Built a destroyer. While not entirely finished, it's usable. Changed the method of designing the hulls; instead of creating a curved hull using 1m triangle corners and inverted triangle corners, I made a much more simple >-shaped bow using wedges at the front, and went for a U-shaped flat bottom instead of a V-shape. The rear deck sticks out from the lower hull over the water, making room for the propellers and rudder beneath.
Top speed is around 13.7m/s(26.6 knots). Slower than what I wanted, but it's kept that top speed throughout the entire construction process while the engines were one of the first things installed, and it doesn't backflip. Propulsion is provided by two 1m steam propellers turned by 8 pistons each, fired by two boilers each capable of burning 8.5mt per second(it only needs about 2/3rd's that for max speed).
Current armament is a pair of depth charge launchers that I might remove since they do too little damage and have a tendency to attack the ship(despite an IFF module and safety fuse), and 4 179mm x 1709mm cannons firing APHE - they're iffy at penetrating armor at the moment though. The cannons achieve a pretty high rate of fire for its caliber, but accuracy is quite bad for some reason.
Combat tested against an Onyx Watch Bastion, manually controlled, but player's repair tentacles disabled. As mentioned, the cannons had trouble piercing armor, but enough hits eventually ripped it off. Before that, the Bastion got a lucky(
very lucky) hit that tore off the rudder completely, forcing me to run while placing down some repair bots. Another lucky hit tore off both rear turrets at once - not sure how, but it might have hit the firing piece of one, causing a chain of ammo cookoffs that killed the other turret. Came back after the repair bots (slowly) got it back into shape, hammered the Bastion's cannons, and eventually gutted the entire AI core with constant pounding.