And presumably it sheets to the dinghy being towed behind :-).
Roy Chandler put a similar rig (but without the mizzen) on a bridgedeck cat based on a couple of Stilleto 30 hulls. It had a masthead roller furling genoa and a staysail on a boom. He also used a spinnaker off the wind. I've scanned the inside cover of his book which shows the rig.
Another option you might want to consider is a masthead cutter where the mast head genoa is essentially a light weather sail and the staysail is a sort of working jib. With both of them on furlers it gives quite efficient sail handling. Examples here http://www.easycatamarans.com.au/