Shom C Nautical Chart – Indian Ocean

Introduction

The Shom C nautical chart for the Indian Ocean is a flat paper nautical chart, generally supplied rolled, intended for navigation and route planning in the various areas of the Indian Ocean covered by the charting of the French Hydrographic and Oceanographic Service (Shom). This range covers in particular the western Indian Ocean, Madagascar, Réunion Island, Mayotte, the islands and archipelagos of the region, as well as certain maritime areas linking Africa, Asia and Australasia.

The Indian Ocean is an extremely large and diverse maritime area. It connects East Africa, Madagascar, the Mascarene Islands, the Seychelles, the Maldives, India, Sri Lanka, Southeast Asia and Australia. It includes open ocean areas, coastal zones, archipelagos, coral reefs, banks, straits, passages and numerous commercial and leisure ports.

The Shom C Indian Ocean nautical chart category therefore covers charts suitable for very different types of navigation: ocean crossings, navigation around Madagascar, approaches to Réunion or Mayotte, navigation in the Mascarenes, planning a route towards the Seychelles, or studying a route between Africa and Asia.

What is a Shom C nautical chart?

A Shom C chart is a flat paper nautical chart, generally supplied rolled in a tube. It differs from the Shom L chart mainly in its presentation: the Shom C is designed to be spread out on a chart table or work surface, whereas the Shom L is folded.

The Shom C format is particularly useful when the navigator needs a large cartographic surface. Depending on the reference, dimensions may correspond to Grand Aigle format or to a format close to A0.

Shom C charts of the Indian Ocean are available at several scales. The category includes coastal, littoral, offshore and oceanic charts. This range makes it possible to distinguish between a chart intended for approaching a coastline and one used to prepare a passage covering several hundred or several thousand nautical miles.

Main areas covered in the Indian Ocean

Shom C charting for the Indian Ocean covers several territories and maritime areas of particular interest to navigators.

Madagascar

Madagascar is one of the main navigation areas in the western Indian Ocean.

Shom C charts may cover different sections of the Malagasy coast, including the approaches to Île Sainte-Marie, Toamasina, Morondava and various coastal sectors.

Reference 6155C, for example, covers the approaches to Île Sainte-Marie, while 6156C covers the area from Île Sainte-Marie to Toamasina. Reference 6230C covers the Morondava anchorage. These references illustrate the diversity of charted areas and scales.

The Malagasy coastline has very different configurations depending on the region: large bays, islands, reefs, estuaries, anchorages and open coastal areas. The choice of chart must therefore be based on the planned route and the level of detail required.

Réunion Island

Réunion is another important area of Shom C charting in the Indian Ocean.

Charts may cover different parts of the island, including the northern, eastern, southern and western coasts and the approaches to the main ports.

Réunion Port, also known as Port Réunion or Port de la Pointe des Galets, is a major maritime location on the island. Saint-Pierre and other coastal areas may also require appropriate charting depending on the navigation planned.

Reference 7328C covers, in particular, the southern part of Réunion, from Pointe des Châteaux to Pointe Marcellin.

Mauritius and the Mascarenes

Navigation in the Mascarenes may involve several charts covering Réunion, Mauritius, Rodrigues and the surrounding maritime areas.

Reference 7349C covers, in particular, the area between Réunion and Mauritius as well as Tromelin Island. This charting places the various islands of the region within their wider maritime environment.

Ports and maritime locations in this region include Port Louis in Mauritius, Port Mathurin on Rodrigues and the port facilities of Réunion.

Mayotte and the Comoros

Mayotte is located in the Mozambique Channel, between Madagascar and the African coast. Its position makes it an important navigation area in the western Indian Ocean.

The waters around Mayotte include reefs, a lagoon, passages and coastal areas whose charting requires an appropriate scale.

The Comoros, located between Madagascar and East Africa, also form an important island group in this part of the Indian Ocean.

Seychelles and other archipelagos

The Seychelles, Maldives and many other Indian Ocean archipelagos are characterised by islands, reefs, banks and lagoons.

These environments require particular attention when selecting the chart scale. A general chart can be used to plan a route between archipelagos, while a more detailed chart becomes necessary when approaching an island, reef pass or anchorage.

Major ports in the Indian Ocean

The Indian Ocean is crossed by major commercial and maritime routes. Several large ports provide important geographical reference points for understanding the organisation of this maritime area.

In East Africa, these include Durban, Richards Bay, Maputo, Dar es Salaam, Mombasa and Port Victoria in the Seychelles.

In the western Indian Ocean, major port locations include Port Louis, Port Réunion, Saint-Pierre, Moroni, Mamoudzou and various Malagasy ports such as Toamasina, Mahajanga, Toliara and Morondava.

Further east, maritime routes may involve Colombo in Sri Lanka, Mumbai, Kochi and Chennai in India, as well as Malé in the Maldives.

In the Asian sector, Singapore, Port Klang, Jakarta and the major Indonesian ports are important maritime hubs.

These ports are given as examples of geographical and maritime reference points. A specific Shom C chart does not necessarily cover all of these ports.

Offshore navigation in the Indian Ocean

The Indian Ocean is crossed by major offshore routes. Navigation between South Africa, Madagascar, Réunion, Mauritius, the Seychelles, India or Asia may involve several hundred or several thousand nautical miles.

For offshore navigation, a small-scale chart provides a general view of the route. It does not, however, provide the same level of detail as a coastal chart.

The navigator should therefore organise charting according to the different stages of the voyage:

• general route planning;

• ocean crossing;

• approach to an island or archipelago;

• coastal navigation;

• entry into a channel or passage;

• harbour approach;

• anchorage navigation.

This sequence of scales is particularly important in the Indian Ocean, where the distances between some islands are considerable.

Reefs, passes, shoals and anchorages

The island environments of the Indian Ocean can present specific navigational challenges.

Coral reefs, shoals, banks, passages and shallow-water areas must be identified using appropriate charting.

When approaching an island, chart accuracy and scale become particularly important. An offshore chart can be used to prepare the approach to the region, but a larger-scale coastal chart is generally required to study approaches, channels and anchorages in greater detail.

Reading soundings, depth contours, buoys, lights, hazards and landmarks is therefore an important part of using a Shom nautical chart.

What information can be found on a Shom C chart?

Depending on the geographical area and scale, a Shom C chart may show:

• soundings and depths;

• depth contours;

• coastlines;

• reefs;

• shoals;

• rocks;

• wrecks;

• channels;

• passages;

• buoys and other aids to navigation;

• lights and their characteristics;

• landmarks;

• ports;

• anchorages;

• certain regulatory limits;

• information required for navigation planning.

The level of detail depends directly on the chart scale. An oceanic chart should therefore not be interpreted in the same way as a chart covering a harbour area.

The importance of scale

Scale is one of the main criteria when selecting a nautical chart.

A small scale makes it possible to represent a large area. It is particularly suitable for offshore navigation and general passage planning.

A large scale represents a smaller area but allows more detail to be displayed. It is particularly suitable for coastal navigation, harbour approaches, reef passes and anchorages.

The Shom C Indian Ocean category includes several levels of coverage, including coastal, littoral, offshore and oceanic areas.

Differences between Shom C, L, G, Z and Raster charts

The Shom C is therefore preferred when a large reading surface and flat presentation are important.

The Shom L uses a folded presentation that is more compact for storage.

The Shom G provides additional information about the nature and distribution of seabed sediments.

The Shom Z adds an overlay concerning exercise and firing areas used by maritime forces.

Shom Raster corresponds to a digital representation intended for certain charting and navigation software.

Shom C chart and Indian Ocean passage planning

A Shom C Indian Ocean chart can form part of the preparation for a long-distance voyage, for example between South Africa and Madagascar, Madagascar and Réunion, Réunion and Mauritius, or between the Mascarenes and the Seychelles.

For longer passages, it may be combined with charts covering the Mozambique Channel, the African coast, India, Sri Lanka, Southeast Asia or Australasia.

Chart preparation should always distinguish between the general route and the local approach. The chart used to cross the ocean is not necessarily the chart appropriate for entering a port or transiting a reef pass.

Complementarity with other nautical documents

A nautical chart is an essential component of navigation documentation, but it forms part of a wider set of resources.

Depending on the type of navigation, the navigator may also need charts at different scales, nautical publications, sailing directions, atlases, sailing guides and navigation manuals.

In the Indian Ocean, this complementarity is particularly useful for preparing passages between islands and continents, followed by approaches to coasts, ports and anchorages.

Paper documentation can also be used alongside digital charting, depending on the electronic equipment available on board.

How to choose a Shom C Indian Ocean nautical chart

Before selecting a reference, it is advisable to check:

• the exact geographical area;

• the country, island or archipelago concerned;

• the departure and destination ports;

• the planned route;

• the required scale;

• whether offshore or coastal navigation is intended;

• the passages or channels to be transited;

• the anchorages being considered;

• the chart edition;

• applicable corrections and nautical information.

For navigation around Madagascar, for example, a chart of the approaches to Île Sainte-Marie will not meet the same requirements as a chart covering the south-western part of the island or the Morondava area.

Likewise, a chart covering Réunion and Mauritius does not serve the same purpose as a detailed chart intended for a harbour approach.

Conclusion

The Shom C Indian Ocean nautical chart category covers a vast range of maritime areas in the Indian Ocean, particularly Madagascar, Réunion, Mauritius, Mayotte, the Mascarenes and various sectors of the western Indian Ocean.

The Shom C format, flat and generally rolled, provides a large reading surface suitable for route planning and studying maritime areas.

The variety of available scales is essential for meeting the different stages of navigation: ocean crossing, approach to an island, coastal navigation, passage through a reef pass, anchoring or harbour entry.

Shom C charts may cover areas including Île Sainte-Marie, Toamasina, Morondava, Réunion, Mauritius, Tromelin and other maritime areas charted by Shom in the Indian Ocean.

For comprehensive voyage preparation, they should be considered alongside the other Shom formats, including C, L, G, Z and Raster, as well as nautical charts at different scales, nautical publications, atlases, sailing directions and navigation manuals.

FAQ – Shom C Indian Ocean Nautical Chart

What is a Shom C Indian Ocean nautical chart?

It is a flat paper nautical chart, generally supplied rolled, covering an Indian Ocean maritime area charted by Shom. Depending on its scale, it may be intended for oceanic, offshore, littoral or coastal navigation.

Which Indian Ocean areas are covered by Shom C charts?

The range includes Madagascar, Réunion, Mauritius, Mayotte, the Mascarenes and various sectors of the western Indian Ocean. Some charts also cover wider areas linking the Indian Ocean with Australasia.

Are there Shom C charts of Madagascar?

Yes. Several references cover different sections of the Malagasy coast, including Île Sainte-Marie, Toamasina and Morondava.

Are there Shom C charts of Réunion?

Yes. Several charts cover different parts of Réunion, including its southern coast and surrounding maritime areas.

Is there a Shom C chart covering Réunion and Mauritius?

Yes. Reference 7349C covers, in particular, the area between Réunion and Mauritius as well as Tromelin Island.

Which ports may be covered by Shom C charting of the Indian Ocean?

Depending on the areas covered, examples include Port Réunion, Saint-Pierre, Port Louis, Port Mathurin, Mamoudzou, Moroni, Toamasina, Mahajanga, Toliara, Morondava, Port Victoria, Dar es Salaam, Mombasa, Durban and Richards Bay.

What is the difference between a Shom C and a Shom L chart?

The Shom C is a flat paper chart, generally supplied rolled, whereas the Shom L is a folded paper chart. The two formats may cover comparable navigation areas, but their physical presentation is different.

What is a Shom G chart used for?

A Shom G chart provides additional information concerning seabed characteristics and the distribution of different sediment types.

What is a Shom Z chart used for?

A Shom Z or Zonex chart contains an overlay identifying exercise and firing areas used by maritime forces.

What is a Shom Raster chart?

Raster is a digital representation of a nautical chart intended for certain compatible charting or navigation software and systems.

Which scale should be chosen for navigation in the Indian Ocean?

For an ocean crossing, a small-scale chart provides a general view of the route. For coastal navigation, a harbour approach, reef pass or anchorage, a larger-scale chart is required.

Is one Shom C chart enough for an Indian Ocean crossing?

This depends on the route, but a long crossing generally requires several charts covering the different stages of the voyage, followed by more detailed charts for coastal and harbour approaches.

Are Shom C charts suitable for navigation around reefs and atolls?

They can be when the reference and scale correspond to the area concerned. For a reef pass, reef, anchorage or coastal approach, it is essential to use charting at an appropriate scale.

Which documents should be used with a Shom C Indian Ocean nautical chart?

Depending on the voyage, charting can be supplemented with other nautical charts, offshore and coastal charts, sailing directions, nautical publications, atlases and navigation manuals.