Smart ™ - Nautical Charts
ever been out on the water in a small boat when the visibility suddenly
changed for the worse?
are often caused by a change in the weather; i.e., a warm or cold front
moves through the area. Fronts can be accompanied by thunder and lightning.
Or, fog will envelop an area due to various weather phenomena. A type of
fog known as advection fog can persist for several days, until a significant
change in the local weather occurs. Another cause of restricted visibility
is rain obscuring the landscape and familiar landmarks.
In any event,
it is very easy to get disoriented on the water, especially if there are
a number of islands in the area and you must thread your way through them
to get back home. This is the time when a basic knowledge of nautical charts
and maps and how to use them comes in very handy. On the water, charts
and maps are different from road maps. They show you where you cannot go
as well as where to go.
As a boater,
you must always know where you are and the best way to reach your destination
safely. Charts are pictures of parts of the earth's surface. They provide
a variety of information to aid you in the navigation of your boat and
are vital to your safety. Nautical Charts: come in various sizes and scales.
Typical charts for small boats are referred to as coastal, lake, harbor,
or small-craft charts. Nautical charts are produced for virtually all coastal
regions, large lakes, and major rivers. Topo maps provide terrain profiles
of the land and outlines of shorelines. They may be the only form of quality
information for areas not covered by nautical charts. They can help you
locate your position, but generally tell little about conditions on and
under the water. Topo maps are produced by the United States Geodetic Survey
differ so that the area of interest is portrayed on the size of paper being
used. Nautical charts can be obtained from local marine stores, from marinas
or directly from the National Oceanic and Atmospheric Administration (NOAA).
Topo maps can be obtained in outdoor stores or from the USGS. Nautical
Chart No. 1 is a booklet that explains the nautical terms and symbols used
on charts. Nautical Charts Show: many items of interest to paddle boaters,
such as the depth of the water.
four colors to describe the makeup of the earth's surface: ¨ White
for deep, safe water ¨ Blue for shallow water ¨ Green for tidal
areas covered at high water ¨ Gold for dry land Direction is another
vital piece of information that may be obtained from a chart. Direction
is measured in degrees from 000º to 360º, clockwise from geographic,
or true, north.
Rose, colored magenta,
has circles marked in degrees like those on a compass. The Compass Rose
shows the difference between true north and magnetic north. The angle between
the directions of geographic north and magnetic north is called variation.
Grid lines on charts and maps generally are oriented toward true north-south
and east-west. If your map has not compass rose, you will need to determine
your local magnetic variation to convert between your compass reading and
your chart. GPS units can be set to display either true or magnetic headings.
paddler should be able to determine from the chart the true course to the
desired destination and be able to establish the compass course to steer
to get there.
Your Position: on the water and on the nautical chart
can be established by use of the latitude (L) and longitude (Lo) grid system.
This system makes it possible to locate any point on the earth. It consists
of two sets of imaginary lines. Parallels of L run east and west and are
parallel to the equator. They are numbered from L 0º at the equator
to L 90º at the poles. Meridians of Lo run north and south to the
geographic poles. Lo 0º passes through Greenwich, England. Lo lines
are numbered east (E) from Greenwich toward Europe and Asia, or west (W)
from Greenwich toward the United States.
is described in degrees and parts of degrees of L and Lo. GPS units can
readily readout your position in degrees of L and Lo and display additional
data valuable to a voyaging paddler.
Measure Distance: on coastal charts, distance is measured
in nautical miles (6076 feet); and in inland waters, distance is measured
in statute miles (5280 feet). Using dividers, you can find distance on
a chart in several ways: ¨ The distance scale will be near the chart
title block ¨ The latitude scale on the side of the chart provides
a means for measuring distance. One minute of latitude is equal to one
nautical mile. ¨ You will find latitude scales on small-craft charts
along certain meridians of longitude. Dividers are useful at home while
planning a trip but most paddlers leave their dividers at home and estimate
distance while underway. Two fingers may be used as a crude set of dividers.
Also, if you calibrate the span from the tip of your thumb to your fingertip,
it is possible to determine reasonable estimates of distance.
to Navigation (ATONs): for boaters, are like street
and caution signs for drivers. Each gives you the information you need
to know to locate and move your vessel safely. ATONs include lights, buoys,
daymarks, lighthouses, foghorns, etc. Buoys are floating objects anchored
at specific locations. The shapes and colors of marks make it easy to identify
them. Numbers and letters further identify many marks and help you find
them on charts.
Use Up-to-Date Charts and Maps
Statement | Trademarks
updated July 8, 2011.