Measuring distances on mercator charts –
To measure the distance between, for example, these two oil rigs in the figure, we will need a set of dividers. It is very important to note that we can…
Chart projections
A navigational chart is a 2-dimensional representation of a 3-dimensional world. And although it results in various distortions, as long as the following two requirements are met we can use…
Finding compass error by transit bearings
When a vessel is navigating in coastal areas, it may be possible to observe two fixed objects, especially landmarks that are directly in line. In such a case, the watch…
Definition of amplitude
The amplitude of a body is the angle at the observer's zenith or the arc of his rational horizon contained between the observer's prime vertical, and the vertical circle through…
Procedure for observing azimuth – Celestial Navigation
Identify a heavenly body whose azimuth you want to take. Ensure that the altitude is not too high or too low (preferably between 20o and 60o Take the compass bearing…
Definition of azimuth
In open seas, heavenly bodies are used to determine the compass error. Watch keepers must calculate compass error at least once every watch and after every major alteration of course.…
Using azimuth circle for taking bearings/ azimuths
Taking a bearing of a terrestrial objectAssume that you are taking a bearing of a lighthouse. Place the azimuth circle on the gyro repeater, and make sure that the circle…
Celestial Navigation – Azimuth circle
Azimuth circle -Azimuth circle is a non magnetic metal ring equipped with sighting devices for observing bearings of objects (celestial bodies, terrestrial bodies, targets, vessels, etc). It consists of a…
Salient features of a navigational chart
Navigational charts are either metric charts or fathom charts. They can be easily distinguished by the colour used on the charts. On the metric charts the land masses are shown…
Celestial Navigation – Use of Star finder
Description1) IntroductionIn earlier days when electronic navigation was not available, navigation in the open sea was solely done using sun and stars to plot the ship's position. Constellations were identified…
Errors and adjustment of a sextant – Celestial Navigation
There are two types of errors on sextants: - Adjustable and Non- adjustable errors.a) Adjustable errorsError of perpendicularity: The index glass must beperpendicular to the plane of the instrument. It…
The Sextant’s Role in Celestial Navigation
Description1) DefinitionThe sextant is a precision instrument used at sea for measuring altitudes of celestial bodies. It can also be used for measuring horizontal and vertical angles between and of…