The loudness of a sound attenuates at 5 - 6 dbA per doubling of distance. This rule of thumb is applied to airboat noise in the graph below.

• The SOLID DARK LINE at the top is an airboat that emits 90 decibels when measured at a distance of 500 feet (90 decibels is the new daytime limit for airboat noise at the shoreline).

• The DOTTED LINE just below this represents the LOUDEST airboat tested by the Maine Warden Service in 2020, operated at full throttle.

• The LIGHT DASHED LINE at the bottom represents a watercraft which can meet the existing standard of 75 decibels at 50 ft.

• The DARK DASHED LINE in the middle represents an airboat which can meet a shoreline limit of 75 decibels at 500 feet, a typical distance from shore when underway.

TAKE-AWAYS:

1. Using a shoreline measurement substantially increases the noise an airboat is allowed to generate compared to the standard for other watercraft, in which sound is measured at just 50 feet.

2. A shoreline limit of 75 db(A) is a major concession to airboats compared to other watercraft (compare the light and dark dashed lines).

3. A limit of 90 db(A) measured at the shoreline offers almost no relief – the loudest boat tested by MWS would meet this when measured at 500 feet, a typical distance of an airboat from the shorefront when underway.