Lower buoyancy on parts

[siimav]

There's some evidence that this would make water physics behave better with FAR.

njits23:

There is a difference, but it's quite minor once you're already down.
Initial landing is quite a bit better, though

JadeOfMaar mentioned that 0.7-0.8 would roughly be the sweet spot for parts that need to float but shouldn't be hard to sink. RationalHydroDynamics configs for ref: https://github.com/JadeOfMaar/RationalHydroDynamics/blob/main/GameData/RationalHydroDynamics/RationalBuoyancy.cfg