Workers had to flee to safety after the Maid of the Loch paddle steamer broke free as it was being winched out of Loch Lomond.
The 65-year-old ship was being taken from the water ahead of restoration work when it slipped its ties.
Members of the restoration team were forced to run from the side of the vessel as it slid back into the water.
It was then taken back to its normal berth at Balloch Pier and the operation called off for the day.
Checks are now under way to ascertain what went wrong.
The Maid of the Loch entered service in 1953, the same year as the Queen’s coronation.
But the Maid fell on hard times as passenger numbers dwindled and the ship was eventually mothballed in 1981.
While the ship did remain watertight while moored at Balloch, copper piping and artefacts disappeared.
The Scottish government has given the restoration project £950,000 and a further £50,000 came from the Paddle Steamer Preservation Society.
The Loch Lomond Steamship Company (LLSC) said the cash would go towards repairing the paddle steamer’s hull and engines.
The restoration is a £5.5m project. Once £1.7m is raised, the Heritage Lottery Fund will release £3.8m of further funding.
The LLSC hopes both the ship and slipway will get industrial museum status.
The restoration plans include reviving the main and aft deck saloons to their original 1950s style and creating an education suite, as well as restoring engines and machinery.
John Beveridge, chairman of the Loch Lomond Steamship Company, said the money would allow them to recreate the ship’s original 1950s style.
He said to “see her engines turning again after 38 years will be magical”.