A new resolution on energy-efficiency regulation of ships was adopted at the 65th session of the Marine Environment Protection Committee (MEPC) of the International Maritime Organization (IMO),...
Sound signals vary. The navigator must use the Light List to determine the exact length of each blast and silent interval. The various types of sound signals also differ in tone, facilitating recognition of the respective stations.
Diaphones produce sound with a slotted piston moved back and forth by compressed air. Blasts may consist of a high and low tone. These alternate-pitch signals are called "two-tone." Diaphones are not used by the Coast Guard, but the mariner may find them on some private navigation aids.
Horns produce sound by means of a disc diaphragm operated pneumatically or electrically. Duplex or triplex horn units of differing pitch produce a chime signal.
Sirens produce sound with either a disc or a cupshaped rotor actuated electrically or pneumatically. Sirens are not used on U.S. navigation aids.
Whistles use compressed air emitted through a circumferential slot into a cylindrical bell chamber.
Bells and gongs are sounded with a mechanically operated hammer.