About Noise Determining acceptable levels of sound can be highly subjective. The smallest difference in noise level that most humans can perceive is 2 dB, while 100 represents the threshold of pain. The decibels are measured on a logarithmic scale, that is, the value of a dB is not a constant. Ten decibels equate to a tenfold change. As a point of reference, inside a car traveling at 70 miles per hour on a smooth road the sound level would be about 68 to 70 dB. Standing near the runway of an airplane taking off would produce about 115 dB. An exposed running boat engine would produce about 100 dB. If you put a simple enclosure around the exposed boat engine, the dB level would drop from 100 to 90.
All modern yachts have some level of sound insulation around the engine compartment.
With a reasonable effort a boatbuilder can reduce the sound level to the mid 80's. 75 dB at seventeen knots. In addition, noise occurs at different frequency levels, and an acceptable dB level for one frequency might be unacceptable at another. Some low frequency sound, such as that emitted by a muffler, can be felt as well as heard. For this reason, we insulate such components from the hull, in order to minimize vibration.