California Experience
After years of having T/T on my dinks, I got stopped by Harbor Patrol who advised me that despite the boat being documented, if the dink was used in the harbor with a motor, inland rules applied and it had to be registered. I had no ID for it or another, but went to the DMV advising that neither had an ID but I was now going to motor and needed to register them (no registration was needed if oars were the sole propulsion). Anyhow, they just registered them as home-built and assigned me numbers. RD