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.
For more detailed questions, tips, photos, etc. go to the Forums in the top menu.
I am perfectly aware that the majority of Wooden Boat aficionados are sensible folk. However, I need to point out that I am an amateur wooden boat enthusiast simply writing in order to try to help other amateur wooden boat enthusiasts. And while I take every care to ensure that the information in DIY Wood Boat.com is correct, anyone acting on the information on this website does so at their own risk.