Ha, you are so right. I totally spaced that. More coffee please. 

To remedy this, you can do the same trick but instead, make a plane (vertex or primitive) and make it a child of the boat. Then move this to be something like .01 above the infinite water plane. Just like before, you'll have two reference shaders. However, one of them should have an alpha value of zero to make it invisible so that the only thing showing is the foam.

This is a similar trick to what was done on the CG boats here to create the boat wakes: http://carrara3d.com/3d_gallery_icebr.html 

Look at the videos and  stills.