8.1 On board communication equipment 2
Communication systems
A cable telephone system on board is a typical solution for ensuring the effective communication between different compartments of the ship due to its simplicity and relatively short distances on board.
A telephone exchange system acts as an intersection between two phone lines. This is because a direct phone line between two establishments does not actually exist. Connections which are established between the two phones are referred to as a circuit. The marine telephone exchanger is a wired system through which on board telephone calls are made and received and the circuit is based on successful circuit switching. To connect one phone to another, a phone call will be routed through a number of switches.
An Auto Telephone System is an electronic telephone switchboard reliable and durable to meet various needs occurring inside or outside the ship. It operates with the interface between the central exchange unit, which is a microcomputer-controlled system and telecommunication equipment.
Marine telephone exchangers are operated in harsh environments; therefore, they require sufficient Ingress Protection (IP).
An electronic equipment malfunctions when water or dust enters the device. The IP code classifies the degree of protection provided against the intrusion of solid objects, dust and water. This standard provides users with more detailed information than vague marketing terms like “waterproof”. Ratings are defined by the letters IP followed by two digits and an optional letter. The first digit refers to the protection against solid objects and is rated on a scale from 0 (no protection) to 6 (no ingress of dust). The second digit indicates how well an enclosure can resist liquids at a scale from 0 (no protection) to 9 (high-pressure hot water from different angles).
Sound-powered telephones use electro-mechanical transducers to provide battery-less audio communication. When a user talks, sound pressure is produced, and the transmitter generates a low voltage that is sent to the receiver, which converts it back into sound. These telephones are used only in the case of blackouts or other emergencies. The main drawback is that you can only use these phones for short distances; therefore, they are used as secondary to the wired telephone systems.
So the internal communication on board is ensured by means of PA, telephone exchangers for wired phone lines, sound-powered telephones in emergencies, and the internal communication is recorded and stored in VDRs for the investigation purposes in cases of any accident or near miss.