Sub-Bottom Profiler Surveys

In 2006 a Hydrography Masters student from the University of Plymouth, Amelie Thebault completed a survey over the site using an Innomar SES-2000 sub-bottom profiler with the kind assistance of Innomar GmbH. Analysis of the sub-bottom data suggested that the remains of the hull lie some 20m from the centre of the designated area. This work was repeated in November 2007 using a dual head SES-2000 system with the transducers mounted 500mm apart on the same deployment pole.

See the Cattewater Photo Album     

Magnetometer Surveys

In 2007 the project was taken on by Elizabeth Swann, also a Hydrography Masters student from the University of Plymouth in partnership with Ashley Gould, Maritime Archaeology & History Masters student from the University of Bristol. Work completed in 2007 included a multibeam echo sounder (MBES) survey along with a sidescan and further sub-bottom profiler surveys. A towed magnetometer survey was completed with the aim of detecting any iron artefacts and material but the data was sparse and lacked detail, so a high resolution magnetometer survey was planned. The site is surrounded by mooring buoys with their associated anchors and ground chains. The area has been used as a haven for ships for centuries contains the debris and shipwreck remains accumulated over this period. Towing a magnetometer between the boats and moorings is difficult as they limit the areas over which you can operate and there is the danger of snagging a mooring with the very expensive towfish. In addition, the position of the towfish is difficult to determine to metre accuracy without using an even more expensive acoustic positioning system. For these reasons we wanted to try a different approach and attach the magnetometer to the boat itself, this way we would obtain the highest position accuracy and be able to sail in amongst the moorings in (relative) safety. The team was joined by Kevin Camidge from CISMAS who brought with him a Geometrics G881 caesium magnetometer on loan from Martin Dean at the University of St Andrews. The University of Plymouth provided a Trimble SPS RTK GPS receiver and 3H Consulting Ltd provided a computer with a prototype version of Site Searcher geophysical survey software which was used for data collection and processing. The aim of this re-survey was to obtain complete coverage of the designated area with 5m line spacing, the highest positioning accuracy achievable and a 10Hz measurement data rate.

The boat used for this task had to be big enough to carry the equipment safely yet small enough to be work amongst the buoys, so something around 5m long seemed suitable. The boat had to have a diesel engine as petrol engines were known to create interference which degrades the magnetometer signal. A small hydrographic survey vessel was loaned to us by Nigel Boston from Geosa Ltd., unfortunately this did not have a wheelhouse or even a small cuddy so we had to improvise a shelter for the electronics. To get the highest position accuracy for the magnetometer measurements the GPS antenna needed to be as close to the magnetometer as possible, but the magnetometer also had to be mounted as far from the boat’s engine as possible. The solution was to fit a wooden bowsprit to the bows of the vessel to which we attached the magnetometer and GPS antenna.

Fortunately, it did not rain and the seas were calm enough so the temporary bowsprit and lashed-together electronics survived the afternoon’s worth of data collection required to cover the whole site. A large tour boat was moored on a buoy over the north-west corner of the site which caused a large distortion in the magnetic field in the area but this was removed by the Site Searcher software in post-processing. Also superimposed on to the magnetometer signal was noise which appeared to be caused by the pitching of the boat. Although it is possible to filter out this noise in software we will soon be investigating methods to reduce it when the data is collected. This magnetometer data was added to the other data sets already contained in the Site Recorder GIS model for the site and the results confirmed that the most significant target is 20m to the East of the centre of the designated area.

Multibeam (MBES) Surveys

Multibeam bathymetric surveys have been undertaken over the site between 2005 and 2007.  In 2005 a dual head Reson SeaBat 8125 system was used by the University of St Andrews during data collection for the the RASSE project.  In 2006 the University of Plymouth deployed a GeoAcoustics GeoSwath system and most recently in 2007 the Royal Navy Hydrographic School mapped the site using a Simrad EM3002.

Migrating Site Data to Site Recorder

Part of this project work has involved migrating the existing information about the Cattewater wreck from paper to electronic form.  This has been done to allow the team to more easily interpret the geophysical data but it also allows publication of the entire dataset at minimal cost.  The first step involved digitising the site plans from the published reports then re-positioning the earlier ones based on the later drawings.  To this were added finds records from the 1973 season along with their drawings.  The site was finally re-positioned based on the results of the geophysical surveys.

Download the Site file to open in the free Site Reader program 

Bibliography

• Interim report on the wreck discovered in the Cattewater, Carpenter A., Ellis K.H., & McKee J., 1974, Maritime Monographs and Reports  No13
• The Tudor Shipwreck at Cattewater. Plymouth, Bax A., 1976
• Cattewater wreck 1st Interim Report, Bax A. and Farrell R., 1976, International Journal of Nautical Archaeology 5
• The Tudor Shipwreck at Cattewater, Mortlock B. and Redknap M., 1977
• The Cattewater Wreck, Plymouth, Devon: Preliminary results of recent work, Mortlock B. and Redknap M., 1978, International Journal of Nautical Archaeology
• The Cattewater Wreck: The investigation of an armed vessel of the early sixteenth century, Redknap M., 1984, BAR British Series 131
• Mount Batten Plymouth, a Prehistoric and Roman Port, Cunliffe B., 1988, Monograph No 26, ISBN 0 947816 267
• Lost Landscapes of Plymouth – Maps, Charts and Plans to 1800, Stuart E., 1991, Alan Sutton Publishing Ltd., ISBN 0 86299 772 0
• Plymouth Sound Maritime Archaeological Recording Project – Rapid Assessment, Wessex Archaeology for Plymouth City Council, 1995, Reference 39057
• The Cattewater Wreck: a contribution to 16th century maritime archaeology’, Redknap M., 1997, in Cederlund, C.O. (ed.) Postmedieval Boat and Ship Archaeology BAR International Series 256
• Artefacts From Wrecks: dated assemblages from the late Middle Ages to the Industrial Revolution, Redknap M., 1997, Oxbow monograph 84, ISBN 1900188392 9781900188395, Oxbow Books
• Plymouth River, a History of the Laira and Cattewater, Gill C., 1997, Devon Books, ISBN 0 86114 911 4
• Historic Shipwrecks, Fenwick V. & Gale A., 1998, Tempus Publishing Ltd., ISBN 07524 1416 X, pp102-103
• High-Resolution Magnetometer Survey of the Cattewater Wreck, Holt P., in Nautical Archaeology Winter 2008, NAS (PDF)
• The Use of GIS in Maritime Archaeology - the Cattewater Wreck Case Study  Holt P. 2007, (PDF)
• Geophysical Investigations of the Cattewater Wreck 1997-2007, Holt P., 2010 (PDF)