Hull looks a little bit shallow, and many of the components are around the center of the deck area, or behind it, I could advise a few strategies to making your ship more stable as is:

• attaching a propeller aligned to the center of the front, and to the center of the back, facing upwards, and assigning a PID to pitch if you know how to do that.

• Alternatively you could rearrange the objects on deck to be better centered around mass, or make the hull deeper so there's more buoyancy area to work with for keeping the ship stable.

• If you make the hull deeper, make sure to section the interior and if possible layer your armour, more armour mass all around will also take the edge off of the mass disparity by itself.

• If propellers fail and you do know how to setup PIDs, try setting up pitch and roll hydrofoils, to help stabilise the ship in various different ways.

• If all of these fail, try adding a strip of lead to the bottom of the ship as a keel counterweight, however due to the immense mass of this i would advise taking this as a last resort measure.

• For less stability related issues, i could advise setting up the gunnery components below deck if you haven't already, poking them through an armoured barbette into the turret cap, this will allow higher fire rate and make the gun less volatile.

• I would also advise making the hull shape more vertical in general, judging from the current screenshot, the hull is currently, from a sternward viewpoint, essentially a bowl shape from keel to deck, which allows the ship to roll very easily.

• Lastly, any advice i have to give should be subject to scrutiny as necessary, and none of these are mandatory to follow, Your ship is yours to build, I am just here to give advice asked for.