I think that everybody who goes
to the sea should know some basics about navigation and that is what I
want to talk about here.
sea chart shows a sector of the Earth that is notified through
longitude and latitude . If you talk about a certain point on the
world, the distance towards the Equator is called its
right angle has got 90° and every degree has 60 minutes. The
latitude is taken as an angle from the middle of the Earth. The angle
is 0° at the Equator and 90° at the poles. It is called
or "south" in accordance to the fact of being north or south of the
nautical mile (1852 metres) is the equivalent to 1 minute of altitude
at any point of the world. Thus the scale of latitude can be used for
measuring distances. The minute of longitude is only equal to a
nautical mile on the Equator, as the meridians are nearer to each other
the nearer you come to the poles. The scale of longitude cannot be used
to measure distances.
SEACHART (MERCATOR PROJECTION):
understand the principle of this projection, you must imagine a globe
with a lamp inside. If you roll a sheet of paper around it in a way
that it touches the globe everywhere on the Equator and then switch on
the lamp, the figures of the globe will get to be seen on the paper.
This paper is our sea chart. All meridians appear as parallel lines,
but towards the poles the degrees of latitude get more and more distant
to each other. Therefore it is necessary to choose the scale for
measuring distances on the sea chart in the region of the same latitude
as you are in the same moment.
ship sailing strictly northward describes a straight line on the sea
chart. Angles and directions are the same on both chart and globe. This
fact makes navigation a lot easier then it was with other projections.
compass is simply a magnetic needle in a circle that is called the
"rose". This circle is divided into 360° clockwise. For a
compass the rose is movable, so that 000° always shows
Further on it has got a line that points into the direction of the
ship's bow - which is actually the direction in which the ship is
steered at the moment. The difference towards 000° indicates
course that is steered.
magnetic field of the Earth and the iron of the ship itself influence
the magnetic compass severely. On the MIR we find a modern giro compass
system, which gives us the true north. It is compensated for all
effects and delivers a corrected course to displays on the bridge and
other prominent places on board the ship. Helmsman and watch officer
find a giro compass repeater next to their posts for convenient work.
Of course modern techniques are liable to failure and so the magnetic
compass gets checked and compared with the giro compass regularly and
the difference between both is noted into the ship's log book at least
at the end of every watch - which means every 4 hours - or every time
when the course is changed.
MIR computer navigation is done by satellite with NAVSTAR (GPS).
Several times a minute the position of MIR is taken by bearings towards
satellites and gets projected onto the computer screen into ECDIS
charts being exact by a few metres. Additionally, useful information
about MIR and from ARPA and AIS the positions, courses and speeds of
other ships inside a certain radius, can be plotted on the screen. Even
information about the kind of vessel, nationality, cargo and
destination can be received that way if the other vessels provide them
for the AIS.
this is very useful, but this type of navigation can only be seen as
additional source of information. It is still necessary to have a
proper lookout, to plot other ships' positions and speed in the
conventional way. Computers are liable to crash down and depend on
electricity. In case of a probable collision, a contact ship-to-ship is
made via VHF, to make sure the other ship is aware of us and the fact
that a square rigged tall ship reacts differently to other vessels.
(What does not mean that we do always have the right of way...)
Automatic Identification System is a new aid for collision avoidance
for ships. It was originally developed as anti-terror-tool, but now
proved very useful for all ships. It submits all important data of all
ships in vicinity and helps the watch officer decide if a close
quarters situation is developing. It also gives him the names and call
signs of the ships to enable him to call them via VHF. For sailing
ships it gives extra safety as it also transmits to other ships if we
are under sails which might change the right of way.
we know our position and know the course we are steering. Unfortunately
this does not mean that we now know where we are actually going. Apart
from the course the helmsman steers with the help of the giro compass,
there exists a course through the water and a course above ground. To
find out this course above ground and to choose the course the helmsman
(or the autopilot) has to steer to enable the ship to sail in the
desired direction is the main duty of the watch officer.
drift influences the course through the water. The higher the ship
sails by the wind the more drift we have. Of course this also depends
from the power of the wind, the aerodynamic forms of the ship and the
angle of its list. The drift can be so strong that she ship makes half
a metre to the side for every metre forward.
and tides affect the course above ground. They influence the drift of
the ship. If they are permanent ones they are normally noted on the sea
charts and handbooks or added by the watch officer due to information
from the GPS. Very often it is necessary to find out about them during
the sailing by comparing the logged course with the one shown by the
satellite navigation screen or by plotting landmarks, tons, other
ships, etc. if there are any.
big the influence of drift and set can be - and high waves, bad
steering, heavy rolling, bad trimming even multiply this - can be seen
in the following example. In December 1999 MIR was hit by a cyclone in
the Baltic Sea. Without any sails they were motor sailing with full
speed ahead. The truth is they were driven backwards with a speed of 3
that from the last waypoint on the position gets logged in accordance
of the course and the speed. To do this logged miles made good are
noted in the sea chart in the direction of the steered course. This
gets repeated regularly until there is an opportunity to see landmarks
or buoys to find out the true position of the ship. As we have seen it
is quite tricky to find out the true course above ground and the true
speed during the voyage and so the chance of landing at a completely
different place is quite good. Means this kind of navigation is nice
for trainees to get a rough idea of where the ship sails, but for the
safe navigation of the ship it is not too useful. It only gets used for
planning the route and scheduling manoeuvres or arrival
is possible to find out the true position of the ship through bearings
towards objects in the sky (celestial navigation) and on the earth. If
you are interested in the first, it is best to ask one of MIR's
navigation teachers or watch officers about it. The work with a sextant
is a tricky thing. On a ship that is permanently moving it is not so
easy to look towards a star and the horizon at the same time and of
course you need to read the tables in the almanacs and nautical
handbooks (which are written in Russian language, of course)...
everybody can easily learn the terrestrial navigation. Most easy this
is done near to shore. You simply look towards 2 prominent points at
the coastline (check the sea chart for church towers or light houses,
etc. first...) and read their bearings on the compass. Now you
calculate 360 minus the bearings and note them on the sea chart. Where
the lines cross is the ship. If you repeat this (with the same
landmarks) a little later you get a new position of the ship. Now make
a line between the first and the second position and you will be able
to find out in which direction the ship sailed, how many miles and at
what speed. If you now prolong the line you can see where you will be
in maybe an hours time. You should check the position again regularly
to make sure your course is steady and the drift has not
shore this kind of navigation is definitely best. In narrow waters 3
persons work together closely. One is permanently looking, the 2nd
notes this on the sea chart and compares it with the GPS and a 3rd - an
experienced helmsman - steers as exact as possible the announced
to her size MIR is required to take on a local pilot when going into
port or sailing in certain waters. As full concentration is needed
then, trainees and cadets have to leave the bridge at these times. The
helm is taken by a sailor from the permanent crew then.
Navigation Trainee on MIR
page was updated 10/07