Brian, AFAIK "clearly visible" means a place that you can get a light and eyeball onto without a lot of fuss. For instance, IN THE BILGE
where it can be clearly seen when you lift
board. Or on the fuel tank
, or underside of the cockpit
, where you could see it by sticking your head
in the lazerette or engine
Since anything you can see or do can easily be painted over, filled in, or ground out, most folks would also put a copy of the number in some rather INaccessible place, where it was unlikely to be found except if you wre searhing for it to prove the boat was yours. That could be the back of a cabinet screwed into the bulkhead, or under a tank, etc.
From the USCG VDC web site:
<<The official number assigned to documented vessels, preceded by the abbreviation "NO." must be marked in block-type Arabic numerals at least three inches
high on some clearly visible interior structural part of the hull.
The number must be permanently affixed so that alteration, removal
, or replacement would be obvious and cause some scarring or damage to the surrounding hull area. >>
Doesn't mean it has to be visible all
the time! Save that space for your Monet or Picasso. :-)