Nautical instruments
In order to execute their voyages safely sailors were obliged to use certain nautical instruments
to apply the rules of navigation. Ships were equipped with the necessary nautical instruments
according to their size, category and length of voyage. The most important instruments were the
astrolabe, the sextant, compass and gyro compass. Other important instruments were the wind
gauge, the gyroscope, the log, the sea gauge et al. Let us examine the use, the form and origin
of the most important nautical instruments.
ASTROLABE
The astrolabe is the instrument used to observe the stars ad determine their position on the
horizon. According to ancient scripts the astrolabe was invented in the 2nd century B.C. by
Ipparch. According to Ptolemy the astrolabe was a type of geographical map. In the Middle
Ages the astrolabe was the main instrument for navigation later to be replaced by the sextant.
The nautical astrolabe and the somewhat similar tetracycle were made for exclusive use on
ships and were used to find the latitude on the open sea by astronomical means.
In its ancient form the astrolabe was a wooden disc tied from an ring or eyelet. At the end of
the disc the subdivisions of the ring were marked. Their was also a view-finder turning around a
central axis used to find the sun and the stars. Over time astrolabes became more sophisticated.
They were later made of metal and also used to tell the time. At the beginning of the 20th
century the prismatic astrolabe appeared, enabling the rays of a celestial body to be reflected
onto a mercury surface to determine the point in time that it reached a certain height on the
horizon.
SEXTANT
This was an instrument used to measure the height of a celestial body from aircraft, spacecraft
or the ship's deck, irrespective of the stability of the observer. The main types are the sextant
used for ships and the bubble sextant used only on aircraft. The sextant became the main
nautical instrument used to determine the angle between the visible horizon and a celestial body
which was usually the sun.
COMPASS
The Compass is a nautical instrument used for the orientation of ships, aircraft and even land
vehicles when in motion towards an unknown destination.
The time and place of its invention remain unknown as well as when it was first applied to
navigation. Supposedly the Chinese used a magnetic compass around 1100 A.D. , the West
European sailors around 1187 A.D., the Arabs around 1220 A.D., and the Scandinavians
around 1300 A.D.
The first nautical compass was made of a magnetized needle set on a wooden splinter floating
in water in a bowl. Later on the needle was set on an obelisk mounted into the base of a
receptacle. The compass changed form many times as it developed to reach its present form. It
was always the most useful and recognizable nautical instrument irrespective of form, although
considered to be problematic and unstable.
GYRO COMPASS
This is a nautical instrument with a gyroscope as a base used to determine the direction of
geographical north.
Gyro compasses appeared at the beginning of the 20th century on naval ships to complement
or replace magnetic compasses.
The gyro compass is made up of a gyroscope hanging by its centre of gravity and supplied with
an electrical current to make it spin rapidly. With the help of a weight the gyroscope maintains
its horizontal position and with an appropriate righting method maintains its positioning towards
geographical north. With certain correcting methods the gyro compass can find the latitude of
the ship, its speed and its acceleration potential.
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