so basically a thing i have thought of is adding a block like the vanilla air blocks (e.g. like the blocks minecraft:air, minecraft:cave_air, minecraft:void_air) and it basically functions like this:
when assembling a ship, replace all sealed air blocks with vs_clockwork:ship_air and if this portion of the ship is sunk into a fluid, don't render the fluid (using a custom shader similar to aero), negate all effects caused by the fluid and provide breathing to players and mobs inside. one potential problem with this approach could be if the physics body is changed to allow leaks, as a placeholder until actual leak physics are made, revert all ship_air blocks into air. it should be checked, say, every 20 ticks (1 second) for changes in all clumps of ship_air and this should be adjustable as a gamerule or in the config.
#suggestion for making submarines actually work (survival air related)
fickle talon
gleaming quest
That was already asked in a different pos