THE Cutty Sark, one of the world鈥檚 last surviving 19th-century clipper ships, now looks set to be saved from rapid decay, despite fears that the ship was doomed. A technique that uses electrolysis to protect the ship鈥檚 iron frame promises to prevent the historic vessel falling apart.
The Cutty Sark was built in 1869, a period when iron-hulled ships were beginning to replace wooden ones, and therein lies problem. The clipper has a teak hull fixed to an iron frame, and what helps to preserve one material does not necessarily help the other.
For the past 50 years, the vessel has been in dry dock by the river Thames in London, where it is on permanent display. But peppering the recesses of its hull are deposits of sodium chloride left over from its seagoing days. When it rains and the hull gets wet, the salt dissolves in the water, producing a solution that accelerates corrosion of the ship鈥檚 iron frame.
Advertisement
A process pioneered by Peter Lawton of the University of Portsmouth, UK, to preserve the iron hull of the first world war ship M33, looked promising as a way of halting this corrosion. He bathed M33 with an electrolyte solution of sodium carbonate and passed a current through it. This eliminates salt by converting the chloride ions to chlorine gas that is released into the atmosphere.
Lawton鈥檚 initial lab tests with a wood-and-iron model to simulate the Cutty Sark鈥檚 construction were disappointing. 鈥淭he wood went black, and when we took it out it smelt awful,鈥� he says. While electrolysis stopped the corrosion of the iron, Lawton believes it also stimulated a bacterial reaction in the wood, producing foul smells. So he added a small amount of bactericide to the electrolyte, and the reaction stopped.
Lawton has now completed a three-month trial on the Cutty Sark itself. He flooded a 3.5-cubic-metre section at the aft end of the ship with electrolyte, and passed a current through it using the iron frame as one of the electrodes. He now thinks the problem of eliminating the salt is all but solved.
