Navigation
In coastal and inland waters, navigation is usually done as terrestrial navigation, where the position is determined by means of visible landmarks (e.g. church towers, prominent buildings, mountains) that are entered on the chart.
Navigation Tools
The following tools are needed for navigation on board:
- Compass (usually a magnetic compass)
- Chart of the area
- Stopwatch
- Course table
- Logbook
- Hand bearing compass
- Course triangle, ruler, dividers, pencil, and eraser
The Chart
From the chart you can read latitude and longitude, depth information, and distances. Distances are taken from the side margin of the chart.
A common scale for inland charts is 1:50000. This means:
- 2 cm on the chart equals 1 km in reality
- 4 cm on the chart equals 2 km in reality
One nautical mile equals 1852 m.
The Magnetic Compass
The magnetic compass is the most common type of compass on board. Its needle points to magnetic north. The compass rose is divided into 360 degrees.
Cardinal Directions
| Direction | Degrees |
|---|---|
| North | 0° / 360° |
| East | 90° |
| South | 180° |
| West | 270° |
Deflections of the Compass Needle
The magnetic compass needle is deflected from geographic north by two influences:
- Variation: deviation of the compass needle from geographic north caused by the Earth's magnetism at the given location.
- Deviation: deviation of the compass needle caused by the boat's own magnetism (e.g. iron parts, electronics on board).
The deviation table is a tabular listing of the deflection of the compass needle by the influence of the boat's magnetism, usually in steps of 10 degrees.
Position Fixing
The most common method of position fixing is the cross bearing. At least two (better three) bearing points are sighted, and their bearing lines are drawn on the chart. The intersection of the lines gives the boat's own position.
Suitable bearing points are clearly visible objects entered on the chart, such as church towers, lighthouses, or prominent buildings.