Routeing Chart

Introduction

A Routeing Chart is a specialist nautical chart designed for planning offshore passages and major ocean routes. Unlike a conventional nautical chart, whose primary purpose is to show depths, hazards, aids to navigation, coastlines and ports, a Routeing Chart provides a summary of the meteorological and oceanographic conditions generally encountered in a specific maritime area during a particular time of year.

It is therefore an important passage-planning tool for offshore navigation, transoceanic crossings, merchant shipping, commercial vessels, large cruising yachts, ocean racing and any voyage requiring prior analysis of winds, currents, storms and seasonal conditions.

ADMIRALTY Routeing Charts are organised by month in order to take seasonal variations into account. Each geographical area is covered by a series of monthly charts showing information such as winds, storms, ocean currents, temperatures, ice limits and major shipping routes.

What is a Routeing Chart?

A Routeing Chart is a small-scale planning chart that brings together a wide range of information useful for determining an ocean route.

It should therefore not be confused with a navigation chart used to conduct a vessel safely close to the coast or within a harbour. Its purpose is different: it allows the navigator to study the overall environment of an ocean passage and identify the meteorological and oceanographic characteristics that may influence the route.

Depending on the area and publisher, a Routeing Chart may show:

• major shipping routes between important ports;

• distances between major ports;

• wind roses;

• frequency and strength of prevailing winds;

• frequency of storms and areas of poor visibility;

• ocean currents;

• air and sea temperatures;

• seasonal ice limits;

• load line zones;

• major commercial shipping routes;

• statistical information allowing conditions to be compared from one month to another.

SHOM also publishes small- and medium-scale general charts and ocean planning charts covering major maritime areas, including the Atlantic and Pacific.

What is a Routeing Chart used for?

The primary purpose of a Routeing Chart is to assist in planning a sea passage while taking prevailing seasonal conditions into account.

Before a passage covering hundreds or thousands of nautical miles, the navigator must consider not only the distance between departure and destination but also the environmental conditions likely to affect the route.

A Routeing Chart can be used to study:

• prevailing wind direction and strength;

• ocean currents;

• areas with a high frequency of depressions or storms;

• seasonal conditions;

• ice hazards;

• major shipping routes;

• distances between major ports;

• specific climatic or regulatory areas.

It therefore allows the navigator to move beyond simply drawing a straight line between two ports and develop a genuine ocean routing strategy.

Routeing Charts are organised by month

One of the key characteristics of Routeing Charts is their seasonal nature.

Navigation conditions in the North Atlantic in January are very different from those encountered in July. The same applies to the Indian Ocean, Pacific Ocean and South Atlantic.

Monthly charts therefore allow the navigator to select the documentation corresponding to the planned passage date.

This is particularly important when analysing:

• trade winds;

• prevailing winds;

• extratropical depressions;

• tropical cyclones;

• monsoon systems;

• fog areas;

• ice limits;

• seasonal ocean currents.

A Routeing Chart does not provide a weather forecast for a specific date. It primarily presents statistical information and average conditions that help the navigator understand what is normally encountered in a particular area and season.

Routeing Chart and North Atlantic crossings

The North Atlantic is one of the classic areas for the use of Routeing Charts.

A passage between Brest, Cherbourg, Southampton or La Coruña and Halifax, Boston, New York or Québec can be analysed according to the time of year.

The navigator can study prevailing winds, depressions, currents and possible areas of ice or reduced visibility before developing a passage strategy.

The Gulf Stream is also an important factor when preparing a North Atlantic crossing. General knowledge of ocean currents helps the navigator understand how their direction and strength can influence speed over the ground and the selected route.

The Routeing Chart should then be complemented by the weather forecasts available immediately before departure and during the passage.

Routeing Chart in the South Atlantic

The South Atlantic also has meteorological and oceanographic conditions that vary according to latitude and season.

Routes linking Dakar, the Cape Verde Islands, Recife, Salvador da Bahia, Rio de Janeiro, Cape Town or Buenos Aires can be studied using the Routeing Chart corresponding to the month of the voyage.

For a sailing yacht crossing between Africa and South America, trade winds, currents and weather systems are important factors in passage planning.

A Routeing Chart provides a broad overview of the basin before the navigator analyses the route in greater detail.

Routeing Chart in the Pacific Ocean

The Pacific covers an enormous area and is particularly well suited to the use of ocean routing charts.

Routeing Charts can be used to study passages between Vancouver, Seattle, San Francisco, Hawaii, Tokyo, Tahiti, Papeete, Nouméa, Auckland or Sydney.

In the South Pacific, understanding prevailing wind patterns, currents and tropical weather systems is particularly important for long-distance passages.

For a voyage between French Polynesia, New Caledonia, New Zealand and Australia, a Routeing Chart helps place the passage within its broader regional meteorological and oceanographic context.

Routeing Chart in the Indian Ocean

The Indian Ocean has a particular characteristic: the strong influence of monsoon systems.

Routes between Durban, Port Louis, Mumbai, Colombo, Malacca, Singapore, Fremantle or Perth can vary considerably depending on the season.

A Routeing Chart allows the navigator to visualise the prevailing wind and current patterns corresponding to the month of navigation.

It is therefore particularly relevant when planning passages between Africa, Madagascar, the Mascarene Islands, India, Sri Lanka, Southeast Asia and Australia.

Winds and wind roses

Wind roses are one of the characteristic features of Routeing Charts.

They provide a statistical representation of wind direction and frequency in a particular area. They may also provide information about wind force.

For the navigator, this information helps identify prevailing wind patterns and understand how they may affect the planned route.

For a sailing yacht, this information is particularly useful because route selection may depend directly on wind direction and strength.

For a power-driven vessel, winds can also affect fuel consumption, sea state, comfort and vessel speed.

Ocean currents

Currents are another essential component of ocean routing.

A favourable current can increase a vessel's speed over the ground, while an adverse current can increase the duration of the passage.

Routeing Charts show major ocean currents and their general characteristics. These data should nevertheless be treated as planning information rather than real-time measurements.

For this reason, Routeing Chart information should be combined with current forecasts and other up-to-date oceanographic data when planning an actual passage.

Routeing Charts and weather

A Routeing Chart does not replace a weather forecast.

It provides climatological and statistical information about an area, while weather forecasts, numerical weather models and marine bulletins allow navigators to analyse the actual or expected conditions over the coming days.

A typical passage-planning process may therefore include:

• studying the Routeing Chart for the month of the voyage;

• identifying prevailing winds and currents;

• assessing seasonal risks;

• determining several possible routes;

• consulting weather forecasts before departure;

• adjusting the route according to actual conditions;

• using the appropriate nautical charts for navigation.

This combination of climatology, meteorology and nautical charting is fundamental to ocean routing.

Routeing Chart and Ocean Passages for the World

Routeing Charts are also complementary to publications used for planning ocean passages.

ADMIRALTY Ocean Passages for the World (NP136) provides information on major ocean routes, including weather conditions, winds, currents, swell, seasonal factors, ice and distances between major ports.

The Routeing Chart provides a graphical and highly condensed representation, while an ocean routing publication allows the navigator to study a particular route in greater depth.

Neither document replaces the official nautical charts required to navigate the vessel.

Routeing Chart and nautical charts

A Routeing Chart is a planning chart, not a detailed coastal navigation chart.

A conventional nautical chart provides information such as soundings, depth contours, wrecks, obstructions, aids to navigation, lights, buoys, hazards and port information.

A Routeing Chart is used earlier in the planning process, when the navigator is studying the general route at ocean or basin scale.

An ocean passage may therefore require several levels of documentation:

• a Routeing Chart for broad-scale route analysis;

• general or ocean charts for geographical planning;

• coastal charts for approaching land;

• approach and harbour charts for the final stages;

• up-to-date meteorological and oceanographic information;

• additional nautical publications appropriate to the area.

ADMIRALTY Routeing Charts

ADMIRALTY, published by the United Kingdom Hydrographic Office, produces a series of Routeing Charts covering major ocean areas including the North Atlantic, South Atlantic, North Pacific, South Pacific and Indian Ocean.

Each area is covered by charts corresponding to the different months of the year. The small scales provide a broad overview of the oceans, while larger-scale charts are available for certain areas of heavy maritime traffic.

ADMIRALTY Routeing Charts are part of a wider range of planning documents intended to complement official navigation charts.

Who uses Routeing Charts?

Ocean routing charts can be used by:

• offshore sailors;

• cruising sailors preparing transoceanic passages;

• large sailing yacht crews;

• commercial vessels;

• merchant navy officers;

• professional routers and passage planners;

• offshore racing crews;

• yacht delivery skippers;

• maritime schools and training centres;

• sailors preparing for a circumnavigation.

They are particularly relevant whenever a route covers several hundred or several thousand nautical miles.

Conclusion

A Routeing Chart is an essential tool for planning long-distance maritime passages. It allows the navigator to analyse winds, currents, storms, temperatures, ice, major shipping routes and seasonal characteristics across an entire ocean.

Its main value lies in placing a passage within its broader meteorological and oceanographic context. ADMIRALTY Routeing Charts and SHOM general or ocean planning charts can therefore be used to prepare passages across the Atlantic, Pacific or Indian Ocean before moving on to the nautical charts required for coastal navigation and harbour approaches.

A Routeing Chart does not prescribe a mandatory route and does not replace weather forecasts or official nautical charts. It is a planning document that helps the navigator understand the conditions normally encountered along a route and develop a navigation strategy appropriate to the season.

Frequently Asked Questions – Routeing Charts and Ocean Routing

What is a Routeing Chart?

A Routeing Chart is a specialist maritime chart designed for planning ocean passages. It shows information such as winds, currents, seasonal weather conditions, shipping routes and distances between major ports.

What is a Routeing Chart used for?

It is used to analyse the general conditions of an ocean or maritime basin before a passage and to develop a routing strategy according to the season.

Are Routeing Charts different for each month?

Yes. ADMIRALTY Routeing Charts are organised by month in order to represent seasonal variations in winds, currents, storms, ice and other ocean conditions.

What is the difference between a Routeing Chart and a conventional nautical chart?

A Routeing Chart is primarily used for broad passage planning. A conventional nautical chart provides the detailed information required for navigation, including depths, hazards, aids to navigation, lights, wrecks, ports and other hydrographic information.

Does a Routeing Chart provide a route to follow?

No. It provides statistical and geographical information that helps the navigator analyse and plan a route. The actual route followed also depends on current weather conditions, the vessel, its speed, destination and navigational constraints.

Can a Routeing Chart be used for an Atlantic crossing?

Yes. Routeing Charts are particularly useful when planning North Atlantic and South Atlantic crossings. They allow the navigator to study prevailing winds, currents and seasonal conditions.

Which ocean areas are covered by ADMIRALTY Routeing Charts?

The series includes major areas such as the North Atlantic, South Atlantic, North Pacific, South Pacific and Indian Ocean.

What is the difference between a Routeing Chart and Ocean Passages for the World?

A Routeing Chart provides a graphical summary of ocean conditions and routes. Ocean Passages for the World provides more detailed written information about major ocean routes, including weather, currents, ice and distances.

Does a Routeing Chart replace weather forecasts?

No. It primarily provides climatological and statistical information. For an actual passage, it must be supplemented by current weather and oceanographic forecasts.

Is a Routeing Chart useful for sailing yachts?

Yes. Information about prevailing winds, currents and seasonal conditions is particularly useful when preparing sailing passages across the Atlantic, Pacific and Indian Ocean.

Is a Routeing Chart useful for a circumnavigation?

Yes. A circumnavigation crosses several ocean basins and climatic regions. Routeing Charts allow each ocean passage to be studied according to the appropriate season and prevailing conditions.