Underwater Corrosion Testing of the Holland 5 – H.M. Submarine No. 5 By David Crosthwaite-EyreDecember 27, 2012
In 1900 the Royal Navy signed a contract to build five ‘Holland’ class submarines. Entering service in 1903, these experimental boats were the Royal Navy’s first submarines, and over the next decade proved the value of the submarine as a weapon of war.
Developments in technology rendered the ‘Hollands’ obsolete and they were either sold for scrap or destined to be used for gunnery practice. HM Submarine No. 5 (the ‘Holland 5’) was en route to a naval yard when it slipped its tow and sunk in 1912. It lay undiscovered off the English south coast until accidentally found in 1995. Now protected by law, it has remained undisturbed on the seabed for almost a century.
In 2010 a Masters student from the School of Applied Sciences at Cranfield University and keen recreational diver, Duncan Harwood, decided to make the Holland 5 the subject of his dissertation. More specifically, he wished to examine the rate of corrosion suffered by the wreck, and to consider the mechanisms and factors which may have affected that rate of corrosion.
Paramount to the collection of current data and the subsequent results of the dissertation was a diving expedition to take Ultrasonic Thickness Gauge (UTG) readings from the Holland 5 using an underwater thickness gauge supplied by Cygnus Instruments of Dorchester, Dorset.
Also of critical import to the dissertation and its findings, Mr. Harwood was able to make comparisons to the “Holland 1” which has been raised, conserved and is now on display to the public in the Royal Navy Submarine Museum. It was found that both submarines have corroded much less than what might have been predicted when compared to published data, and it is Mr. Harwood’s hypothesis that this is due primarily to marine growth and concretion which had built up over the decades. Fishing nets and adverse human interactions are believed to remove layers of concretion which exposes the steel to the harsh and corrosive marine environment.
The work Mr. Harwood has subsequently presented has applications for all metal shipwrecks, and may be used as the starting point in any discussion about the level of protection to be afforded to any shipwreck. The number of shipwrecks in the world will continue to grow with time, particularly with the increasing amount of cargo being transported by sea. And it is clear that the usefulness of the information gained from this project may have implications for many underwater sites throughout the world.
The use of UTG measurements had previously been dismissed for applications such as these, on the grounds that the technique requires extensive surface preparation of the metal. However, this particular range of thickness gauges are designed to measure through a coating up to 20 mm thick and requires minimal or no surface preparation, unlike other ultrasonic gauges which require the removal of surface coatings and preparation of the metal.
The successful use of the multiple echo gauge in obtaining thickness measurements on the Holland 5 negated the requirement to revert to the method of taking coupons (10cm diameter pieces of metal cut from various locations throughout the ship), as employed on the USS Arizona. The UTG carried the additional advantage of producing accurate measurements of the hull thickness despite only having access to the outer surface of the hull. Furthermore the results could have still been compared with those obtained from the “coupon method”, had it been previously applied.
Naturally the “coupon method” would be impossible on an intact pressure hull, as the cutting would flood the interior of the hull. As it has been established that the hull of the Holland 5 is no longer intact, it would have been possible for Mr. Harwood to remove coupons from it. Such work would require the permission of English Heritage who would have to grant a new license to allow the removal of a sample from the site, and the work would have to be done by a commercial diving company using surface-supplied equipment due to health and safety legislation (Diving at Work Regulations 1997). A hydraulic drill would be required to cut out the coupon, and consideration given to a method to “plug up” the hole in order to reduce localized corrosion around the edge of the hole once the coupon is removed. English Heritage would have had to decide whether the amount of information gained from the recovery and analysis of a coupon would justify the financial outlay required to obtain it.
Mr. Harwood’s project has therefore identified a superior methodology which may be used when assessing metal shipwrecks. It is believed this is the first time an ultrasonic thickness gauge has been used in the calculation of a corrosion rate on an underwater archaeological wreck of such historical importance.
Due to financial and time constraints the practical collection of data of Mr Harwood’s was limited to a single dive on the Holland 5. In order to gain sufficient data to develop a model for corrosion on the wreck it would be necessary to conduct further dives and expand the methods and type of data collected.
As part of his dissertation, Mr Harwood carried out historical research which has confirmed that the Holland 5 was one of the first two submarines commissioned into the Royal Navy, on the same day as the Holland 3. The Holland 5 is one of the first two Royal Navy submarines commissioned into service, and as such she is of great historical significance. Left untouched she will eventually disappear, a forgotten relic of Britain’s mighty naval past. Submarine conservation projects do not arise very often, even less so for such iconic and historically important submarines as the Holland 5. With her hull almost completely intact and corroding less than would be predicted, she would appear to be a prime candidate for raising and conservation. It is hoped that this thesis may begin to lay the groundwork for such a day.
This article was based on Duncan Harwood’s paper, An Investigation Into Corrosion On The Holland 5 Submarine. with his permission and was edited by David Crosthwaite-Eyre, managing director of Cygnus Instruments. Mr. Harwood is a graduate of Cranfield University.
Editor’s Note: The MUA does not endorse any product or company but does encourage discussion about tools and techniques that may be of use to professional underwater archaeologists. We invite reader comments on this post and the equipment discussed therein.