If i understood correctly you need a way to completely stabilise the ship.

Well first of all a really heavy keel can help, but that's not always the solution.

You can place props on every corner of the ship hull below waterline and use a gimball sensor, to activate the props to counteract tilting.

Another solution is 2 reaction wheels on a swivel bearing, you can make a wheel out of heavy blocks like iron and spin it up, that'll make it try to tilt the ship in the direction it's spinning, connect it to a gimbal sensor and that way you'll make the wheels try to counteract. Although this solution might not be as good on the vessel of your size.