On 7 February your 0800 zone time DR position is LAT 22°16.0'N, LONG 92°26.0'W. Your vessel is on course 270°T at a speed of 20.0 knots. What is the zone time of local apparent noon (LAN)?
• Local Apparent Noon (LAN) occurs when the Sun crosses your meridian (highest altitude) • Relationship between longitude and time: 15° of longitude = 1 hour of time • How to use DR (dead reckoning) position at LAN to get the time from a known earlier DR position
• From 0800, how long will it take your vessel, on course 270°T at 20 knots, to reach the longitude where the Sun will be on your meridian? • What is your change in longitude per hour when steaming due west at 20 knots at this latitude? Think in terms of miles per degree of longitude at 22°N. • Once you know how many hours after 0800 you reach your LAN longitude, what clock time does that give you?
• Calculate degrees of longitude per hour you are moving at 22°N using the meridian/parallel sailing concept (distance along a parallel vs degrees of longitude). • Confirm the DR longitude at LAN by adding the westing you make from 0800 until LAN. • Add the correct elapsed time to 0800 ZT and be careful about minutes rounding when converting miles to degrees and minutes.
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