Small Shot -Reloads very quickly and does small hole damage on the ship. Also has a smaller blast radius and is often found but not as often as cannon balls. Something that increases the pace of cannons instead of just WHAT kind of shot. It would also make the opposing ship spend more wood on those smaller holes.
(Non realistic) Skele ball - A cursed cannon ball that spawns a skeleton who is stuck to the ship wherever part of the hull its hit, the skeleton is stuck in the hole that was made and slashes at any pirate nearby. The repairmen have to kill the skeleton before they can repair the hole.
Proud of this next one
Giant harpoon shot - A big harpoon fires into the enemy ship, if on top, nothing special happens. But if it hits the side of the hull, a rope between the cannon and the opposing ship is made as well as a big hole on the hull with the end of the harpoon sticking through oozing water. If a new cannon is loaded, the rope cuts, but the harpoon stays. The harpoon rope cannot be cut with attacks, Either the line of rope needs to be abrupted or the repairmen needs to find the harpoon in their ship and remove it with a bit lengthy [Hold] activation as long as it takes to repair a big hole. Then they can continue to repair that hole.
The harpoon shot acts like the harpoon does but is LOCKED (Not reeling in) without player input.
This should hopefully get players to discover "my" beloved vortex strategy with the normal harpoon and have players strategize and use teamwork, and give those who use it another means of vortexing without using up a player for the harpoon. This is also one of those cannon shots that I think would benefit from having it preloaded on the 4th cannon of the galleon
Cannon ball Helmet - An item which you equip automatically if you have it in your inventory and climb into a cannon. If you hit the hull of a ship, you not only make a hole but you also appear inside of it and loose 90 health. A very powerful tool and emits a very distinct sound when it hits a ship. Also rare.
I guess its... not realistic. It does not use magic at least. Should satisfy those who like to board, just be sure to prepare your best food before making the shot. It also encourages teamwork