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Nautical Chart Challenge

For as long as anyone in his family could remember, 

Francis Beaufort wanted to make scientific observations 

from the deck of a ship. In 1789 at the age of fourteen, 

he set sail as a sort of officer-in-training aboard the 

Vansittart, an East India Company tradesman bound for 

China and the Indies. A central goal of the Vansittart’s 

journey was to survey the Gaspar Strait, where sister 

ships of the East India Company had been lost on 

dangerous and poorly charted shoals.

The Vansittart found the shoals...by running hard 

aground, and taking on water so rapidly that the crew was 

forced to abandon ship on a tiny reef in the Java Sea. 

The waters were filled with pirates, so the crew threw 

thirteen treasure chests overboard, hoping to return 

later to reclaim them. But when they eventually made 

their way back aboard two British ships, Malay pirates 

had burned and pillaged the Vansittart and the crew 

managed to recover only three of the treasure chests.

~ based on Defi ning the Wind: The Beaufort Scale, and How a

19th-Century Admiral Turned Science Into Poetry by Scott Huler, 2004

The sinking of the Vansittart provided dramatic evidence of the value 

of an accurate nautical chart, and Francis Beaufort later became one 

of history’s premier hydrographers. Today, NOAA’s O ce of Coast Survey 

produces accurate nautical 

charts and many other 

navigational aids that help 

mariners navigate safely in 

and out of U.S. ports and 

along the U.S. coastline as 

far as 200 nautical miles 

from shore. How important 

is ocean navigation? You 

may be surprised to know 

that even in the “space 

age,” over 98% of the 

nation’s cargo is carried by 

waterborne transportation.

Here’s a chance to try your 

hand at coastal nav- igation using a modern nautical chart. Watch out for 

shoals!

What You Will Do

Discover some of the ways a nautical chart 

can help a mariner safely 

navigate in unfamiliar coastal waters

iWreck of U.S. Revenue Cutter TAHOMA which struck an 

uncharted pinnacle rock off Agattu Island, western Aleutians, 

September 20, 1914. Courtesy NOAA Ship Collection
National Oceanic and Atmospheric Administration (NOAA) 29

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What You Will Need

❒ “Segment of NOAA Nautical Chart 11445, Bahia 

Honda Key to Sugarloaf Key”

How to Do It

1. Before beginning your cruise, you need to 

know a few things about nautical charts. 

Most charts contain A LOT of information, 

including lights, buoys, wrecks, information 

about the sea bottom, shoreline features, 

water depth, and much more. These features 

are often very close together, so charts use 

many symbols and abbreviations. A complete 

list of these symbols is available in a booklet 

known as “Chart No. 1,” which can be downloaded from www.nauticalcharts.noaa.gov/mcd/

chartno1.htm (the fi le containing the entire 

publication is 85 Mb, but smaller fi les containing specifi c kinds of information are also 

available). Here are a few basics:

• The compass rose is a tool provided on all 

nautical charts to simplify the process 

of measuring directions. On the sample 

chart, the compass rose is near the upper 

center of the chart. The most commonly 

used reference point for direction on nautical charts is Earth’s geographic north 

pole (“true north”). 

• Depths on nautical charts are shown as 

many small numbers scattered over water 

areas. Depths indicated by these numbers are expressed in feet, fathoms (one 

fathom is equal to six feet), or meters. 

Contour lines (called “depth curves”) 

connect points of equal depth, typically 

6, 12, 18, 30, 60 and multiples of 60 feet. 

It’s important to remember that depths 

shown on charts are average depths, so 

the actual depth at a given location may 

be less than that shown on the chart.

• The general rule for coastal navigation is 

“red, right, returning.” This means that 

red markers, lights, or buoys should be 

on the right side of a vessel when coming 

into port. There are many exceptions to 

this general rule, though, so it is essential 

to have a chart that shows the arrangement of markers for a specifi c part of the 

coast.

• In shallow water, markers are often fl at 

“signs” fastened to wood or metal stakes. 

Red markers are usually triangular, and 

green markers are square. These markers 

are shown on a chart by red triangles and 

green squares, and usually have a number 

that also is shown on the chart.

• Buoys are shown on nautical charts by diamond-shaped symbols and a small open 

circle that indicates the location of the 

buoy. 

• Red buoys are printed in magenta and often 

have the letter “R” nearby.

• Green buoys are printed in green with the 

letter “G” nearby. 

• A number in quotation marks is the number 

painted on the buoy’s structure. 

• Lighted buoys are indicated by a magenta 

disk printed over the small circle that 

marks the buoy’s position. 

• The shape of unlighted buoys is normally 

shown by a letter. “C’ indicates a “can” 

buoy whose top has a cylindrical shape

• “N” indicates a “nun” buoy whose top is shaped 

like a cone with the pointed end cut off (this 

is called a “truncated” cone).

• Lights on nautical charts are all shown by a 

magenta symbol that looks like an exclamation point and a black dot indicating 

the light’s position. Notes alongside these 

symbols describe the color of the light 

and how it fl ashes. Some commonly used 

abbreviations are:

• Q: A light fl ashing at a rate of not less 

than 60 fl ashes per minute

• R: A red light.

• G: A green light

• If no color is indicated for a light, it is 

understood to be a white light.

• Numbers next to the symbol for a light show 

the height of the light. 
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• If numbers are inside quotation marks, this 

number is painted onto the light structure. 

• Numbers followed by the letter “M” show the 

approximate range of visibility of the light 

in miles. 

For example:

 Q R 16ft “6” 9M

 indicates a red light, 16 ft high, fl ashing at a rate of not less than 60 fl ashes 

per minute (“quick fl ashing”), with the 

number “6” painted on the structure, with 

a visibility of about 9 miles

2. Now it’s time to take the Chart Challenge! 

 We will use part of NOAA Nautical Chart 

11445, which includes the Florida Keys from 

Bahia Honda Key to Sugarloaf Key. Suppose 

you are the captain of a 24-foot fi shing boat, 

and are taking some friends around the 

Keys. As the captain of a vessel, it is very 

important to know how much water is under 

your boat (underkeel clearance). This can 

vary depending on how much cargo you are 

carrying (or in this case, how many friends 

are aboard). Let’s say that your boat draws 2 

feet, which is another way of saying that the 

bottom (keel) of your boat is two feet below 

the surface. So, you’ll need to subtract two 

feet from the depths indicated on the chart 

to fi nd your underkeel clearance.

a. You and your friends board your boat at the 

dock in Doctors Arm Bay on Big Pine Key 

(to the right of the compass rose). What 

kind of markers show the location of this 

dock?

b. After casting off from the dock, you steer 

southeast into Bogie Channel. What is the 

maximum depth shown on the chart for 

the Channel?

c. As you pass through Spanish Harbor, you 

notice a low bridge ahead. The highest 

point on your boat is 10 feet above the 

water. Can you pass beneath the bridge?

d. You continue heading southeast until your 

depth sounder shows a depth of 10 feet. 

What does the chart show is probably on 

the bottom in this area?

e. Your friends are interested in snorkeling, 

so you decide to take them to the buoyed 

snorkeling area to the south of Newfound 

Harbor Keys, which is part of NOAA’s 

Florida Keys National Marine Sanctuary. 

Looking at the chart, you see that there 

are several shallow coral heads marked 

“Co” that are not marked with buoys. 

What is the water depth over these coral 

heads?

f. Since the water over the coral heads is very 

shallow, you want to steer a course that 

will avoid them. How could you use your 

depth sounder to help steer clear of these 

dangers?

g. As you travel toward the snorkeling area, 

one of your friends notices the vegetation 

on the islands to the north. According to 

the chart, what kind of vegetation is this?

h. According to the chart, the snorkeling area 

is marked by buoys labeled “A,” “B,” “C,” 

and “D.” What is the color and shape of 

these buoys?

i. After snorkeling, you decide to visit Ramrod 

Key. One of your friends says that he can 

see open water between Hopkins Island 

and Cook Island. Would this be a good way 

to go to Ramrod Key?

j. After looking at the chart, you decide to go 

to the southwest of Munson Island to enter Newfound Harbor Channel. What light 

could you use to be sure you avoid the 

shallow area to the southwest of Munson 

Island? How tall is this light?

k. After passing Munson Island, you notice 

four markers that showing the location 

of Newfound Harbor Channel. What are 

the color, shape, and numbers of these 

markers, and how would you use them to 

stay in the Channel?

SCIENCE | Service | Stewardship
National Oceanic and Atmospheric Administration (NOAA) 31

SCIENCE | Service | Stewardship Explore the Ear

l. As you enter Newfound Harbor, you notice 

three green markers and a red marker 

leading into a marina. What is the water 

depth near these markers?

m. You change your mind, and decide to visit 

Little Torch Key instead. You want to go to 

a marina that is to the east of the microwave tower on Little Torch Key. Can your 

vessel pass beneath the bridge between 

Little Torch and Big Pine Key?

n. Just before you pass beneath the bridge, 

one of your friends notices something 

sticking up out of the water. Does the 

chart show anything in this area?

o. After you pass under the bridge, you notice 

a large marina on the west side of Big 

Pine Key. Are there any obstacles between 

your vessel and this marina?

Want to Do More?

For more about nautical charts and how to use 

them, see “Plot Your Course” at oceanservice.

noaa.gov/education/lessons/plot_course.html.

To make your own nautical charts, go to: https://

oceanservice.noaa.gov/education/nautical_

charts/makechart.html St. Brendan striking out into the Atlantic - about 6th Century A.D. St. Brendan checking depths with his sounding pole. 

Courtesy NOAA.
noaa.gov

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Segment of NOAA Nautical Chart 11445, Bahia Honda Key to Sugarloaf Key
National Oceanic and Atmospheric Administration (NOAA) 33

SCIENCE | Service | Stewardship Explore the Ear

a. A red triangle numbered “2” and a green 

square numbered “1”

b. 12 feet

c. Yes, because the vertical clearance beneath the 

bridge is 11 feet

d. rocks (“rky”)

e. one to three feet

f. You could use the depth sounder to follow the 

12-foot depth contour line, which will keep 

you away from the coral heads. 

g. Mangroves

h. The buoys are yellow “cans” that have a cylindrical shape.

i. No, because the chart shows depths of less 

than one foot between these islands.

j. The flashing red light which has the number “2” 

painted on the structure, and is 16 ft tall and 

visible for about three miles.

k. There are two square green markers numbered 

“3” and “5” and two triangular red markers 

numbered “2” and “6”. You would steer your 

vessel so that the red markers are to the 

right of the vessel and the green markers are 

to the left. 

l. one to two feet

m. You can pass beneath the west end of the 

bridge because the vertical clearance is 

15 feet, but the clearance is only nine feet 

under the east end of the bridge.

n. The chart shows three poles on the south side 

of the bridge.

o. The chart shows submerged pilings to the west 

of Big Pine Key.

Don’t Peek...

Answers to the Chart Challenge

Until you have answered ALL of the Chart Challenge questions!