On 3 May your 1009 zone time DR position is LAT 30°01.0'N, LONG 123°15.0'W. Your vessel is on course 330°T at a speed of 8.6 knots. What is the zone time of local apparent noon (LAN)?
• Local Apparent Noon (LAN) occurs when the Sun is on your local meridian (Sun’s LHA = 000°). • Relationship between longitude and time (4 minutes of time per degree of longitude). • How course and speed affect the DR position at the moment of LAN.
• First, estimate around what clock time the Sun will cross your local meridian at about 123°W, compared with the standard 1200 zone time meridian. • Figure how far you will move along course 330°T between 1200 and the probable LAN time, and how that changes your longitude. • Decide whether LAN will occur before or after 1200 based on your changing longitude and refine your time estimate accordingly.
• Verify which time zone meridian applies to LONG 123°15.0'W and how far your DR longitude is from that meridian in degrees and minutes. • Convert the longitude difference to time difference using 4 minutes of time per degree of longitude (and proportion for minutes of arc). • Check the sign of the correction: are you west or east of the time zone meridian, and does that make LAN earlier or later than 1200 local zone time?
No comments yet
Be the first to share your thoughts!