For the water spume effect I used the same 3D fractal model explosion that I used a few years ago for my exploding Star Wars ships.
I sectioned the fractal model into several pieces, switched them around, affixed the four 'boom bits' to pennies (to add a bit of weight) and was off to the races.
The airbrush made fairly short work of them, with only a few layers of green and white added with the brush. Blamo-Presto: Water Explosions!
The freighter is fairly stock work, but I did drill out the stern deck to provide a magnetised mounting for a deck gun to be swapped in if a scenario required it. Sadly, the painting is a bit uninspired (I blame the rush to finally get it finished) and it frankly shows. Nonetheless, it's done and we have a juicy target for future torpedo/bomb runs.