They’ve already survived more than 100 years, but original wooden cannon carriages inside the USS Cairo are being removed and replaced with custom-built replicas.

&#8220I’ve seen a definite change in them over the years,” said Elizabeth Joyner, curator of the Vicksburg National Military Park’s museum and display of the Civil War ironclad.

The project, being financed through $500,000 in federal funds, is to take two to three weeks and will result in the carriages being moved from under the canopy which protects the site.

The replicas were built by the NPS’ Historic Preservation Training Center in Frederick, Md., and the work began Friday as exhibit specialist Dean Wigfield led a crew of four to add a temporary floor to accommodate the moves.

The gunboat was sunk by a Confederate mine in the Yazoo River on Dec. 12, 1862. It was recovered from the river bottom about 100 years later and eventually restored as a museum.

The gunboat has been under canopies practically since it was recovered. The current one, bigger than previous versions for added protection, was completed by 2003. Since, the exhibit has not been rained on and birds have not been a problem but temperature and humidity have continued to wear on the carriages.

Joyner said 13 cannons and carriages were recovered with the Cairo. Then one was moved indoors, to the adjacent Cairo museum, and a replica of it was put in place.

After the current project, the 12 remaining carriages will be in storage in a local, climate-controlled site, Joyner said.

During the project visitors will not be allowed to board the Cairo but may view it from the walkway above the museum, Joyner said.

&#8220It’s a good vantage point,” she said.

Wigfield said the same kind of wood, white oak, was used for the structures and a Pennsylvania blacksmith was selected to re-create the hardware.

Reconstructionists tried to go by 1851 Department of Ordnance drawings but they proved imprecise, he said. Architects also found precise measurements impossible to make with the cannon tubes still in place. The first carriage that was put in place, for example, had to be tweaked slightly on the spot but ended up fitting fine, Wigfield said.

&#8220There was a little bit of guesswork,” Wigfield said.

The heaviest of the cannon weighs 8,200 pounds, Wigfield said.