Switching controllers?

I'm making a game where you control a boat, and when you come to land(triggered by cubes), you switch to a land-based player.

So I would like to make a script where when you come in contact with a cube, it switches your controller to a different object.

Any advice?

The 2d Platformer Tutorial shows how to switch control and the camera from one object to another. You can download it here (it contains all the scripts you need):

http://unity3d.com/support/resources/tutorials/2d-gameplay-tutorial

Use OnCollisionEnter to see when you hit the cube and switch control to the other object like the tutorial does it.