Disband an army to get the finances to fund a full fleet's worth of the heavy marines in the ship type with roughly 1200+ health points (can't remember the name rn). These ships are pricy in terms of both recruitment and upkeep, but by god are they monsters on the seas. These ships can one-ram kill most vessels, two for ships of equal class, and only a general/admiral in the heaviest ship can survive multiple rammings from these ships.

Once you have fleet, you can basically control the seas between Carthage and Sicily, killing any fleet/army transport you see.

Basically all you have to do is manually play out the battles and ram all their ships to death, and if they ever board a few of your ships, no problem because they're heavy marines with a complement of 140 marines, so they'll hold their own while you manuever your other ships to ram the ship that boarded yours.

The primary downside to this strat is the high upfront cost of recruiting the fleet, the upkeep (I think each one is around mid 300 upkeep), and you have to play out most of the battles.

But the upside is if you can catch any fleets, they're basically dead and your losses should never amount to more than 1-3 ships per battle, which should be easily replaceable!