There must be many enthusiasts out there who are sailors or know someone who is. Starting races with a stopwatch and manual horn is just fraught with problems. Commercially available race start timers are available but cost up to $1,000. I'm sure that an Arduino based system could be built for $100.
I'd like to know if anybody would be interested in co-operating on such a project.
How would this system work? Would there be a centralized control point that “starts” the race and communicates with the boats via RF?
Or do the boats all have independent systems that are pre-coordinated (ie, everyone start at time T)? Maybe a GPS-based virtual “starting gun” or similar?
With all the testing required, unless your time is free/cheap, you're going to spend a lot more than that $1,000 to make it work as well as a commercial system.
For added fun: you're going to get the complaints if something goes wrong while racing!
Better than that would be robotic race marks. Tell them where to go. They go there and hold position. You can tell them to adjust position if wind shifts. Then, when the race is over, tell them to either go home or to the committee boat for retrieval.
Holding position is the hard part - GPS may not be accurate enough. Otherwise it sounds like a really fun project, and with modern battery technology it should be totally feasible (you have to be able to run the motor constantly for a day).