Cannonball

The cannonball is an ammo item used by the Ship Cannon. To load a cannonball inside a cannon, press E (default key) when you face the fuse. Cannonballs can be stacked into outerwear slots, like arrows.

Source

 * Crafting: 1 Hardstone Ore + 1 Volatile Ore = 3 Cannonballs
 * Looted from Storage Crate
 * Found as a bonus for finding Ship Cannons
 * Sold by the Village Trader