I built a pretty cool ship/barge in From the Depths. It has four small tribarrel 40mm AA guns mounted on deck, and 120 vertical cell missile launchers down the middle (2, 60-cell launchers).
Top speed is 10m/s... In ship mode.
Hold down "o" for a few seconds and the ship rises up out of the water until its flat bottom is resting on the surface, held up by downward facing props. As the ship rises its main props come out of the water, so you may as well shut them off. As soon as it is up and the main props are off, you can kick on the real main drive, two massive jet engines. Top speed? 145m/s.
Under the centerline of the ship are two hydrofoil pylons, each set to different fixed angles discovered via a great deal of trial and error. These keep the ship level when at top speed, otherwise it would pitch one way or another due to weight imbalances. I tried to autobalance the hydrofoils with a PID, but that worked poorly at best. This thing seems to be more stable if the front and back hydrofoils are set differently, not simply mirroring each other.
There is a nice big bare spot on the deck, right over the engines where I couldn't fit recessed missile cells. I ought to put a cannon turret there, but then I would have to rebalance the hydrofoils... I probably will put something there at some point.
Really, there are only two things I don't like about this ship:
1) It goes really, really fast, but you pay for it in fuel. Lots and lots of fuel.
2) The AI can't use the fancy main drive properly. I ended up removing the naval AI card and just driving it myself if it needs to go somewhere while in play. Luckilly it sits really low in the water and has strong shields, so just letting it sit off to the side and pound stuff with its missiles works just fine (the shields run off RTGs, so the only thing that takes fuel is the main drive).