Attached Link: http://homepage.mac.com/scottspringer/resources/discussion/water_composite.html

I think that all the solutions involving 3D geometry or transparency maps are great if you actually have a need to solve this problem with geometry.

Unfortunately, if you're not lined up exactly, you may see a gap between the water and the boat hull. Which would ruin your illusion.

I think the simplest, fastest, almost no-brainer way to solve this problem is to use compositing. If you're making a still image, it's perfect. If you are making an animation, it's a wee bit trickier, but still doable.

http://homepage.mac.com/scottspringer/resources/discussion/water_composite.html

Follow this link to see a quick example of what I'm talking about.

Using previous models I built, I was able to animate, render and composite this animation (using Photoshop of all things!) in about 2 hours of total work.

Most of the time was spent screwing around w/ Photoshop (for some reason my copy of QuickTime Pro stopped exporting otherwise I would have used that.