Lesson 15: Voyage Planning and Time

1
Lesson 15 Voyage Planning and Time

• Learning Objectives
• Apply correct procedures to determine zone time
  for specific locations.
• Apply correct procedures to determine zone time
  at another location if zone time is known at a
  given location.
• Apply correct procedures to convert longitude or
  arc units into equivalent time units.
• Comprehend the process of planning for an
  extended ocean voyage, and the services and
  publications that can be of assistance during
  voyage planning.
• Comprehend the procedures for plotting a great
  circle route on a gnomonic projection,
  transferring the track to a mercator projection,
  and labeling the track appropriately.
• Applicable reading Hobbs, pp. 255-277.

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Voyage Planning and Time

• Time - Time is of major importance in every
  voyage planning process almost every planning
  action is concerned with the timely arrival at
  the ultimate destination and at intermediate
  points en route.
• Estimated time of arrival (ETA) The time and
  date of arrival that must be met. They are
  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. The ETAs
  at several points along the track must also be
  computed in order to check progress .
• Development of Zone Time - The rate at which the
  sun moves across the sky varies from day to day
  due to the earths elliptic path around the sun.
  To avoid difficulties that arise from this fact,
  the concept of a theoretical mean sun passing
  completely around the earth at the equator once
  every 24 hours has been adopted.
• The Mean sun completes one circuit around the
  earth every 24 hours and moves at the rate of 15
  degrees of longitude every hour.

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Voyage Planning and Time

• Time zones Vertical sectors that divide the
  earths surface into twenty four zones. Each zone
  is 15 degrees of longitude in width (1524360
  degrees).
• Zone time (ZT) Time within each zone is reckoned
  according to the position of the mean sun in
  relation to the central meridian of the zone.
• Clocks are changed by one hour increments when
  transiting from one 15 degree zone to another.
• Each time zone is defined by the number of hours
  of difference existing between the time kept in
  that zone and the time kept within the zone
  centered on the prime meridian.
• Time zone indicators Each zone is labeled with
  a letters that assists in identification of the
  zone.

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Voyage Planning and Time

• Greenwich Mean Time (GMT) Time based upon the
  relationship of the mean sun with the prime
  meridian. It is often referred to as ZULU time,
  because of its time zone indicator letter.
• Times zones to the west of Greenwich keep earlier
  time in relation to GMT. This is indicated by
  placing a plus sign in front of the hourly
  difference figure to indicate the number of hours
  that must be added to the local zone time to
  convert it to GMT.
• Times zones to the east of Greenwich keep later
  time relative to GMT. This fact is indicated by
  placing a minus sign in front of the hourly
  difference. This gives the number of hours that
  must be subtracted from local zone time to obtain
  GMT.

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Voyage Planning and Time

• The Greenwich Time Zone is centered at the prime
  meridian, and extends 7 1/2 degrees to either
  side. A new time zone boundary lies every 15
  degrees thereafter across both the eastern and
  western hemispheres, resulting in the twenty
  fourth time zone being split into two halves by
  the 180th meridian. The half on the west side of
  this meridian keeps time 12 hours behind GMT
  making its difference 12 hours. The half on the
  east keeps time 12 hours ahead, resulting in a
  difference of -12 hours.
• Zone difference or zone description( ZD) There
  are actually 25 different time zones , numbered
  from 1 through 12 to the west of the Greenwich
  time zone, and -1 through -12 to the east. These
  differences are known as zone differences.

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Voyage Planning and Time

• The standard time zone in which any particular
  position on earth is located can be found by
  dividing its longitude by 15.
• If the remainder is less than 7 1/2 degrees, the
  quotient represents the number of the zone if
  the remainder is greater than 7 1/2 degrees, the
  location is the next zone away from the Greenwich
  Meridian.
• Example Determine the standard time zone of
  Norfolk, Virginia. Its longitude, 076o18.0 West,
  is divided by 15 to yield a quotient of 5 with a
  remainder of 1o 18. Thus, it is located in the
  5 time zone, which has the time zone indicator
  letter R.
• 15 degree time zones are of use to a navigator at
  sea, but strict adherence to these time zones is
  not practical for conducting business and travel.
  Consequently, time zones are often drawn along
  state and county boundaries.

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Voyage Planning and Time

• Daylight savings time is a device adopted by some
  countries, including the United States, to extend
  the hours of daylight during the summer.
  Locations keeping daylight savings time keep the
  time of the next zone to the east of the time
  zone in which they are located.
• Example When Norfolk observes daylight savings
  time, it keeps 4Q time rather than 5R time.
• The time kept at any particular location and time
  of year can normally be found in the applicable
  volume of the Sailing Directions for foreign
  ports or the Coast Pilots for U.S. ports.
• Time conversions- All times are converted to GMT
  prior to the initial planning stages of the
  voyage to avoid the difficulties inherent in
  working with several different time zones. After
  all ETAs and ETDs have been computed in GMT,
  certain times of interest can then be converted
  to local time zones.
• The following formulas are used to convert zone
  time to GMT and GMT to zone time ZTZDGMT
  (converting zone to GMT)
• ZTGMT-ZD (converting GMT to zone)

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TIME ZONES AROUND THE WORLD
M
Y
L
X
W
K
V
J
I
U
H
T
G
S
F
R
5
E
-5
-4
4
D
-3
Q
3
-2
2
-1
1
P
C
O
B
N
A
Z
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Voyage Planning and Time

• Example Convert 0800 local zone time on 30 June
  at Naples, Italy to Greenwich Mean Time. The
  longitude of Naples is 14o16 East, so it lies in
  the -1A time zone. The local time to be converted
  is written 0800A 30 June. The zone difference is
  applied to this time giving GMT of 0700Z 30 June.
  
• Note The date may change as a result of the
  conversion process. For example, converting
  0030A 30 June to GMT would yield a computed time
  of 2330Z 29 June.
• Date-time group an alphanumeric format used in
  labeling the track, as well as in writing
  messages. An example is shown below
• 1 7 1 0 0 0 R J U N 8 9
• DAY 4-DIGIT TIME
  3 LETTER LAST
• OF TIME ZONE
  MONTH TWO
• MONTH INDICATOR ABB
  DIGITS
• 
  OF YEAR

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Voyage Planning and Time

• During a transit, the ships clocks are set to
  the time zone in which the ship is located.
• When transiting in an easterly direction, ships
  clocks will be periodically set ahead 1 hour to
  conform to proper time zone.
• When traveling in a westerly direction, clocks
  will be periodically set back to conform.
• The 180th meridian is designated as the
  International Date Line, because the time kept in
  the 7 1/2o -wide zones on either side of it
  differs by 24 hours, or one complete day.
• When crossing the dateline on a westerly heading,
  the zone description changes from 12 to -12.
  Clocks must be advanced 24 hours, thereby losing
  one calendar day.
• When crossing in an easterly direction, clocks
  are retarded 24 hours, thereby gaining one
  calendar day.

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Voyage Planning and Time

• The voyage planning process In the case of Navy
  ships, the first notification of a deployment and
  its associated transits is normally received via
  the Yearly Employment Schedule. Confirmed
  deployment dates or changes to a ships schedule
  will be reflected in Quarterly Employment
  Schedules. Navigators must take into account
  numerous publication/chart, equipment, personnel,
  and operational chart considerations when
  beginning the planning process
• Obtaining and updating charts and publications
• The navigator will consult applicable chart
  allowance lists in order to determine which
  charts should be in the ships inventory. Any
  outdated or missing charts are ordered from the
  Defense Mapping Agency or National Ocean Service.
• The navigator will also consult the DMA Catalog
  of Maps, Charts and Related Publications and the
  NOS Nautical Chart Catalog 1 to find the numbers
  of all charts and Coast Pilots and Sailing
  Directions volumes that will be of use in the
  voyage.
• The Chart Petty Officer will pull all applicable
  charts and their correction cards and update all
  information.

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Voyage Planning and Time

• Determination of departure and arrival dates
• Regardless of whether a ship will transit
  independently or in company with other ships, an
  ETA (estimated time of arrival) will be
  promulgated by a higher authority. It is up to
  the navigator to calculate an estimated time of
  departure that will allow the ship to arrive at
  the assigned time.
• Example A ship will transit from Norfolk to
  Naples, Italy with an ETA OF 0800A 30 June.
• First Determine the distance between Norfolk
  and Naples using Publication No. 151, Distance
  Between Ports. A great circle route can be sailed
  from Norfolk to Gibraltar (3,335 miles), then
  from Gibraltar to Messina (1.049 miles), and
  finally from Messina to Naples (175 miles).
  Adding the three together yields a total distance
  of 4,559 miles. Maximum SOA (speed of advance)
  will be promulgated by higher authority for this
  example a maximum SOA of 16 kts is assumed.
  Using the speed-time-distance equation, a total
  time in transit of 285 hours, or 11 days and 21
  hours is obtained.

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Voyage Planning and Time

• Second Norfolk is in time zone 5R while Naples
  is located in time zone -1A. Consequently, 6
  hours will be lost due to time zone changes
  during the transit. The ship must depart Norfolk
  12 days and 3 hours before the scheduled arrival
  in Naples. Subtracting this time from the ETA of
  0800A 30 June yields a departure time from
  Norfolk of 0500R 18 June. An alternative method
  would be to convert the ETA to GMT, subtract 285
  hours, then convert this GMT time to 5R for
  Norfolk.
• Tides and currents must be taken into account
  when determining ETD and ETA as the calculated
  underway and arrival times may need to be
  adjusted to compensate for these factors.

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Voyage Planning and Time

• Plotting the intended track
• The navigator will consult a climatological
  summary provided by the National Oceanography
  Command Center, in order to account for
  prevailing weather for the period of the transit.
  This survey provides normal wind speeds and
  directions, wave heights, currents, and the
  probability of rain and storms enroute. Other
  sources of this type of information are the
  appropriate editions of Sailing Directions
  Planning Guides, and Coast Pilots.
• Consulting these references ensures that the
  optimum route is chosen for the voyage. It is
  possible that heavy weather could slow a ship
  along a great circle route, and that a longer
  track may save time by avoiding bad weather.
• An Optimum Track Shipping Routing will also be
  requested from the National Oceanography Center.
  This track is an optimum track for the specific
  ship requesting the service based on actual
  climatological and hydrographic forecasts
  covering the time of the voyage.
• Once the OTSR is received, it will be compared to
  the track proposed by the navigator. The track
  may be altered to adjust for bad weather
  identified by the OTSR.

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Voyage Planning and Time

• After determining the optimum track, the
  navigator will plot the track on a gnomonic
  chart.

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Voyage Planning and Time

• The great circle track obtained from this plot is
  then transferred onto a mercator chart by picking
  convenient points every 300 to 500 miles apart
  and plotting them on the mercator projection (see
  App. A).

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Voyage Planning and Time

• These points are labeled either with letters or
  sequential alphanumeric designation such as R-1,
  R-2 etc. These points are then connected with
  rhumb lines.
• Since the area covered by the chart depicting the
  North Atlantic is so large and the scale so
  small, the points on the track are also plotted
  on larger scale, smaller area charts for
  day-to-day use.

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Voyage Planning and Time

• Completing the Track
• After the track from point A off Hampton Roads to
  the entrance to Naples has been laid down, the
  exit track from Norfolk and the entrance track to
  Naples are both plotted on the appropriate
  charts.( PILOTING CHARTS)
• The navigator then measures the distance along
  the rhumb line tracks and compares the total to
  the distance obtained from Publication No. 151,
  Distance Between Ports. After computing the
  speed of advance for each leg, each junction
  point on the large-scale chart is labeled with
  the distance remaining to the destination and the
  computed ETA at each point, expressed in both GMT
  and local time zone. As a minimum, each rhumb
  line segment on the large-scale plot should be
  labeled with the track direction and speed of
  advance, and each junction point should be
  labeled with the distance remaining and the ETA
  in local time zone. A portion of the completed
  track

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Voyage Planning and Time

• Position of intended movement (PIM) The
  theoretical position of the ship on the intended
  track at any time. The PIM moves along the track
  at the SOA, and the actual ships position can be
  described in relation to it. If the ship arrives
  two hours ahead of the planned ETA at point C,
  for example, it is said that the ship is two
  hours ahead of PIM at that point.