A KSP mod that uses double precision measurements for buoyancy calculations and allows for high-speed horizontal ditching.

Density can also be configured per-CelestialBody by using the config file to set density for a particular body index.
The default density value can also be set.

Source: https://github.com/ferram4/BetterBuoyancy

Changelog:

v1.4
Confirmed compatible with KSP 1.0.4
Upgrade to MM 2.6.6
Water surface interface now removes more energy from splashes
Fix female Kerbals sinking after ragdolling
Change splash FX to appear at lower speeds / not as often

v1.3
Update for KSP 1.0.3
Upgrade to MM 2.6.5
Fix some situations where things that should float did not due to incorrect volume calculation

v1.2
Update for KSP 1.0, 1.0.1, 1.0.2 Upgrade to MM 2.6.3

v1.1
Added null checking on vessel spawning watcher
Fixed ragdoll EVA sinking
Upgrade to MM 2.5.9

v1.0
Initial release