If the sailor wears a wet suit he/she should have no issues with sinking. A 6mm steamer has serious buoyancy.

Saying that, even skiffies wear pdfs approved to required standards. Generally they aren't needed BUT its insurance one should never leave on the beach!! Tampering with a pdf is "darwin award" material..

I would guess the ISAF classes are are required to uphold the ISAF rules on pdfs.. So I'm guessing that if the sailor is on a T then the boat is open to disqualification.