First longboat (and last) of mine that was ever destroyed I "set anchor" a good swim away from shore, in the meadows (about 50 yards from the boundary of a Plains biome). I wasn't 100 yards into the plains and I heard a "crunch" I stopped...listened... another "crunch". I ran back to the boat and a gobby, treading water... was already beating on it. He managed to destroy my boat before I could do anything about it.

Thankfully all your loot floats in crates.

I've been very cautious on how I make land fall ever since.