On the map, the white water is the shoreline. Serpents HATE that. So that's the safe shallow water. Deaper spots have a chance to spawn. They move FAST too. So even at top speed, you may get hit once as a serpent hits you from the front. You CANNOT outrun them against the wind, so if you need to flee, turn fast, catch the wind with your sail and run.

They WILL chase you to the shore, and if you have any dwarves on shore, they will fight them. Gives you a distraction to either shoot arrows or run.

I'm only on boss 3, but have tested a few things with my serpents and frost arrows and fire arrows do extra damage.

On the open water tho, going solo is ill advised as a serpent can destroy your boat fast. meaning you are then in the water and drowning or food.

Anyone want to see the serpents in my world, you can friend me and visit