So I've still been thinking this over and this is what I've come up with:
Participants:
Two non-svs "referee" ships
One war galleon per team
Ideally four war sloops per team
Crew size to be determined
The Regatta:
Each team will start at (starting point to be determined), make one lap around (TBD) then return back to the starting point.
To win, a team must get their galleon from the starting line around the course to the finish. Each team will use their sloops to defend their galleon and attempt to sink the opposing team's ship.
If a sloop is sunk, it is not allowed to rejoin the race. If a galleon is sunk, it may re-join the race, but only after it has gone back to the starting point.
(Any ship sunk by a non-regatta ship will be allowed to rejoin the race without having to go back to the starting line.)
First team to get their galleon across the finish line wins.
(Credit to MikhailSkulls, Eric Sailcutter and ElizaCreststeel for the ideas they contributed)
Who is interested? Does this sound like it will work?