Vessel operators may not hear sound signals or voices if the engine is not adequately muffled.
- Any motorized vessel operated on the inland waters of California or on ocean waters within one mile of the coastline must be muffled or otherwise prevented from exceeding the following noise levels:
- 90 decibels using a stationary sound level test as defined by SAE J-2005 if the engine was manufactured before January 1, 1993, or...
- 88 decibels using a stationary sound level test as defined by SAE J-2005 if the engine was manufactured on or after January 1, 1993, or...
- 75 decibels measured as defined by SAE J-1970 for all engines. However, such measurement shall not preclude a stationary sound level test as prescribed by SAE J-2005.
- Exceptions to the above restrictions are made for vessels participating in permitted regattas, boat races, or speed trials.
- Authorities generally agree that unbaffled exhaust pipes (stacks) and most water-injected pipes do not meet the above noise level requirements. Unmodified outboards usually meet legal requirements.