I have a submersible that is moderately dense, and I'm trying to decide between different ballast methods.

On one hand, leave my various negative spaces empty, and have doors to the exterior to be able to flood them.

On the other hand, have a series of cargo containers connected to a collector and ejectors, to pull in and eject ice as needed.

I understand Ice is less dense than water, so option 2 won't make the ship quite as heavy, though I believe it should still increase the overall density. But it will allow more granular control if I hook up event controllers or sorters to control which containers get filled.

Any thoughts or opinions? What was your best ballast system?