I think a vessel left that long without someone responsible for checking it does fit the definition of "derelict". Maybe the owner is out of the country, sick, incarcerated, or dead. Any way you slice it, if there is nobody in charge and the authorities aren't able to contact the registered owner AND they have tried -- that's the harbormaster's problem.

What I wrote in my other post above isn't wisdom -- it's just common sense if one wants to avoid problems. Everyone who watches TV, reads a newspaper or goes to school knows we live in a society of laws and people whose job is to enforce them, and if you don't know the laws that's not a valid defense. So the average Joe Cruiser should take steps to secure his boat where he or someone else can be responsible for checking on it, and leave contact information with the authorities if you don't. You can't leave a car parked in one place on a public road for 6 months either, without someone towing it (or stripping it).

How far should they go in expending effort to find him? Should they launch an all-out investigation? Or should they do their job and exercise "due process"?