Harpoon/Grapple Gun
An implementation of a harpoon/grapple-like gun would be an interesting concept, in my opinion. It's title would serve as a tool, not a weapon. You could use the mechanism to kill and reel in sharks, which could then be sold to the merchant at an outpost. More importantly, the only way to obtain a shark would be to harpoon it and reel it aboard your ship, whereas simply shooting it and pulling it up a ladder cannot be.
Also, the grapple could be used to latch onto another ship for you (and your crew) to have options on how y'all choose to invade an enemy vessel, making the harpoon/grapple gun a versatile tool for a pirate.
I spoke with a fellow Bilge Rat about the idea, and he noted that the tool would be best utilized if it were mounted atop the Crow's Nest of your ship. The vantage point would allow one to Harpoon sharks, latch onto ships (and island shores) easier, as well as zip-lining would be a far more exciting passage!
