The captain's log from an 18th century ship on which a failed mutiny took place during a voyage from Cork to Australia is expected to reach more than €200,000 when it goes for auction next month at Christie's in London.
The ship's captain, Irishman Michael Hogan, has been the subject of several books and is a celebrated historical villain in the US and Australia.
The existence of this log, however, was not known to the general public until very recently.
The Marquis Cornwallis was the first convict ship to carry political prisoners from Ireland, including members from two dissident groups of the time, the Catholic Defenders and the Protestant Peep-o'-Day Boys. They had been fighting each other on religious grounds while simultaneously fighting together against the English on nationalist grounds.
The ship had only been at sea for a month in 1795 when some of the convicts joined forces with the guards and staged a mutiny to try to take the ship to America.
But the plot was betrayed to Hogan and the ship's officers, who fired on the mutineers as they tried to break out onto the deck and captured and flogged 48 of the convicts, including six women.
Up to 20 people died as a result of the mutiny, including the informer, who was strangled below decks. Capt Hogan was cleared of any charges of "inhuman treatment or false imprisonment" at an inquiry on arrival in Botany Bay.
A spokesperson for Christie's said: "This is undoubtedly one of the highlights of the sale, and we are expecting a lot of interest from buyers in Ireland and Australia.
"This was a very bloody mutiny, and only occurred one month into a voyage of half a year, so you can imagine the atmosphere of fear and terror for the remainder of the journey, in what were already dreadful conditions.
"There were several women on board, and children as young as 12. Some of those who died may have lain wounded for months."
The owners of the log do not want their identity revealed.
Mr Nicholas Lambourn, a specialist at Christie's, said that the log had "real power as a relic of this fearsome time".
"The coarse linen cover . . . is highly evocative, as are the pages inside, stained with sea water and spilt ink, all describing this rough and terrible passage in history."
Born in Clare in 1766, Capt Hogan went on from Australia to amass a personal fortune as a slave trader in Cape Town.
The log covers the period of time before the ship arrived in Australia and the subsequent landing of the ship and arrest of the mutinous convicts.
Two manuscript charts showing the ship's passage and a contemporary painting of the ship by François Balthazr Solvyns will be sold with the log at the sale on September 23rd in Christie's King Street offices in London.