Navigation


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.

POSITION:

The 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 latitude.  A 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 "north" or "south" in accordance to the fact of being north or south of the Equator.
A 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. 

THE SEACHART (MERCATOR PROJECTION):

To 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.
A 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:

A compass is simply a magnetic needle in a circle that is called the "rose". This circle is divided into 360° clockwise. For a ship's compass the rose is movable, so that 000° always shows northward. 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 the course that is steered. 

GIRO COMPASS:

The 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. 

COMPUTERNAVIGATION:

On 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.
All 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...)

AIS:

The 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.

COURSE:

Now 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.
The 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. 
Currents 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. 
How 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 knots!

DEAD RECKONING NAVIGATION:

Means 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 times. 

TERRESTRIAL NAVIGATION:

It 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)...
However, 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 changed. 
Near 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 course.

PILOTAGE:

Due 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.


Navigational abbreviations
Collision Avoidance


Navigation Trainee on MIR

this page was updated 10/07

1