Something fun to spice the humdrum of waiting on trade fleets...
Random events at sea.
From time to time get a rare "event" reported by a trade fleet- "Your trade fleet encountered X [a sea monster(s), NPC pirate(s), unusual anomaly (uncharted island, ship wreck), whale pod, etc.] while in route to Y port."
Player would then have the choice to send a fleet to investigate the anomaly or hunt down the NPC Pirates/Military Armada/whales, etc. They would have to decide to send a fleet right then- no saving the opportunity for later. Whales, pirates and sea monsters would not stick around while you got something together to send back at them.
Gold or credits could be the prize, or a stash of rum that boosts yer crew's moral... which may or may not be a good thing.
Loot gained would be higher if any battles with monsters or NPC characters are won in a single round, loot would be less if player had to make multiple attacks.
Significant sea monsters could be created that would be worthy of note, and whales could occasionally yield ambergris, which is a very valuable prize.
Just a simple suggestion to spice up a player's day a bit. No real change to game play, and would be simple to implement.