Carpow Logboat
The excavation, recovery and conservation of a 3,000 year old logboat.
Background
In August 2006 Perth and Kinross Heritage Trust (PKHT) successfully completed the excavation and recovery of a Late Bronze Age logboat from the Tay Estuary. This was the end of the first stage of a project which had started five years earlier, with overall aims to recover, conserve, preserve and eventually present the vessel to the public.
A logboat is a vessel carved from a single tree trunk, and is a type of water craft first used in early prehistory. The earliest recorded example from Europe was found in Denmark, dating to around 7,000 BC, and they have continued to be used since this period, in some cases up to the 18th and 19th centuries. Logboats also continue to be used in other parts of the world to this day.
Approximately 150 logboats have been recorded from Scotland, mainly dating from the period 500BC to AD1000. There are records of 7 logboats from the Tay estuary, all discovered during the 19th century. Only one of these survives today, in the McManus Museum and Art Galleries in Dundee, one of two found by fishermen near Errol. Two other logboats, both found at Lindores around 1816, were broken up and used as building lintels in Newburgh.
The Carpow logboat was first reported in 2001 by metal-detectorists who were detecting on the sands and gravels of the Carpow Bank, at the head of the Tay Estuary. One of the detectorists, Scott McGuckin, recognised what he considered was a possible logboat, partially buried within the sands, and reported the discovery to PKHT. The site was subsequently visited in September 2001 by representatives from PKHT, Fife Council, Historic Scotland, the National Museums of Scotland, Perth Museum and Art Gallery and the Royal Commission on the Ancient and Historical Monuments of Scotland. The find was verified as a logboat, with the location established to be within the administrative boundaries of Perth and Kinross.
Initial survey
Preliminary analysis of the exposed section of the vessel established that its condition was fair, although subject to continual erosion and abrasion by the high-energy environment of the Tay. Initial archaeological evaluations, involving small-scale excavations and scale drawing were undertaken in 2002 and 2003 to establish the date, length, and condition of the buried part of the vessel. The location of the boat, situated on inter-tidal sand and mud banks, made excavation complicated. The River Tay has a mean annual discharge of 160m³/sec, with the volume of water flowing downstream as a result of rainfall or melting snow seriously affecting the tidal level. Only a low tide preceded by a dry period of around one week exposed the logboat, giving a tidal window of around 3 to 4 hours, which limited the number of possible visits to the site. The Tay estuary also has a number of environmental designations, as a Site of Special Scientific Interest (SSSI) and a Special Protection Area (SPA), which affected the project design.
The results of the preliminary excavations were signicant, with carbon14-dating the vessel to 1130-970 BC, making it the second oldest logboat to have been discovered in Scotland. Excavation established the boat was 9.25m, or 30ft long, with the buried portion surviving in excellent condition. This included an intact transom-board, a separate back-board inserted into the vessel, which is a feature rarely found surviving in such examples. The late-Bronze Age date and excellent preservation of this vessel make it one of the best preserved and most important prehistoric boats to survive in Britain.
Monitoring following this initial research, however, showed that the exposed prow of the boat was rapidly eroding as a result of inter-tidal action. Given the importance of the vessel, a plan for its long-term preservation was required, with the boat secured in the short-term by a protective barrier of sandbags to reduce the tidal impact.
Excavation
By 2006 the strategy and funding were in place to fully excavate and recover the logboat for conservation. The final excavation and lift was carried out over seven days in July and August 2006 by PKHT, with support from CFA Archaeology Ltd, and archaeological contracting unit, and Moorings and Marine Services, a local marine engineering firm.
The logboat was carefully excavated to avoid damage to the buried section of the vessel. Digging down into the sands and gravels, the stern was discovered to lie almost 1m below the ground surface, with the base held within a layer of clay. Although the excavations took place at low tide, the bottom of the trench lay below the low tide water table. This resulted in a constant stream of water seeping in from the sides of the trench, and required pumps to remove the collecting water.
Once the logboat was fully excavated from the clay and grave, the plan was to use the incoming tide to float the logboat over to the soft mud of the riverbank, where it would rest overnight. The boat was rigged to float using air-filled barrels, secured to the vessel with protective padding and straps. It was unclear at this stage, however, whether the vessel would float or not, as this process had never been undertaken before.
As the tide came in, water started to flow into and gradually fill the excavation trench. Slowly at first, the logboat started to float, and with members of the excavation team at the bow and the stern, the boat was slowly manoeuvred out of the trench and across to the riverbank.
The following day the logboat was secured using protective netting, with a motorboat used to slowly tow the vessel 1.5km downstream to Newburgh quay. At the quayside it was carefully floated into a custom-built lifting frame and suspended using flexi-boards and straps. The boat was then transported to the National Museums of Scotland for the conservation process to begin.
Conservation
Once out of the river water, the vessel was at constant risk of drying out and disintegrating, with the loss of water causing the cells of the wood to collapse. During the first stage of the conservation process, the boat was kept wet to prevent this breakdown, enabling the cleaning process to take place. This initial stage of conservation uncovered details of the logboat’s construction, including a second dwarf transom groove, tool-markings on the inner face of the transom board, and evidence for repairs made in prehistory. The vessel was subsequently cut into three sections to allow it to be soaked in tanks of PEG (polyethylene glycol) solution. This process replaces the water in the cells of the wood with a more stable chemical compound, allowing the boat to be displayed in a museum atmosphere without the need to be kept wet. Once the process of impregnation with PEG is complete, a final phase of freeze-drying will be used to remove any remaining water. Once this conservation process is complete, the logboat will return to Perthshire, where it will go on display in Perth Museum and Art Gallery.