The mother of one of four men who died on a fishing trip on waters near Hobart says she is disappointed the investigating coroner did not recommend changes to Tasmania's marine safety legislation.

Key points: The boat sank in July 2016, causing the suspected drownings of four men onboard

The boat sank in July 2016, causing the suspected drownings of four men onboard A grieving mother has called for mandatory marine safety checks on second-hand boats

A grieving mother has called for mandatory marine safety checks on second-hand boats Coroner Simon Cooper described a valid boat licence as "a matter of life and death"

Luke Davies, 32, Magnus Ritter, 34, Anthony "Jamie" Roche, 35, and Aleksander Drobnjak, 26, all drowned or are suspected to have drowned on Frederick Henry Bay, east of Hobart in July 2016.

The fibreglass boat and the body of Mr Roche has never been found.

The inquest held in May investigated whether an oversized engine may have caused the boat to flip and sink.

It heard the recently purchased, second-hand boat had a rotting hull, no functioning life jackets onboard, no radio or registered beacon and that none of the men had a valid boat licence.

In Tasmania, there is no mandatory requirement for second-hand boats to be inspected for seaworthiness at the point of sale.

Magnus Ritter was one of the four men who went missing while fishing. ( Supplied: Facebook )

It is a fact that Mr Ritter's grieving mother Sabine Wagner has been campaigning to change since the death of her son.

"We know that cars have to be roadworthy and I believe boats should be seaworthy too," she said.

"What I would like to see is changes to the legislation so that people are not allowed to sell a boat without it being checked."

Speaking outside court, Ms Wagner said the deaths of the men aboard what she previously described as "a death trap" were a tragedy.

"There are more than 100 people whose lives are affected by [these deaths] and they are changed forever," she said.

"Every parent who loses a child has a before and after life, before the child died and after the child dies and life is never the same after, you will always carry that sadness.

"There are a lot of people responsible, I think, and Magnus is one of them. He bought the boat, he went out, he didn't have a licence, he did the wrong thing.

"If the boat was faulty, the previous boat owners are responsible too."

'I can't stop now'

The boat's previous owner, James Castle, sold the boat for a loss to Mr Ritter six weeks after he had purchased it but continually told the inquest there were no problems with the vessel.

Coroner Simon Cooper described Mr Castle as an unimpressive and uncooperative witness.

Handing down his findings, Coroner Cooper told the inquest "a reasonable hypothesis that it may have been due to the failure of the boat's hull, or possibly transom, due to rot".

He recommended all second-hand boats be professionally inspected by a qualified person before being used.

Coroner Cooper told the inquiry that few people would buy a second-hand car without having it professionally inspected and the same rule should apply to second-hand boats.

He told the inquest it was "critically important" for boaters to wear a life jacket and that a boat licence is "not just a piece of paper", but "a matter of life and death".

Ms Wagner vowed to continue fighting for the legislation to be changed and urged others to thoroughly check second-hand boats to prevent similar incidents from happening.

"I need to keep going. I can't stop now. I don't give up easily," she said.