Grade 10 – Nautical Science

December 10, 2020

Practical example of a position determined by horizontal sextant angle and vertical sextant angle

Problem: Your vessel is anchored approximately 2 miles west of Cape Light. A horizontal sextant angle between the following points was taken: Cape Light and the water tower south of the light = 65° At the same time a vertical sextant angle was taken of Cape Light. The sextant reading […]
December 10, 2020

Measurement of time at sea

Introduction. Because of the international nature of sea travel where vessels traverse large distances, especially in east/west directions, time is a very important aspect of the mariner’s life. For convenience sake a “24 hour clock” is used. This means that by merely looking at the time will indicate whether forenoon […]
December 10, 2020

Zone time at sea

A uniform time keeping system has been adopted for use at sea to ensure that all vessels within certain defined limits of longitude keep the same time. The world has been divided longitudinally into 24 zones of 15° each with the system centred on the meridian of Greenwich. The centre […]
December 10, 2020

Standard time on land and Universal Time/Greenwich Mean Time

Standard time on land. The boundaries of time zones on land generally agree with that at sea, which are defined by the meridians 7½°, 22½°, etc, except when modified as necessary by the territorial limits of the countries concerned. Zone time on land is referred to as standard time. For […]
December 10, 2020

Zone designations and local mean time

Zone designations. A ship’s clocks will not necessarily be altered the moment she enters a new zone. The fact that she is crossing a dividing meridian and entering a new zone does not alter the time she is keeping. Her clocks are altered to suit the convenience of those onboard. […]