Authorities launched a second search for the Margrel on Tuesday morning after the man on board, Tony Higgins, reported it was taking on water in rough seas off Granite Island, south of Adelaide.

Early on Wednesday morning, a commercial fisherman discovered a number of items of debris washed ashore several kilometres southeast from the Murray Mouth.

“The debris appears consistent with items from the missing boat,” SA Police said in a statement.

Patrols and a police helicopter are making their way to the area to conduct a coastal search.

A fixed-wing aircraft will focus on searching open waters in the same area.

The find comes after debris was discovered in the water on Tuesday afternoon by a Challenger aircraft provided by the Australian Maritime Safety Authority.

That debris is “currently being examined”, police said.

The aircraft searched the area until 11pm on Tuesday night using infrared radar.

Higgins, 57, and Derek Robinson, 48, were the subject of a major search south of Port Lincoln earlier this month after nothing was heard from the pair for several days.

The Margrel was eventually spotted off Coorong and towed to shore.

Higgins aboard the boat being taken under tow by a police launch. Photo: ABC News

Higgins was later fined $1000 fine for having insufficient safety equipment and no boat operator’s licence.

He insisted at the time he didn’t ask to be rescued and the pair “knew exactly where we were”.

SA Police Commissioner Grant Stevens said on Tuesday while search operations would always be conducted there was an “element of frustration” that the state’s resources had been called on again.

He said the first search cost about $650,000.

“Search and rescue efforts will always be undertaken but there is an obligation that sits with all of us to act in a way that doesn’t put ourselves at risk,” Mr Stevens said.

“It’s unfortunate we are doing this again for the same person in such a short period of time.”

Paramedics and police remain on standby onshore.

-AAP