Cannons were the mainstay of sea battles in the eighteenth century, using gunpowder to launch iron balls at about nine hundred miles an hour. A cannonball could be anywhere from two to six inches in diameter, depending on the bore of the cannon. But there were other things besides mere balls a pirate could shoot at another ship.
Yes, you can dump a bunch of silverware, nails, and whatever else is expendable into a cannon and shoot it. This is known as a blunderbuss shot, and while not at all effective in breeching the hull, it would be downright nasty if it hit a person on deck.
They also used bomb shots-- a hollowed out cannonball full of gunpowder, with a fuse. The fuse is lit just before putting the bomb in the cannon. If you time it right, the bomb explodes just as it is hitting the opposing ship. If you time it wrong, it could land on deck and blow up later; or it could blow up in the air and be wasted. If you time it drastically wrong, or if your flash pan doesn't light, it could blow up your cannon and kill you.
What do you get when you attach two cannonballs to a length of chain? You get chain shot. A chain shot spins in the air, and if you shoot it at the rigging, it can wrap around ropes, tear sails and break off the spars, to prevent your prey from sailing away.