In this tutorial you will learn how to make a realistic boat in Unity. There are multiple ways to make a boat in Unity, and so far I've identified the following:
Just add a box collider to your boat, and place it so it will look like the bottom of the boat is below the water line.
Use Unity's built-in wheel colliders. You can find a good explanation of the basic idea here: Physics-based Ship Movement.
Create a model that looks realistic, but is fake (as explained here: Floating an object on water)
Create a model using the real physics equations from mother nature. We will focus on this method in this tutorial. It will be slower but look much more realistic.