Sorry for the delay in getting back in touch – not much spare time lately. 

Don't worry about not 'getting it'. This is one of those things that you'll finally slap your head when you understand it and wonder why it took so long. It's not real obvious so don't feal bad.

For my simplified example, I have three shaders: Blue, White and WaterBlend. The Blue is for the water, White for the Wake and WaterBlend for getting the two shaders to play together for the wake.

The WaterBlend shader is a Complex Shader that uses Carrara's Reference Shader ability to subscribe to the two colors. The WaterBlend shader is applied to an infinite plane I have in the scene that is the geometry for the water.

I have another object in the scene called Wake. It is a spline object but it could also be a vertex object – it doesn't matter. However, this object is visual shape of the wake we will make on the water. The object can have it's Visibility turned off and it will still create the wake pattern thanks to Terrain Tools. 

Now, in the Multi Channel Mixer, I reference the Blue, then the White and blend them with the Terrain Tools Intersect function. **Important: you have to tell the function what it should interact with so I've typed in the word Wake which is the name of the spline object. If this is not typed perfectly to match the name of the object, it will not work.

I set the size for 1 ft and didn't add any noise or modify the radial falloff. You can do that later to suit what you want to see the wake turbulance to look like. 

To implment this, you then make the Wake object a child of the boat in your scene and turn off the visibiltiy of the Wake object. Now, wherever your boat goes on the infinite plane, the wake will follow. 

To make it look more realistic, the 'blue' shader can be swapped for a water shader. I just use simple colors to start to reduce preview and render times. 

Hope this helps.