Today's update adds the Cargo Management screen to the boats MFD so make sure you bound the MFD + and MFD - buttons as they are required to use the cargo screens.
From this screen you can load cargo into various bays. Loading cargo modifies the boats centre of gravity and mass which is reflected in the buoyancy of the boat.
You can also adjust the ballast of the boat as well as move the ballast fore and aft to balance as you see fit.
All boats have been upgraded with this new system so you can tweak the handling of everything from the Mako to the T800!
The next step is to provide areas where you can pick up specific cargo and points to drop them off. Currently you can load/unload anything anywhere!