Having and understanding Nautical or Marine charts is essential for safe boat navigation a sea.
While GPS will take much of the uncertainty out of fixing your position, a chart is needed for all that crucial information such as seabed depth, hazards, and tidal information and much more.
Nautical charts these
days come as the traditional paper chart or as
computerised electronic charts.
Electronic charts are becoming increasingly sophisticated and easy to
However, most sensible
boaters still carry
paper charts for reference
and as a back up just in case the electronics fail.
Charts may be classified as.
Harbor plans and Physical charts.
Many coastal charts will
harbor plans as inserts.
Almost all marine charts are drawn using the Mercator projection.
Mercator projections allow the navigator to take magnetic
from and plot bearings
directly on to the
Gnomic projections are some times used for very large or very small
Understanding Marine Charts.
A nautical chart will
give you all the information needed to make a
safe passage in your boat.
However, to get the most
form your charts you
need to understand the abbreviations and symbols which are
Charts have been
honed over the
centuries to contain all the information needed by the navigator at
There is such a wealth
of information that it
would be impossible show it without resorting to a form or
And as sea travel is
such an international
occupation this short hand has become fairly well standardized world
Many of the charts
published, especially for
the leisure boater have a guide to the symbols and abbreviations
printed on the
reverse side and there are various publications with quick
However, most of the
abbreviations are fairly self explanatory once you begin to understand
shorthand and develop an understanding of boat navigation.
Of course it will depend
on the scale of the
chart as to how much information it can show.
first thing to remember is that the top of the marine chart is always true
north, rather than magnetic
But it will also include
depicting the variation between magnetic and true north at that
location and at
the time of publication.
The next thing to be
aware of is that
although some charts may display a distance scale, distances should be
from the latitude scale on the side of the chart.
Distances at sea are
measured in nautical
miles, one nautical mile is one minute of latitude.
Because of the
must be measured from the scale adjacent to the area being
To get the best pilotage
your chart you need to have an understanding of how your particular
displays the information.
Depths for instance are
shown on most charts
However, some old charts
and those published
by the United States Government may use feet or fathoms.
how they are displayed
will depend on the chart datum used.
This will be indicated
The most commonly used
datums are 'lowest astronomical tide' and 'mean lower low
Most marine charts will also
show such things as the
nature of the seabed, navigational hazards, symbols for lights,
buoys and land structures and features, and a host of other aids to
Tidal information, such
as tidal races and
other strong currents are also displayed using symbols.
tidal flow information
can be found by reference to tidal diamonds and their accompanying
will indicate the
rate and bearing of
the tidal flows for each hour of the tidal cycle.
As comprehensive as the
information on marine
charts is, the prudent navigator can supplement this knowledge with
books, sailing directions, tide tables, lists of lights and
increasingly popular because of their ease of use, particularly where
incorporated into GPS
systems and plotters.
However, call me old fashioned if you will but I would strongly
having paper marine charts of your sailing area on hand as well.
Before buying a system it will aid your choice to understand some of
and acronyms used to describe the systems.
ECDIS (Electronic Chart
Information System) are approved by the IMO
Organization) for use on SOLAS (merchant) class vessels.
ECS (Electronic Chart
all other types of electronic charts.
There are also two different types of electronic chart data.
charts are compiled from a
database of digitized chart data which have been authorized by
They can be incorporated into systems which can display either the
or a selected area.
They can also be programmed to give warning of impending danger.
marine charts which conform to
IHO specifications are produced by scanning a paper charts.
To get more detailed information these can be zoomed in on.
Any subsidiary information is supplied by integrating on board data
Any marine chart can
correct at the time of its publication.
There are areas where
the profile of the
seabed changes due to erosion shifting sand banks etc and artificial
aids may be moved or altered for various reasons.
therefore unwise to
use old, uncorrected charts for navigation.
Any changes to the
position of lights and
buoys will be issued as "Notices to
These corrections should
be added to your
charts as soon as practicable.
All publishers of marine
charts provide a
system to inform you of any changes.
Government and coast
guard agencies also
issue notifications of chart corrections by way of Notice to Mariners,
Notice to Mariners, Summary of Corrections, and Broadcast Notice to
and radio broadcasts of any urgent corrections.
Corrections to paper
charts should be done as
neatly as possible and in waterproof ink.
marine charts have a
variety of methods for inserting corrections.