Basically, new movecraft types to spice things up. These are meant to be independent from each other, so this suggestion isn't meant to suggest adding all of them.

Monitors: Monitors are small coastal or river defense ships with little-to-no armour, are slow, and have disproportionally large guns for naval bombardment. Monitors have no armour and have 50 firepower with access to 9 and 12-inch guns with a top speed of 13.5m/s. Their minimum size would be 500 blocks and their maximum would be 2,000. Their rotation cooldown is 6 seconds. These would be good for small nations who need a coastal defense ship but has bigger guns than 4-inch.

Battlecruisers: A ship with the firepower of a dreadnought and the speed of a cruiser, achieved by sacrificing significant amounts of armour in order to reach higher speeds. Battlecruisers have the same speed and rotation cooldown as a cruiser and have 160 firepower, enough for six 14-inch guns or eight 12-inch guns. Their armour percentages are 15-18% terracotta and 5-8% glazed-terracotta. Their minimum size is 5,000 and their maximum size is 8,000. Battlecruisers are good for chasing smaller ships, escorting merchants, are cheaper than dreadnoughts and therefore can serve as capital ships for smaller navies, and are balanced in that they simply do not have the armour necessary or firepower to fight the superior armour and firepower of a dreadnought.

Ironclads: Ironclads are warships in between sailboats and metal warships. They have terracotta armour but don't have access to powerful cannons and use sailboat cannons instead. Ironclads have a top speed of 12m/s with a rotation cooldown of 5 seconds. They must be at least 40% wood and can have up to 0.35% chests, up to 10% terracotta, and up to 3.5% glazed terracotta. They have a firepower limit of 8.