It was stated some where I cant quite recall you can set who is able to use stuff in your land and set individual permissions on different items in your land. As far as the boat goes I would assume it could be stolen.( I may have even read it on the wiki)
Added
Here you go.
Designation Edit This concerns both macro- and micromanagement aspects of 'land' management.
You can designate an area as private to you, private to an organization, private to a settlement, private to a family, private to a list of people, or private to a nation-state. You can also mark a space as common with the same specific designations. Within a space, you can also designate certain items and emplacements as public or private. You can also designate a space for a particular activity which helps OPCs and NPCs find the stuff they're looking for. (E.g you can designate a room as your "shop" and then tell your xPC to "tend the shop" and they would be able to find the appropriate place more easily.) You can also designate restrictions based on time, or timespan (this is common every other day, or this is common throughout the month of Ocei), and you can designate what behaviors are valid in an area based on implicit contracts bound to the area (aka you can have "house rules"