Fog Signals
Sound is conveyed in a very capricious way through the atmosphere and the following points should be borne in mind:
Fog signals are heard at greatly varying distances.
Under certain atmospheric conditions, if a fog signal is a combination of high and low tones, one of the tones may be inaudible.
There are occasionally areas around a station in which the fog signal is wholly inaudible.
Fog may exist a short distance from a station and not be observable from it, so that the signal may not be sounded.
Some fog signal emitters cannot be started immediately signs of fog are observed.
Mariners are therefore warned that fog signals should never be relied upon implicitly. Particular attention should be given to placing look-outs in positions in which the noises in the ship are least likely to interfere with the hearing of a fog signal; experience shows that through such a signal may not be heard from the deck or bridge when the engines are moving, it may be heard when the ship is stopped, or from a quiet position.
Fog signal emitters of all types vary greatly in power; reserve emitters are often especially weak.
Fog signals are mainly produced by the following types of emitters:
The diaphone uses compressed air and generally emits a powerful, low-pitched sound.
The horn uses compressed air or electricity to vibrate a diaphragm and exists in a variety of types which differ greatly in their sound and power.
The siren uses compressed air and exists in a variety of types, which differ considerably in their sound and power.
The reed uses compressed air and emits a weak, high-pitched sound; it is particularly weak when hand-operated.
The explosive emitter produces short reports by the firing of explosive charges.
The bell, the gong or the whistle may be operated by machinery, sounding a regular character; by hand, sounding a somewhat irregular character; or by wave action, sounding erratically.
Oral presentation 4
Electronic Nautical Chart
ECDIS is an abbreviation for Electronic Chart Display and Information System. Thus, ECDIS is more than an electronic nautical chart. It is also an information system. As an information system, ECDIS enables the user to call up information on the items displayed in addition to the graphic presentation. ECDIS stores various details in a geographic object-oriented database. Hence ECDIS belongs to the group of Geographic Information System (GIS).
ECDIS consists of hardware, software and the data. The hardware of the ECDIS is generally a computer with graphical capability linked with other items of ship’s equipment.
The software consists of the user interface (UI) and the so-called ECDIS kernel, that makes possible to read the data and display a chart. This software is also called “function library”. In addition to the chart picture, the user interface shows buttons and keys for operating the nautical chart.
The official original data of the electronic nautical chart is usually supplied on CD-ROM, or in case of up-dates, via digital or satellite communication systems. These original data are also called electronic nautical charts (ENC). The publishers of official data for the electronic charts are the national Hydrographic offices (HOs) of the maritime nations as in the case for the paper nautical charts.
The chart database is arranged in cells that cover the entire earth’s surface without overlapping. The cells store all nautical chart objects as well as objects created only during the operation of the system. The database is crucial for ECDIS deployment.
ECDIS must offer reading ENC data and transferring them to the SENC (System Electronic Nautical Chart), presentation of objects and their characteristics, anti-grounding function, warning of obstructions to shipping, updating. Various types of chart work must be possible, namely entering fixed position, route planning, entering notes and observations, sounding, measuring of distances, etc.
ECDIS is used primarily by professional navigators in the shipping sector, and in particular on ferries in dangerous waters, for national coastal and environmental protection, oil spill clearance duties, surveillance by aircraft and by sea rescue service, in simulation systems used for the basic and advanced training of navigators, pilots, etc.
Oral presentation 6