Well, this is something i have yet to try, but from what ive seen it looks great.
plaster or paper mache, poor it down, and with the plaster when tis semi dry, use your hands and press down on it, making little "waves" in between your fingers, then when the plaster is dry, use plastercine to make the wakes coming off side of ship, now, to make the plaster keep shape, we ned to seal it with something, this is were MEK comes in, get some MEK (methyl ethyl ketone) and some spare plastic sprue, cut lots of little bits of sprue up, and leave them in the mek for a couple of days, after then, the mek and sprue shouldve formed a sort of paste, paint it over your plastercine waves, and let it dry for a day or so, then you can paint it up, and cover it in varnish after its dry, to give it that "wet" look.
sounds easy huh? might have to try it myself! :-) 
same deal with the paper mache, except you should be able to make the wakes with the mache instead of plastercine.
cheers, hope it helps! 
 
  