Charts are the marine word for maps. You get them in paper or digital.
You can download the digitals from a CD to any laptop computer or
digital marine navigation unit. They can be combined with your GPS,
radar and autopilot, to simplify your navigation (or require you become
a computer hacker).
Because the risk of power shortage or electronic failure is major on an
Atlantic trip however, paper charts should still be your major source
A labeled grid-system points out our position on the earth, and this is
how it works: Look at a tabletop globe (the kind hiding the whisky will
also work fine). Locate the equator encircling the middle. This is zero
Now move to the North Pole. This is 90 degrees north. Between every
degree, there are 60 minutes - also called nautical miles (NM). One
nautical mile is 1852 meter.
The straight distance between the Equator and the North Pole is 90
degrees x 60 NM x 1.852 km = 10000.8 km. The distance all the way around
the globe will be 360 degrees or 40000 km.
On a chart, these nautical miles will be divided into tenths, each
marked by parallel lines . These lines, encircling the globe, are called
latitudes. Remember: One degree
on the latitudes always marks 60 nautical miles.
Where you are - according to the latitude - will be stated by three sets
of figures, and an indication whether you are north or south of the
Example: "Lat. N. 14 22.5 ", shows that you are 14 degrees and 22.5 NM
north of the Equator.
Well, now that we can find our way north and south (just as the Vikings
could) letís ad another dimension, east and west.
This time we start at London, or more accurate, Greenwich. Once again,
look at the globe. Follow the line that goes all the way from the North
Pole, through London and down to the South Pole. This is called a
Longitude. The circle around the globe is 360į
. Every degree is divided into 60 minutes. Every minute is then divided
However, a minute when looking at longitudes is not related to distance.
If you look at the globe and follow the longitudes north, you will see
that the distance between them will narrow.
Remember: The purpose of longitude is to give position, not to give
Just as the latitude will be connected to a north or south of the
Equator, the longitude will be connected to an east or west of
Take the course from a chart
To make the globe readable on a chart, there is a standard procedure
called Mercators projection. Lay down the chart on a flat surface. To
the right youīll find the latitude scale, at the bottom the longitude
To check a distance or plot a course you need three things: a pair of
dividers, a conveyor (triangle with degrees on) and a pencil.
Now, letís make this very practical. Take a chart or a normal map where
you can see Tenerife in the Canary Islands as well as St. Lucia in the
Do a straight line between Tenerife and St. Lucia with the help of a
ruler (use a pencil so you can erase the line later).
Before we check the exact course itís good to make out in your head what
it should be. If we go towards the Caribbean it should be pretty much
going west and some south. So we could expect a course of around 230
degrees (see the chapter about the compass below).
At the base (the long side) of the conveyor you will see a straight
line. Move the conveyor so that the line printed on it touches exactly
the line you just draw.
At the middle of the conveyor base line there is a crossing line. Move
the conveyor along the pencil line so that the cross is at a line on the
chart that is going from down to up , a longitude.
Keep the conveyor at that position. Close to the top of the conveyor
there is a scale that crosses the same longitude as the cross at the
base line. You will now have two figures , one will be close to 230
degrees, which will be your course to St. Lucia, the other will be
closer to 50 degrees, which will take you the opposite direction.
Make a note of the course on the map and a small arrow indicating which
way you are going. "How dumb do they think I am?" you might think. Well,
going without sleep and hot food for a couple of days, in the middle of
the Ocean, a pitch-black night , that arrow might come very handy.
The best way from Tenerife to St. Lucia is however not the straight one.
You will be best off by first going down to the Cape Verde Islands, and
then do the crossing. Doing the course is simple though , just do two
separate lines with your pencil instead of one.
Checking the distance
Take the divider. Adjust them at the
right side of the chart so that the distance between the
needles is a suitable distance (1NM, 10 NM, 1 degree, depending on the
scale of the chart you are using). Put one needle at Tenerife and "walk"
along the course you marked until you arrive at St. Lucia. Count the
"steps" you are taking and multiple with the chosen distance between the
needles. This is easier done than described , have someone show you.
Stuff affecting your course
The wind might be more favorable at different places of the ocean. Orthe
current might push your boat side ways , so you have to compensate for
By using a wind and current chart like the "Atlantic Pilot Atlas" you
will not only get the current and wind information, but also how it
changes for each month of the year!
A more complicated matter is the influence of the Magnetic Pole. All
your charts will show the North Pole straight up and the South Pole
straight down. However, the north on your compass will point towards the
magnetic North Pole, which is way off the real Pole (120 NM down in
This is called the magnetic variation and it changes a little from year
to year, and a lot depending on where you are. If you look at the chart,
there will be a compass rose. That one will show you the way your
magnetic compass will go. There will also be information about how it
changes from year to year (donít forget to check which year the chart
At the Canary Islands your compass will point you more to the left than
the course you just plotted, which will end you down in South America ,
nice, but maybe not what you intended. Adjust the course you are going
for by adding the variation to the course you got from the charts.
Adjusting and checking the course
When under sail you have to constantly check your course and adjust it.
This is how we do it.
Every 4-hour bring up the chart, the pencil, the conveyor and the
dividers. Put on the GPS ,write down your position and time doing a
small cross on the chart. Check the distance , write it down, and adjust
the course if necessary.
Remember: Always write down your position , if your GPS fails you, this
information is extremely important.
Navigating close to land
The principle is the same as out on open sea. However you have more to
think about. There are islands, depth readings, lighthouses and other
markings to regard.
Always use an up to date chart. Radar is great for identifying islands.
A sonar will guide you into harbors and anchorages.
When getting close to islands and reefs , never trust the charts. There
have been plenty of times when lighthouses are missing and the charts
are smile wrong. An example is Isla la Tortugas outside Venezuela.
Comparing a chart with a detailed guidebook , not even the shape of the
island corresponded, even less the reefs.
The rules applied to buoys and markes will also differ widely from what
you learned at your navigation course back home. Always read up on the
Navigating by the stars
You donít need to learn how to cross the Atlantic. But if you got the
time, learn how and you have a great back-up as well as something to
look at during those lonely passage nights.
Which charts to use
There are two books you need. One is the "Atlantic Pilot Atlas" by
James Clark (Adlard Coles Nautical), $ 70. The other is "The Atlantic
Crossing Guide" by Anne Hammick and Gavin McLaren (Adlard Coles
Nautical), $ 45. In the last one you will get information of all the
charts you need for the passage.
The Compass is divided in 360į ; where north
is 0į or 360į .
Since the compass is magnetic the engine and other metallic stuff on the
boat will influence it. What you need to do is to check and correct the
compass for the boats magnetic deviation.
The way to do this is to take a chart and find two distinct objects.
Draw a line between them and check the course. Adjust for the deviation
from the magnetic Pole. By motor approach the two objects so they line
up perfectly. Note you should have both the objects in front of the
boat, moving slowly towards them.
Check the course on the compass and compare it to the one you got on the
Adjust the position of the compass until the course shown on the compass
is coherent with the one on the chart.
Do this test a couple of times and also with different objects.
When adding more iron to the boat you have to redo the deviation. Be
careful when sailing when putting metallic things close to the compass.