Lesson 15 Voyage Planning and Time Lesson 15

Lesson 15: Voyage Planning and Time

Lesson 15: Voyage Planning and Time • AGENDA: – ETA/ETD – Determining Zone Time – Date-time Group (DTG) Format – The Voyage Planning Process – Optimum Track Ship Routing (OTSR) • Applicable reading: Hobbs pg. 252 -274.

Terms and Definitions • Estimated Time of Arrival (ETA): the time and date of arrival that must be achieved. Usually specified by higher authority. • Estimated Time of Departure (ETD): a computed estimate of the time and date of departure that will allow the ship to arrive on time.

Terms and Definitions Speed of Advance (SOA) – The speed intended to be made good along the track. • The average speed in knots which must be maintained during a passage to arrive at a destination at an appointed time.

Terms and Definitions PIM • Planned track movement based on required SOA • USS Indianapolis • Indicated every 4 hours • Needed for ALL Voyage Plans • PIM symbol must be different from standard navigation symbols. Ex: 0 12 0 IM P Z

The Mean Sun & Zone Time • The mean sun completes one circuit around the earth every 24 hours, or 15 degrees of longitude each hour. • Each 15 degrees of arc is a time zone. • Within each zone, time is reckoned according to the position of the mean sun in relation to the central meridian of the zone.

Greenwich Mean Time (GMT) • Centered on prime meridian. • Extends 7. 5 o east and west of the prime meridian. • Referred to as “zulu” time, because the time zone is designated by “Z. ” • Each additional time zone (as we move east or west) has a boundary every 15 degrees past 7. 5 o.

The International Date Line • The 24 th time zone is split in half, with each zone on either side of the 180 th meridian being only 7. 5 o wide.

Determining the Time Zone • To determine the time zone, simply divide the longitude of a location by 15. • If the remainder is < 7 1/2°, quotient is the zone • If the remainder is > 7 1/2°, shift to the next zone • For eastern longitudes, place a negative sign (-) in front of the number; for western longitudes, place a positive sign (+) in front of the number.

Time Zone Example • The longitude of Norfolk, Virginia is 076 o 18. 0’ W. What time zone is this? • Answer: – 076° 18. 0/15 = 5 w/remainder of 1° 18’ – 1° 18’ < 7° 30’ Zone description = 5 – Since longitude is west, time zone is +5. – The time zone indicator letter for this zone is R, so the zone is completely described as +5 R

Daylight Savings Time • As an example, when Norfolk observes daylight savings time, it keeps +4 Q instead of +5 R time. • The time kept at any particular location and time of the year can be determined from either Coast Pilots or Sailing Directions.

Time Conversions • During voyage planning, all times are normally expressed in Zulu (GMT) to avoid confusion. • As necessary, times are converted to the local time zone for ease of use. • The formula for all conversions is: Zone time + zone description = GMT

Time Conversion Example • It’s 0800 (local zone time) in Naples, Italy. What is this time, expressed as GMT? • Answer: – Longitude of Naples is 014 o 16’ E, so the time zone is -1 A. – GMT= ZT + ZD = 0800 - 1 hour = 0700 Z

Date Time Group (DTG) • Official Navy format for expressing time and date. Also in all naval message traffic. • An example: 171000 RJUN 89 translates to: 17 1000 DAY OF MONTH 4 -DIGIT TIME R JUN TIME 3 LETTER ZONE MONTH INDICATOR 89 LAST TWO DIGITS OF YEAR

Shipboard Time • During a transit, the ship’s clocks are set to the time zone in which the ship is located. • As the ship transits eastward, clocks are periodically advanced 1 hour to conform to the proper time zone, and vice versa for westward travel.

Rhumbline Track on Mercator Chart • Rhumbline Sailing: – Appears As a More Direct Route on Mercator Projection – Maintains Constant True Direction and the Same Angle at All Longitude Meridians – For Short Distance Tracks: • Rhumbline Is Same As GC Track

Track Development • Steps: – Select Great Circle and Mercator Charts – Depart and Destination Positions Plotted – Start at First 5° Long Meridian & Retrieve Latitude and Longitude every 5° Meridian thereafter – Transfer Track Positions to Mercator Projection – Record Positions on PIM Sheet

The Voyage Planning Process • Obtain and update charts and pubs • Determine time of arrival and departure. • Plot the intended track – Plot a great circle on a gnomonic projection – Transfer rhumb lines to a mercator projection – Construct a track summary listing courses, distances, and times for each leg.

Optimum Track Ship Routing (OTSR) OTSR Provides: • • Preliminary planning Route Recommendations Route Surveillance Divert Recommendations

REVIEW • • What is SOA? What is OTSR? ZULU time is also known as _______? What time zone is Voyage Planning completed in?