Grade 10 – Nautical Science

December 8, 2020

Cocked hat

Cocked hat. When three or more bearings are taken from a moving ship, the resulting position lines will not as a rule meet in a point, but form a triangle. This triangle is known as a cocked hat. The name “cocked hat” probably refers to the type of hat worn […]
December 8, 2020

Radio direction finding (DF) bearings

Radio direction finding (DF) bearings. Use may be made of radio transmissions to obtain a position line. It would necessitate either the ship having a radio direction finding capability or asking a shore radio station that is equipped to take DF bearings to take a bearing of the ship’s transmissions. […]
December 9, 2020

Fixing by position circles

A fix may be obtained by using the range of objects ashore, the position of which is known from the ship. The range may be obtained from various sources, ie vertical sextant angle of an object, the height of which is known, range-finder or distance meter, a horizontal sextant angle […]
December 9, 2020

Distance by vertical sextant angle

Using a sextant, a distance may be obtained of a vertical object of known height, by measuring the angle subtended by the object at the eye of the observer. The determination of the distance is then merely a problem of solving a right angled triangle. One can either do this […]
December 9, 2020

Horizontal sextant angle (HSA)

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 […]