From the official site:
For those who can't get to watch the live broadcast of the start of the Race on the Seven Network across Australia, Yahoo!7 will webcast the program. You can also watch the same webcast on the home page of the Rolex Sydney Hobart Yacht Race website.
The official race website Rolex Sydney Hobart Yacht Race 2013
is one of the most popular Australian sporting websites during the Christmas New Year holiday period and is your information portal for everything there is to know about the 628 nautical blue water classic.
Included on the website is the complete list of yachts entered, along with a photograph and description of each boat, a rundown on the crew, and the boat's past racing record.
There's also archival data including results of past races since the first in 1945, the weather they encountered; a summary of line and overall handicap winners of those races; historical reports and statistical information; designers of those line and overall winners; and profiles of some of the race luminaries over the years.
You'll also be able to follow the event on twitter for race updates http://twitter.com/rshyr
and via Facebook https://www.facebook.com/RolexSydneyHobart
No US TV rebroadcast mentioned, so it looks like it is the web for us, or likely youtube within an hour.