Coastal navigation is a navigational method concerning the vessel’s movement in relation to the approximate shore, the visible objects in the sea (islets, rocks, buoys, light vessels) and the sea depths. Coastal navigation demands great experience. The mariner has to be in continuous vigilance, given that in open sea a possible fault can be corrected in time, whereas in coastal navigation the potential of correcting these faults is too small.
Position Line is a line in a specific point of which the vessel can be located in a given time. Every point of this line may be a possible position of the vessel.This possible point is called geometrical locus of the vessel’s spot.
The types of position lines are the following:
(a) Bearing: the bearing of an object, which we count with the sight vane or the radar.
(b) Alignment: the bearing of two objects, when one of them is located in the prolongation of the bearing of the other, that is measured with the sight vane or the radar.
(c) Distance: it is measured by the radar.
(d) Depth Contour: it is the curve in which the depths are equal. It is counted by the bathymeter.
(e) Horizontal Angle: it is the angle between two visible objects and it is measured by the sextant.
The vessel’s spot is its geographical position in the sea. There are various ways of determining the vessel’s position. However, the vessel’s position is determined according to its length and breadth terrestrial coordinates. The determination of the vessel’s exact coastal position is usually done via visual observations or via radar observations of the visible, by the vessel, land points. As previously noted, a position line represents the series of the vessel’s successive positions. However, if we can have, at the same time, two or more intersected position lines, then the unique position on the earth and the chart that meets the requirements (being at the same time on these two or more position lines) is the intersection between the two or more position lines observed by the bridge of the vessel. The specific intersection point is the “accuracy coastal position” (Fix). This can also be achieved by combining two or more position lines such as:
(a) Simultaneous Bearings
(b) Simultaneous Transits
(c) Simultaneous Distances
(d) Simultaneous Horizontal Angles
(e) Simultaneous bearings- distances