# Grade 10 – Nautical Science

December 9, 2020

## Danger angles

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 […]
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 […]