Why should they attack?
(Yes I know, using Chameleon is the cheap way to go. did it once 'natural' style)
This reminded me why I often kill all the pirates even though they add 'color' and sing songs. They are a miserable bunch. I usually step near the boat, allthough remain on public property, goad them into attacking and then kill them without a bounty.
Surprisingly, the rich gal who often appears at the waterfront to tell us all how wonderful it is she lives in the expensive district came to my aid. I restored her health as she suffered some damage. Dont' recall her name, but you know her. Pedestrians helping out and getting killed is one reason that I kill the pirates late at night. Lost a Npc I liked once.