That is quite an impressive scene. One thing struck me though. The sea is rough and the run off's are spewing water, there is foam on that big wave.
The U-boat looks totally dry. I would of thought that there would of been some wash and foamy bits and a wet boat would be at least a bit shiny.
Nether the less it is still impressive!
As to making the water, there are as many ways of doing that as there is of cooking potatoes! Some are easier than others. Getting it to look good is the hard part. Its a trial and error thing.
One simple and effective way is make a base out of what ever you normally would. Plaster, expanded polystyrene, what ever, just to get the wave tops and the swell. When that is totally dry scrunch up some cooking foil a bit and then glue that on top. I would suggest the dull side up. Use pva wood glue and paint the top with it as well.
When that has dried its the challenge of painting. I would thing that fairly translucent colours in loads of coats. This will give the surface depth. The last couple of coats should be almost clear.
Where you want the foamy bits you can add white. As for the actual foam on top, its either white paint or a bottle of vallejo's foam/snow effect.
The process is slow and gets better with practise. If I was you I would try a couple of small ones without the kit, just a base to figure it out.
Ian M