Sorry, disagee. All it requires is a real time data feed and then the trapping of this data. I would be very surprised if Google Earth do not already have standard interface(s) that you can tap into (for a fee no doubt) that will provide the lat/long in real time based on an imput via a GPS provider/monitor.
The only problem may be formatting the data that is being sent to the "Sydney Hobart race control" people into the form that Google Earth will accept, which I cannot see as being difficult.
Just a bit like a real time feed into a web site.
I think that you are underestimating the problem, writing some software for google earth is maybe a few days work.
The real problem is gathering the actual data and putting it into to the software.
The cheapest would be to place a cheap garmin GPS onboard from which you daily upload the track data to google earth. They use a lithium battery which lasts long enough and are very light. Sure its not realtime but I dont think that would matter to much.
Realtime tracking is much more challenging to do on beachcats than on yachts.
To do it properly you would have to use something like satellite Argos beacons [color:"blue"] (which is probably what they use with sydney-hobart)[/color] which require big batteries and are very heavy. 
