We are having a boat naval battle thing need ideas!!!?

my friends and i are making like sail boats out of random materials (like wood and duct tape and pvc pipes) to make it like old ships almost and sails and stuff and we wanted to have naval battles (we dont really care if ship sinks) its in salt water our battles but we are wondering what we should use as cannons to like shoot each other with or to fight with, our only ideas is to use paintball guns u have any ideas what to use?