Ships found with compasses could have other "usages" other than sinking.
For example you could be able to hire navy ships to protect your fleet.
Merchant navy ships could make deals with you/exchange cargo.
And pirates could have, well something intresting.
Anyways main point is, that they could have some non-aggressive positions in
game.

Running on that... I had a quick brainstorm on other potential colours
of ships to add to the compass rainbow.

-Raiding ships, either Zhents or Vikings to keep in theme of the events.
Your crew happens upon a vessel who is intent on raiding some hapless
coastal town. Main difference would be soldiers on ship alongside sailors

-Plague Ship- some poor seamen have fallen to the curse of undeath. It
spread quickly through the crew, and the ship is now pulled along the
tradelanes.. waiting for some unlucky soul to happen upon them.

-Monster Hunters- These hardy souls sail the seas hunting the horrors of
the depths. Heavy fighters, ready with axes and harpoons to fight off
tentacles or worse.

-Fishermen. These are career fishermen and don't really have much to offer
in terms of fighting sport or booty. Kill them anyway?

-Luxury ship-Royalty. As soon as the we spied the vessel, we new it was
worth the trouble of catching it. It held its share of bodyguards and
soldiers but the wealth more than made up for the work to take it.

-Treasure Hunters- We thought them fishermen at first but they fought
back with much determination. That had been using a simple diving bell