Hello, I am about to start a new diorama with a 1-350 aircraft carrier called the USS Yortown, I have tried 3 types of water effects and to be honest, I was quite disappointed with all of them, that's not to say the product is no good, just that my skill isn't quite up to speed. I have brought something called water effect on a roll, basically a sheet of plastic that you paint the under side, cut out the shape and simply place in the middle. Again, this will be a small diorama, not much bigger than the size of the ship 30" x 4" so the area would be about 36" x 7" - the problem I have is making the waves in front, sides and back of the ship, as silly as this might sound, I don't know how big these are suppose to be, I would like a rough stormy sea, again its going to be my skill level which isn't that good, any help on this subject would be great. Look forward to your reply.

No silly questions. If you don't ask you'll never know.
The size of the waves depends on the weather. The higher the waves the rougher the water. One thing to realize is the trough of the wave. We are all familiar with the top end of the wave with the nice white cap. A wave in the high seas is measured from the base of the trough to the peak of the cap. Do a quick google image search on wave trough and you'll see what I mean.
Make sure you can represent the low side of a wave just as well as top side. So, I think what I am saying is - the rougher the sea, the bigger the wave, and the deeper/taller your diorama will be. If you have a waterline ship then go low seas, small white caps. If you have a full hull ship and ambition to fill big waves then you can build up some good size waves.