Indian Ocean Nautical Charts

Introduction

An Indian Ocean nautical chart is an essential tool for planning offshore navigation, an ocean passage or coastal navigation in one of the largest and most diverse maritime regions in the world. The Indian Ocean extends between Africa, Asia, Australia and Antarctica and includes many very different navigation areas: the Arabian Sea, Bay of Bengal, Mozambique Channel, Andaman Sea, Laccadive Sea, Seychelles waters and the maritime areas around Madagascar, Réunion, Mauritius, the Seychelles and the Maldives.

An Indian Ocean nautical chart represents depths, isolated dangers, reefs, shoals, islands, lights and buoys, traffic separation schemes, harbour approaches and the main navigational features required for safe passage. Depending on its scale, a chart may be intended for ocean passage planning, coastal navigation or detailed port approaches.

Indian Ocean nautical charts are available in different formats: paper charts, raster charts, vector charts and electronic navigational charts, or ENCs. The appropriate format depends on the area being navigated, the type of navigation and the level of detail required.

The Main Areas Covered by Indian Ocean Nautical Charts

The Indian Ocean covers a vast geographical area with highly diverse environments. A single chart therefore cannot provide the level of detail required for every stage of a voyage.

The main charted areas include:

• the western Indian Ocean;

• the Arabian Sea;

• the Gulf of Aden and approaches to Bab-el-Mandeb;

• the Bay of Bengal;

• the Laccadive Sea;

• the Andaman Sea;

• the Mozambique Channel;

• the East African coast;

• Madagascar and its surrounding islands;

• the Seychelles;

• the Maldives;

• the Comoros and Mayotte;

• Réunion and Mauritius;

• the Chagos Archipelago;

• the Kerguelen, Crozet and Amsterdam islands;

• the southern Indian Ocean towards the Southern Ocean;

• approaches to Western and Southern Australia.

This geographical diversity explains why careful chart preparation generally requires several different chart scales.

Arabian Sea and Gulf of Aden

The north-western part of the Indian Ocean includes the Arabian Sea, bordered by India, Pakistan, Oman, Yemen and the Arabian Peninsula.

Nautical charts for this region are used for navigation between ports on the Arabian Peninsula, India and East Africa. They can be used to plan routes between ports such as Mumbai, Kochi, Karachi, Salalah, Muscat, Aden and Djibouti.

The Gulf of Aden is a strategically important maritime area linking the Indian Ocean with the Red Sea through the Bab-el-Mandeb Strait. Charts for this area must therefore be selected with particular attention to commercial shipping routes, harbour approaches and areas of heavy traffic.

Bay of Bengal and Andaman Sea

East of India lies the Bay of Bengal, a vast maritime area bordered by India, Bangladesh, Myanmar and Sri Lanka.

Nautical charts for this region may be used to plan navigation between ports such as Chennai, Kolkata, Visakhapatnam, Chittagong, Yangon and Colombo.

Further east, the Andaman Sea includes the coasts of Myanmar and Thailand as well as the Andaman and Nicobar Islands. Navigators must take into account a particularly complex geography, with numerous islands, channels, reefs and shallow coastal areas.

Madagascar, Mozambique Channel and East Africa

The Mozambique Channel is a major region of the western Indian Ocean. It separates Madagascar from the African mainland and forms an important maritime route between southern Africa, Madagascar, the Comoros, Mayotte, the Seychelles and the Mascarene Islands.

Nautical charts may cover both offshore routes and detailed coastal and harbour approaches. Important areas include the coasts of Mozambique, Tanzania and Kenya, as well as the western and eastern coasts of Madagascar.

Ports such as Maputo, Beira, Quelimane, Mombasa, Dar es Salaam, Moroni, Mahajanga, Toamasina and Toliara may require charts at a much larger scale than those used for an ocean crossing.

For Madagascar, charting must also take into account the numerous bays, islands, reefs and anchorages that characterise its coastline.

Seychelles, Maldives, Mauritius and Réunion

The islands and archipelagos of the Indian Ocean are particularly important for both cruising and offshore sailing routes.

The Seychelles, with ports and anchorages around Mahé, Praslin and the other islands, require charts that allow navigators to identify reefs, channels and shallow areas accurately.

The Maldives present a specific cartographic challenge because of their succession of atolls and coral reefs. A suitable nautical chart for navigation in the Maldives must allow navigators to distinguish channels, lagoons, reefs and approaches to anchorages.

Further south-west, charts of Mauritius and Réunion are used for both inter-island passages and harbour approaches. Port Louis and Port Victoria, together with the port facilities of Réunion, are examples of areas where larger-scale charts may be required.

Chart Publishers and Hydrographic Services

Several organisations produce or distribute nautical charts covering the Indian Ocean.

The Shom, the French Hydrographic and Oceanographic Service, provides significant coverage of the Indian Ocean, particularly around French territories and a number of areas of the western and southern Indian Ocean. Shom chart series include general, coastal and approach charts. Coverage includes areas around Réunion, Mayotte, the Éparses Islands, Madagascar, the Mozambique Channel and the Crozet, Kerguelen and Amsterdam islands.

Admiralty charts, published by the United Kingdom Hydrographic Office, are also an important international reference for Indian Ocean maritime cartography. Admiralty series cover Mauritius, Réunion, the Seychelles, Madagascar and numerous international shipping routes.

The Indian Naval Hydrographic Department plays an important role in the production and maintenance of nautical charts for Indian waters and the wider Indian Ocean region. It produces both paper charts and ENCs and participates in international hydrographic programmes in the region.

Other national hydrographic services also contribute to chart coverage depending on the area concerned, including South Africa, Australia, Indonesia, Sri Lanka, Bangladesh, Myanmar, Kenya, Tanzania, Mozambique and Mauritius.

Paper, Raster and Vector Nautical Charts

The choice of chart format depends on the intended use.

Paper nautical charts remain particularly useful for route planning, work on board and maintaining an independent representation of the navigational area. They also provide a valuable overview when planning an ocean passage.

A raster chart is a digital reproduction of a paper chart or other cartographic document. It retains the general visual appearance of the original chart and can be used with compatible navigation software.

A vector chart, particularly in ENC format, represents charted objects as digital data. It provides greater interaction with the navigation system and may display different information depending on the zoom level and the objects selected.

Shom and Admiralty charts are available in different formats and scales depending on the geographical area. Actual coverage always depends on the chart series, geographical sector and product type.

The Importance of Chart Scale

For navigation in the Indian Ocean, chart scale is a key consideration.

A small-scale chart is suitable for planning a passage between continents or island groups. It provides a broad overview and allows the general route to be established.

A medium-scale chart provides greater detail for regional navigation.

A large-scale chart becomes essential for coastal approaches, channels, harbours, passes and certain anchorages.

A complete navigation plan may therefore combine:

• an ocean chart for the overall route;

• one or more regional charts;

• coastal charts;

• approach charts;

• harbour plans where required.

Planning an Indian Ocean Passage

An Indian Ocean passage requires particularly careful chart preparation. The considerable distances between ports of call make it important to distinguish between ocean passage planning and coastal navigation.

A navigator planning a route between South Africa, Madagascar, Mauritius, Réunion, the Seychelles or India will need to select charts corresponding to each stage of the voyage.

Preparation is not limited to plotting a route. It must also take into account depths, charted dangers, restricted areas, traffic separation schemes, port approaches and any recommended routes.

For offshore navigation, general charts are used to establish the route at a broad scale. As the vessel approaches land, the navigator progressively changes to larger-scale charts providing more detail.

Conclusion

Indian Ocean nautical charts are a central element of navigation planning in this vast maritime region. From the Arabian Sea to the Bay of Bengal, from the Mozambique Channel to the Seychelles, from Madagascar to Réunion and Mauritius and as far as the Southern Ocean, charting requirements vary considerably according to the geographical area and type of navigation.

Shom, Admiralty and the various national hydrographic services provide chart coverage adapted to the different regions. The choice between paper, raster, vector or ENC charts then depends on the intended use, required scale and navigation system being used.

For an ocean passage as well as coastal navigation, good chart preparation should make it possible to move progressively from a broad overview of the route to a detailed representation of coastlines, hazards, ports and navigational areas.

FAQ – Indian Ocean Nautical Charts

What is an Indian Ocean nautical chart used for?

It is used to plan and conduct navigation in the Indian Ocean, from offshore passage planning to coastal navigation and harbour approaches.

Which areas are covered by Indian Ocean nautical charts?

Depending on the chart series, coverage may include the Arabian Sea, Bay of Bengal, Mozambique Channel, Madagascar, Seychelles, Maldives, Comoros, Mayotte, Réunion, Mauritius, the Chagos Archipelago and the Southern Ocean.

What are the main nautical charts used in the Indian Ocean?

Major international references include Shom and Admiralty charts, together with charts produced by the national hydrographic services of the countries bordering the Indian Ocean.

Which chart should be used for an Indian Ocean crossing?

For an ocean passage, a general or ocean chart is used to plan the route at a broad scale. Regional and coastal charts are then required for the different areas visited.

Are there detailed nautical charts of Madagascar?

Yes. Several chart series cover the coastline of Madagascar, including its bays, ports, islands, reefs and major anchorages.

Which nautical chart should be used for Réunion and Mauritius?

Both islands have dedicated chart coverage for general approaches, coastal navigation and port areas. The appropriate chart depends on the specific area and scale required.

Are the Maldives covered by nautical charts?

Yes. Nautical charts of the Maldives represent the atolls, reefs, channels, lagoons and coastal areas. A sufficiently large scale is important when navigating between atolls.

What is the difference between a paper nautical chart and a digital chart?

A paper chart provides a physical representation that is independent of an electronic system. A digital chart may be raster or vector and can be used with compatible navigation software or electronic navigation systems.

What is an ENC?

An ENC, or Electronic Navigational Chart, is an official vector electronic chart designed for use in a compliant ECDIS system.

What scale should be used for an Indian Ocean nautical chart?

A small scale is suitable for ocean crossings, while larger scales are required for coastal navigation, harbour approaches, channels and anchorages.