lots of enemy will chase your boat if you get near a shore.
the dangerous ones are
- if you go near a swamp, leeches will chase and chew on your boat. wraiths as well, but they are rare.
- if you go near plains, dethsquitos will cause A LOT OF damage to your boat if they hit it.
- out in the ocean, sea serpent.

in all cases you can kill or drive off the enemy with a bow. Rafts can't take the hits from most of these, so you will be sunk and die if you do not outrun or shoot them.

the other stuff that chases you cannot catch even a raft sailing with the wind, eg grey dwarves and trolls will swim after you but they can't keep up and are mostly harmless.