Navigation: Read a Marine Chart Part 2

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This is part two in a two-part article about learning the basics of reading a marine chart. Part one, Navigation: Read a Marine Chart Part 1, covered reading the basics discovered at first glance, like the chart’s scale, name and variation. This part is about the specific symbols on a chart, like water depths, lights, buoys, underwater features and more. Although there are more symbols than found in this article on a chart, learning to read these basic symbols will help you while studying others. For most paddlers, these will be plenty.

Soundings

The numbers that appear all over the water portions of the chart are soundings. They show how deep the water is at that point. Sounds are either in feet, meters or fathoms. A fathom is 6 feet. Typically, soundings given in fathoms or meter are given in fathoms and feet or meters and fractions. The last digit in the reading is feet or fractions and the rest are fathoms. For example, if the sounding is 45₃, the reading is 45 fathoms 3 feet. In metric, a 4₅ means4-1/2 meters. Related to sounds are depth contours, which are lines that show a similar depth. They look like contour lines and are different shades of blue on color charts. They are typically given at 4, 3, 2 and 1 fathoms. Additional sounding may appear within the depth contours. For example, the inside the depth contours around Little Siskiwit Island, depths of 3, 8, 5 and 10 feet are shown.

Lights, buoys and day markers

A few aids to navigation include lights, buoys and day markers. During the day, features like color, shape and labels help differentiate one aid from an other. At night, some markers have lights, which flash at different rates and in different colors. Sometimes, they may have sounds, too, like a bell or a horn. These features are labeled on the chart.

For a light, a chart typically lists: color, phase, period, height above chart datum and distance visible from. For example, the Rock of Ages Light is white (because it isn’t designated on the chart). It flashes every ten seconds (Fl 10s). It is 130 feet (130ft) above the chart datum, and sailors can see it from 12 statute miles away (12 St M).

Buoys and other markers, typically use the same types of designations. A floating buoy is drawn at an angle on the chart and beacons fixed to the sea floor are drawn vertical. Common labels include color, shape, designation and sound. If the marker has a light, the light’s characteristics are labeled. The two main buoy colors are green and red. In the Americas, when returning to a harbor, you keep the red buoys on your starboard. The rhyme to remember is “red right returning.” The two common shapes are cans or nuns. A can looks like the top of a soup can and a nun is pointed like a cone. Buoys are typically labeled with a letter or number. Red buoys are labeled with an even numbers and green buoys with an odd numbers. For example, the buoy southwest of Rock of Ages is a red (R), nun (N) buoy, which is labeled number 2 (“2”). There are many types of buoys, it’s best to read your chart before a trip and lookup the buoys that you don’t know in Marine Chart No. 1.

Seabed qualities

For paddlers, two important seabed qualities are shipwrecks and danger designations. Two common symbols for a shipwreck are shown in the Rock of Ages lighthouse example. One looks like half a hexagon shaded black, and the other looks like three lines crossing a single line. The first means that the wreck is visible, and the second, if surrounded by dotted lines, means the wreck’s masts are visible at chart datum. Related to the second are areas outlined by dotted lines. These indicate danger areas. Within these rings, rocks are shown as asterisks, pluses or pluses with dots around them. These mean rocks that cover and uncover, dangerous unknown depth and just under the surface at chart datum, respectively.

Along the shoreline, some charts show a green shaded area with a dotted edge or a jagged edge. These areas show the nature of the seabed in intertidal areas. The dotted edge designates a stone, gravel, mud, sand or shingle seabed. The jagged edge means rock or coral.

Chart Tidal Features

Example tidal features on a marine chart

As the tide comes in and goes out, it can create currents, especially in areas that have constricted openings. In these areas, the currents might create tide rips, eddies, overfalls or races. On a NOAA marine chart, the currents are shown as arrows with labels. The labels tell you the speed of the current and whether it flows that direction on a flood or ebb. In the example Port Townsend chart, near the R “6” buoy the currents are labeled “E 2.6 kn” and “F 2.2 kn.” The first means it flows at 2.6 knots on an Ebb flow, which is when the water is going out to sea (low tide). The second means it flows at 2.2 knots on a flood current, which is when the water returns from the sea to the shore (high tide). Sometimes ebb and flood isn’t labeled with a letter. In these cases, the flood arrow looks like it has feathers on its end. Although, the chart current labels give you an idea of the flow, you still should check the area’s current and tide tables for timing.

An other symbol or label to look for is something that looks like waves or an ‘@’ symbol without the ‘a’. These indicate tide races or eddies, respectively. If the feature is present, but not called out with a symbol, it might be labeled. For example, on the Port Townsend chart example tide rips are labeled “Tide rips.”

Landmarks

Charts show various landmarks that can help you navigate. One common symbol is a circle with a dot in it. These often represent many types of landmarks, like towers, tanks, chimneys, churches, spires, monuments and more. Next to each circle, you’ll see a label that tells you exactly what it is. For example, on Admiralty Head a circle is labeled TOWER (Aband Lt Ho), which means that it marks an abandoned lighthouse.

Natural Features

Natural features on a chart show the nature of the coastline, its relief, water features, like rivers and shoreline vegetation. These give a good idea on where a canoe or kayak can land, but a topo map typically describes the shoreline in more detail. If the chart shows the shoreline as a solid line, then it has been survey. If not, you’ll see a dotted line. Black lines against the shoreline show cliffs. Several bands of dark lines mean a steeper cliff. A solid shoreline with small dots can mean sand. If the dots are larger or circles, then the shoreline is stones. Not all charts use all the shoreline symbols even if the shore could be labeled.

Sometimes, relief on a chart is shown like relief on a topo map with contour lines. Each line designates a set height from the last line. For example, on the Apostle Island chart, each line is 20 feet from the last line. The closer the lines are together, the steeper the hill or cliff. On Oak islands east side, the lines are close together and could designate a cliff and most likely means that a canoe or kayak couldn’t land there. Other times, charts show relief with form lines and spot heights. The form lines look like contour lines, but only show near turns in the land. Spot height show the high points on land with a circle and a number. A spot height of 1075 feet is on Oak Island’s high point.

Example of vegitation and rivers on a chart.

Natural features show rivers as blue indents at the mouth and black lines leading away from the shore when the river becomes unnavigable. The chart may also show the type of vegetation along the shoreline. This can range from little symbols of trees to swamps to dotted lines surrounding a text label. In the Raspberry Bay chart example, notice the river in the bay’s southwest corner and notice the grass-like symbols along the shore. That symbol designates a marsh.

Marine Chart Number 1

NOAA’s marine chart number 1 lists all the symbols shown on a NOAA chart. It’s a big book and probably too big to bring along on a kayak or canoe trip, but it’s free. Get the Marine Chart No. 1 for free. It’s also available online in a searchable format.