Interpreting A Nautical Chart…Vital or Not?

With an array of symbols, shapes, colors, contours and numbers, properly reading a nautical chart is not only useful, but should be mandatory.

FSF Staff November 16, 2009

The purpose of a nautical chart is to provide mariners essential information needed to reach their desired destinations in a safe and timely manner. The year was 1807 and Thomas Jefferson was interested in the efficiency and well-being of marine transportation. The tough task of charting the 3.4 million square nautical miles in the U.S. Exclusive Economic Zone began with the introduction of The Office of Coast Survey (OCS). Now the oldest scientific organization in the country, the OCS is part of the National Oceanic and Atmospheric Administration. While the idea originated in 1807, it wasn’t until 1844 when the OCS released its first official nautical chart.

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To the untrained eye interpreting a nautical chart may seem like a daunting task. Photo: USCG

It’s very likely that your vessel is equipped with a technologically advanced chartplotter that provides essential data for safe navigation. And while compact, powerful, and user-friendly electronic charts feature highly desirable features such as satellite imagery linked to chart locations, weather overlay and 3D bathymetry just to name a few, there’s absolutely no substitute for high-quality printed charts. However, even updated paper charts won’t help you one bit if you don’t understand what you’re looking at.

…knowing how to properly interpret a nautical chart will enable you to compare what you see on the chart from your perspective on the water.

Upon close inspection, modern NOAA charts, which most fishing charts are overlayed on top of, provide mariners the general configuration of the seafloor, water depths, currents, locations of hazards to navigation, information about aids to navigation such as buoys and beacons, and so much more. All charts are derived from a common system of geographic coordinates known as the latitude-longitude system that’s based on imaginary circles that encompass the earth. Degrees of latitude and longitude can be found on the outer edges of every nautical chart. Latitudes run east-west, while longitudes run north-south. Because degrees of latitude are spaced evenly they are commonly used to measure distance, with 60-minutes in a degree and one minute equaling one nautical mile.

Pick up an official NOAA chart or a fishing chart derived from a NOAA chart for your particular region. At first glance you will notice a general information block that reveals the chart title, unit of depth measurement, type of projection scale, description of covered area, and general notes. One of the most essential features of a nautical chart is to display depth and bottom contours through numbers, colors and contour lines. The soundings may be referenced in either feet or fathoms, and it’s important to remember that depths are recorded at mean lower low water. White areas indicate deep water, while shallower depths are displayed in shades of blue and should be approached with caution. Shallow areas and submerged obstructions are often surrounded by dotted lines to indicate areas of hazardous navigation. A nautical chart’s contour lines are also referred to as depth curves and connect areas of similar depth.

The U.S. Coast Guard maintains various aids to navigation that utilize colors, shapes, numbers, and light characteristics to notify mariners of channels, waterways, and underwater obstructions. These aids can include beacons, buoys, markers and range lights and are abbreviated with letters, numbers and/or symbols to promote safe navigation. For example, if you see FL G 15ft 3m 5 on your chart you are looking at a flashing green buoy that’s 15-feet high, can be seen for 3-miles, and is labeled #5. There are many other abbreviations you may notice on charts as well, such as Co (coral), Rf (reef), Tr (tower), Bn (beacon) and Whf (wharf) to name a few. All symbols and abbreviations can be found in Chart No. 1, available for download at www.nauticalcharts.noaa.gov (highly recommended). The best way to learn how to read a nautical chart is to open one up and spend time studying it. The amount of information revealed on the chart is monumental.

There are no road signs or highway exits on the water and knowing how to properly interpret a nautical chart will enable you to compare what you see on the chart from your perspective on the water. The more knowledge you have, the safer you will be, not to mention that much of the information on charts such as reef locations and sharp bottom contours help keen-eyed anglers narrow down focal points likely to produce outstanding catches.

Local Notice To Mariners

The U.S. Coast Guard’s Local Notice To Mariners is a weekly report that updates corrections and discrepancies regarding important information to mariners. This information may include reports of channel conditions, obstructions, hazards and aids to navigation, dangers, anchorages, restricted areas, and information on bridges. To find the corresponding Local Notice to Mariners for your region visit www.navcen.uscg.gov.

NOAA Chart Abbreviations

Aids to Navigation
AERO – Aeronautical
Al – Alternating
B – Black
Bn – Beacon
C – Can
DIA – Diaphone
F – Fixed
Fl – Flasing
G – Green
IQ – Interrupted Quick
Iso – Isophase
LT HO – Lighthouse
M – Nautical Mile
m – Minutes
MICRO TR – Microwave Tower
Mkr – Marker
Mo – Morse Code
N – Nun
OBSC – Obscured
Oc – Occulting
Or – Orange
Q – Quick
R – Red
Ra Ref – Radar Reflector
R Bn – Radiobeacon
R TR – Radio Tower
Rot – Rotating
S – Seconds
SEC – Sector
St M – Statute Miles
VQ – Very Quick
W – White
WHIS – Whistle
Y – Yellow

Bottom Characteristics
Blds – Boulders
bk – Broken
Cy – Clay
Co – Coral
G – Gravel
Grs – Grass
gy – Gray
h – Hard
M – Mud
Oys – Oysters
Rk – Rock
S – Sand
so – Soft
Sh – Shells
sy – Sticky

(For a complete list of symbols and abbreviations, download NOAA Chart No. 1 at www.nauticalcharts.noaa.gov)

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