Expanding on what Eric said,
NPC ships are all the same when it comes to the mechanics. A galleon, a light sloop, a frigate, etc, all go at the same speed with the same turning radius, etc, and when aggro-ed, move at instant full speed. This is a TLOPO thing. POTCO had different ships moving at different speeds and radii.
Ships are hidden from view in the game unless you go to the "known" hangouts for NPC ships. In POTCO you could see ships well beyond the ability to read their names or distinguish which ships they were, all across the Caribbean. In TLOPO, the ships are hidden, not sure exactly why, until you come into their "turf".
And recapping what I mentioned earlier in a different thread is that they keep sailing inside each other, where sometimes you can have up to 20 (or more) ships sailing in a circle as you sail around and around, doing the "rodeo roundup" for loot. Mesh colliders needed here, lol.
Now, agreeing with Shamus, there are many a time too many NPC ships are inside or right on shore and it can be a challenge when launching at some islands, such as Raven's Cove, with a Storm Reaper a Phantom and a Death Omen lurking with nothing better to do.
And lastly, too much of the Caribbean has no ships whatsoever, with the density in the known hangouts extreme and over packed.