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Using a whistle for a ship's navigational operation might seem a bit outdated in today's technologically advanced world. But no matter how simple and unusable a whistle may seem, it is still considered as the most important tool in the ship's navigation and manoeuvring process. A ship's whistle is being used since the early days of wooden sail ships. A versatile equipment, the whistle has withstood the test of time and technological advancement because of its peculiar utility and high reliability.
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A whistle is of utmost help in times of bad weather condition and poor visibility, when alerting the nearby ship becomes imperative. Also an important equipment in times of emergency situations, the whistle is used to beckon audible help from a nearby relief source. According to the international regulations all the sea faring ships should compulsorily have a whistle on board. Moreover, the whistle should be in good working condition with clear audibility. The whistle should be designed to provide prolonged blast at appropriate time intervals. The whistle can be both manually operated or electrically set up.
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Construction and Operation
The figure shows a general type of air operated whistle. The simple arrangement consists of a diaphragm with an air inlet port. The diaphragm is contained in a conical shaped curved structure horn, which helps in amplifying and spreading the sound.
When the compressed air is allowed to act on the diaphragm, it vibrates to produce sound waves which passes through the horn and gets amplified in it. Initially the horns were operated manually, but now they come attached with a air flow control system.
The control system is an electrical arrangement which is used to control the supply of the compressed air coming from the air compressor. The arrangement is so made that the whistle provides the sound making operation as long as any of the switches is in the "on" position. This arrangement is generally made for making long blasts. In order to make short blasts, the operating switch can be given short on off operations, since cut off occurs instantaneously after each blast. Though, nowadays , fully automatic control systems are available to provide both long and short blasts. This sophisticated control system consists of timing gears, which are adjusted according to the duration of time interval required.
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Location of Whistle Control
The whistle operating switches are usually located on the bridge wings and inside the bridge. The whistle can also be operated manually from the lanyard, which extends from the bridge and where the whistle is fixed. The system is designed in such a way that in spite of fluctuation in the compressed air the quality of sound signal is not affected.
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Introduction of Marine Engineering 2nd Edition by D.A Taylor