Nightwing has summed it up very well in the preceding post.
But to put it very simply:
In order to be stopped and detained by the NHMP, for any amount of time, the officer must have had articulable suspicion that a violation has, is or is about to be committed.
The NHMP cannot stop you solely to inspect your vessel if they have no reason to believe you have or are about to violate the law.
The Courts have been very clear about this, and have specifically addressed it in the case cited by Mee-n-Mac.
The SOP cited in the Court decision further verifies Nightwing's explanation that no one is stopped solely to conduct an inspection, but when stopped for a violation fully expect an inspection to occur, as authorized by the RSA cited.
The original post that started this thread laid out a situation where the poster was not aware of any offenses occuring, and asking if random stops were authorized as is done with landside DWI checkpoints.
My opinion is no, random stops are not authorized. And while it is posible that the NHMP could get court permission to conduct lakeside BWI checks, I am not aware if they have ever attempted to do so. Maybe Nightwing could comment on that.
And no, the scenario laid out above that a partnership with the USCG could allow cicumvention of fourth ammendment rights is not applicable. Those standards apply only in a very narrow venue and then only within port security and coastal areas under USCG jurisdiction, Lake Winnipesaukee not being one of the areas of operation.
Let me close by reinforcing what Nightwing has said, you will not be randomly stopped and boarded by the NHMP on the Lake. But if the officer has stopped you for what he can articulate was belief that an offense was occuring, expect a full safey inspection.
As a sidebar, since we always seem to equate boating laws in some way with motor vehicle law, let me offer this up for thought.
Many years ago police officers, after stopping a car, would order the operator to open the trunk so the safety of the spare tire could be verified. And interestingly enough, many things were always discovered in the trunk. The citizens and the courts finally had enough, and that practice has long since been snuffed out due to the abuses it offered. If indeed unbridled/unauthorized stops and inspections were occuring across our inland waters, I would expect the same outrage and results from the boating public. However, I seldom if ever read of reliable first person experiences...its usually qualified with "I thought I saw" or "my buddy told me" or "I think I heard...." type stories. 