Thank you all for the feedback!
raymond, Age of Pirates 2 looks interesting. Is it playable in stock form? I mean, I don't care if it has a steep learning curve or you need trial and error but is it relatively free of frustrating bugs? There's also that upcoming game,
Pirates of the Caribbean: Armada of the Damned. I like the fact that you can leave the ship and explore the land too.
Sonarman thanks for letting me know about the site. I'm gonna watch it too. Maybe even going to start modelling some ships after I finish my current project.
Now for a proper sim, among the features I would enjoy in such a game, besides good physics, would be a simulated night sky with some of the actual stars and planets (with an option to display labels for them

). There are many open source programs for this. The lack of precision of early navigation could be challenging. You'd have the option to use tools like astrolabs, back staffs or the early sextant yourself or get the navigator do it for you. For longitude you'd have a range of clocks of different precisions.
I wonder how the in-game map should look and work. It might not be enough to have a fog of war effect. I think it needs a new mechanic, like displaying newly discovered map objects (such as islands) based on your navigation error and skill.