Though 3G might be possible as a Coast Guard before, in the South China Sea alone and you will have problems with the network.
Satellite network might help but i think the data transmission will cost a fortune. I remembered the first UN mission when my Commander briefed us on the cost of making a satellite phone call......geez.....
My guess is they monitor the yachts at the marina and not when the yachts are sailing. 3G is possible if the sail route is within reception range. Reckon a few test run required to ascertain the feasibility. I did an assessment at a local marina and brought up some issues that many did not realise.
In the air, I know there are limitations but at sea, I think there must be a solution somewhere out there and someone must have thought of this issue before me?