For those that may not be aware the Chinese have Invaded the disputed Islands which Vietnam lay claim too in the South China sea . For any Yacht that plan to sail that region it would be ill advised for the time being http://edition.cnn.com/2010/WORLD/asiapcf/10/02/japan.anti.china.protest/
Hi, You might find it is Japan that lays claim to these not Vietnam and this has been going on for years. Maybe after the earthquake that have moved into Chinese waters.
I would stay well away from them no matter who claims them. Most of these 'islands' are at sea level or permanently submerged. The highest point of the Spratleys is 4 meter above chart datum. Nobody is interested in these 'islands', it is the fishing grounds around them. You can cross this area without problem provided you're not cruising a navy ship or a fishing trawler.
China is also flexing in some new uncharted waters: http://www.cnn.com/video/#/video/world/2011/03/13/gps.china.flex.cnn