OK, that's it. I submitted my storyboard after I made some major improvements. The translucency of the sails is correct now, the foam distribution and the animation of it are reworked and I switched off motion blur to get rid of the grainy blurred parts. I really miss the real displacement on the sails, but with RTE on I will still be alive (hopefully) if this animation will be rendered some time.
(I gave up rendering the higher resolution animation, and keep on rendering a 640X360 test animation).
I really need to do something else now, because I spent a lot of time with this animation, but it was great fun!
Here is a smaller version of my submitted storyboard:
(I forgot to mention, that I sharpened it a little bit. Otherwise there is no postwork)