The 27-year-old Tasmanian man was onboard Gulf Livestock 1 with 42 other crew members and 6000 cattle when it sailed into the belly of Typhoon Haishen on September 2 as it traversed Japanese waters en route to China.

The Japanese Coast Guard conducted land and sea searches when it received reports the ship had capsized, but were only able to recover two survivors.

The carrier had seven life craft onboard: two lifeboats and five life rafts.

One empty lifeboat and two life rafts have since been found.

Mr Mainprize's sister, Emily Hasting, said new information this week had revealed the crew members were in the vicinity of the life-saving equipment while the ship went down.

Unfortunately, this information coincided with the coast guard's decision to downscale search and rescue efforts to a regular patrols.

Mrs Hastings said the family held out a small amount of hope Mr Mainprize was on one of the life crafts and felt an injustice more was not being done to find him and the other crew members.

"Initially we felt absolute shock and it was really, really devastating for all of us," she said.

"We weren't doing well at all. We couldn't even think about his life being cut short.

"Now we really sense how time-sensitive this new information and we've entered a zone where we are focused on getting him back.

"We're holding it together, staying strong, and focusing on the search and rescue efforts.

"There is no evidence that says there isn't a possibility that he isn't out there."

Perth man Tom Suttor knows both Mr Mainprize and the carrier he was on well.

He said the pair were housemates while they studied at Charles Sturt Uiversity in Bathurst, New South Wales.

"He is a very inspiring person," Mr Suttor said.

"Anything was possible to him. Nothing was too outrageous.

"He is also a very compassionate, empathetic man."

Mr Suttor said he spoke to Mr Mainprize the night the boat capsized.

"Will was speaking to me pretty much every day he was on that vessel," he said.

"He told me the ship was going pretty much into the eye of the typhoon.

"I didn't think anything of that as you trust the decisions of the captain.

"The last time he wrote to me, he said: engine control room taking on water. The ship is floating sideways in a big f--king swell. Pretty hardcore."

Mr Suttor said he felt disbelief when news reached him that the ship was missing.

"This isn't the 18^th Century - ships shouldn't go missing in storms," he said.

"I've been on many of those boats, they are enormous vessels.

"It must have been such a violent storm for that ship to sink."

Cradle Mountain Canyons owner Anthony O'Horn employed Mr Mainprize as a tour guide over the past three summers in Tasmania.

He described Mr Mainprize as a humble and genuinely nice person who engaged well with those he interacted with.

"He is a really adventurous guy," Mr O'Horn said.

"He connected so well with people and so quickly. He was always interested in other people's stories."

Mr Suttor said he believed the coast guard's decision to downgrade the search could be due to resources constraits.

He said given two Australians were onboard the carrier - the other being 25-year-old Lukas Orda - the Australian Government needed to step up and offer whatever assistance was needed.

A change.org petition has been launched by Mr Mainprize's friends and family, demanding full-scale search efforts resume with assistance from Department of Foreign Affairs and Trade.

"Anything we can do right now to make noise, spread awareness and create attention to this issue is absolutely necessary," the petition reads.

"We believe Will and these men to still be alive, but time is of the essence."

A state government spokesperson said:

"In regard to William Mainprize, the Premier's office has been in contact with both the Departments of Home Affairs and Foreign Affairs, seeking their support for continuing search efforts."