from my experience on OSI, this action (being booted off of a boat after a disconnect) would occurr if, when the player got disconnected the boat was still moving, when the player logs in, there will be no "support" to hold his character (since the boat was moving when he disconnected), and so it shoots the player to the "LAST" piece of land he was at. That's how it worked on OSI anyways, but I havent played there in like a year in a half or so :P
Im guessing you are an Admin or GM on this shard? Well, it's up to you whether you want to "reimburse" him for his lost item :P If when you recall onto the boat key (MUST BE THE ORIGINAL, as per OSI when I played, Im sure its the same here with RunUO but I dont have much experiences with boats on RunUO yet
) the character doesn't get transported to the boat, what most likely occurred is the user forgot to refresh the boat (double clicking either of the planks with 1 of the 2 "master" "a ship key" 's on his person).
Hope that helps