World Time Zone Chart

Introduction

A World Time Zone Chart is a specialist nautical document used to understand and determine the standard time or zone time corresponding to a vessel's geographical position. It is particularly useful for offshore navigation, ocean passages, commercial shipping, celestial navigation, watchkeeping and international voyages during which a vessel crosses several time zones.

At sea, time management is not simply a matter of moving the ship's clock forward or backward when crossing a time zone. The navigator must also distinguish between Universal Time, UTC, zone time, local time in a port and, in some countries, seasonal time changes. A maritime time zone chart provides a worldwide representation of this organisation of time.

Time zone charts published by major hydrographic organisations and nautical publishers, including SHOM and ADMIRALTY, are designed as reference documents for maritime navigation. The ADMIRALTY World Time Zone Chart was developed so that mariners anywhere in the world can relate local time to a common Greenwich-based reference.

What is a maritime time zone chart?

A time zone chart represents the geographical distribution of time zones around the world. In the standard system, the Earth is divided into 24 theoretical time zones, each corresponding to approximately 15 degrees of longitude.

The Greenwich meridian provides the reference for the system. From this reference, the different zones are associated with time differences in relation to UTC or the standard time reference used for navigation.

A nautical time zone chart can show:

• the boundaries of the different time zones;

• the time difference from UTC;

• the Greenwich prime meridian;

• the International Date Line;

• the main continents, seas and oceans;

• the geographical areas crossed by major shipping routes;

• references needed to convert between Universal Time and zone time.

However, theoretical time zones should be distinguished from the legal times actually used on land. National borders and administrative boundaries do not necessarily follow the geographical boundaries of theoretical time zones. ADMIRALTY documentation notes that countries may adopt a standard legal time that does not correspond exactly to their geographical position within a time zone.

Why use a time zone chart for navigation?

Time management is an important part of marine navigation. A geographical position is expressed in latitude and longitude, while many navigational operations also depend on an accurate time reference.

A World Time Zone Chart allows navigators to determine the appropriate time reference for the vessel's position and to plan changes of ship's time during a passage.

It is particularly useful for:

• organising navigation watches;

• determining local time during a port approach;

• converting local time to UTC;

• planning an ocean passage;

• coordinating communications with shore-based operations;

• interpreting weather information;

• carrying out certain celestial navigation calculations;

• coordinating operations between vessel, shipowner, port and maritime authorities.

During a voyage lasting several weeks, time management becomes an integral part of passage planning.

UTC, zone time and local time

The concept of UTC is fundamental to international navigation. It provides a common time reference that avoids ambiguity between different local times.

On board a vessel, several time references may be used simultaneously. Universal Time may be retained for communications, navigation or specific calculations, while zone time may be used for the organisation of daily life and watchkeeping.

It is therefore important to distinguish between:

• UTC: a universal time reference used for many maritime and navigational applications;

• zone time: the time corresponding to the time zone in which the vessel is located;

• local or legal time: the time officially used within a particular territory or port;

• ship's time: the time selected by the master for the practical organisation of the vessel.

The conversion rules and time conventions used on board should be clearly established in order to avoid confusion.

Time zones and ocean passages

The usefulness of a World Time Zone Chart becomes particularly obvious during long-distance passages.

In the North Atlantic, for example, a yacht leaving Brest, Lorient, La Rochelle, Cherbourg or Southampton for Halifax, New York, Boston or Québec progressively crosses several time zones.

The same applies to passages between Europe and the Caribbean. A route from Lisbon or the Canary Islands to Fort-de-France, Pointe-à-Pitre or Saint Martin involves a progressive change in time reference.

In the South Atlantic, a voyage between Dakar, Recife, Salvador da Bahia, Rio de Janeiro and Buenos Aires also requires careful management of time differences.

In the Pacific, the differences can become much greater. A passage between the west coast of North America and Hawaii, Tahiti, New Caledonia, New Zealand or Australia may cross numerous time zones and approach the International Date Line.

The International Date Line

The International Date Line is one of the most important features shown on a worldwide time zone chart.

It lies approximately along the 180th meridian in the Pacific, although its course is not a straight geographical line. Its shape takes into account, among other factors, the distribution of island territories and political boundaries.

When a vessel crosses this area, the calendar date may change by one day. This is particularly important for logbooks, passage planning, port calls, communications and the organisation of navigation.

A World Time Zone Chart allows the navigator to identify this area and prepare for the change of date before it is encountered at sea.

Time zones and celestial navigation

Time management is especially important in celestial navigation.

Observations of the Sun, Moon, stars or planets are associated with an exact time. An error in time can therefore produce an error in the calculated position.

A time zone chart is consequently a useful reference for understanding the relationship between longitude, time and the rotation of the Earth.

It also helps explain why local solar time varies with longitude and why standard and zone time systems were introduced to simplify human and maritime activities.

Time zones and port operations

Time is also essential when approaching a port.

A vessel arriving at Marseille, Gibraltar, Las Palmas, Dakar, Fort-de-France, New York, Panama, Papeete, Sydney or Singapore must take the local time of the port into account when planning its arrival and operations.

This becomes particularly important when information from different sources uses different time references.

Tide predictions, weather bulletins, radio communications, appointments with ship agents and port operating hours must all be interpreted using the correct time reference.

Tide predictions, for example, are generally presented according to the standard local time of the location concerned, with particular attention required where daylight-saving or legal-time changes apply.

Time zones in the Atlantic, Pacific and Indian Ocean

A worldwide time zone chart is particularly useful for international maritime routes.

North Atlantic

It is relevant to routes between:

• Brest and Halifax;

• Cherbourg and New York;

• Southampton and Boston;

• Lisbon and Bermuda;

• the Canary Islands and the Caribbean.

South Atlantic

It helps visualise the time differences between:

• Dakar;

• Recife;

• Salvador da Bahia;

• Rio de Janeiro;

• Cape Town;

• Buenos Aires.

Pacific Ocean

It is particularly useful on routes between:

• Vancouver;

• Seattle;

• San Francisco;

• Hawaii;

• Tahiti;

• Papeete;

• Nouméa;

• Auckland;

• Sydney;

• Tokyo.

Crossing the International Date Line creates a specific additional consideration in this region.

Indian Ocean

It is relevant to passages between:

• Durban;

• Port Louis, Mauritius;

• Mumbai;

• Colombo;

• Singapore;

• Fremantle;

• Perth.

These major routes illustrate the value of a worldwide representation rather than a simple time indication associated with a single country.

SHOM and ADMIRALTY time zone charts

World time zone charts are published by recognised hydrographic organisations and specialist nautical publishers.

SHOM, the French Hydrographic and Oceanographic Service, publishes a maritime world time zone planisphere designed as a navigation reference document.

ADMIRALTY, published by the United Kingdom Hydrographic Office, also produces the ADMIRALTY 5006 – The World: Time Zone Chart. The chart is included among ADMIRALTY's reference and plotting charts, which are designed to be used alongside official navigation charts for passage planning.

These documents complement conventional nautical charts. A time zone chart is not intended to determine depths, navigational hazards, aids to navigation or channels. Its purpose is specifically related to the representation and management of time.

A useful chart for passage planning

A World Time Zone Chart can be used before departure to prepare a passage plan and anticipate changes of ship's time.

For an ocean crossing, the navigator can identify:

• the time zones that will be crossed;

• the planned time changes;

• any crossing of the International Date Line;

• the difference between ship's time and local time;

• the expected local arrival time in ports;

• the time references used for communications.

It therefore provides a useful overview during the preparation of long-distance passages.

ADMIRALTY also provides navigational planning products designed to work alongside official navigation charts, including gnomonic charts, magnetic variation charts and plotting sheets.

A chart complementary to nautical charts

A World Time Zone Chart does not replace a nautical chart. It serves a different purpose.

SHOM, ADMIRALTY, Imray and other hydrographic chart publishers provide navigational information such as depths, hazards, buoys, lights, ports, channels, restricted areas and other essential nautical information.

A time zone chart, by contrast, provides a worldwide view of the organisation of time.

It can therefore be regarded as a complementary reference document for nautical charts, passage-planning documents and celestial navigation publications.

Who uses a World Time Zone Chart?

A maritime time zone chart can be useful to a wide range of users:

• cruising sailors preparing an ocean passage;

• offshore sailing crews;

• navigators practising celestial navigation;

• merchant navy officers;

• masters and crews of commercial vessels;

• maritime schools and training centres;

• offshore racing crews;

• delivery skippers and yacht delivery crews;

• sailors preparing for a circumnavigation.

Its usefulness generally increases with the distance travelled and the number of time zones crossed.

Conclusion

A World Time Zone Chart is a straightforward but important nautical reference document for understanding the organisation of time worldwide. It allows navigators to visualise time zones, differences from UTC and the International Date Line.

For coastal navigation, its use may be occasional. During an Atlantic, Pacific or Indian Ocean crossing, however, it becomes a practical passage-planning tool.

Used alongside SHOM, ADMIRALTY or Imray nautical charts, passage-planning documents and electronic navigation systems, a time zone chart helps maintain a consistent time reference throughout a voyage.

Frequently Asked Questions – Maritime Time Zone Charts

What is a World Time Zone Chart used for in navigation?

It shows the time differences between geographical regions and helps navigators plan changes of ship's time during a voyage, particularly on ocean passages.

What is the difference between UTC and local time?

UTC is a universal time reference. Local time is the time officially used in a particular region or port and may differ from UTC according to the applicable time zone and local regulations.

Is a time zone chart useful for an Atlantic crossing?

Yes. A passage between Europe, the Caribbean or North America can cross several time zones. A time zone chart helps the navigator anticipate these changes and maintain a consistent time reference on board.

Why is the International Date Line important to sailors?

Crossing the International Date Line may result in a change of calendar date. This must be taken into account when maintaining the logbook, planning port calls and managing the passage.

Do time zones always follow meridians?

No. The theoretical time zones are based on longitude, but legal time is established by individual countries and may therefore differ from the purely geographical boundaries of the time zones.

Is a time zone chart useful for celestial navigation?

Yes. It is particularly useful for understanding the relationship between longitude, Universal Time and local time. Accurate timekeeping is fundamental to celestial navigation calculations.

What is the difference between an SHOM and an ADMIRALTY time zone chart?

Both are specialist documents representing worldwide time zones for maritime use. SHOM publishes a maritime time zone planisphere, while ADMIRALTY publishes chart 5006, The World – Time Zone Chart. ADMIRALTY identifies chart 5006 as part of its reference and plotting chart series.

Does a time zone chart replace a nautical chart?

No. It does not provide essential navigational information such as depths, hazards, aids to navigation or channels. It is a complementary reference document specifically concerned with the organisation of time.

Why use a time zone chart during a circumnavigation?

A circumnavigation crosses numerous time zones and may include a crossing of the International Date Line. A worldwide chart therefore makes it easier to anticipate changes of time and date throughout the voyage.