Vertical danger angle. A vertical sextant angle can be used to ensure the safety of a ship in the vicinity of dangers. If the danger is close to high land or a lighthouse, the height of the land or lighthouse can be used as a reference for determining the sextant…
A position circle can be obtained from the rising or dipping of navigation lights over the horizon. The South African List of Lights and Radio Signals has a table of geographical ranges of lights. By entering the table with the height of the observer’s eye above water level and the…
Leading lights and markers are usually used in the approaches to harbours or in channels where maneuvering room is very restricted. Their purpose is to guide vessels clear of dangers or down the best channel. They are shown on the chart by a line drawn through them called a leading…
The GPS will provide a position expressed in latitude and longitude. This will be plotted as a small cross, the centre of which is encircled, with GPS written alongside it.
If an observer sees two object in line ashore, ie beacons, then he must lie somewhere on the extended line joining them. This provides an excellent position line, provided the distance between the observer and the nearer of the two objects is no more than three times the distance between…
Using a sextant, an angle can be measured between two objects ashore, the position of which is known. By plotting the intersection of two lines forming the horizontal sextant angles between the two objects, a circular position line can be drawn. Remember that all angles subtended by a chord in…
