I do not have info on how the 75db level was arrived at.
It is restrictive. I think that it is the most restrictive in the nation.
I have some responses to the use of the 75db rule.
1) I have taken numerous readings of normally exhaust ported outboards,
IO's and even older thru the hulls exhausted craft.
What i have witnessed is that 99% of all craft will pass the 75db at fifty feet.
And if they do not pass a fifty feet they will absolutely pass at 100 feet.
Boats that will pass at one hundred feet are not an issue on the lakes.
Even boats that will pass at a two hundred foot reading in most cases are not an issue.
The boats that we are having an issue with are boats that would not pass at 300 feet or greater.
So 75db seems restrictive yet it really is not. I could understand how it would be restrictive if you are not in compliance. We have a Baja on the lake that
runs so quiet I can't even hear it coming down the lake. So compliance with the
regulation is possible.
75db is also a decent regulation point die to the low ambient noise levels on Maine's lakes and ponds.
Now Maine is not performing the operational test yet. LRSLA has been working with the State for the commencement of operational testing next summer.
The boats that were cited this season have been muffling to comply with the
stationary test. Next year they might be forced to retool their muffling for the
operational test.
There is no boat that will comply with the cutout part of the test. Remember,
boats with cutouts in Maine must be able to pass the 75db reg when tested with the
cutout engaged. And they there is the issue with normal exhaust operational
testing.
The operational test in Maine is the same for the most part as the NH test.
Most agencies will not use it due to the inherent danger of the test.
There is a move a foot to develop a more real world test procedure.
I have posted a copy of one of the sound traces that I captured this season.
These traces are take at A and some of the reading are taken at C scale.
I do this to show the level of low frequency sound that is not captured on the
A scale measurment.
This test showed a Max A weighted level of 84.9dB
and a peak C weighted level of 106.4dB, the trace was taken
over a 32 second period as the boat passed at about sixty MPH+
I was two hundred feet from the source as it passed.
So add 6dB to 100feet and 6dB to fifty feet for an add of 12dB.
You get an A rated reading at 50 feet of 96.9dB then add ten
10db to bring your to 106.9. Only .5dB off what a C scale reading would be.
If the boat was traveling at 60mph then the the test shows a trace over a half mile of operation. You can read the trace from left to right. The boat is
traveling through the sound scape left to right as graphed.
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