What size paddles?

[steamboatmad]

Hi there,  new to this site so please bear with me if I ask questions with an obvious answer!  The hull I'm planning on using for my project is 17 feet long with a beam of 5 foot, so what do I need to do to work out the paddle diameter and width?  I hope to fit a beam engine to this boat (at this stage) so there wont be lots of RPM involved.