Most lighthouses and offshore light platforms, as well as some minor light structures and buoys, Charts and Light Lists contain the information required for positive identification. Buoys fitted with bells, gongs, or whistles actuated by wave motion may produce no sound when the sea is calm. Sound signals are not designed to identify the buoy or beacon for navigation purposes. Rather, they allow the mariner to pass clear of the buoy or beacon during low visibility.

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.

• Long range identification and tracking-LRIT - 2010-01-12 - 10:30:50
• Navigation Equipment - 2010-01-11 - 11:35:38
• Private Aids To Navigation - 2009-04-02 - 03:49:46
• Limitations Of Sound Signals - 2009-04-02 - 03:06:28
• Description Of The U.S. Aids to Navigation System - 2009-04-02 - 02:31:02
• Chart Symbols And Abbreviations - 2009-04-02 - 02:13:58
• Buoyage System - IALA New Dangers - 2009-04-02 - 02:00:57
• Buoyage System - IALA Special Marks - 2009-04-02 - 01:47:49
• Buoyage System - IALA Safe Water Marks - 2009-04-02 - 01:31:10

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