Decibels (dB) are a measure of the amount of pressure created by sound.  When the pressure hits our ear our eardrum, nerve system and mind create the sense of sound. Unwanted sound is noise.

Sound level meters are also called decibel meters. Decibel meters can be purchased online for a few hundred dollars. However, there are many apps available for smartphones that will also measure decibels. Make sure the app has a slow response and the A-weighting settings.

Smartphone apps may not be as accurate as a decibel meter but will be useful to help determine the approximate noise pressure coming from your boat.

The regulations and laws in the USA are based on SAE J1970 – Shoreline Sound Level Measurement Procedure for Recreational Motorboats (often referred to as “pass-by”) and SAE J2005 – Stationary Sound Level Measurement Procedure for Recreational Motorboats (often referred to as “stand-still”). The boat must be able to pass both standards.

SAE J2005 – Standstill

  1. Find a location that is relatively quiet and away from buildings or natural structures. The measurement can be taken at the dock or on the water.
  2. Set the decibel meter to Slow Response and A Weighting scale (AS)
  3. Take a measurement of the ambient dB before starting your boat and after the boat is turned off.
  4. Run your boat at idle for at least a minute.
  5. Take the measurement with the meter/phone 1 meter behind the transom/swim platform and 1.2 to 1.5 meters above the water.
  6. The ambient dB pressure before and after the reading must be 10 dB below the boat muffler level.
  7. If the reading is 88 dB(AS) or below your boat passes the proposed legislation using SAE J2005.

SAE J1970 – Pass-by

  1. The measurement location is anywhere on shore, no more than 6 meters out into the water (ie on a dock), anywhere on shore, at least 3 meters in front of a wall or other obstruction, held at least 1 meter above the ground with no one standing near or in front of the meter. The meter/phone should be pointed toward the boat as it passes by at speed.
  2. Set the decibel meter to Slow Response and A Weighting scale (AS)
  3. Take an ambient measure of the dB before and after the measurement.
  4. Have the boat pass by the measurement site at high speed. The applicable reading does not require the measured boat to be at any specific distance from the shoreline or microphone.
  5. If the maximum reading is 75 dB(AS) or below your boat passes the proposed legislation using SAE J1970. The ambient dB before and after the reading must be at least 6 dB below the measurement of the boat