I just had a really bizarre experience... I sailed back to my main home from my new sandstone palace (really, more of a shack at the moment
) to grab something I forgot. When I got there, my game suddenly went black and I had to force quit Minecraft. I reloaded that world, and I was back in front of my main house and everything looked ok, so I grabbed what I needed and hopped back in my boat.
And that's when I discovered a line of 4 boats just floating there in the water between my two houses, and a 5th boat at the dock of my sandstone house. They're still there after exiting Minecraft normally and coming back.
Free boats! There's a fourth one in the water just out of visibility range.
(edit: linked image as it was a little big...)