Astronomical Navigation - Tesina

English:

Astronomical Navigation

Fire systems

Istituto Tecnico Nautico Luigi Rizzo – Materia : Inglese

Sergio Calabrò – classe : V ATM – a.s. 2012/2013

ASTRONOMICAL NAVIGATION

Until the compilation of new astronomical tables to assist the air navigator in

obtaining a quick position by celestial observations, the solution of a Sun, Moon, or

star sight, by which a position line on a chart could be obtained, required a

knowledge of spherical trigonometry and the solving of what is known as the PZX

triangle, where P is the position of the celestial pole, Z is the observer’s zenith (i.e.,

the point in the sky directly overhead), and X is the celestial body. The triangle is

solved by calculations on the lines of the Cosine Theory and involve extensive use of

mathematical tables.

But the new air navigations tables, now in wide use by many navigators at sea, have

made the solutions very much simpler, and with these and Nautical Almanac, a

navigator can obtain his true position without the long calculations previously

necessary. From his observed attitude of the celestial body a navigator obtains from

the tables the true zenith distance of the body and from the Nautical Almanac the

zenith distance from his dead reckoning or assumed position. The difference between

these two distances is known as the intercept, and shows the navigator how far his

real position is from his assumed position in one direction. He finds this direction

from the exact time at which he took his sight which, from the tables, gives him the

Greenwich Hour Angle.

His assumed longitude then gives him the Local Hour Angle and, using the body’s

declination from the Nautical Almanac, the azimuth, or bearing, is obtained. By

drawing this bearing on the chart from his assumed (DR) position and measuring off

the intercept, a line drawn through that point at right angles to the azimuth provides a

position line. A similar sight taken at the same time of a second celestial body on a

different bearing will provide a second position line and the observer’s true position

is at the point of intersection of these two position lines. An alternative method for

use during daylight hours when the Sun is normally the only celestial body in sight is

to take a second observation of the Sun some 3 or 4 hours later when its azimuth has

altered sufficiently to provide a satisfactory angle of cut, which should never be less

than 30 degrees. Fire systems

Fire Protection

The basic fire-fighting medium is seawater, supported by steam smothering CO ,

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foam, and portable extinguisher systems in particular areas. Water systems consist of

fixed water lines completely separated from other services and clearly defined for

each type and size of ship. The fire line is often used for other services such as deck

washing, tank cleaning and anchor chain washing. The emergency fire pumps, like on

tankers are fitted forward and are diesel-driven.

They often employ a two-pump arrangement, one for lifting water to the deck and the

other for providing the necessary pressure for fire service. On the deck there is a

water spray system.

Steam smothering was the conventional protection for cargo spaces but it was

superseded by CO for cargo holds and inert gas system and foam for cargo tanks.

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Fixed foam system has been superseded by monitor fire-system where the possibility