Yeah, we could probably do just the plating with a revision, but there's been huge changes to the sea environment, and we've yet to replace our existing boats. Now they fight with mages and ballistas, always have trailing winds, and can use rigging and keel changes to take advantage of that. We could use protection for the ballista postions, or design ones that can carry more than one, and have space for carpets.
There's a lot of room for improvement, in addition to the speed and protection from the plating. The rigging and keel changes should also add speed, and adamantium magazines for the fire pots, as well as protected fire positions would also be very good ideas. There's a whole raft of changes, and all of them would be beneficial.
Basically, think of it as a new boat to take notice of the change to long-ranged artillery battles with magazines and secure ballista positions, and the always-on wind direction for greater speed. Having adamantine plating further increases the speed and maneuverability (due to our hulls having less friction and being immune to barnacles and sea decay), as well as significantly increased survivability, with little extra difficulty because nailing sheets of soft supermetal to the outside of a hull is really quite easy, and it's light and strong enough to add quite a bit of toughness over wooden beams, without running into the topweight problem inherant in normal steel armor.