Adventurer Pete Goss, leading the expedition, yesterday described injured team-mate Mark Maidment as a "bloody hero", because of his stoic outlook after becoming a casualty of a fierce storm.
A huge wall of water struck the Spirit of Mystery during high winds and heavy rains, knocking the boat over. It washed away the life-raft and dinghy and caused some damage.
Mr Goss said: "We had just come out of a storm that had lasted for two-and-a-half days and given us a right old pasting when we were hit by a freak wave. There was no warning, just a huge wall of water that smashed into the boat rolling her more than 90 degrees on to her side.
"There was carnage below with water everywhere, which got into the communications systems. The boat was fantastic, though, and I wouldn't have wanted to be in any other.
"She just shook herself off and came upright – but when she did, Mark's leg was broken."
The sailors have been receiving medical advice via their support team in Melbourne. They have made contact with the Australian Maritime Safety Authority, which issued guidance and sent a search-and-rescue aircraft out to drop supplies.
Mr Maidment's leg is in a splint and he was taken below deck and given morphine. He is expected to be airlifted from the boat at the next opportunity.
Mr Goss said: "Mark has been a bloody hero. It is a great shame for him, especially so close to the end, but he is keen not to draw attention away from the project, which is about shining a light on the bravery of those seven Cornishmen who made this perilous journey 154 years ago to seek a new life in the Victorian gold fields of Australia.
"They didn't have the benefit of modern communications and safety equipment, so this just goes to emphasise the depth of their achievement."
The crew is retracing the voyage of Mystery, a fishing boat in which seven Cornishmen sailed from Newlyn to Australia during the gold rush 154 years ago. It took them from November 1854 until March 1855 to reach Australia. Mr Goss and his crew expect to reach Melbourne next week.
In February 1855, Captain Richard Nicholls recorded in his log that the Mystery had been hit by "a complete hurricane", with "seas mountains high". He added: "Our gallant little vessel rode beautifully, not shipping any water whatever."
Then another hurricane arrived with "mountains of sea and very heavy rain". There were even heavy showers of snow and sleet.
For more information on the voyage, visit www.petegoss.com