Always interesting reading these posts, although the best advice was given in Wolfeboro_baja's post; when in doubt always call the NHMP.
People often look at the law, and then throw a thousand "what ifs" in a way to circumvent or find fault with the written regulation. But obviously no few paragraphs can cover every contingency. Nothing is etched in stone, and that is why the defendant is offered the opportunity to have his/her day in court.
But what is often overlooked in these debates is the key element of intent. In most cases, when you have your day in court, the prosecution not only has to prove the violation occurred, but that you also had the intent to break that regulation.
This is an excellent example. And while some of us are hung up on the term boat, the actual definition we should be using is vessel. In some minds the term boat constitutes too narrow of a definition.
Simply put a vessel is anything that is used to cross the water for the intended purpose of transportation, regardless of what that mode of transportation may be.
So if you are simply floating about your shoreline in a swim raft, inner tube or surfboard your intent is simply rest & relaxation, not transportation.
Take that same innertube, swim raft or even a cardboard box and rig it so that you are now crossing the broads or island hopping and your intent now is clearly one of transportation (along with the rest & relaxation it may provide). Under these circumstances your device is now a vessel (or boat if you prefer) and you fall under the applicable legal requirements for that type of vessel. And obviously many items are clearly vessels no matter how you intend to use them, so they always fall under the pertinent regulation.
It's kind of like the town drunk that decides to use the riding lawnmower to get that third case of beer. Normally the lawnmower is not considered a vehicle, but take it out on the main drag while intoxicated and you will be successfully prosecuted (hopefully) for Driving While Intoxicated! It all fell back to what your intent was when you took that mower out on the open road.
Yes, it is a judgement call on the officer's part, but he will clearly need to articulate to a judge why he formed the opinion that you were using your particular item as a vessel for transportation purposes. That is the legal standard necessary to define the so called "gray area" between an item being used as a vessel or simply for recreational purposes.
Hope this helps explain it a little better. And the call to the NHMP is necessary as they may have already determined as a matter of policy that this particular device is a vessel, and officers are instructed/ordered to react as such.
None the less an interesting discussion with some very good points being made!