The 14 carvings will hang from the ceiling in arts venue The Box, due to open in the spring

A collection of 19th-century wooden figureheads from British naval warships has been lovingly restored from the ravages of years at sea and will form a striking display at a new heritage and arts complex in Plymouth.

The 14 figureheads, some of which were so badly water-damaged that their insides had turned into a soggy mulch, are to be suspended from the ceiling of The Box gallery and museum, which is due to open in the spring.

They include a two tonne, 4 metre-high (13ft) figure of William IV carved in Devonport, Plymouth in 1833 that once stood tall and bold at the prow of the ship HMS Royal William, and a depiction of a bearded river god inspired by the River Tamar, the traditional border between Devon and Cornwall.

After they were retired from service, William IV and the other figureheads were stored in various locations, sometimes exposed to the elements. In the 1950s or 60s, while at the Devonport Naval Heritage Centre, some were given a coating of fibreglass to help protect them.

This technique preserved the surface but did not allow the wood to breathe and dry. When the idea of suspending them above the atrium to The Box using steel cables was hatched, concerns were raised by structural engineers that they might not all be stable enough.

Facebook Twitter Pinterest The figurehead of the HMS Tamar. Photograph: Midas PR/PA

Experts used a method called sonic tomography, usually employed by arborists to check the integrity of living trees, to map the internal state of the figureheads.

Some were so wet that water poured out when the surface was pierced. The internal sections had to be dried in large purpose-built chambers to minimise warping and shrinkage.

One of the most badly damaged of the figureheads was from the frigate HMS Topaze, which was carved in Devonport (at a cost of £28.10). The figure, a woman in a tight bodice and full skirt, was found to have rot in 90% of its structure.

A second badly damaged figurehead was from the 19th- century troopship HMS Tamar. It is the figure of a bearded river god with a laurel wreath adorning its head.

Three specialist conservation teams in Devon, Cornwall and London, led by Orbis Conservation, have spent more than two years painstakingly restoring the figureheads.

Another challenge was restoring the colour of the carvings. Experts carried out microscopic analysis of the paint the figureheads had been decorated with over the years.

Some were found to have started off white, but the decision was made to keep them colourful. Some of the hues used are based on those to be seen on a set of 1912 cigarette cards depicting navy figureheads.

The figureheads are in the final stages of restoration and are being brought back to Plymouth ahead of the opening of The Box in the spring.

Maxwell Malden, co-founder and director of Orbis Conservation, said: “In terms of scale and complexity, this project has been one of the most challenging that the team has ever encountered.

“Our analysis of both the surface paint layers and the structural integrity of the figureheads allowed us to develop a treatment methodology that saved the original carved surface and the figurehead itself.

“Throughout this project we have uncovered the previously obscured craftsmanship and virtuoso carving of these formidable figures, which otherwise might have been lost to future generations.”

Facebook Twitter Pinterest The Windsor Castle and Defiance figureheads in transit. Photograph: Midas PR/PA

Tudor Evans, the leader of Plymouth city council, said: “The figureheads are more than just wooden sculptures; they’re iconic symbols of the history of the city of Plymouth and the Royal Navy. They’re also fantastic representations of the craftsmanship and skill of the sculptors who made them over 200 years ago.”

The Box is billed as the flagship building for the Mayflower 400 commemorations, which will celebrate next year’s anniversary of the sailing of the pilgrims from Plymouth to Massachusetts.

Evans added: “Right from the start when we were developing our original concepts for The Box, we wanted to have a ‘flotilla’ of figureheads suspended from the ceiling of the new entrance in a nod to Plymouth’s important maritime history and as the place where great journeys start from.”