Bounded Buoyancy makes things float properly.

Most engines apply buoyancy as a force on the body's own mass, so anything much less dense than water can accelerate without limit: released under water, an air bubble reaches 815g in its first frame. Real bubbles start at about 2g, because the water around them has to move too. Bounded Buoyancy adds the mass of that water to each body every physics step, so nothing falls faster than g and light objects rise no faster than about 2g, whatever their density.

Features

• Light objects stay stable, and floats settle without added damping.
• Any shape: sphere, box, cylinder, capsule and convex shapes, alone or combined, or a closed mesh. Bodies tilt, tip over and right themselves, and a low centre of mass acts as ballast.
• Water nodes with waves and currents, placed anywhere: pools, lakes, rivers or the sea.
• Air and wind: helium and hot-air balloons, gusts, and sails that let boats run before the wind and heel.
• Splashes and ripples, with water_entered and water_exited signals for sounds.
• A full 2D version for RigidBody2D.
• An optional native kernel for Windows and Linux keeps 300 bodies on waves at about 3 ms per frame.
• Works with Godot Physics and Jolt.

Getting started

Enable the plugin under Project Settings > Plugins. Add a BoundedBuoyancyBody (a RigidBody3D) with collision shapes, set its Density in kg/m³ (water is 1000), and add a BoundedBuoyancyWater node. To see everything it can do, open addons/bounded_buoyancy/demo/demo.tscn and press F6.

Full documentation, tests and the Unity version are on GitHub. The physics is set out in the companion paper: https://doi.org/10.5281/zenodo.23304509

AI disclosure: developed with the help of Claude, an AI assistant from Anthropic, which wrote much of the code under my direction. Every result is checked by the included test suite against the benchmarks in the companion paper.