CHARTING &
PILOTING
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Contents....
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Charting
Piloting
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| To travel anywhere safely in his boat, a skipper
must have knowledge of water depths, shoals and channels. He must also know the location
of aids to navigation and landmarks, and where ports and harbors can be found. At any
given position, h can generally measure the depth, and he may see some landmarks; but for
true safety he has to know the depth ahead, the actual location of the aids to navigation
he can see, and where more aids lie on the course he will follow. To plan the best route
to his destination, he must know the dangers to navigation along the way. This information
can best be determined from up-to-date nautical charts. The skipper must not only have the
required charts on board, but he must also know how to use them. |
| What is a nautical chart? |
| A nautical chart is a representation in miniature, on
a plane surface, of a portion of the earth' surface emphasizing the water areas and
natural and man-made features of particular interest to a navigator. |
| A chart includes information about depth of water,
obstructions and other dangers to navigation, and the location and types of aids to
navigation. Adjacent land areas are only portrayed in details that aid a navigator-the
shoreline, harbor facilities, and prominent natural or man-made features. |
| Charts are printed on heavy-weight, durable paper so
that they may be used as worksheets on which courses may be plotted and positions
determined. For skippers on small craft, there are even special charts with details on
marinas and similar facilities. |
| A chart's basic purpose is to give the navigator
information that enables him to make the right decision on time to avoid danger. |
| Geographic Coordinates |
| Charts show a series of intersecting lines to aid in
describing a specific position on the water. These lines are charted representations of a
system of geographic coordinates that exist on the earth's surface. Geographic coordinates
are defined by two sets of great and small circles. One is a set of great circles each of
which passes through the north and south geographic poles-these are MERIDIANS OF
LONGITUDE. The other set is a series of circles each established by a plane cutting
through the earth perpendicular to the polar axis. The largest of these is midway between
the poles and thus passes through the center of the earth, becoming a great circle; this
is the EQUATOR. Other parallel planes form small circles known as the PARALLELS OF
LATITUDE. Geographic coordinates are measured in terms of degrees. |
| Geographic coordinates are measured in terms of
degrees. The meridian that passes through Greenwich, England, is the reference for all
measurements of longitude and is designated as the PRIME MERIDIAN, or 0 degrees. The
longitude of any position is described as __ degrees East or West of Greenwich, to a
maximum in either direction of 180 degrees. Parallels of latitude are measured in degrees
north or south from the equator, from 0 degrees to 90 degrees at each pole. For greater
position precision in position accuracy, degrees are subdivided into minutes and seconds. |
| Measurements of Direction |
| To facilitate the measurement of direction, as in
plotting bearings and laying out courses, most charts have Compass Roses printed on them.
A compass rose consists of two or three concentric circles, several inches in diameter,
and accurately subdivided. The outer circle has its zero at true north; this is emphasized
with a star. The next circle or circles are oriented to magnetic north. |
| Distance |
| Distances on charts are measured in statute or in
nautical miles. Use of the statute (or land) mile of 5,280 feet is limited to the Great
Lakes, inland rivers, ad the Atlantic and Gulf Intracoastal Waterways. The nautical mile
of 6,076.1 feet is used on ocean and coastal waters. You may sometimes need to convert
from one unit to the other. This is not difficult-1 nautical mile equals 1.15 statute
miles, or roughly 7 nautical miles equals 8 statute miles. |
| Scale |
| Because a chart is a miniature representation of
navigable water area,, actual distances must be scaled down to much shorter dimensions on
paper. This reduction is the scale of a chart and it may be expressed as a ratio, 1:80,000
meaning that 1 unit on the chart represents 80,000 units on the actual land or water
surface. The ratio of a chart to actual distance can also be expressed as a numerical or
equivalent scale, such as "1 inch equals 1.1 miles." |
| What Charts Show |
| The General Information Block on a chart indicates the
waters covered, the type of projection used and scale, the unit of depth measurement (feet
or fathoms-one fathom equals six feet), and the datum plane for such soundings. Elsewhere
on the chart where space is available (normally in land areas), you will find other
information including the meaning of certain commonly used abbreviations, units and the
datum for heights above water, notes of caution regarding dangers, tidal information,
references to anchorage areas, and a statement of the applicable Coast Pilot
volume. |
| The edition number and date appear in the margin at
the lower left-hand corner; immediately following these figures are the date of the last
revised printing, if any. Most nautical charts are printed to supply a normal demand of
one to two years for active areas, and from 4 to 12 years in areas where few changes
occur. |
| Charts may be printed as-is when the stock runs low,
but a Revised Print is more likely if a new edition is not published. Revisions include
all of the changes published in Notices to Mariners since the last revision. |
| Use of Color |
| Most charts use color to emphasize various features
and so facilitate reading and interpretation. Although colors vary with the agency
publishing the chart, boaters most commonly see the NOS color system, which utilizes five
multipurpose colors in either solids or shades-black, magenta, gold, blue and green. |
| Land areas are a screened tint of gold; water areas
are white, the color of the paper, except for the shallower regions which are shown in a
screened blue. Areas that are submerged at some tidal stages but uncovered at others, like
sandbars, mud flats, coral reefs, and marshes, are green. |
| Magenta ink is used for many purposes on charts; it
has good visibility under red light, which is used for reading charts during darkness
because it does not destroy night vision as white light does. Red buoys are printed in
magenta as are red daybeacon signals. Lighted buoys of any kind have a magenta disc over
the small circle portion of the symbol to assist in identifying it as a lighted aid. A
magenta flare symbol extending from a position dot is used with lights, lighted rages,
etc. Caution and danger symbols and notes are printed in magenta; also compass roses,
usually, and recommended courses where shown. Black is used for most symbols and printed
information. |
| Water Features |
| The principal feature f concern to boaters is the
depth. For any system of depth information, there must be a depth plane or datum. This I
obvious in coastal areas where depths may change hourly as the result of tidal action; it
is likewise true in inland areas where lake or river levels may also change, though more
slowly on a seasonal basis. Depth information is shown on a chart by many small printed
figures. These indicate the depth at that point, usually measured in feet or fathoms.
Depths printed are usually in "mean lower low water", which is an average of all
lowest water levels for tidal days over a period of time. |
| Nature of the Bottom |
| The nature of the bottom, such as sand, rocky, mud,
grass or "hard" or "soft" is indicated for many areas by
abbreviations. This information is especially valuable when you are anchoring, so take
advantage of it wherever it appears. The meanings of these and other abbreviations are
usually given on the face of the chart near the basic identification block; many are
self-evident. |
| Man-Made Features |
| Man-made features are shown in detail where they
relate directly to water-borne traffic. Examples are piers, bridges, overhead power
cables, and breakwaters. Locations of prominent isolated objects, tanks, stacks, spires,
etc. are shown accurately so they may be used for taking bearings. |
| Symbols and Abbreviations |
| Simple inspection of many symbols will reveal a
pattern in the way they are formed. Of you know the general principles of chart symbols,
you'll have an easier time learning the details. |
| Buoys, except mooring buoys, are shown by a
diamond-shaped symbol and a small open circle indicating the position. On most charts, red
buoys are in magenta; the letter "R" may also be shown adjacent to the symbol.
Green buoys are shown in that color with the letter "G" nearby. Other buoys are
shown by open outline symbols with the color indicated by an appropriate abbreviation. The
type and shape of unlighted buoys is normally indicated by an abbreviation such as
"C" for can or "N" for nun. |
| How to Obtain Charts |
| Charts can be purchased or ordered from most marine
retailers. You can also go directly to headquarters or field offices of the issuing
agencies. |
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| Piloting is the use of landmarks, aids to navigation,
and soundings to conduct a vessel safely through channels and harbors, and along coasts
where depths of water and dangers to navigation require constant attention to the boat's
position and course. An adjunct to piloting is "dead reckoning", a procedure by
which a boat's approximate position is determined at any time by its movements since its
last accurate determination of position. |
| The basic dimensions of piloting are: |
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 DIRECTION - the position of one
point relative to another point without reference to the distance between them.
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DISTANCE - is defined as the
spatial separation between two points without regard to the direction of one from the
other.
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TIME - Although the pilot does not
need so accurate a knowledge of the exact time of day as does a celestial navigator,
ability to determine the passage of time and to perform calculations of elapsed time is
essential.
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| Other quantities that may be measured, calculated, or
used, include speed, position, and depths and heights. |
| Piloting Tools |
| For piloting in coastal and inland waters, you will
need a few simple tools or instruments. They are not particularly expensive items, but
should be of good quality, well cared for, and used with respect. Here's what you'll need: |
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 CHART: newly revised chart of local
area featuring appropriate scale. A flat and relatively steady working surface is needed
for drawing course lines and plotting positions.
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COMPASS: used primarily to
determine the direction in which the boat is headed. Compasses can be mounted on your boat
or can be carried by hand.
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COURSE PLOTTERS: used to determine
the direction of a course or bearing from a given point, these plastic devices, usually
rectangular in shape, have one or more semi-circular angular scales marked on them.
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PARALLEL RULERS: a traditional
instrument used for measuring and plotting directions on charts. The device consists of
two rulers that are connected by linkages that keep their edges parallel.
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DIVIDERS: distance is measured on
a chart with a pair of dividers by opening the two arms and pivoting between the charted
points.
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| Practice Makes Perfect |
| Piloting is a learned art. It requires much practice
and diligence. Knowing how to pilot provides a sense of confidence for the skipper, by
giving him the knowledge to safely guide his boat from one point to another. Practicing in
fair weather ill help new pilots for unexpected and foul weather situations. |
| To Learn More About Piloting… |
| For boaters interested in learning more about
piloting, we recommend taking a boating course. Courses offered by the U.S. Coast Guard
Auxiliary and U.S. Power Squadrons cover piloting procedures and practices in detail. Call
the BoatU.S. Foundation Courseline toll-free at 1-800-336-2628 to find a course in your
neighborhood, or visit our directory of courses on the Internet at www.boatus.com. |
For further reading on these topics and other
boating information, The BoatU.S. Foundation recommends any of the following: |
| All of these can be found through
your local BoatU.S. Marine Center, the BoatU.S. Catalog or the New Online Store! (www.boatus.com) |
 Chapman's Piloting by: Elbert S. Maloney Chapman's Hands-On Powerboating CD ROM
The Annapolis Book of Seamanship by: John Rousmaniere
US Power Squadron Booklets (Knots, Sailing, GPS, Radar,
etc.)
US Coast Guard Auxiliary's Skipper's Safe Boating Course
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