(My thinking being: pirates generally use speedboats, and a harpoon gun is plenty good at shooting holes in fiberglass and/or destroying outboard motors; and so pirates wouldn't want to get near your boat if you had one. But this sort of setup is not really useful for shooting at people — especially people less than 50ft away from the boat, which puts them in a "blind spot" for aiming, and especially not people who have already boarded — and so it would be irrelevant when docked.)