Wild Oats XI claimed line honours in the Sydney to Hobart yacht race on Tuesday night, but a protest could see it stripped of the trophy.
The supermaxi crossed the finishing line shortly after 8:30pm (AEDT), recording a race time of two days, seven hours and 37 minutes.
Investec LOYAL was the second to cross the finish line shortly after midnight, about three and a half hours behind.
Race committee chairman Tim Cox says Wild Oats XI failed to have an operational HF radio as it passed Green Cape on Monday - a compulsory reporting stage at the entrance to Bass Strait.
English yacht RAN also faces a protest for this.
Cox says a five-man jury will decide the fate of both yachts in Hobart on Wednesday afternoon.
Wild Oats owner Bob Oately says he is confident his crew did not breach the race protocol.
He says the call was recorded, so there is evidence the crew followed protocol.
Wild Oats has previously won four line-honours victories.
The ABC reports the compulsory reporting rule was the rule was brought in after a disastrous race in 1998, in which six sailors died. Only 44 yachts finished the race.
Cruising Yacht Club of Australia Commodore Garry Linacre said sanctions range from minor time penalties to disqualification without any avenue of appeal.
A total of 16 boats have withdrawn from this year's race.