Depends on distance of the race.
But anytime you need:
a FFV license (get it at the organising yachtclub, includes liability insurance)
CM membership (one race only or full) the CM will be present at the race. Subscribe there.
Doctors attest (If your GP does not want to d it without giving you a full test, visit one in France, but you need to arrange that)
And for longer races:
a TPS or similair
an Isaf safety course