I have a few ideas for weapons that could be implemented.

-First and foremost, the flintlock pistol. Each time it is fired it will remove from your inventory 1 gunpowder, and 1 of whatever the “Shot” is chosen to be (Maybe iron ingots or flint), and will fly straighter but do slightly less damage than an arrow.

-Second is the Stinkpot. The stench this weapon created was so powerful men would often hurl themselves into the sea to escape it. It would be crafted  with rotten flesh in the middle of  the GUI, an iron ingot on each side and directly below it, and string on top of it as a fuse. When rightclicked, it would throw a splash potion of nausea, which is only available through commands. The Stink Pot could keep the pistol from becoming to OP by making it harder to aim.

Third and final is the grappling rope. It would be loaded into a cannon, and when it hits a ship, pull it a block closer. This would make it easier to board ships so you can fight the crew and steal the cargo like real pirates. It would have a quite limited range to keep it from becoming too op.