I had a similar issue but with necks annoyingly enough. It wasn't even an event. When I first settled there I noticed there were 2 areas somewhat close where necks spawned in pairs so I made an admittedly crappy dock away from those spawns and yet, every time I turned around 6-8 of them had congregated from who knows where and decided "screw this boat in particular". This cost me at least 6 rafts until I was able to make a krave. By then I had also made a ward so I instead found myself constantly running directly to my boat whenever the ward got pinged and sure enough, it was almost always the neck horde trying to murder my boat again. The krave + ward meant I stopped losing the boat to them, but I constantly had to go defend it as well despite having workshops on both sides of the dock area.

Now that I have reached the iron age, I went a tad overboard addressing this issue but it has FINALLY stopped. All it took was a large stone boat garage with an abundance of fire pits (most of which I hid, except the hearth and the two flanking the entrance that I use as lighthouses to guide into the dock during bad weather):
https://steamcommunity.com/sharedfiles/filedetails/?id=2619638908