Good luck with the search for the offending craft, but I suspect that your point of view may go over the head of someone who blasts through a sailing fleet at speed.
Like Jelly, I to have experiance in Plymouth parting the fleet around large military and civilian vessels during racing.
The first problem is that many dinghy sailers have no concept of self preservation and want to sail under the bow of a ferry, especially students and the 29er, 49er fleets. There are ways as Jelly hinted, usually involving a group of skilled RiB drivers forming a wall and blocking the way! This is where the experiance and skill comes in to driving a 1 ton rib alongside a racing dingy at 1 m
Back at the point, you vs Sunseeker is unfortunately simple. Let them go, try to get the name for the authorities, pick up the pieces of your fleet.
Oh and if you run an event in a port like Plymouth, get to know the local MOD Police, Customs, Fisheries and Coastguard as the Blue light will get their attention when you go after them. They are very friendly chaps and have local knowledge that is vital to visiting safety craft running an event!
I had a simular occasion this summer with the RYA SW Region Youth Regatta we were running. My 5m Tornado was too slow, the 6.1m Environment Agency Rib was smart enough not to play chicken and the MOD Police could only keep up. It took the Fisheries pursuit boat to get there attention and hove too for a short talk.
Keep looking at the horizon for the next vessel and if you have the resources, get yourself a skilled task group to deal with such problems and that don't take prisoners.