If the cooling process which gives rise to cloud formation is continued, the droplets of which the cloud consists grow in size until they become too heavy to remain suspended in the air and they fall to the ground as rain. The longer the droplets are held aloft by the updrafts of wind in the…
The formation of fog and mist is basically the same as that of clouds. In cloud the resulting condensation into visible particles takes place high above the ground, but for fog or mist, the condensation takes place on the surface of the sea or ground. The only difference between fog and mist is the degree…
Clouds are formed when warm, moist air rises until it reaches the air’s saturation point (dew point). After this the moisture in the air condenses into visible droplets and clouds are formed. There are two basic types of cloud. Cumulus clouds. When air is heated by the surface of the earth or water, it expands,…
The amount of water vapour in the air varies from place to place and from time to time, and is an important factor in determining the nature of the weather. The amount of water vapour that the air can hold in an invisible state is limited and varies with the temperature. Warm air can hold…
The atmosphere is divided up into a number of layers as follows: The Troposphere. This layer stretches from the surface of the earth up to 18 kilometers above the earth. Most of the weather changes occur in this layer. Stratosphere. This layer stretches from 18 to 32 kilometers above the earth. Very little water vapour…
The met instruments usually carried aboard merchant vessels and warships are the following: Barometer. This instrument measures the atmospheric pressure (usually in millibars). They can either be mercury barometers or aneroid barometers. The first type uses a column of mercury to measure to measure the pressure, whilst the aneroid uses a metal diaphragm. Thermometer. This…
Sources of meteorological information available to the mariner include the following: Maritime coastal radio stations (Walvis Bay, Luderitz, Cape Town, Port Elizabeth, East London, Durban). These provide storm warnings and weather forecasts. Cape Naval Radio (Silvermine, Cape Town). They provide facsimile weather maps and weather forecasts on behalf of the SA Weather Service. “Navtex” stations…
Tugs are in effect marine tractors. Their purpose is to push/tow vessels when they cannot use their own engines or do not have any form of self propulsion. They are designed according to the environment in which they will operate, ie harbours, rivers or deep sea and according to their purpose, ie berthing/unberthing of ships,…
Dredgers come in a variety of forms, types and sizes. Their purpose is to remove silt or sand from harbours, rivers or entrance channels to harbours, in order that seagoing vessels have sufficient depth to navigate safely in these confined spaces. They are also used in underwater mining operations. Whilst there are still examples of…
