Back in the 70's, Bob Dull and I organized a 24 hour Laser Marathon during the October Annapolis Sailboat Show. We ran it out of SSA, taped flashlights to the bow eye (colored red and green for the appropriate side). We had a lot of fun. Teams were anywhere from super organized 6-8 sailors to teams that were trying to recruit people off the dock at 3 am. We did it for two years and then wrapped it up. We couldn't do it now as the show is too popular and the harbor too crowded for it to be safe.
I found a video of Dutch juniors doing a 6 hour relay race in Lasers. A fair bit of breeze and the skipper changeover, in it's various permutations, is hilarious.
The barge carrying the cement truck crossing the race course is a nice touch.
6 uren from Floris Wijnbergh on Vimeo.
And the grandaddy of all 24 hour dinghy races is the Southport race hosted by the West Lancashire YC in England. Teams race in doublehanded Enterprises (blue sails), GP 14's or Lark dinghies. The action around the gybe mark gets very hairy.
The Vanguard 15 class should look into doing something similar in the U.S.