Understanding chart symbols

→ How to read and decipher chart symbols

Understanding chart symbols takes a little practice before you set sail. Knowing how to read a nautical chart and decipher the symbols it contains will save you a lot of trouble when sailing, even though electronics are increasingly present on board today.

To help you make sense of things, a nautical chart provides essential information such as water depth, obstacles, currents, beacons and danger zones. In line with maritime signage standards, it facilitates orientation and location at sea, by grouping together essential data.

The nautical charts take into account weather and ocean conditions, including tides, currents, sea state and potential hazards on your route.

Chart information and symbols, including depths, hazards and seabed features, are standardized worldwide. In France, SHOM (Service Hydrographique et Océanographique de la Marine) ensures that French charts are aligned with international standards.

So it's essential to understand your marine environment, as well as chart symbols, so you can plan your navigations with complete peace of mind. Atlantic card

→ Using nautical charts: our essential tips

To read a maritime chart and understand chart symbols, you need to refer to your chart's nomenclature and identify the information you need: depth zone colors, numbers on soundings and levels, letters, and symbols and markings.

Mastering the reading of geographic coordinates will enable you to read a nautical chart with greater precision. Here are a few steps to follow before you start deciphering your nautical chart.

➡️ Understanding symbols Learn the symbols before you sail.

➡️ Compass rose Use it to orient yourself.

➡️ Calculating distances Distances on nautical charts are in nautical miles, slightly longer than land miles.

➡️ Tides and currents Tides and currents: consult information on tides and currents to plan your route safely.

➡️ Updates Check that your maps are up to date, especially before you leave.

➡️ Chartplotter Use a chartplotter or GPS app, such as Savvy Navvy, to track your position in real time.

➡️ Navigation techniques Combine maps, GPS and visual observations for safe navigation.

→ Chart symbols: color coding and markings

Nautical charts use a color code to indicate depths : blue for deep water, and colors such as green, yellow and brown for shallow areas. Land features appear in brown, while water features are in blue or green. Navigational hazards, such as rocks or wrecks, are in black or red.

It's crucial to consult the legend to fully understand chart symbols, and to use additional information (depths, tides, currents) to navigate safely. Electronic systems can simplify reading, but an emergency paper chart remains indispensable.

To help you decide which chart to choose, whether it's a Atlantic card , a seabed chart or a Mediterranean marine chart , if you're sailing in the South, take into account the activity you're involved in and the distance from the coast in miles.

→ The different types of paper charts

There are 3 types of navigation charts:

▪️ Yellow charts (scale 1/25000 to 1/10000; use: coastal navigation)

▪️ Red charts (scale: between 1/60,000 and 1/40,000; use: offshore navigation; distance from coast: 5 miles)

▪️ Green charts (scale: 1:1,100,000 to 1:300,000; use: crossings; distance from coast: 10 miles)

On a nautical chart, different colors are used to distinguish different zones.

▪️ White: these are areas of deep water, i. e. waters over 10 meters deep.

▪️ Blue: these are shallow water zones, i. e. waters between 0 and 10 meters deep.

▪️ Green: this is the area known as "foreshore", i. e. the strip of coastline that is submerged at high tide, but likely to emerge at low tide.

▪️ Bistre (brown): this is simply the color that represents dry land.

→ Nautical chart symbols in pictures

The symbols on the nautical charts represent marine features and hazards. A nautical chart probe indicates water depth. Lighthouses and beacons indicate dangerous areas.

Rocks, shoals or the charted wreck symbol, represented by circles or an "X", mark potential hazards. Channels are indicated by a charted sounding line, and anchor symbols show safe areas for dropping anchor.

Navigation buoys, identified by shape, color and illumination, mark channels and hazards. The International Hydrographic Organization (IHO) standardizes these chart symbols to ensure safe navigation. The letters below the buoyage are also part of the chart symbols and indicate the buoy colors:

▪️ B for Black

▪️ W for White

▪️ G for Green

▪️ Y for Yellow

▪️ R for Red

All the following marker symbols can be found here:

How to read and decipher the main chart symbols

Numbers in italics on navigational charts indicate the minimum depth of water at a given point, measured from level 0 corresponding to the lowest tide for a coefficient of 120. The first number represents meters, the second decimeters.

Example: 23 means 2.3 meters deep. If the number is underlined, it indicates a negative probe, where the bottom rises above the surface at low tide. Numbers in brackets indicate a slight offset between the actual position and that shown on the chart, to avoid information overload.

Upper-case letters on charts designate the nature of the seabed , with abbreviations in English such as S for sand, M for mud and R for rock. Lower-case letters describe the quality of the seabed, with "f" for fine or "h" for hard.

This information is essential for navigators to understand the depth and characteristics of the seabed, particularly useful for anchoring or navigating in shallow areas.

→ How do you find your way around chart symbols?

To find your bearings at sea, it's crucial to know how to read the basic markings on a navigation chart boat , such as scale, latitude and longitude. So you can accurately interpret your environment at sea and navigate safely.

➡️ The scale

The scale of a map is usually located at the bottom right or bottom left of the map. It corresponds to the map's reduction factor in relation to reality. So, for a scale of 1/25,000 (also known as 1:25,000), 1 centimeter on the map corresponds to 25,000 centimeters in reality, or 250 meters.

➡️ Longitude and latitude

Geographical coordinates are expressed in longitude (G) and latitude (L) in the DMS system (degrees, minutes, seconds). One degree comprises 60 minutes, and one minute 60 seconds, with 1 minute equivalent to 1 nautical mile (1.852 km).

▪️ Longitude: Represented by vertical lines (meridians). East of Greenwich (0°), we note X°E, and west, X°W.

▪️ Latitude: Represented by horizontal lines (parallels). North of the equator, we note X°N, and south, X°S.

Example: A point with a longitude of 45°46'24.6 "N and a latitude of 4°47'51.7 "E reads: 45 degrees, 46 minutes, 24 seconds, 6 tenths North, 4 degrees, 47 minutes, 51 seconds, 7 tenths East.

→ Reading a nautical chart: Nautisports advises you

At Nautisports, if you're browsing our marine bookshop and you'd like to find a wide selection of nautical charts, we've got just what you need: Navicarte charts, Shom marine chart or seabed charts. You'll be able to find the marine chart that meets your navigation needs.

Finally, because of the composition of paper charts, the plastic sleeve is an essential waterproof accessory to protect your chart and SHOM chart from splashing water.

You can find all the details, areas covered, material, dimensions of a chart by consulting its product data sheet, where all this essential information appears.

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