(1) Often sound signals are located on or adjacent to aids to navigation. When visual signals are obscured, sound signals warn mariners of the proximity of danger.

(a) Sound signals are distinguished by their tone and phase characteristics.

(b) Tones are determined by the devices producing the sound (i.e., diaphones, diaphragm horns, reed horns, sirens, whistles, bells, and gongs).

(c) Phase characteristics are defined by the signal's sound pattern, i.e., the number of blasts and silent periods per minute and their durations.

(2) Where no live watch is maintained, sound signals are normally operated continuously. Mariners should not rely solely on sound signals to determine their positions for the following reasons:

(a) Distance cannot be accurately determined by sound intensity.

(b) Occasionally sound signals may not be heard in areas close to their location.

(c) As previously noted, buoy positions are not always reliable. Therefore, their sound signals cannot be assumed to be emanating from a fixed position.