Shom G Nautical Chart – Sedimentological Chart

Introduction

The Shom G nautical chart is a sedimentological chart showing, in addition to standard nautical information, the nature and distribution of seabed sediments. Published by the French Hydrographic and Oceanographic Service (Shom), it is a specialized document that is particularly useful for understanding seabed characteristics in coastal areas and on the continental shelf.

A Shom G chart combines the main information found on a conventional Shom nautical chart with additional sedimentological information: pebbles, gravel, sand and other types of seabed formations. Sediment information is shown as an overlay on the underlying nautical chart.

These charts are particularly useful for fishing, marine environmental studies, anchoring, maritime works and professional activities requiring detailed knowledge of the seabed. They can also provide useful additional information for sailors wishing to better understand the nature of the seabed along a coastal route.

What is a Shom G nautical chart?

The letter “G” identifies Shom seabed nature charts. Their specific feature is that sedimentological information is displayed directly on a marine cartographic base.

The chart therefore combines conventional nautical information with the distribution of different types of seabed. It includes soundings, depth contours, hazards, wrecks, rocks, buoys, lights, channels and other information required to understand the maritime environment.

The sedimentological layer provides additional information about the seabed: areas of sand, gravel, pebbles and other sediment categories. This information comes from different sources and acquisition methods, including hydrographic data and seabed characterization techniques.

Marine sedimentology is important for understanding hydrodynamics, wave propagation, certain risk areas and anchoring conditions.

A Shom G chart should nevertheless not be considered a replacement for a standard navigational chart. Shom specifies that G charts provide complementary sedimentological information and are not intended to replace nautical charts.

What is a Shom G sedimentological chart used for?

Knowledge of seabed characteristics can be important in many maritime situations.

It can be used to:

• identify areas dominated by sand, gravel or pebbles;

• study potential anchoring areas;

• complement the analysis of fishing grounds;

• understand continental shelf characteristics;

• support certain environmental or marine studies;

• analyze seabeds in connection with underwater works;

• study sediment transport and seabed dynamics;

• complement anchorage and anchor-holding studies;

• obtain a synthetic representation of the underwater environment.

Marine sedimentology is also relevant to studies involving submarine cables and pipelines, marine aggregates, offshore renewable energy projects, underwater research and the location of submerged objects and wrecks.

The nature of the seabed plays an important role in the burial and re-emergence of certain objects under the effects of currents and waves.

The different types of Shom nautical charts

Shom provides several types and formats of nautical charts. The letters C, L, G and Z refer to products with different characteristics, while Raster charts provide a digital version of nautical charts.

Shom L charts contain the same cartographic information as the corresponding C charts with the same chart number, but are supplied folded. G charts add sedimentological information, while Z charts include an overlay relating to exercise areas.

Raster charts are georeferenced digital images of nautical charts. Shom distributes these charts notably in GeoTIFF format, with a resolution of 300 dpi for the corresponding georeferenced digital images.

Shom G charts and seabed characteristics

The main advantage of a sedimentological chart is that it allows the spatial distribution of different seabed types to be visualized.

Seabed characteristics influence many coastal processes. A sandy area does not necessarily have the same characteristics as an area of gravel or pebbles. Sediments contribute to the dynamics of the coastline and continental shelf and can be transported by currents and wave action.

For sailors, this information can complement anchorage analysis. For professional fishermen, it provides a cartographic representation of the types of seabed found in a given area.

The G chart is therefore primarily a specialized document, particularly useful when seabed characteristics are an important parameter for a maritime activity.

Where are Shom G charts available?

Shom G charts cover various French maritime areas in the English Channel, Atlantic Ocean and Mediterranean Sea. The Nautic Way catalogue includes sedimentological charts covering areas in the English Channel, Atlantic and Mediterranean.

In the English Channel, mapped areas can include sectors such as the Bay of Seine, Cotentin, Barfleur, the Saint-Marcouf Islands and the approaches to Cherbourg.

Along the Atlantic coast, G charts may be relevant to Brittany, Vendée, Charente-Maritime, the Gironde estuary, the Bay of Biscay and the Aquitaine coast. The marine environments around Brest, Lorient, La Rochelle, Royan, Arcachon and the mouth of the Gironde have very different seabed configurations.

In the Mediterranean, sedimentological mapping covers various areas of the French coast, from the Gulf of Lion to Provence and the French Riviera. Areas around Marseille, Toulon, Cannes, Nice and Cap Ferrat can therefore be studied using documents adapted to their marine environment.

The Shom catalogue includes, for example, chart G 7422G, covering the area from Pointe de Barfleur to Pointe de la Percée and the Saint-Marcouf Islands; G 7426G, covering the area from Pointe de la Coubre to Pointe de la Négade and the Gironde estuary; and G 7443G, covering the area from Cap Ferrat to Cap San Lorenzo.

Shom G charts, fishing and professional activities

Charts showing seabed characteristics are particularly important for professional fishing. Sediment distribution is an environmental factor that can complement other data used to characterize fishing grounds.

This information is also relevant to marine studies. Sedimentological data can be used in environmental assessments, maritime development projects, underwater infrastructure and scientific research.

Shom explains that sedimentological data are incorporated into a database in order to produce sediment maps at different scales, from detailed coastal studies to smaller-scale representations of the continental shelf and deep-ocean areas.

Shom G charts and navigation

A Shom G chart retains a marine cartographic base that allows the main geographical and nautical features to be located. It can therefore be used alongside a conventional nautical chart.

When preparing a voyage, it is important to distinguish between the functions of the various documents:

• the nautical chart is used for navigation and identifying hazards;

• the G chart adds information about seabed characteristics;

• sailing directions provide descriptive information about coastlines, ports and approaches;

• specialized atlases and publications can complement the study of a particular area;

• digital charts can be used with compatible navigation software.

The G chart should therefore be regarded as a complementary source of information rather than a replacement for the other documents required for properly planned navigation.

Comparison with other nautical chart publishers

Shom is the French national hydrographic service and its charts cover French maritime areas and waters under French responsibility. For international navigation, other hydrographic offices and nautical chart publishers are also widely used.

Admiralty, the United Kingdom's nautical charting service, publishes charts covering British waters, the English Channel, North Sea, Atlantic Ocean and numerous international shipping routes.

Imray is particularly well established in recreational and cruising cartography, with extensive coverage of the Mediterranean, Atlantic Ocean, Caribbean and other cruising areas.

NV Charts also publishes paper and digital nautical charts, particularly for Europe, the Mediterranean and various cruising regions.

For navigation around ports such as Brest, Cherbourg, La Rochelle, Marseille, Toulon or Nice, the appropriate document depends on the geographical area, chart scale, type of navigation and intended use.

Format and presentation of a Shom G chart

Shom G charts are supplied folded to A4 size, with an unfolded chart of approximately 84 × 119 cm depending on the characteristics indicated by Nautic Way.

This format makes it easier to store and consult a large cartographic area without having to keep the entire chart permanently unfolded.

The chart number is the essential reference for accurately identifying a particular area. It is important to check the chart number, geographical coverage and edition before use.

Why choose a Shom G nautical chart?

A Shom G chart meets a specific requirement: it provides both marine cartographic information and specialized information about seabed characteristics.

It is particularly relevant when knowledge of the seabed complements conventional nautical information. It is useful for professional fishermen, marine consultants, maritime construction specialists, marine environmental professionals and sailors wishing to gain a deeper understanding of a particular area.

When identifying the appropriate chart, the main factors to consider are:

• geographical area;

• Shom chart number;

• scale;

• type of maritime activity;

• level of detail required;

• edition date or year;

• compatibility with other nautical documents.

Conclusion

The Shom G nautical chart is a specialized cartographic document dedicated to seabed characteristics. It combines nautical chart information with a sedimentological representation showing the distribution of major seabed types, including sand, gravel and pebbles.

It is useful for fishing, seabed studies, anchoring, maritime works, environmental studies and the analysis of coastal and continental shelf areas. It is particularly valuable when knowledge of the seabed complements conventional navigational information.

For complete nautical use, the Shom G chart should be considered a complementary document rather than a substitute for a navigational nautical chart. Its particular value lies in combining marine cartography with detailed knowledge of seabed sedimentology.

FAQ – Shom G Nautical Chart

What is a Shom G nautical chart?

A Shom G chart is a sedimentological chart published by the French Hydrographic and Oceanographic Service. It uses a marine cartographic base and adds information showing the nature and distribution of seabed sediments.

What do Shom G sedimentological charts show?

They show the distribution of different types of sediment, including sand, gravel and pebbles. This information is superimposed on conventional nautical chart information.

Does a Shom G chart replace a conventional nautical chart?

No. Shom specifies that a G chart provides complementary sedimentological information and is not intended to replace a nautical chart.

What is a Shom G chart used for in fishing?

It shows seabed characteristics in a given area and provides useful additional information for professional fishing activities.

Are Shom G charts available for the Mediterranean Sea?

Yes. Shom's sedimentological G charts cover various areas of the English Channel, Atlantic Ocean and Mediterranean Sea. The exact coverage depends on the chart number and geographical area.

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

A Shom C chart is a standard paper nautical chart. A Shom G chart uses marine cartographic information and adds specific information about seabed characteristics.

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

A Shom L chart is a folded paper nautical chart. A Shom G chart is also folded, but includes an additional sedimentological overlay showing seabed characteristics.

What is the difference between a Shom G chart and a Shom Z chart?

A G chart adds information about seabed characteristics. A Z, or Zonex, chart includes an overlay showing exercise and firing areas. They are therefore two different types of specialized charts providing different additional information.

Are digital Shom nautical charts available?

Yes. Shom distributes digital raster nautical charts, including georeferenced images available in formats such as GeoTIFF.

Which maritime areas are covered by Shom G charts?

G charts cover various areas of the English Channel, Atlantic coast and French Mediterranean coast. Exact coverage depends on the individual chart number and geographical area.