According to the SI's (available on-line), ties in a series are settled by first using the throw-out score, then using the cumulative corrected time for all four races. A DNF counts as infinite time.  Ties in the season Championship will be resolved by using the best throw-out, and then the next best and so on.  Unresolvable ties will result in Co-champions. 

The corrected time for two boats can end up the same,  or the race committee can declare that they are unable to resolve the winner between two boats (has happened once in fifteen years!).  The boats then share the points.