The Australian model, who lives in Sydney and has a 12,000-strong following on Instagram, was working as part of the crew on the six-storey super yacht Mayan Queen IV in Argostoli off the Greek island of Kefalonia. 

Reports from the Greek news outlet the Kefalonian Matata have suggested McNamara was found entangled in a rope off the back of the boat and despite the efforts of crew onboard, was unable to be resuscitated while enroute to Hygeia hospital in Athens.

The yacht is owned by owned by 87-year-old Mexican mining magnate, billionaire Alberto Baillères. According to the Bloomberg Billionaires Index, Mr Bailleres is worth AU$9.6 billion. Bailleres controls Industrias Penoles, a metal producer that operates in South America.

The Mexico-based company was the world's largest producer of refined silver in 2017 when it had revenue of $4.5 billion. His other investments include stakes in Grupo Palacio de Hierro and Coca-Cola bottler Femsa.

It has been reported Mr Bailleres was not on the vessel at the time – the boat was only manned by crew who were directed to stay on board while the preliminary investigation took place.

The Argostoli Port Authority is conducting the investigation while the Department of Foreign ­Affairs is assisting her mother Kylie, and sister Lauren, in Greece. 

Read more: 'Rest In Peace gorgeous': Australian Instagram model dies in Greece

It is believed her father is also travelling to Greece to be with the family and assist in arrangements to bring their daughter home. Brother Jake, 21, who has played with the Newcastle Knights reserve grade squad, is devastated by the news.

Ms McNamara celebrated her 20th birthday less than a month ago. She arrived in Greece in mid-June this year after travelling to Bali, Alaska and the Whitsundays.

She is a 2016 graduate of the Northern Beaches Secondary College Freshwater Senior Campus in Sydney.

Before that, Ms McNamara and her family lived in Port Macquarie where she attended St Josephs Regional College and enjoyed the coastal lifestyle as a part of the local ‘girl surfer’ group.

She moved to Sydney before her senior schooling years.

 Principal, Jim Dempsey, said many staff and students would remember Sinead from her time at the school.

“Our thoughts and prayers are with the McNamara family at this sad time,” Mr Dempsey said.

There has been an outpouring of condolences on her Instagram profile in the days following her death.