Electronic nav charts
The charts are based on official paper charts of
hydrographic organizations, partly completed by yachting charts of different
These paper charts are digitalized.
There are two different methods:
1. Raster charts
In this technique the chart is scanned into the computer and a longitude/latitude
grid is laid over it. Because this method is simple to realize, these charts
are affordable and perfect to start with. They they look like paper charts,
so it is quite easy to work with them.
Chart manufacturers :
- Maptech / chart format BSB or BSB4
- Delius Klasing / own chart format
- Maptech Chart
- Raymarine Raytech
This method has one disadvantage: You always have to switch between
charts and scales.(Fugawi).
From track chart to detailed charts and the harbour plan, like known with
Some programs automatically change to the chart with the best scale
That means, when you reach the coast, they automatically switch to detailed
Some programs also show the detailed maps inside the track chart, when
a certain scale is chosen (MaxSea
When you zoom in these charts, information, like numbers, lines and
buoys appear bigger.
2. Vector charts
From paper charts the information, like buoys, depth contours, shore
lines, nav aids, prohibited areas etc. is copied by hand. The information
is then stored together with the position. In the data base appears e.g.
"red buoy, 54°N 12°E". When this chart area is shown, the program
draws a red buoy in this position. If you zoom in, the buoy is alway shown
in the same position and size. This technique also allows to fade information
in or out. You can seamlessly scroll from one area to the other. Also you
don´t have to change charts, it´s all in one. The production
is very compex, that´s why these charts are more expensive than raster
2a Vektor charts for Chart Plotters
These vector charts are also used in chart plotters on memory modules
In course of time different versions were developed, wich often caused
you can find an overview.
C-Map CF85 modules (from 1985 on), C-Map NT 95 modules (from 1995 on),
NT+ Module (from 2001on), C-Map MAX
(from 2005 on), C-Map
CM93 CDs (from 1993 on)
(credit card size, from 1985 on), Navcharts
(from 1994 on), Gold
Charts (on CF, MMC & SD cards from 2001 on), Platinum
Charts ( from 2006 on), Magellan
Please read your manual closely, which memory modules are required;
you also can ask us.
Paper chart information already are partly incorrect, so digital charts
cannot be better. Many charts have been surveyed about 30 to 50 years ago
with former methods, they contain incorrect positions. With todays GPS
technology you have an accurracy of approx.10 m.With the old surveying
techniques, that was not possible. So, e.g.the last chart of New Zealand
that was drawn by Captain Cook, was again surveyed and edited just in 2002.
That means, you can never rely on electronic charts on board of recreational
yachts. Often you can find deviations of 100-300m. You are depentent on
the lookout, the paper chart and accuracy in navigation.
For sure, electronic charts are improved continuously.The worldwide
nautical data bases of the manufacturers are revised in turns every 2 to
4 years. But it also can happen, that some harbours already exist for 3
years and didn´t appear in the charts yet. On the other hand, some
changes (e.g. in the notices to mariners) can be inserted faster.
In general, neither in paper- nor in electronic charts remote areas
are registered as well as frequently travelled areas.
Recognized mistakes can be reported to the manufacturers, and will be
corrected in the following versions. Navionics
offers a special correction form.
The costs for these cards considerably dropped in the last couple of
years. Faster PCs and larger sized memory cards let the mapped areas grow.
So Navionics already offers XL9
charts and C-Map offers Max Mega Wide
modules. The coverage with raster charts grows annually.