What triggers need to be met to allow entry to the boat? Doing item underflow repeatedly on the same stack I was able to get the Captain's Cap into my inventory as early as Fireburg, but even then the ship in the Ship Dock remains away. Is it the conversation with Kaeli that brings the boat closer, or am I missing/forgetting a step that brings it against the dock and the Kaeli conversation merely allows entry?

I'm trying to find a way to skip Pazuzu btw, you can activate the Thunder Rock cutscene as soon as the road to Pazuzu's Tower is created and enter Spencer's Cave, but even after doing that I'm lacking access to the boat.

You have to talk to kaeli which is exactly the problem with skipping pazuzu. you need to lose kaeli from the party for her to be there so you can talk to her. you dont even need the cap at all really, all the triggers are activated by talking to her.