Looking good.
As for the hull shading, the by-the-book way is to draw only narrow shading around the bottom with 2-4 pixels according to each prefered style, but this way isen't bad either, just don't overdo it with trying to chase a shape that flat pixel art cannot catch. One has to still remember keep his upper and under work in relative balance together. Your style with the actuall ship isen't posturing with lot of shading and IMO thats the reall indivdual treat in your style, so by that logic, I would keep the underwater parts in similar balance as well.
Thank for the comment Golly