitude you used. If it doesn’t, refine and recalc.
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