While GPS works nearly everywhere, there's no simple affordable system to transmit your location.

Oceans are huge, and even sattelite transmitters don't cover everything. Example:

http://www.gpstrackersandmore.com/spot2-gps-tracker

http://www.findmespot.eu/en/index.php?cid=102

Even if something like that worked perfectly, oceans are extremely dangerous. A huge wave can destroy even a large sailboat in seconds.