Lost in a storm crossing the Firth of Forth in 1633, the ship was loaded with the King's priceless possessions.
The archaeologists believe it could be the most important find for them since the discovery of the Tudor warship the Mary Rose. The Blessing foundered shortly after leaving Burntisland, bound for Leith. Twenty carts loaded with the King's personal possessions from his hunting palace at Falkland were aboard.
The wooden ferry, known to treasure hunters as "Britain's Tutankhamun", was also carrying a 280-piece silver dinner service commissioned by King Henry VIII and other ornate tapestries, silks and trappings for Charles's coronation tour of Scotland. The king watched helplessly from his flagship, the Dreadnought, as a large slice of royal Stuart treasure vanished under the waves and more than 30 of his entourage perished. There were only two survivors.
The distressed monarch cut short his tour and returned to London where 16 years later he lost more than his silverware. Details of the wreck, 120ft down and one mile offshore, are to be disclosed at Kinghorn, Fife - one day before the 350th anniversary of the execution of the King in London.
Navy experts and marine archaeologists are not expected to be able to say it definitely is the ship.
But according to defence sources the wreck, buried under several feet of silt, matches the size and shape of the barge and there is "growing optimism" it is the Blessing of Burntisland. The ship could contain silver used by the King at his coronation, and also a "time capsule" with masses of preserved artefacts from the period.
The search began in 1997 and the site was finally located by HMS Roebuck, a Royal Navy hydrographic survey ship. It was the outcome of a joint effort between the Royal Navy and the charitable Burntisland Heritage Trust. Computer-produced images of the wreck site led to detailed investigation by divers in December, and the task of verifying whether it is the historic wreck is still under way.
Another royal ferry sank in the same waters 44 years earlier, carrying the dowry of Ann of Denmark for her wedding to King James VI of Scotland, Charles's father.
With either vessel of great significance, Donald Dewar, Secretary of State for Scotland, has imposed a Protection of Wrecks Order on the site.
It is expected that final confirmation that it is the Blessing will come in the summer then delicate work on raising the wreck will begin. The wreck is said to lie at the very point fixed last May by the successful English map dowser Jim Longton. He sailed the route of the ill-fated vessel with his metal divining rod and pendulum.Reuse content