You can easily use NeoFPS + NSC + Crest, no coding required, A perfect example is the submarine, as it can go beneath the water.

Setup Scene as per normal.

Setup your character for swimming. Or use the Neo Swimming demo character.

Ensure you have the Board component added to your character.

Simply open the Seating Controller Manager and setup the Submarine GameObject (found in the Crest Submarine demo scene) as you normally would via quick setup (leave all default values for the driver seat).

In the driver seat section add the Submarine Component and the Submarine Camera Component to Components To Enable array. Optionally you can just remove the submarine camera entirely if using another camera or remove that component from the Submarine GameObject if you setup that camera with NeoFPS.

Add the Crest Simple Floating Object component to the Submarine GameObject.

Then add the freshly added component to the driver seat Components To Enable array.

Ensure that the Board component has been added to your character.

Add a GameObject with a Box Collider and Basic Water Zone, set the GameObject layer to “Water” and Is Trigger on the Box Collider to true. Scale it to size you wish to play in.

Press play, its good to go.

NOTE: You can also use the Custom Water Height and the relative component to have your character float with the waves.