The National Maritime Museum in DúLaoghaire, Co Dublin, is to close for at least a year while extensive conservation work is carried out to save the building.
Some €1.5 million has been allocated by the Government for the work but urgent additional finance is required for the full project, according to the Maritime Institute of Ireland.
The 19th century building, formerly a church, requires renovations of its fabric and interior, including restoration of the north transept stained glass window, stripping and replacement of plasterwork, and provision of wheelchair access and new toilets.
The institute hopes to retain the building's historic character, while providing exhibition areas for many artefacts and over 7,000 books and documents in its library. The artefacts include the optic from the Baily Lighthouse in Howth, Co Dublin, and a model of the Great Eastern - the ship that laid the transatlantic cable under the command of Wicklow man Capt Robert Halpin.
The tiny museum also exhibited the Bantry longboat for many years until it was reclaimed by the National Museum of Ireland.
