The twin-engine jet boats are also 10 dBA noisier than either outboard boat, at both idle and wide open throttle. Even more annoying, the small, high-revving engines of the jet boats produce a high-frequency scream. It's impossible to get away from the noise. For example, at a No Wake 6 mph, when the outboard is turning a quiet 1200 rpm, the engines in the Sea-Doo are already spinning at 3500 rpm to maintain the same speed.
http://www.popularmechanics.com/adventure/outdoors/a5328/1276876/
Start at the source. The number one source of background noise inside a vessel is vibration induced by machinery into the boat structure which radiates through the hull. This is important as many of the commonly thought of noise reduction techniques will not produce the “attenuation” expected if this conduit of sound is not reduced.
http://www.yachtwork.com/report-sond.htm
EVINRUDE E-TEC. 25 HP, 40 HP, 50 HP, 60 HP & 60 H.O. Small engines with a lot of punch. Tougher than the other outboard motors in its class with more electrical output. And with the incredible Evinrude tiller, you're in total control of your engine. And your time on the water.
http://www.evinrude.com/en-us/engines/e-tec/25-hp-60-ho.html
The brass section playing fortissimo can drown out practically the whole orchestra. One-third of the total power of a 75-piece orchestra comes from the bass drum. High frequency sounds of 2-4,000 Hz are the most damaging. The uppermost octave of the piccolo is 2,048-4,096 Hz. Aging causes gradual hearing loss, mostly in the high frequencies.
http://www.hearnet.com/at_risk/risk_trivia.shtml
Marine Sound Attenuation. Sound attenuation, or reducing the onboard noise is often considered an art. The industry has progressed to a state that boat crews often step outside from their cabin only to realize the vessels engines are running and she has already left the dock.
http://www.yachtwork.com/report-sond.htm
NOTES: 1  The brass section playing fortissimo can drown out practically the whole orchestra. 2  One-third of the total power of a 75-piece orchestra comes from the bass drum. 3  High frequency sounds of 2-4,000 Hz are the most damaging.  Aging causes gradual hearing loss, mostly in the high frequencies.
http://www.hearnet.com/at_risk/risk_trivia.shtml
After a brief definition of what noise. actually is, this paper will attempt to. clarify ‘noise’ as applied to MAN B&W’s. two-stroke engines, and will then go on. to discuss the primary noise sources. and types of engine-related noise. emissions, noise level limitation, and. the current situation in relation to noise.
http://www.dieselduck.info/library/05%20environmental/MAN%20B&W%20noise%20pollution.pdf
Normally, it is the sound pressure level. which is measured, and when nothing. else is given, it will be re 2 x 10−5 Pa. On the basis of the above, a sound in-. tensity of 10−12 W/m2. 2 corresponds to a. sound level of 0 dB, and a sound inten-. sity of 1 W/m2.
http://www.dieselduck.info/library/05%20environmental/MAN%20B&W%20noise%20pollution.pdf
posted 04-16-2013 11:39 PM ET (US) [Measure of sound pressure levels in a decibel scale] are not the whole story. A lot depends on the layout of the boat and air flow aft over the motor at cruise. Some boats will reflect more noise forward than others. If you spend a lot of time at idle you might prefer a four-stroke. If you spend most of the time at cruise there won't be much difference in the noise produced by the two types.
http://continuouswave.com/ubb/Forum4/HTML/007876.html
This similar bowrider is 17 ft. 7 in. long, weighs just over 1800 pounds and comes with a more powerful 125-hp version of the same Mercury outboard. Including boat, motor and trailer, the Bayliner lists for a bargain $11,895.
http://www.popularmechanics.com/adventure/outdoors/a5328/1276876/
how many decibels of noise is a speed boat motor
A speed boat motor is 10 decibels of noise. There are 10 decibels of noise is a speed boat motor.