This is what you are looking for: http://en.wikipedia.org/wiki/Automatic_Identification_System Many of these do not transmit particularly far (especially horizontally). Class B's, like you might expect on a personal ship, only broadcast at two watts.

You have to keep in mind though that for all of our advancements, the ocean is still a fundamentally hostile environment. One rogue wave takes your ship out and by the time that search and rescue people can be in the area any survivors could potentially be hundreds of miles away. They had a satellite phone with them, so I am inclined to think that they also had a AIS transponder, but these sorts of situations are difficult regardless.