Navigation and Seamanship (1+1)

Aim 

Aim: To fix the vessel's position by using latitude and longitude values.

Learning Outcome: At the end of this practical, the students will understand the method of position fixing by latitudes & longitude.

Materials Required: Parallel ruler, Pencil, nautical chart

Latitudes and longitudes are the imaginary lines but important for navigation purpose. These lines are drawn along the earth to denote a particular place in the earth. Latitudes are the lines that are drawn horizontally, whereas longitudes are vertical lines. Zero degree latitude is marked at the Equator which divides earth into two hemispheres, the one above zero degree latitude is called Northern Hemisphere and the one below, is called Southern Hemisphere.  The reference longitude marked at zero degree is called Greenwich meridian. The one to the right of Greenwich meridian is called Eastern Hemisphere and to the left is called Western Hemisphere. The latitudes and longitudes are highly useful in navigation particularly in chart work to know the correct position in the sea.

Position Fixing

There are a number of ways to fix the position of a vessel at sea depending on the circumstances. For coastal fixes the selected features for bearing observations must also be marked on the chart being used. The following are some of the common methods of position fixing for the fishing vessels in coastal waters,

1) Latitude and Longitude

2) Cross bearing

3) Bearing and distance

4) Running fix

5) Transit fix

6) Dead reckoning

7) Bearing and sounding

8) Sextant angles

Procedure:

In this practical, a position in a given chart will be fixed for the given values of latitude and longitude and latitude and longitude values will be marked for the given position.

1) To find the position for the given latitude and longitude

1. The given latitude and longitude are identified and marked in their corresponding scales.

2. Then lines are drawn from the points perpendicular to their axis of latitude and longitude scales

3. The point intersect of these two lines of latitude (horizontal) and longitude (vertical) is the position of the vessel

2) To find the latitude and longitude for the given position

1. The parallel ruler is fixed to the latitude nearest to the given position on the chart
2. Then by moving the parallel ruler, the line is transferred to the position
3. This line intersects in the latitude scale is marked and note the value with the suffix either ^oN or ^oS according to the chart given.
4. Similarly the longitude value is marked corresponding to the position of interest. The value is noted suffix either in ^oE or ^oW according to the chart given.

Observation

Mark the Position for the given latitude and longitude on a chart 

Latitude and longitude for the given position lat.