James Lake-Kusviandy Blee, 24, is accused of plotting with his father James Lake Blee and two divers to obtain a 57kg package of cocaine on May 9, 2022.
The drugs were concealed within the hull of the Arti Gr Majura which had transported soy bean meal from Argentina to the Port of Newcastle.
"The plan went awry, however, when only one of those divers returned," crown prosecutor Katrina Curry said as Blee Jr's criminal trial started on Thursday.
The package, which contained 42 individual packets of cocaine and was wrapped in black tarp, was found by water police washed up on nearby Kooragang Island, a jury of 12 was told in Sydney's Downing Centre District Court.
The 24-year-old has pleaded not guilty to one count of attempting to possess a commercial quantity of an unlawfully imported border controlled drug.
In examining the package washed ashore, NSW Police found it contained almost 35kg in pure cocaine.
Ms Curry said there was a circumstantial case against Blee Jr from which jurors could infer he was aware of the plan.
The 24-year-old ran errands for his father, for instance by purchasing dive equipment used in the operation, and then stayed on the foreshore monitoring the nighttime retrieval, she said.
The divers were equipped with a variety of equipment, including rebreathers and seabobs, to dive down 10 metres and obtain the drugs from a compartment on the cargo ship known as the sea chest, the jury heard.
In March 2022, Blee Sr researched training for rebreathers which allowed divers to remain underwater for longer in a covert manner without bubbles appearing on the surface, Ms Curry said.
The prosecutor said the father and son travelled by yacht from Darwin to Bali in Indonesia a month earlier.
Blee Sr then travelled to Dubai where he met with a man known as Irish to get details about the drug plot.
In April 2022, the father and son then left Bali on a yacht bound for Darwin with the two divers.
In the months before the botched operation, jurors would infer that Blee Jr used encrypted applications to talk with his father about the plan, Ms Curry argued.
After one diver failed to return, Blee Jr bought a one-way plane ticket back to his home in the Gold Coast.
Defence barrister Daniel Pace said his client did not dispute there was a commercial quantity of cocaine involved, but denied he knew about them.
There was no direct evidence that the father and son had ever discussed a plan to obtain the cocaine, he said.
Blee Jr was following directions from his father, he added.
The trial continues.
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