The ships
 

In lotr and its appendixes it talks about Gondor and the Haradrim having ships and fighting each other. How was this done? I am sure that it wasn't with cannons or else they would of had guns.

Just a though, maybe theyhad long spears attached to the helm of the ship and they rammed the other ship.

Presumably any or all of the ship-to-ship weapons that they used to use before the invention of cannon: underwater rams; ballistae; archers; boarding parties and perhaps even Greek fire.

OK...blonde moment here. Is Greek fire the same as flaming arrows?

Islidur I know its not Tolkien, but it's a great fan fic and it has a great ship to ship battle in it. They do not use cannons, but underwater rams, catapults, and boarding parties. Cirdan takes part in it (he was on his way to the duel between Sauron, Gil-Galad, and Elendil).

Greek Fire is an ancient form of the flame thrower. It is basically a large hand pump filled with oil. The oil is directed through a nozzle and into a pilot lite. It will still burn when on water.

Or as I heard it put once, an early form of napalm.