From the FAQ on the recent blog:

The waves and rocking boats will be toggleable. They add a bit of immersion to the demo, but we don't want players getting sea sick in real life! We can also look at other techniques to help this, such as zooming the camera out further when controlling a boat, or making the render distance much smaller when walking around in your boat.

In particular, I think watching the outer world move around your screen while focusing on a large static boat in the center of your screen may be nauseating for some, so we will need to put some focus into options that mitigate that effect.