Reprinted by permission of
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Quieting the iron beast. Using sound-deadening tiles on the mechanical jib. by Michael Facius |
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Our 2QM15 Yanmar diesel is a hard-working, and reliable iron jib.
But it tends to be a bit loud. You know the type: give them a
little juice, and you can't get them to shut up. We knew we would
love it if our engine's sound level were lower, so when Nick Canero of
Sailor's Solutions asked if we would be interested in testing his SPM
sound proofing tiles, I jumped at the chance. When I mentioned the test to Jerry Powlas, Good Old Boat's technical editor, his response was to "be as scientific as possible." He said, " Get a sound-level measuring device, and document the level before and after under the same conditions. I work at a video-production company that has a sound engineer on staff so I was able to borrow a digital sound-level meter that can measure from 50 to 126 decibels in 10-decibel increments. |
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My Internet research turned up some interesting information
about sound levels. The human ear has the ability to sense a very
wide range of sound, which is described as a pressure and is
measured in pascals. The human ear begins to sense sound at
about 20 micropascals and experiences pain from sound at
1,000,000,000 micropascals. The ratio between these pressures
is five million to one. Because the human ear perceives pressure
changes logarithmically over a large range, sound pressure level
is measured in decibels (dB). The decibel is logarithmic in relation to sound pressure, giving us a more manageable scale. Normal conversation is approximately 60 dBs or 20,000 to 30,000 micropascals, while a rock concert is 120 dBs or 20,000,000 to 45,000,000 micropascals. One of the lessons is that conventional linear math can't be used. For example, if you have two 60-dB sound sources, the overall sound level will be 63 dB, not 120 dB. While a 3-dB change is generall perceptible, a 10-dB change, either up or down, is approximately twice of half as loud. Our C&C 30 would require about 20 tiles to completely cover the inside of the engine compartment according to Nick. He was right. The actual installation was easy. My wife Patty, and I had planned to install the tiles on a Saturday morning while at anchor. The night before we carefully cleaned all the surfaces that were to receive the tiles according to the supplied instructions. |
The tiles are 12 inches square, about an inch thick and weight 19 ounces
each. The surface that faces the engine is a shiny metallic over a dense
vinyl material. Between that side and the side that sticks to the walls of
the engine room is soft foam. The adhesive side is covered with a
waxy paper that protects the sticky surface until you a ready to apply it. Cutting the tiles to fit is easy. Have measuring tools, straightedges , and a thin-pointed indelible pen to mark the cut lines. I found that the adhesive would stick to the blades after a few cuts but some acetone removed it quickly. The whole process took us a little over two hours. After we cleaned up and made some lunch, it was time to turn the Yanmar on and listen to what we had accomplished. The sound level in the cabin at idle had been 79 dB, and at 5 knots it had been 80 dB. With the tiles installed, we cut the level by 3 dBs. The sound level at idle now is 76 dB, and at knots it has improved even more to 74 dB. We can now talk to each other instead of yelling. While the Yanmar is still a strong presence, it's much quiter than it was before. As an added bonus, the inside of our engine compartment looks great.
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