There is a sort of minimumum crew weight - the class rules require the crew to be able to right the boat unaided in all normal sailing conditions. It is permitted to use righting devices. This means that a paricularly light crew say, <60Kg, will need to carry a righting bag or pole. I'm 65Kg and I can just about nright the boat in no wind which is the worst scenario.
The organisers of an F16 event can require any crew over which there is doubt to demonstrate that they can comply with this class rule.