A safe landing

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Innovative chemistry has saved the historic submarine Holland 1 from a slow decay, says Maria Burke.

Without the judicious use of practical chemistry, an iconic piece of British naval heritage and internationally important artefact would by now be little more than a heap of rust. The Royal Navy Submarine Museum (RNSM) and conservator Ian Clark successfully halted corrosion in Holland 1, the world’s most historic submarine, after an innovative six-year experiment. They were rewarded for their efforts when they won The Pilgrim Trust Award for Conservation 2002 last November. Now Holland 1 has pride of place in its own special dehumidified gallery at the museum in Gosport, Hampshire.

’It’s a fascinating story, pivotal to British naval prowess; a bold conservation procedure based on sound scientific principles and carried out on an unprecedented scale’, said Loyd Grossman, chair of the judging panel for the award. Holland 1 is the only surviving example in the world of the first submarine to operate effectively. The basic design elements from Holland 1 were used by navies the world over to build submarines. Holland 1, the Royal Navy’s first ever submarine was built in 1901 and took her name from her designer, John Philip Holland, so-called father of the submarine.

Although Holland was born in Ireland in 1841, he emigrated to America in 1873 and secured funding for his first successful submarine design from Irish nationalists seeking Ireland’s liberation from Britain. His first experimental submarine was a success and led to the launch of a bigger vessel in 1878 called the Fenian Ram. In 1900, the US Navy accepted Holland’s sixth prototype, which one US newspaper described as ’Uncle Sam’s Devil of the Deep’.

Not long after, the British Admiralty, though initially sceptical that a submarine could be a serious threat to the giant battleships of the Royal Navy, contracted the American Electric Boat Company to build five Holland design submarines at the Vickers Maxim shipyard in Barrow-in-Furness at a cost of £35,000 each. Eight months later in 1901, Britain’s first submarine was finished. Holland 1 was a bigger and more powerful version than the US Navy’s first submarine, the Holland Type 6.

Because the Admiralty still regarded submarines ’in the nature of an experiment’, the launch of Holland 1 was carried out in secrecy and was only given a proper launch ceremony in February 1902.

In September 1902 the first submarine flotilla, commanded by Captain Reginald Bacon, arrived in Portsmouth. It consisted of two completed Holland boats (2 and 3) and the gunboat HMS Hazard that served as a floating submarine base. Designed for coastal defence, Holland 1 was used mainly for training by the navy. She came to the end of her working life in 1913 when she sank near the Eddystone Lighthouse off Plymouth while under tow to a breakers yard.

In 1980, with the assistance of Royal Navy mine sweepers, the Royal Navy Submarine Museum initiated a search for the wreck of Holland 1. They found it in 1981. It took a month for Royal Navy divers to salvage the sub, the same year that the higher profile Mary Rose was brought up.

According to Bob Mealings, curator of the RNSM, Holland 1 was in relatively good condition when she was salvaged. ’Because she’d been buried in anaerobic mud, corrosion was modest. The hull was sound, but there was localised damage.’ Holland 1 was cleaned and treated with an anti-corrosion chemical, a rust inhibitor developed for central heating systems. Based on tannic acid, the chemical was supposed to form a hard, black coating to prevent moisture from reaching the metal underneath.

In 1982, the museum put Holland 1 on display outside. ’It was a disaster’, says Mealings. ’The wet, sea air triggered the start of serious corrosion, leaving parts of her in a perilous condition. Many cast iron components started to disintegrate and had to be thrown away, although the steel hull was pretty much intact.’

The corrosion was particularly acute because the vessel had absorbed high levels of chloride during her 69 years on the seabed. Corrosion in iron and steel in high chloride conditions occurs roughly five times faster than corrosion when the chloride levels are low, explains Mealings. And the corrosion cycle will continue in high chloride concentrations even when water and oxygen are present only in small quantities.

The museum realised that standard anti-corrosion methods for iron and steel, such as applying paint or sealants, wouldn’t work. Conservators needed to look at new ways to halt the decay. But they had another, conflicting requirement: not only did they have to stop the corrosion, they had to produce a conserved vessel that visitors could explore without causing damage. ’We had not to lose sight of the fact that the Holland 1 was an integral part of a maritime collection of international importance where access and education were paramount’, recalls Ian Clark, a freelance conservator who helped to formulate the conservation strategy. ’The choice of conservation treatment would directly influence visitors’ initial perception and lasting memories.’

After much deliberation, the museum decided to remove the chlorides absorbed in the metal fabric of the submarine. This should reduce its sensitivity to air and water, and halt corrosion. The process of chloride extraction is well-established on archaeological and marine artefacts, but nothing had ever been done on anything this size before, reports Mealings. Holland 1 weighs more than 100t. What was usually carried out on a lab workbench had to be scaled up thousands of times. In the lab, platinum or platinised titanium serve as anodes, but this was too expensive so the team used 316 stainless steel meshes.

In 1994, the museum built a giant fibre-glass tank to house the fragile submarine. The tank was filled with 800,000l of a 5 per cent sodium carbonate solution with a pH of 9, the equivalent pH of seawater. The alkaline solution prevented corrosion from occurring and allowed the gradual movement of chloride ions from the metal surface into the solution where they combined with sodium ions to form soluble sodium chloride.

In the past, chloride extraction had been used on the steam compound engine from the steamship SS Xantho. Here the conservators had used an electric current to ’drive’ the electrolytic migration of the chloride ions from the metal surface to an anode. But in doing so they had damaged the engine. Bearing this is mind, the museum opted instead for a less risky, ’passive’ treatment, involving a pump-driven capillary pipe distribution system to keep the solution free-flowing around the submarine. In this way, even the deepest crevice inside the submarine should have received constant soaking attention.

The use of a soaking system is directly analogous to dissolving sugar in a cup of tea, explains Peter Lawton of Hampshire County Council Museums Service, who advised the RNSM. ’The solid sugar is the sodium chloride more or less ionised dependent on the available moisture in a crevice and the soaking solution is the tea. If you simply leave the sugar in the tea without any stirring the tea will be cold and the sugar will still be only partially dissolved. The action of pumping the solution round the tank is the same as stirring. High concentrations of sodium and chloride ions are removed locally, for example at the mouth of a crevice, and as thermodynamic laws require equilibrium in a system, the deeper and more concentrated areas give up their sodium chloride into solution.’

For six years, Holland 1 lay soaking in its alkali bath. The Hampshire County Council museums’ Service team, assisted by students from the University of Portsmouth, used various methods to determine the level of chloride ions in the solution including simple titration against silver nitrate, potentiometric titration or the use of an ion-sensitive electrode. ’Knowing the volume of the solution and its starting chloride level, the total weight of chloride and thus salt removed at any one time can be calculated’, explains Lawton.

A team from the University of Portsmouth also used advanced data logging techniques to record the reference potentials from a number of reference electrodes. ’This was important as this information was used to adjust the solution pH and so prevent electrolytic cells between the various dissimilar metals’, explains Lawton.

Three times, the museum drained the tank and refilled it with fresh solution. In 1998, chloride levels in the soak solution had ceased to rise and further soaking was not needed. At this stage, a team from the University of Portsmouth and Hampshire County Council Museums Service used electrolysis on a limited portion of a ballast tank of the torpedo tube. Lawton explains: ’A stainless steel anode was immersed and a very high current density of 6A per square metre run for seven days. Analysis of the solution at the end of this time showed no increase whatsoever in chloride ion levels.’

All the other samples tested showed suitably low levels of chloride ions, that is not more than 42mg l ¹ equivalent which was the level in the soak solution. ’We were very relieved that it had worked’, says Mealings. ’Some people thought corrosion crevices such as rivets and other nooks and crannies wouldn’t get touched by a passive washing process. It was a very slow process but this was the secret of its success. We have a cast iron toilet bowl that was mistakenly left out and have been soaking that for over a year now, and there is still chloride coming out. It takes a long, long time.’

Once the metal surfaces were relatively free of chloride ions, the conservators could concentrate on how they would conserve the vessel for the long-term. ’The hull had a rough weathered appearance and was no longer sea-worthy. We weren’t keen to repaint it the vessel was being conserved not restored and knew that whatever was put on had to come off easily if further investigation into corrosion became necessary later on’, Mealings elaborates.

To prepare the surface, they used a ’sensitive’ air abrasive method called a ’flash blast’. This was a copper slag abrasive delivered using a blast of dried compressed air applied at a rate of over 7m ³ per minute, comments Clark. This technique gives a more even finish than scraping by hand while also preserving the patina of the metal plates. The museum team chose to coat the vessel with a wax sealant, Shell Ensis TX fluid, which is relatively easy to remove, provides protection against moisture and physical touch, and is air permeable. Using this kind of product on an artefact the size of Holland 1 was a major departure from convention, says Mealings. Traditionally, conservators blast surfaces until smooth and then paint them as though they were new.

Clark added a vegetable pigment to the brown-coloured Ensis TX fluid to darken what ’could have become a uniform solid colour’. He continues: ’The resultant colour is one that has produced random tones when exposed to a mixture of natural and false lighting.’ Mealings says the coating has performed well as a protective seal and describes the resulting finish as ’one of the triumphs of the project’.

However, parts of the vessel did receive a coat of paint. For example, the inside of the submarine is painted white; historically, all submarines have been - and still are today - painted white to maximise working light for the crew. ’To have coated the entire interior in brown wax would have resulted in an impression of sub so different from that which prevailed that it would hinder its effective interpretation. The outside of the hull is now white and grey above the waterline to illustrate how these colours were used for camouflage’, says Mealings.

The submarine is now housed in a dry-air gallery. Because moisture breathed into the atmosphere from visitors could start off once again the insidious process of corrosive decay, a powerful dehumidification system keeps the atmosphere well below 30 per cent relative humidity, even inside the sub as well.

’This project was groundbreaking in many areas’, concludes Clark. ’No object of this size had ever been passively treated in this way, or treated with this protective coating within a public exhibition gallery. And a display gallery of this scale and use has never been constructed before in this country.’ The design and construction of the purpose-built gallery was an integral part of Holland 1’s conservation strategy, because the controlled atmosphere will be pivotal to the long-term conservation of the submarine. ’The conservation of artefacts such as Holland 1 is at the cutting edge of technique’, says Lawton. ’Only time will tell if there were inherent problems which we failed to understand.’

Source: Chemistry in Britain