The rules take effect on Jan 1 (2013, in this case).
The rule cycle is dictated by the dates the Olympic years. Meaning, the rule dates end on the year the Olympics are held (i.e., Olympics in 2012 = rules in effect from 2009-2012).
The reason behind this logic is, it gives sailors and officials time to get used to the new rules (and any changes in tactics that result), and gives time to make minor adjustments if issues arise (they usually do). The goal is not to have any rule changes during the year leading up to the Olympic finals.
Hope this helps.
Mike
