An addendum

Barring gunpowder from a D&D setting, ships could still have cannons instead of catapults/ballistae. How? Ship wizard and a wand of fireballs. Same cannon set up as with gunpowder, but instead of lighting it, the wizzie just pops a fireball into the cannon.

Now, why do that instead of just hitting an enemy ship with a fireball?

1) Damage control - Fireball's obviously gonna light the bitch up, burning the ship and treasure....makes plundering a bit difficult, unless you like your booty cajun style.

2)Awe - If yer pirate ship is the only one blasting lead balls into yer opponents, everyone's gonna fear Captain One Thumb and his Brass Balls Boyz in their ship Shot Through the Heart.

Maybe the whole arquebus thing below is misinformation meant to throw my players off of the real plot, that being hordes of imps invading the Prime Material with the sole purpose of invisibly sodomizing Crenius (and making Rachel watch to ensure she really knows what sodomy is).