[fingpilot]

My marina measures length overall. In my 40' slip, I have 3' of overhang. That is allowed. They actually come measure the amount I stick out into the fairway. The beam (width) has to be 6 inches less than the width of the slip. Mine, at 14', is 12 inches narrower than the slip.

Google 'Plimsoll Mark' , and you'll get a description of 'displacement tonnage' at various temps and salinities, and how it affects draft. In college, I ran a ferryboat on SanFran Bay. The gross tonnage was 135-ish. The net tons was always 99.7 or something like that. At 100 tons, everything gets big time. My license at the time was 100 tons. I later ran a large yacht, 175 feet, 670 gross tons. 499 net tons. Yes, just under my 500 ton license. Any 'machinery spaces' were deducted from the gross tonnage capability (the idea being that those spaces were not useable for hauling things). I used to illustrate that point by showing guests the closet in my deckhouse quarters. There was no door on the closet. Nestled inside it was the radar computer box, about two square feet of sealed box with cables running in and out of it. It was actually inconvienient (in the radar scheme of things) having it in there. But it made my entire cabin 'machinery space', exempt from net tonnage calculations. That went on all over the ship.

HTH.