Archaeological Services in Relation to The Protection of Wrecks Act (1973) Ultrasonic Thickness Measurement Methodology Development and Testing

Transcription

1 Wessex Archaeology Archaeological Services in Relation to The Protection of Wrecks Act (1973) Ultrasonic Thickness Measurement Methodology Development and Testing Holland No. 5 and HMS/m A1 Ref: November 2012

2 ARCHAEOLOGICAL SERVICES IN RELATION TO THE PROTECTION OF WRECKS ACT (1973) ULTRASONIC THICKNESS MEASUREMENT METHODOLOGY DEVELOPMENT AND TESTING HM SUBMARINES HOLLAND NO. 5 AND A1 Prepared by: Wessex Archaeology Portway House Old Sarum Park Salisbury WILTSHIRE SP4 6EB Prepared for: English Heritage Fort Cumberland Fort Cumberland Road Eastney Portsmouth PO4 9LD Ref: November 2012 Wessex Archaeology Limited 2012 Wessex Archaeology Ltd is a company limited by guarantee registered in England, company number It is also a Charity registered in England and Wales, number ; and in Scotland, Scottish Charity number SC Our registered office is at Portway House, Old Sarum Park, Salisbury, Wilts SP4 6EB.

3 ARCHAEOLOGICAL SERVICES IN RELATION TO THE PROTECTION OF WRECKS ACT (1973) ULTRASONIC THICKNESS MEASUREMENT METHODOLOGY DEVELOPMENT AND TESTING HM SUBMARINES HOLLAND NO. 5 AND A1 Ref: Ultrasonic Thickness Measurement Title: Methodology Development and Testing. HM Submarines Holland No. 5 and A1 Principal Author(s): Hanna Steyne Managed by: Toby Gane Origination date: 9th July 2012 Date of last revision: 9th November 2012 Version: 02 Wessex Archaeology QA: Toby Gane Status: Final Draft Summary of changes: Client comments Associated reports: jj; ii; aaa; qqq Client Approval: English Heritage i

4 ARCHAEOLOGICAL SERVICES IN RELATION TO THE PROTECTION OF WRECKS ACT (1973) ULTRASONIC THICKNESS MEASUREMENT METHODOLOGY DEVELOPMENT AND TESTING HM SUBMARINES HOLLAND NO. 5 AND A1 Ref: Summary Wessex Archaeology was commissioned by English Heritage to develop a methodology for testing metal hull thickness using a Cygnus DIVE Ultrasonic Thickness gauge as part of the contract for archaeological services in relation to the Protection of Wrecks Act (1973). This report presents the background and methodological development undertaken by Wessex Archaeology and the results achieved during visits to the Protected Wrecks Holland No.5 and A1. The project has developed a methodology to collect information about hull thickness using basic hand tools to remove concretion and the Cygnus DIVE gauge. A readily available aquatic epoxy putty was used to replace the removed concretion and should ensure a long term seal for the test location metal, and facilitate relocation of test locations. The variability encountered in hull thicknesses highlighted the need for numerous measurements to be taken on any single shipwreck, preferably as paired measurements, in order for any valid assessment of a wreck s overall condition to be made. The need to identify the potential factors influencing hull thickness variability, and accounting for this when taking measurements is a key conclusion from this research, and will be fundamental to the validity of any assessments of site condition made on the basis of this methodology. This research indicates that, given a suitable number of measurements, the methodology developed here is an appropriate tool to assess and monitor the condition of iron and steel hulled historic shipwrecks, and could form the basis of an active heritage management programme for these sites. ii

5 ARCHAEOLOGICAL SERVICES IN RELATION TO THE PROTECTION OF WRECKS ACT (1973) ULTRASONIC THICKNESS MEASUREMENT METHODOLOGY DEVELOPMENT AND TESTING HM SUBMARINES HOLLAND NO. 5 AND A1 Ref: Acknowledgements This research project was commissioned by English Heritage as part of the contract for Archaeological Services in Relation to the Protection of Wrecks Act (1973). The assistance provided by Mark Dunkley of English Heritage both during fieldwork planning and actual fieldwork is gratefully acknowledged. Wessex Archaeology would also like to thank the following people for their assistance: Nominated archaeologist and licensee for the Holland No.5 Mark Beattie-Edwards from Nautical Archaeology Society; Ian MacLeod of the Western Australian Museum; Michael Keane, licensee for Holland No.5 ; Martin Davies, licensee for A1. The fieldwork was carried out by divers Graham Scott, Dan Pascoe, Kevin Stratford, Mark Dunkley and Hanna Steyne, with the assistance of boat skipper; Bjorn Melin, and crew; Mark James. Hanna Steyne supervised the fieldwork and Graham Scott and Dan Pascoe supervised the diving. The report was compiled by Hanna Steyne and Karen Nichols prepared the illustrations. The project was managed for Wessex Archaeology by Toby Gane. iii

6 ARCHAEOLOGICAL SERVICES IN RELATION TO THE PROTECTION OF WRECKS ACT (1973) ULTRASONIC THICKNESS MEASUREMENT METHODOLOGY DEVELOPMENT AND TESTING HM SUBMARINES HOLLAND NO. 5 AND A1 Ref: Contents 1. INTRODUCTION PROJECT OBJECTIVES BACKGROUND PREVIOUS WORK ON HOLLAND NO PREVIOUS WORK ON A METHODOLOGY INTRODUCTION EQUIPMENT PRE-DIVE GAUGE TEST IDENTIFYING TEST LOCATIONS SITE ENVIRONMENT HOLLAND NO.5 AND A1 CONSTRUCTION DETAILS RESULTS HOLLAND NO A DISCUSSION CONCLUSIONS RECOMMENDATIONS REFERENCES APPENDIX I: DIVER OBSERVATIONS HOLLAND NO A1..15 APPENDIX II: SITE RISK ASSESSMENTS HOLLAND NO A1..17 APPENDIX III: DIVE LOGS & SITE INFORMATION HOLLAND NO A1..19 iv

7 Figures Figure 1: Figure 2: Multibeam data of Holland No.5 showing the location of thickness measurements made by WA and estimated locations of thickness measurements made by Harwood in Multibeam data of A1 showing the locations of thickness measurements made by WA. Plates Plate 1: Cygnus DIVE gauge testing: heavily corroded metal in air Plate 2: Cygnus DIVE gauge testing: cleaned metal in air Plate 3: Cygnus DIVE gauge testing: heavily corroded metal in water Plate 4: Cygnus DIVE gauge testing: cleaned metal in water Plate 5: Clean solid metal on Holland No.5 beneath concretion layer Plate 6: Test hole on Holland No.5 filled with epoxy putty Plate 7: Hard marine growth and concretion layer on A1 at Test Location 1 Plate 8: Clean solid metal on A1 beneath concretion layer at Test Location 2 Plate 9: Clean solid metal on A1 beneath concretion layer at Test Location 4 Plate 10: Successful thickness measurement on A1 at Test Location 4 v

8 ARCHAEOLOGICAL SERVICES IN RELATION TO THE PROTECTION OF WRECKS ACT (1973) ULTRASONIC THICKNESS MEASUREMENT METHODOLOGY DEVELOPMENT AND TESTING HM SUBMARINES HOLLAND NO. 5 AND A1 Ref: INTRODUCTION Wessex Archaeology were commissioned by English Heritage to develop a methodology for testing metal hull thickness using a Cygnus DIVE Ultrasonic Thickness gauge as part of the contract for archaeological services in relation to the Protection of Wrecks Act (1973) This report presents the background and methodological development undertaken by Wessex Archaeology, the results achieved during visits to the Protected Wrecks Holland No.5 and A1, and an assessment of the methodology in relation to its validity as a heritage management tool for assessing, monitoring and managing iron and steel hulled historic shipwrecks PROJECT OBJECTIVES The objectives of work on the Holland No.5 and A1 laid out in the Briefs provided by English Heritage are summarised below: Primary objectives for Holland No.5: Contact Licensees Mark Beattie-Edwards (principal licensee) and Michael Keane and offer participation in the fieldwork; With reference to previous investigations and reports, undertake ultrasonic thickness measurements at key hull locations; Make good any removal of corrosion scale; Undertake a Risk Assessment with reference to English Heritage s Risk Management Handbook; Produced a structured record of field observations. Key elements are to be subject to detailed examination and recording. Operational flexibility with specific recording will be undertaken through liaison with the on-site curatorial team. Secondary objectives for Holland No.5: Undertake swim-over video survey of Holland No.5. Primary objectives for A1: Contact Martin Davies, Licensee of the A1 and offer participation in the fieldwork; With reference to previous investigations and reports, undertake ultrasonic thickness measurements at key hull locations; Make good any removal of corrosion scale; 1

9 Undertake a Risk Assessment with reference to English Heritage s Risk Management Handbook; Produced a structured record of field observations. Key elements are to be subject to detailed examination and recording. Operational flexibility with specific recording will be undertaken through liaison with the on-site curatorial team. Secondary objectives for A1: Undertake swim-over video survey of A Discussions with English Heritage during the fieldwork planning stage established that the Primary on-site objective was to undertake the ultrasonic thickness measurements, and that any additional recording of key elements should be opportunistic rather than a focus of fieldwork. As such, in discussion with Mark Dunkley (Maritime Designation Adviser) who was present for the majority of the fieldwork, the focus of all dives was on testing the use of the Cygnus DIVE gauge to collect ultrasonic thickness measurements. This work is the focus of this report Observations made during dives regarding the condition of the two wreck sites is summarised in Appendix I A Risk Assessment for each site, according to the Risk Management Handbook is presented in Appendix II BACKGROUND Research into the degradation, stabilisation and management of metal shipwrecks is an under researched area internationally, with a small number of exceptions in North America and Australia. In addition, there has been a notable lack of research undertaken on later 19 th century or 20 th century shipwrecks in the UK, which is understandable given the time depth from which shipwrecks are found in UK waters. With huge numbers of pre-19 th century shipwrecks located within UK waters, the focus for management activities under the Protection of Wrecks Act (1973) by English Heritage has fallen on these early, wooden and composite built shipwreck sites. Of the 47 protected shipwrecks in England, just three are metal hulled; Iona II, Holland No. 5 and A1. This work represents the first steps to develop an active management regime to understand the changes and deterioration of historic metal shipwrecks Two approaches have generally been used to monitor the degradation of metal shipwrecks; corrosion rate measurements carried out either by corrosion potential measurements for iron hulled wrecks (MacLeod 1995; McCarthy 1988; MacLeod and Steyne 2011) or through analysis of concretion (Henderson 1989; Johnson et al. 2003; Russell et al. 2006) and direct hull thickness measurements (Johnson et al 2003, Russell et al 2006 and Harwood 2010). Corrosion potential measurements can provide reasonably accurate rates of corrosion and metal loss for metal objects underwater. However, they require a degree of post-processing to convert the voltage measurements collected on-site into useable corrosion rates. The process also requires numerous repeated measurements over time to understand the stability, or otherwise, of a site, through varying corrosion rates. Equally, corrosion rates estimated through the analysis of concretion require a suite of chemical and analytical tests in order to provide useful information. Direct hull thickness measurements have the advantage of providing an immediate indication of metal loss since construction, when compared to builder s records. The approach used on the USS Arizona required the removal of sections of hull plating for measurement and is inherently destructive (Russell et al. 2006). An 2

10 established marine industry approach to metal thickness testing is the use of ultrasonic gauges, which is non-destructive, and was tested by Harwood on the Holland No.5 (2010) PREVIOUS WORK ON HOLLAND NO The wreck of the Holland No.5 was first discovered in 1995 by local diver Gerry Dowd. The Archaeological Diving Unit (ADU) was first provided with information relating to the position of the wreck in The ADU undertook geophysical surveys on Holland No. 5 in 2000 and 2001, which showed the site to be complete and intact sitting upright on the seabed, although no diving operations were undertaken (ADU 2001) The Holland No.5 has previously been subject to non-disturbance diver surveys by Wessex Archaeology in 2005, 2007, 2008 on behalf of English Heritage (Wessex Archaeology 2006, 2007, 2009). Between 2005 and 2008 the wreck was observed to be in a generally good condition, with varying quantities of rope, wire cable and netting on the site. Key features confirming the wrecks identification as a Holland Class submarine were recorded and a site plan was produced The 2008 Wessex Archaeology survey reported that key features identified in previous visits remained in situ with the exception of the nose cone of the propeller (Wessex Archaeology 2009: 5) and that overall the wreck seemed to be in a similar condition to previous visits, although less fishing gear was present The Nautical Archaeology Society (NAS) has been involved in survey and research on the Holland No.5 since 2006 and Mark Beattie-Edwards, NAS Programme Director, is currently the licensee for the site. The NAS s work on Holland No.5 has included clearing fishing net and wire from the site, undertaking video, photographic and measured survey and undertaking comparative studies with the Holland No.1 in the Royal Navy Submarine Museum, Gosport. The NAS work has enabled re-colonisation of marine life on the site after the clearance of numerous fishing nets and has identified a number of features where the deck of Holland No.5 differs to that of Holland No.1. The regular visits undertaken by the NAS to the site have enabled a level of site monitoring to be undertaken, and it was the NAS who identified that the torpedo tube hatch had been illegally removed sometime between September 2008 and June 2010 (NAS website accessed 2012) In 2010 Mark Beattie-Edwards assisted Duncan Harwood, a Masters student from Cranfield University, to undertake ultrasonic thickness measurements on Holland No.5 as part of his dissertation research into corrosion on the Holland No.5 (Harwood 2010) Harwood used a Cygnus 1 gauge to take metal thickness measurements on the hull of both Holland No.5 and No.1. Measurements taken on Holland No.5 were made without the removal of any marine growth or concretion. Comparative measurements from Holland No.1 were only able to be obtained from the port side, providing 5 comparative measurements. Location 5 was near the outer edge of the propeller, which is made of brass, and is not included in the results below. The measurements taken by Harwood are presented below (measurements are in millimetres): Location Average (Locations 1-4) Holland No N/A Holland No N/A N/A N/A Harwood s research demonstrated that the Cygnus gauge was capable of taking measurements on the clean hull of the Holland No.1, where three repeatable measurements were able to be taken at each location (Harwood 2010: 83). He records that taking 3

11 measurements at many locations was not possible on Holland No.5 due to the nature of the surface, but it is not clear whether he was able to take repeatable measurements at the successful location on Holland No Harwood s measurement locations were identified on a sketch plan, however it was not of sufficient detail to enable relocation of the measurement points, and therefore corroborate, or otherwise, the measurements he took in PREVIOUS WORK ON A The wreck of the A1 was first dived and identified in 1989 by Martin Woodward, after reports of a fishing snag. Mr Woodward subsequently bought the wreck from the Ministry of Defence (MoD). The ADU were first made aware of the site in 1996 but in each subsequent year to 2000 the ADU recorded damage to the site through divers illegally removing pieces of the wreck, including portholes, deadlights, hatches and other fittings. The ADU undertook geophysical surveys of the site between 1998 and 2005 which assisted with continued diver monitoring of the sites general condition throughout this period (Archaeological Diving Unit 1997; 1998; 1999) Wessex Archaeology visited the site in 2005 on behalf of English Heritage in order to undertake a structured survey of the site and assessment of threats and vulnerability of the site to further damage by divers (Wessex Archaeology 2006). The survey used still and video photography and measured drawing to create a measured plan of the site. Despite the damage from illegal removal of objects from the site, it was reported to be in relatively good condition. The major threats to the site were identified as further unlicensed diving and removal of fixtures and fittings, and corrosion (Wessex Archaeology 2006: 10). 2. METHODOLOGY 2.1. INTRODUCTION The decision by English Heritage to use the Cygnus DIVE Ultrasonic Thickness gauge to measure hull thickness was based on the hypothesis that monitoring hull thickness over time can provide information relating to the overall condition, stability or degradation of the shipwrecks through time, by measuring the amount of corroded metal lost through time. The approach is effectively a non-destructive (or at least less destructive, as only the concretion is damaged and not the actual hull) version of the direct measurement approach taken by Russell et al. (2006) and importantly requires minimal post-dive processing. This aspect of the methodology is important for use in the UK environment where many of the monitoring visits to protected shipwreck sites are undertaken by non-professional divers and licensees. The simplicity of the Ultrasonic Thickness gauge methodology, both underwater and in terms of post-dive assessment, makes this approach to direct thickness measurement potentially suitable for use by non-professional licensee divers EQUIPMENT The Cygnus DIVE Underwater Thickness Gauge is designed for commercial divers to carry out metal thickness surveys in shallow and deep water. It consists of a large wrist-mounted display unit attached to a 25mm diameter probe head with a coiled cable. The unit is powered by rechargeable bespoke batteries The unit takes measurements using the Cygnus multiple echo technique whereby the probe transmits a short ultrasonic pulse and receives the returning echoes. The DIVE gauge confirms a valid thickness measurement when three equally spaced return echoes are received by the probe head. The use of multiple echoes enables coatings such as paint and 4

12 light marine growth to be discounted, and only the thickness of metal to be displayed (Cygnus 2012: 8) The gauge can be calibrated to test a range of materials by setting the velocity of sound within the instrument. The gauge is set to Mild Steel as standard, at 5920 m/s. A table of velocities and conversion factors from Mild Steel to other metals is provided in the user manual (Cygnus 2012: 78) The DIVE has a Deep Coat function which the Cygnus literature suggests enables the unit to measure metal thickness through coatings up to 20mm thick (Cygnus 2012), although the manual qualifies this indicating that the Deep Coat mode provides the ability to measure through coatings thicker than the standard 3mm, depending on the coating material (Cygnus 2012: 76). It is assumed that references to coatings relates to applied coatings such as paint. The gauge readings may also be affected by pitting on both sides of the metal plate. It is not clear whether concretion on the inside of the submarine had any effect on the measurements It was uncertain as to whether the Cygnus DIVE would be able to measure through corrosion product and concretion on the Holland No.5 and A1. To test whether any measurements taken through concretion or corrosion product were accurate it was planned to remove concretion and take thickness measurements against bare metal, in addition to through concretion Furthermore, it was uncertain how the gauge would react to heavily corroded metal as the operating manual suggested that the uneven surfaces created as a result of corrosion would cause the ultrasound echo pulses to scatter and be absorbed. The ultrasound will be reflected from multiple points as there is no one true metal thickness (Cygnus 2012: 29). The operating manual suggests the best option is to slowly move the probe around the area of interest to locate areas of least pitting where a reading may be achieved The nature, hardness and thickness of any corrosion product or concretion on the two submarines was unknown, and as such two approaches to remove concretion were identified. The first involved the use of a small pneumatic hand drill with a 32mm hole saw bit powered by a 12l SCUBA tank, and the second used a 25mm cold chisel and small lump hammer. Both sets of tools were selected as being capable of removing as small an area of concretion as possible, but large enough for the probe head to reach bare metal The removal of any corrosion product or concretion from the test sites would reintroduce seawater to the metal and potentially increase localised corrosion if left exposed. In order to reduce any potential damage or destabilisation of the metal by such exposure, the removed concretion was replaced with a non-toxic aquatic epoxy putty as soon as thickness tests were completed. Surex Aquastick was selected for use as this product comes in a rod form with the curing agent encapsulated in the base material, which is a contrasting colour. When the two parts are mixed together the epoxy turns from aquamarine to white and can be used in fresh and sea water environments The Sonardyne SCOUT ROV acoustic tracking system was used to navigate the diver to around the site, and position test locations, using georeferenced multibeam images of the sites. The process of site selection, concretion removal, testing and backfilling was recorded using diver helmet mounded video and derived stills images PRE-DIVE GAUGE TEST In order to have an indication of how the Cygnus DIVE worked, and to test its ability to measure corroded metal, the gauge was tested in the dry using a rusted square of metal measuring 15.1cm x 15.1cm. The metal test square was of uneven thickness, ranging from 5

13 4.2mm to 5.0mm (measured with a ruler), having corroded differentially across its surface. The default setting for mild steel was used for the gauge, although the metal type could only be guessed as being such. The equipment provided with the Cygnus DIVE includes an ultrasonic couplant gel which enables ultrasonic thickness measurements to be taken in an air environment The test square had heavy corrosion on one surface, which was flaky and could be easily removed by hand. No thickness measurements could be obtained in an air environment through this surface, and the gauge was unable to read a single echo, depicted by just one bar displayed (Plate 1) An area of the flaky rust was removed using a hammer, to reveal a solid, but not clean, surface. This surface was pitted, but similar as to that which might be expected to be found on a submerged historic metal shipwreck, beneath a concretion layer. The gauge was able to measure the thickness of the metal, although the probe head needed to be moved around a little to achieve a stable measurement, and when held in an area which did provide a measurement, the thickness would flash up only occasionally, indicating that the gauge was experiencing difficulty establishing a reliable thickness measurement. At one point, a measurement of 14.5mm was shown, nevertheless, repeated thicknesses of 4.8mm were obtained (Plate 2). This corresponded well with measurements taken with a ruler which suggested thicknesses of between 4.8mm and 5.0mm The gauge was then tested on the test square in a bucket of water, to better simulate the environment in which the gauge would be used. It was thought that the use of water as a couplant, as opposed to the provided gel, might be more effective and increase the ease with which the gauge could take measurements. In the event, the gauge was still unable to read a single echo on the heavily corroded area (Plate 3) but did more easily achieve a reading on the cleaned area of 4.8mm (Plate 4) In addition to the use of the test square, the gauge was tested on the marina piles at Ramsgate Harbour in and out of the water. The piles were round with a paint coating, and in some areas were visibly heavily corroded. Out of the water no results were able to be obtained either through the paint or through rust, with the use of the couplant. Holding the probe in the water enabled the gauge to obtain some readings through the paint layers, although thicknesses flashed up and were not stable. No readings were achieved on areas of rust, which lifted the paint and created a laminated type environment unsuitable for ultrasonic measurements This pre-dive testing indicated that it was unlikely that the gauge would be able to take measurements through the concretion layer, and that the metal would most likely need to be cleaned back to a solid state in order to achieve any readings IDENTIFYING TEST LOCATIONS A literature search focused on marine corrosion and shipwreck corrosion identified a number of factors which could create differential corrosion rates around the shipwrecks, thereby affecting the metal thickness of hull plating. More detailed explanation of these factors can be found in numerous other publications (MacLeod 1981; 1989; Warren 1980; Collier 2000) and will not be dealt with here. The major factors which affect the corrosion rates of metal shipwrecks in seawater, can be summarised as: The type of metal used for the ship construction (the type of iron or steel); The presence or absence of non-ferrous metal fixings or fixtures which could inhibit or promote corrosion of the shipwreck; 6

14 Seawater salinity, where an increased concentration of Chloride ions promotes corrosion; Dissolved Oxygen in the water, where an increased concentration of oxygen in the water promotes corrosion; Temperature, where increased temperatures promote chemical reactions, and therefore corrosion; Water movement around the site, where increased water movement affects salinity, dissolved oxygen and water temperature and therefore corrosion; Marine growth, where increased marine growth can create a protective barrier between metal and seawater, thereby inhibiting corrosion A number of site specific factors were identified which could affect metal thickness readings on the Holland No.5 and A1 at specific measurement locations. These factors can be divided into those which can be identified as directly affecting the thickness of metal being tested (primarily ship construction related), and those which might create differential corrosion rates and therefore variations in metal thickness (primarily environmental). Factors identified as directly affecting metal thickness included: The original as built thickness of the hull plating; The location and nature of hull plating joins; The location of internal frames; The location of external or internal fixtures and fittings, which could affect either the direct thickness of metal in a specific location; Direct damage to the shipwreck hulls, such as knocks and scrapes caused, for example, by anchor or beam trawling equipment Factors which were identified as potentially creating variations in metal thickness through differential corrosion rates include: The location of non-ferrous metal fixings and fixtures; The direction of predominant tidal flow across and around the wrecks; Damage or holes in the shipwreck hulls which could alter water flow around the site and internally The selection of thickness measurement locations, and the design of the methodology was focused to counter any potential variation in metal thickness around the ship, and the possibility for one off, non-representative thickness measurements Historic plans and documents detailing the construction details of the Holland and A1 were consulted to provide information regarding the as built thickness of hull plating (see below section 2.6), plate joins and the location of internal framing. In addition site plans and photographs from recent visits to the shipwreck sites were consulted to provide information about the condition of the hulls, the presence of any damage, holes or external features and fittings. These two sources were used as a guide to assist the diver in identifying suitable and unsuitable measurement locations on the two sites In order to ensure that measurements were repeatable and indicative of the thickness of the hull in a particular area four measurements would be taken at two points at each test location, approximately 10-20cm apart. Two measurements would be taken through the concretion as it was unclear as to whether the Cygnus DIVE gauge could successfully take measurements through concretion. The concretion would then be removed at these two positions to enable two further measurements on bare metal. It was hoped that this approach would identify any variations in thickness caused by differential corrosion across hull plating, or the accidental location of internal/unseen metal fixtures or fittings such as framing. 7

15 2.5. SITE ENVIRONMENT The wreck of the Holland No.5 lies in approximately 30m of water and is orientated roughly north-west (stern) by south-east (bow) and stands proud of the seabed. The seabed is sandy with patches of gravel. A sand ridge has built up across the site, running approximately WSW-ENE, roughly in the same direction as the prevailing tides. The majority of the sand bank lies on the east (port) side of the wreck. A small amount of scouring around the stern was reported previously (WA 2009) Fish including tompot blenny (Parablennius gattorugine) and pouting (Trisopterus luscus) have been observed on the wreck in some years, but absent in others. Other marine life noted on the site includes small edible crabs (Cancer pagurus), anemone (Actinothoe sphyrodeta) and a variety of seaweeds The wreck of the A1 lies in approximately 10-13m of water and is orientated roughly northwest (bow) by south-east (stern), with the bow standing proud of the seabed by 1m above an area of scour. The stern of the vessel is buried in sediment from the stern lifting rings aft The wreck sits within a narrow scour filled in with a fine, highly mobile silt, overlying a medium to firm clay. Around the scour, the seabed is hard with a surface cover of gravel and broken shell Marine life observed on the A1 was highly varied, with fish species such as tompot blenny (Parablennius gattorugine) and bib (Trisopterus luscus), seaweeds, anemones and hornwrack (Flustra foliacea) The tidal flow over the A1 runs approximately east-west, although minimal current was experienced during 2012 diving operations HOLLAND NO.5 AND A1 CONSTRUCTION DETAILS Fundamental to the success of direct thickness measurement for assessing the current condition of a shipwreck is knowing what the original metal thickness was at the time of sinking. This enables the total metal lost and rate of loss to be calculated, and provides a baseline for assessing a sites stability or otherwise Harrison s (1979) account of the construction details and development of the Holland Class and A Class submarines provides the best (and most easily accessible) summary and account of the as-built designs of the two classes of submarine. He draws together information from official records and drawings and personal notes whilst working on the design and refitting of submarines between 1928 and 1939, however he notes that information for a submarine or class of submarines often varied considerably, depending on the source, practices of the reporting authority and whether the details recorded referred to the vessel as designed, as first built or after some years in service The records relating to the Holland No.5 and A1 are not entirely clear about the thicknesses of the hull plating used, reflecting their experimental nature and rapid pace of development, however it seems that the same approach to plating was used for both ships, outlined below Vickers documents record the use of 7/16 in. (11.1mm) plating on the Holland boats, whilst the Director of Naval Construction (DNC) records state that the bottom plating was 7/16 in. thick and the plates to frames were ½ in. (12.7mm) thick (Harrison 1979). The DNC records suggest that the pressure hull plating was worked in raised and sunken strakes and that the plates at the maximum beam were inner strakes of ½ in. plating. From the available evidence, Harrison concludes that the Holland boats had raised and sunken plating worked in 8

16 eight strakes, with sunken strakes at the maximum beam and keel. The top plate of the pressure hull is thought to have been a raised strake which was flattened in the middle to touch the frame line DNC records indicate that the pressure hull plating for the A Class boats was increased to ½ in. plating, although Vickers records show 7/16 in. plating for all the A Class boats. The dimensions of the A Class boats recorded by Vickers indicate that the inner plates were ½ in. and the outer strakes were 7/16 in, which is in accordance with the DNC records, suggesting that the Holland and A Class boats were constructed using the same combination of raised and sunken strakes (Harrison 1979) The main frames of both Holland and A class submarines were 3 ½ in x 3 in x 7.8lb angle bars spaced 18 in apart, reduced at the ends. The 18 in frame spacing was constant, except for frames in the Holland boats which were 17 in apart, and frame which were 19 in apart. There were no internal bulkheads within the boats. 3. RESULTS 3.1. HOLLAND NO Two dives were achieved on Holland No.5 (Appendix III), only one of which was during a workable slack water, achieving a total of 25 minutes bottom time. Due to the time limitations, and recording requirements, only one test location was completed during the dive A position approximately 5m aft of the bow on the starboard side was selected as an appropriate test location, being safe to work away from fishing nets on the site, with clear line of sight between the diver and the USBL for positioning purposes (Figure 1). It was not possible to access many of the positions measured previously by Harwood due to fishing nets on site and line of sight issues between the diver and the USBL transceiver. An area approximately 200mm x 100mm was cleaned of soft marine growth using a hand held wire brush. A number of attempts were made to take thickness measurements through the concretion, however the gauge flashed readings between 5.5mm and 15mm and no consistent measurements were recorded Using a hammer and 25mm wide cold chisel a small area of concretion was gently removed. The concretion came away easily revealing clean, silvery steel metal beneath (Plate 5). A thickness measurement was taken and a consistent reading of 6.5mm recorded. The probe head was placed on the clean metal a number of times to confirm the reading. The removed concretion was replaced with epoxy putty (Plate 6). Bottom time did not allow for a second test nearby A The longer slack waters at the A1 enabled three working dives with a total bottom time of 213 minutes. During these dives four test locations were completed in addition to a failed test location (TL3) at the stern, where no solid metal was encountered beneath the concretion (Figure 2) The wreck lies at an extreme angle into the seabed, with the bow unsupported from the seabed by 1m and the stern buried in sediment. As such, it was impossible to take measurements at pre-determined points across the site at the same height above keel. Test Locations (TL) were identified based on a combination of factors, including those outlined above, but also line of sight to the boat to enable accurate positioning with the USBL and comfortable/safe working conditions for the diver. 9

17 TL1 and TL2 were located approximately 1m aft of the bow, TL 3 was located 3.85m aft of the conning tower and TL4 and TL5 were located in line with the front of the conning tower. The results of ultrasonic testing are summarised below in Table 2. Test Location Thickness through concretion Fail Fail Fail Fail Fail Thickness on bare metal Fail 5.6mm Fail no solid metal 8.4mm 5.7mm Depth of concretion 15-20mm 15-18mm 10mm 9-11mm At each test location, soft marine growth, primarily seaweeds, were cleaned back using a wire hand brush to expose the hard concretion (Plate 7). A thickness measurement was attempted at each location through the concretion, however none were achieved. A small piece of concretion was then removed using a hammer and chisel to reveal the solid metal of the hull beneath the concretion (Plates 8 and 9). The surface of metal in TL1 and TL2 were noted to be heavily pitted. TL5 located a 5mm deep perfectly round recess in the plating, of unknown function. The area of removed concretion was enlarged at this location to enable thickness measurements to be taken slightly away from the feature The metal beneath the concretion at TL3 was black in colour, heavily corroded and laminated making it quite soft and easily damaged by the chisel. As no clean solid metal could be located, no thickness measurement was taken in this location. In the vicinity of TL3, on the top of the wreck, the hull plating is missing, exposing exhaust piping and the inside of the hull plating TL2, TL4 and TL5 all exposed clean, shiny, solid metal from which good repeatable thickness measurements which were logged by the Cygnus gauge (Plate 10). All removed concretion was replaced with epoxy putty. 4. DISCUSSION From a methodological point of view, the work on the Holland No.5 and A1 established that the Cygnus DIVE gauge is capable of taking metal thickness measurements on historic shipwrecks, although see below for further discussion of the actual measurements. Divers found the DIVE gauge easy to deploy and turn on underwater, although some of the divers found that wearing the gauge on the wrist was workable, and others preferred to hold the gauge. The wrist strap was far too big for some of the divers, and a lanyard was used to secure the gauge to the diver instead. The gauge display was easy to read and clearly displayed any verifiable measurements Divers found that in some Test Locations the probe needed to be moved around a little to achieve a verifiable measurement, which is likely to be a result of corroded surfaces. As the probe is relatively sensitive to uneven surfaces, it was unpractical for the area of removed concretion to be limited to the c. 25mm of the probe head as originally intended. Instead, larger holes (c. 40mm - 60mm) were made to find a point at which the probe was able to take a verifiable thickness measurement. One diver noted that an air bubble was present on the probe head, which was preventing measurements being taken. Whilst the probe head membrane is secured with a Knurled Ring, it seems that it is relatively easy to catch the edge of the polyurethane membrane, especially when trying to take measurements on rough concretion surfaces, and allow a water/air bubble between the membrane and probe head The divers established that the use of a small lump hammer and cold chisel were perfectly suitable to remove overlying concretion up to 20mm thick and that this approach was much easier than anticipated. TL3 on A1, where heavily corroded metal was encountered, 10

18 highlighted that care must be taken when removing the concretion, especially when the condition of the underlying metal is unknown. Fragile metal was able to be exposed by using the chisel at a shallow angle, without damaging the metal surfaces too much. Where solid metal was encountered, it was able to take reasonably hard knocks from the chisel used perpendicular to the hull metal, creating clean edges to the concretion The use of the Surex Aquastick aquatic epoxy putty was successful, in that it was able to be mixed underwater and to neatly replace the areas of removed concretion layer. Some divers found that mixing the two parts together was quite hard work in cold water as the putty was not very pliable and took some time to mix fully. The mixed putty was, however, relatively easy to work into the edge of the concretion to make a good seal, although it also adhered readily to neoprene gloves. The epoxy putty is a white/grey colour, and should be easily identifiable, thereby facilitating the relocation of test locations. The epoxy putty seems to create a solid attachment to the shipwrecks between dives, and it can be expected that it will adhere to the shipwrecks long term. Whether the epoxy putty becomes colonized by marine growth is not yet known, but hopefully the white colouration will ensure that it is visible to future divers The collection of paired measurements (at 200mm gap) was justified by the variations in thickness measurements encountered at TL4 and TL5, and by the failure to collect a reading at TL1 versus success at TL2. This approach is important when collecting this sort of data, where so many variables can result in differential metal thicknesses. The use of (at least) paired measurements is particularly important in the initial stages of such work, where so little is known regarding the condition and stability of shipwreck sites From a site management point of view, too few thickness measurements were achieved to provide any useful results in relation to the overall condition of the two submarines. The single measurement taken on Holland No.5 corresponded well with the average thickness measurement presented in Harwood s (2010) thesis, although not with any of his actual readings. Without further testing on the site it is impossible to make any further use of either sets of measurements so far taken on this site Although more measurements were collected from A1 they are quite varied and difficult to interpret. The lack of a positive result at TL1 could be a result of the corrosion pitting on the metal, as noted by the diver, or heavy corrosion on the inside of the hull plating. An air bubble on the probe head was noted by the diver whilst attempting to take this measurement, however this was fixed on the surface (during the dive), and repeated attempts at the same location with the fixed probe head were not successful The lack of solid metal at TL3 could be due to increased corrosion in the area as a result of the missing plating, enabling higher water movement around both the inside and outside of the test area. It is also thought that the test site was located on casing plates not hull plates, which would have been much thinner, and therefore likely to have become fully corroded much sooner than thicker hull plating. The failure to identify solid metal at this test location highlights the potential for differential corrosion and hull plating thicknesses around shipwrecks The thickness measurements at TL2 and TL5 were similar at 5.6mm and 5.7mm, however the larger measurement at TL4 (of 8.4mm), just 200mm from TL5, illustrates the anticipated problems of hull thickness variability. These measurements, in addition to the corroded metal at TL3, highlight the need for numerous test measurements to be taken across a site to identify the difference between erroneous one off measurements and actual hull thickness variability. 11

19 Using the small number of thickness measurements alone make it impossible to draw any conclusions regarding the overall condition of the hull plating on A1, however, the condition of the metal as described by the divers, and the thickness of the overlying concretion suggest that the area around the conning tower may be experiencing lower corrosion rates than the bow and stern of the wreck. This could be a result of lower water movements in the area of the conning tower created by the upstanding nature of that feature, versus the relatively exposed situation of both the bow (effectively in mid water) and the stern (where plating is missing) It is unfortunate that it was not possible to evaluate, or retest the locations of Harwood s 2010 thickness measurements made through concretion, but it is worth noting that the Cygnus DIVE gauge used for this project was repeatedly unable to take any measurement through the concretion. Whilst the two pieces of equipment were different, they use the same Cygnus system of multiple echoes and, based on information in the user manuals, seem to have the same technical specifications. As such, it could be expected that the two gauges would behave similarly underwater. How or why the Cygnus 1 was able to take measurements through concretion where the Cygnus DIVE could not remains unanswered. 5. CONCLUSIONS This project has developed a simple methodology to collect information about hull thickness, and therefore condition, from metal hulled historic shipwreck sites. The Cygnus DIVE gauge is unable to collect thickness measurements through concretion, however the use of simple hand tools has been demonstrated as sufficient to remove small areas of concretion. This demonstrated that the Cygnus DIVE gauge is a suitable, easy to use piece of equipment to take thickness measurements on the hulls of metal shipwreck sites, although the selection of measurement locations, and the number of measurement locations is key to the success and validity of any subsequent interpretations. The use of aquatic epoxy putty to replace the removed concretion was relatively straight forward, and should ensure a long term seal for the test location metal, and facilitate relocation of test locations The demonstrated variability in hull thicknesses highlights the need for numerous measurements to be taken on any single shipwreck, preferably as paired measurements, in order for any valid assessment of a wreck s overall condition to be made. The need to identify the potential factors influencing hull thickness variability, and accounting for this when taking measurements is a key conclusion from this research, and will be fundamental to the validity of any assessments of site condition made on the basis of this methodology This research indicates that, given a suitable number of measurements, the methodology developed here is an appropriate tool to assess and monitor the condition of iron and steel hulled historic shipwrecks, and could form the basis of an active heritage management program for these sites. 6. RECOMMENDATIONS Based on the initial success of this project it is recommended that a more comprehensive set of measurements are taken on the each of the three metal hulled protected historic shipwrecks; Holland No.5, A1 and Iona II. A comprehensive set of measurements for each site will provide a good indication of the condition of the hull, and a baseline from which any future site management program can be developed The test sites established during this project should be monitored to determine whether the use of epoxy putty is effective at maintaining a seal within the concretion over the long term. It would also be of interest to investigate whether there is any evidence of accelerated corrosion within the test site areas as a result of the work. 12

20 The project has illustrated that in order to take well documented measurements, from relocatable positions takes time, with each measurement during this project taking approximately 30 minutes from start to end. Further practice using all the equipment will undoubtedly speed up the process, as will reduced need for detailed recording of each phase of work. Despite this, the three steps (removing concretion, taking a measurement, sealing up the removed concretion) will always be relatively slow. Any future projects aimed at undertaking comprehensive thickness measurement surveys for site management purposes should ensure that sufficient time is programmed for multiple, paired measurements to be collected along both sides of each shipwreck. 7. REFERENCES Archaeological Diving Unit Unpublished Monitoring Report A1. Report Number 97/21 Archaeological Diving Unit Unpublished Monitoring Report A1. Report Number 98/25 and 98/27 Archaeological Diving Unit Unpublished Monitoring Report A1. Report Number 99/30 Archaeological Diving Unit Unpublished Monitoring Report HM Submarine Holland No. 5. Report Number 01/10 Collier, E The boatowner's guide to corrosion: A complete reference for boatowners and marine professionals. Camden, ME. International Marine. Cygnus Cygnus DIVE: Underwater Ultrasonic Thickness Gauge. Model M1-DIVE. [Accessed 09/07/2012] Harrison, A.H The Development of HM Submarines from Holland No.1 (1901) to Porpoise (1930). MoD, BR3043. Available online [Accessed 5/07/2012] Harwood, D. An Investigation into Corrosion on the Holland 5 Submarine. MSc thesis, Cranfield University. Henderson, S. 1989, Biofouling and Corrosion Study. In: D.L.Lenihan (ed) Submerged Cultural Resources Study: USS Arizona Memorial and Pearl Harbour National Historic Landmark. Santa Fe, NM. Johnson, D.L., Makinson, J.D., De Angelis, R., Wilson, B., and Weins, W.N Metallurgical and Corrosion Study of Battleship USS Arizona, USS Arizona Memorial, Pearl Harbour. Santa Fe, NM. McCarthy, M SS Xantho: The pre-disturbance, assessment, excavation and management of an iron steam shipwreck off the coast of Western Australia. International Journal of Nautical Archaeology. 17.4: MacLeod, I.D. 1981, Shipwrecks and applied electrochemistry. Journal of Electroanalytical Chemistry. 118: MacLeod, I.D The application of Corrosion Science to the Management of Maritime Archaeological Sites. Bulletin of the Australian Institute for Maritime Archaeology. 13.2: 7-16 MacLeod, I.D In situ corrosion studies on the Duart Point wreck, International Journal of Nautical Archaeology. 24.1:

21 MacLeod, I.D. & Steyne, H Managing a Monitor the case of HMVS Cerberus in Port Phillip Bay: Intergration of Corrosion Measurements with Site Management Strategies. Conservation and Management of Archaeological Sites. 13.4: Nautical Archaeology Society Holland No.5 Project website: [Accessed 09/07/2012] Russell, M. A. et al A Minumum-Impact Method for Measuring Corrosion Rate of Steel-Hulled Shipwrecks in Seawater. International Journal of Nautical Archaeology. 35.2: Warren, N Metal Corrosion in Boats. London: Adlard Coles. Wessex Archaeology, 2006a, A1, Bracklesham Bay, Designated Site Assessment Archaeological Report, Unpublished Report Ref: jj Wessex Archaeology, 2006b, HMS/m Holland No. 5, English Channel, Designated Site Assessment, Unpublished Report Ref: ii Wessex Archaeology, 2007, HMS/m Holland No. 5, English Channel, Designated Site Assessment, Unpublished Report Ref: aaa Wessex Archaeology, 2009, HMS/m Holland No. 5, English Channel, Designated Site Assessment, Unpublished Report Ref: qqq 14

22 HOLLAND NO.5 APPENDIX I: DIVER OBSERVATIONS A cursory inspection of the bow area was made, from where the Torpedo Tube Cap has been illegally removed. A brass ring which is visible in this location on Holland No.1 was not visible on Holland No.5 and could not easily be located, as might be expected. It is unclear as to whether this brass ring has also been removed Large amounts of fishing net were reported in the stern area of the wreck, on the port side. A The conning tower was inspected following reports of a recent 'crack'. What looked like plate separation was observed in the forward lower half, c. 1m, of the conning tower, with a gap of up to around 100mm forming in some places. The plates are however very solid, and it is possible that the gap was a feature of the conning tower casing, forming some kind of cutwater, although nothing like this is obvious from the plans. A round tube was felt inside the gap, again, nothing of this nature is obvious from the plans, but it could be part of the support system for the conning tower The stern area is buried from the clover shaped lifting rings aft, with much of the upper plating missing between the lifting rings and conning tower as previously reported (WA 2005). The bow is unsupported and is approximately 1m above the seabed with a small area of scour beneath. 15

23 APPENDIX II: SITE RISK ASSESSMENTS HOLLAND NO. 5 Name SI Number Holland No /3249 NMR Number EH Region Restricted Area Principal Land Use TV 79 SE 14 South East 200m radius Marine SI National Grid Map sheet Class Listing Period Status Submarine Modern Designated wreck site Licensee Nominated Archaeologist Principal Ownership Category Mark Beattie-Edwards Michael Keane Mark Beattie-Edwards Crown / MoD Seabed Owner Navigational Administrative Responsibility Crown Estate Environmental Designations None Seabed Sediment Sand with gravel patches Nil Energy Medium Survival Very Good Overall Condition Generally satisfactory but with significant localised problems Condition Principal Vulnerability Trend Declining Trawling & Fishing Mechanical Degradation Unlicensed diving Amenity Value: Visibility Substantial above bed structural remains that are highly visible and legible without further information. Amenity Value: Physical Restricted. Access subject to licence or other authorisation. Amenity Value: Intellectual Accessibility No interpretation Field Risk Assessment High Risk Management Action Action identified/agreed but not implemented Management Prescription A B C D E F G H I J K L M N X X X 16

24 Notes The Holland No.5 survives relatively intact and upright on the seabed in approximately 30m. Work by the NAS has identified with unique technological developments which differ to the conserved Holland No.1. The site has regularly been found covered with fishing and trawl nets covering it, and on occasion loose metal cables which have caused damage to the surviving outer fittings and corroding metal structure. The placement of a marker buoy on the site demonstrably reduced the amount of fishing/trawl nets on the site, however since the loss of the buoy such nets have returned to the site. In addition to damage caused by fishing/trawling, the site has recently been subject to unlicensed diving and the apparent theft of previously secure fixings. In addition to external damage, the Holland No.5 is a steel hulled vessel which is experiencing natural corrosion in the sea water environment. It is likely that this process has reached some sort of stable equilibrium, however the extent of damage caused through corrosion is at present unknown. Damage to the protective concretion and direct physical damage to metal structures from fishing/trawl gear will promote increased corrosion. No current management plan is being implemented for the site. Risk is assessed as HIGH. A1 Name SI Number A1 1998/2708 NMR No EH Region Restricted Area Principal Land Use SZ 79 SE 3 South East 100m radius Marine SI National Grid Map sheet Class Listing Period Status Submarine Modern Designated wreck site Licensee Nominated Archaeologist Principal Ownership Category Martin Davies No Private Martin Woodward Seabed Owner Navigational Administrative Responsibility Crown Estate Environmental Designations None Seabed Sediment Clay with soft silt Nil Energy Medium Survival Good Overall Condition Condition Trend Principal Vulnerability General Declining Mechanical degradation satisfactory with Unlicensed diving 17

25 some damage significant Amenity Value: Visibility Substantial above bed structural remains that are highly visible and legible without further information. Amenity Value: Physical Restricted. Access subject to licence or other authorisation. Amenity Value: Intellectual Accessibility Unknown Field Risk Assessment MEDIUM - HIGH Management Action Action identified/agreed but not implemented Management Prescription A B C D E F G H I J K L M N X X X Notes The A1 survives relatively intact and upright on the seabed in approximately 10m. The A1 represents the remains of the first truly British designed and built submarine. After the construction of A1 significant changes were made to the A Class submarines making A1 a unique example of early British submarine design. The site has been subjected to significant damage through the illegal removal of many of the external fixtures and fittings since 1990s. Illegal removal of parts of the wreck have continued to cause problems, with evidence of divers opening hatches to gain access to the interior of the wreck. In addition to this damage by divers, A1 is a steel hulled vessel which is experiencing natural corrosion in the sea water environment. It is likely that this process has reached some sort of stable equilibrium, however the extent of damage caused through corrosion is at present unknown. Damage to the protective concretion, and direct physical damage to metal structures from illegal diving will promote increased corrosion. No current management plan is being implemented for the site. Risk is assessed as HIGH. 18

26 APPENDIX III: DIVE LOGS & SITE INFORMATION HOLLAND NO Transit time from Eastbourne marina 1h 10 minutes in calm seas. Marina locks operate on the hour and half hour Single stern anchor deployed, sufficient to hold the boat approximately 15m from the site. Date Predicted HW Predicted LW Predicted Slack Slack observed 29/05/ :06 / 17:53 12:00 12:26 12:25 Dive No. Date Diver Time In - Out Bottom Time Depth Current /05/2012 Dunkley 12:42 13:17 25 mins 30m Slack /05/2012 Pascoe 13:32 13:51 15 mins 31m Strong (too strong to work in) A Transit time from Chichester marina approximately 1h 2 minutes in calm seas, due to speed restrictions in Chichester Harbour. Marina locks operate as required Single stern anchor deployed due to numerous lobster pots around the site causing hazards for boat manoeuvring, but sufficient to hold the boat approximately 10m from the site. Date Predicted HW Predicted LW Predicted Slack Slack observed 30/05/ :34 12:21 10:00 12:00 09:45 13:00 31/05/ :46 13:30 11:00 13:00 11:30 13:30 Dive No. Date Diver Time In - Out Bottom Time Depth Current 02 30/05/2012 Scott 09:56 11:28 88 mins 12m Slack 03 31/05/2012 Steyne 11:42 13:07 82 mins 10.5m Slack 04 31/05/2012 Dunkley 13:19 13:59 39 mins 10m Slack to slight Pascoe 13:32 13:49 16 mins 10m Slight 19

27 Holland No m Thickness measurement WA 2012 Harwood 2010 Wessex Archaeology UTM WGS84 Z31N Data collected by ADU, St Andrews University, modified by WA. NB: Positions are approximate due to a 2.5m shift to the north east between the multibeam data and diver tracking positions Contains Ordnance Survey data Crown Copyright and database right 2010 This material is for client report only Wessex Archaeology. No unauthorised reproduction. Date: 26/07/2012 Revision Number: 0 Scale: 1:200 Path: Illustrator: KMN U:\Projects\53111\7 Drawing Office\Report Figures\2012\Holland 5 and A1sub Multibeam data of the Holland No.5 showing approximate ultrasonic thickness measurement location Figure 1

28 HMS/m A Test locations 1 & Test locations 4 & 5 Test location m UTM WGS84 Z30N NB: Positions are approximate due to a 6m shift to the north west between the multibeam data and diver tracking positions Contains Ordnance Survey data Crown Copyright and database right 2010 This material is for client report only Wessex Archaeology. No unauthorised reproduction. Date: 26/07/2012 Revision Number: 0 Wessex Archaeology Scale: 1:200 Illustrator: KMN Path: U:\Projects\53111\7 Drawing Office\Report Figures\2012\Holland 5 and A1sub Multibeam data of the HMS/m A1 showing approximate ultrasonic thickness measurement locations Figure 2

29 Plate 1: Cygnus DIVE gauge testing: heavily corroded metal in air Plate 2: Cygnus DIVE gauge testing: cleaned metal in air This material is for client report only Wessex Archaeology. No unauthorised reproduction. Date: Wessex Archaeology Scale: Path: 26/07/2012 N/A Revision Number: Illustrator: 0 KMN U:\Projects\53111\7 Drawing Office\Report Figures\2012\Holland 5 and A1sub Plates 1 & 2

30 Plate 3: Cygnus DIVE gauge testing: heavily corroded metal in water Plate 4: Cygnus DIVE gauge testing: cleaned metal in water This material is for client report only Wessex Archaeology. No unauthorised reproduction. Date: Wessex Archaeology Scale: Path: 26/07/2012 N/A Revision Number: Illustrator: 0 KMN U:\Projects\53111\7 Drawing Office\Report Figures\2012\Holland 5 and A1sub Plates 3 & 4

31 Plate 5: Clean solid metal on Holland No.5 beneath concretion layer Plate 6: Test hole on Holland No.5 filled with epoxy putty This material is for client report only Wessex Archaeology. No unauthorised reproduction. Date: Wessex Archaeology Scale: Path: 26/07/2012 N/A Revision Number: Illustrator: 0 KMN U:\Projects\53111\7 Drawing Office\Report Figures\2012\Holland 5 and A1sub Plates 5 & 6

32 Plate 7: Hard marine growth and concretion layer on A1 at Test Location 1 Plate 8: Clean solid metal on A1 beneath concretion layer at Test Location 2 This material is for client report only Wessex Archaeology. No unauthorised reproduction. Date: Wessex Archaeology Scale: Path: 26/07/2012 N/A Revision Number: Illustrator: 0 KMN U:\Projects\53111\7 Drawing Office\Report Figures\2012\Holland 5 and A1sub Plates 7 & 8

33 Plate 9: Clean solid metal on A1 beneath concretion layer at Test Location 4 Plate 10: Successful thickness measurement on A1 at Test Location 4 This material is for client report only Wessex Archaeology. No unauthorised reproduction. Date: Wessex Archaeology Scale: Path: 26/07/2012 N/A Revision Number: Illustrator: 0 KMN U:\Projects\53111\7 Drawing Office\Report Figures\2012\Holland 5 and A1sub Plates 9 & 10

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