MP would be responsible.
You could also file a suit under the tort laws against the State of NH under Part First Article 2-A. The court would then decide for the State or send it back to the Legislature for immediate relief.
You would use the statute NH RSA 270:37 as fact that the Legislature has intent to limit the noise coming from a vessel.
http://www.gencourt.state.nh.us/rsa/...270/270-37.htm
There is no other reason to actually require muffling exhaust in the case of a water vessel that I can think of. And the muffler requirements do not state only after dark or any other period of enforcement limitation.