Rusty wreck mystery at Reiss
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With this week's extremely low tides in Sinclair's Bay a strange phenomenon could be observed on the rusting wreck of an old trawler that has lain on the beach for over 60 years.
The Jean Stephen was shipwrecked during a storm in January 1958 but still commands a strong presence along the golden sands of Reiss beach.
The rusting hulk of the boiler is a local landmark and though much of the structure has been cut away or disintegrated into the highly corrosive salty sea, some parts are incredibly intact and sparkling like new.
At the rear of the boiler, several metallic elements can be clearly observed, appearing as if they had just been fitted in the local shipyard and contrasting sharply against the rusty, barnacle-encrusted structure they are attached to.
When the images were posted on social media a Twitter user, Gair Dunlop, said he thought it could be "cathodic protection" at work. "The copper will be attached to another, more reactive metal which is differentially corroding intensely instead," he wrote.
Flat bars of metal such as zinc or aluminium are used as sacrificial anodes to protect underwater parts of a ship from rusting. Anodes are commonly used to help protect the hull in the case of galvanic corrosion caused by electrical current flowing between connections and between dissimilar metals. It is unclear if this process is at work on these parts of the Jean Stephen, however.
Wick man David Carter has examined many underwater sites as part of the Hellsmouth Diving and Shipwreck Company and said: "Like most vessels the Jean Stephen had a lot of brass and copper fittings which resist the effects of sea water corrosion. [It's] very common to see brass shining all over the seabed on wreck sites."
Over time though, copper pipes will usually turn a bluish-green colour with exposure to seawater – the parts at the rear of the boiler that appear to be copper show no such staining.
Professor Iain Baikie from Wick, is well-versed in the scientific analysis of such chemical processes and was asked what he thought about the images presented here.
"At first glance some of the parts are stainless steel, usually used for components such as valves for liquid that need protection from corrosion," he said.
"It must be that marine growth does not adhere to stainless steel. Copper is a marine biocide and will kill marine growth, so I would not expect any build-up on copper pipe.
"You can also see that the fine sand has been cleaning the surface moving weakly detached marine organisms. Where the sand has not done this effectively there is some black tarnish, but this would probably wipe off. The copper surface is smooth too so probably the sand ablation and the biocide effect account for this."
Professor Baikie also mentioned the role of sacrificial anodes to protect parts of the ship but said they have to be replaced every few years.
"Copper would be protected by a zinc anode, but if the trawler had an anode originally then it is long gone. Copper may receive some small electrochemical protection from iron, but these are too close on the electrochemical series to guarantee this.
"In any case, much of the surface iron is oxidised and iron oxide is a poor electrical conductor so this would not guarantee any protection."
He added: "It could be that the iron inside the hull that has both undergone corrosion offers some galvanic protection but I suspect this would be a weak effect."
Perhaps the constant tidal action in Sinclair's Bay is "sandblasting" the surfaces. In this particular area of the wreck, crashing waves filled with abrasive particles of sand hit against the solid wall of the boiler and may be removing any buildup on the surfaces.
Check for low tides in the bay and pop along to look for yourself.
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