Following on from the recent PAS visit to the Scottish Crannog Centre we bring you a report on the construction of this fascinating project and invite you all to drop in for a visit before the summer's over.

Introduction

The most important development in 1994 was the commencement of the experimental crannog reconstruction project in Loch Tay being carried out with the Scottish Trust for Underwater Archaeology (STUA). The unique design of the life-size crannog is based on evidence obtained through research and underwater excavations of the late Bronze/early Iron Age site of Oakbank Crannog off the village of Fearnan in Loch Tay. The materials being used match those found on the original site. The reconstruction represents the first phase of an environmental, education and tourist development at Kenmore, where it is hoped to generate income to support further underwater research. Other highlights of the year included the discovery and investigation of a dugout canoe, and sampling and survey exercises in Loch Tay, Lochindorb, and Loch Finlaggan.

The Crannog Reconstruction - Survey at Croft-na-Caber, Kenmore, Perthshire

Gordon Thomas from this Department assisted the authors in carrying out a land survey at the Croft-na-Caber Activities Centre in Kenmore to produce plans and levels of the area in which we proposed to build the crannog. Locals and engineers say the water level here reaches its maximum flood level every 60 years or so, but this has been reached, if not surpassed, in three consecutive years. The land survey complemented an underwater survey carried out last year.

The foreshore and shallows immediately opposite the Croft's waterfront were also surveyed, to ensure that the nature of the lochbed and its contours were suitable for building. There are pebbles and stones running out from the shore down a slope for some 14 metres before giving way to a reasonably soft lochbed. No major obstructions were located, and the depths remained favourable.

The results of the survey were submitted with the planning application. A copy was also required for our engineers, Crouch Hogg Waterman of Glasgow, who kept as close to the archaeological requirements of the reconstruction as possible, while still complying with building controls and the need for public safety.

Reconstruction Preparations

The major part of 1994 was taken up with preparations for building the crannog. This included the construction of three models to test the viability of the project: (i) the first was very much an impression of the site as it will appear after construction; (ii) the second was based on very accurate engineers' drawings and explains in detail how the different timbers of the reconstruction are jointed together for strength; (iii) the final model was constructed on site at Kenmore using logs sawn from alder trees too large for the reconstruction. A mock-up was made of part of the crannog's foundation structure, and once the details of the technique were understood, the task of building in several metres of water was considered with more confidence.

While the third model was being built, a floating perimeter was placed around the spot chosen to build the crannog. Being situated next to a watersports centre meant that inexperienced dinghy sailors, windsurfers and kayakers all ended up entering the exclusion zone. Since they could easily injure the divers in the water as well as themselves, a roped demarcation line was necessary. Once the floating perimeter was in place, it was necessary to erect a scaffold frame from which to work out in the water, and to set markers on the lochbed as guides for the timber piles. The frames for two 5m high towers were made up on shore and assembled underwater. This may sound like cheating, but the crannog builders would have used timber scaffolding and rafts.

Experimental Archaeology: Methods and Procedures

The majority of the 8-10m long trees being used for the piles are alder, which are very buoyant in the water and easy to manoeuvre. However, pulling them into the vertical was not simple. After three attempts a method was developed which involved hard pulling by volunteers on the scaffold platform while the pile was steadied by others on a floating raft. While this method worked, it was exhausting for those involved and only 4 or 5 piles could be erected in a day. The problem was overcome by using a 1 ton chain hoist for the raising.

An issue which has been of concern since piles were first examined at Oakbank was how to drive them into the lochbed. Professional piling rigs had been offered and considered, but were turned down in the efforts to build the crannog "by hand". Such rigs were certainly not available to the builders in the past and yet they drove hundreds of piles so it was essential to try and work out how they may have done the job.

The real piling breakthrough came with the very first experiment. A crosspole was lashed perpendicular to the upright pile, and was twisted back and forth. The momentum generated, with the weight of the pile, was sufficient to "drive" it into the lochbed to a depth of between 1 and 2 metres, the same depth to which the original 2,600 year old piles had been driven at Oakbank. It is almost certain that this was the method used by the original crannog builders.

Support for this theory came from the driving of two piles on the site. A simple pile-driver or slip-hammer had been constructed of heavy tubular steel casing and a heavy steel weight used in oil drilling rigs. The equipment was so massive as to be unusable in most circumstances. The engineers had asked for loading test results to determine the resistance properties of the lochbed which required driving two piles with this machine. It took up to 27 blows of the weight to drive the pile 25 millimetres (one inch) into the lochbed. Clearly such a method, hitting the pile with a weight, could not have been used in the past. Using the first method, a team of four - one of them in the water to place the pile point accurately - can now effectively raise and drive piles so successfully that the placement of 15 piles in a day is not unreasonable. Attaching the crosspieces and radial timbers that hold the structure together and give it strength takes longer, however, and is more exacting than the task of driving the piles.

There are about 150 piles in total to be driven in, dozens of crosspieces and floor supports to be jointed, pegged, and lashed in place, hundreds of round poles to be installed as floor timbers and roof supports, and masses of hazel to be woven into hurdles for the house walls. It is easy to understand why the crannog dwellers valued their timber, understood its selection, and practised coppicing and general principles of conservation and woodland management.

By Autumn 1994 the inner part of the structure, including the piles which support the roof had been erected. Once completed, the thatched roundhouse will have a diameter of 10 metres, surrounded by a walkway and connected to the shore by a timber causeway.

The site is open to the public and has created great interest in the project - with an on-site exhibition which includes interpretive photographs, the models, video of activities above and below water (including excavation of a log-boat discovered during the reconstruction), and a record of the work as it continues and develops.

T.N. Dixon & B.L. Andrian

THE SCOTTISH CRANNOG CENTRE
Kenmore - Loch Tay - Perthshire
Scotland - PH15 2HW
Tel : 01887 830583

The Centre is OPEN : April through October
Group Bookings and school parties welcome.

www.crannog.co.uk

Acknowledgments

We are grateful to a number of sources for providing grants, equipment, and labour. Although too numerous to list in full, they include: the Carnegie Trust, Glenfiddich Living Scotland Award, the Moray Endowment Fund, the Russell Trust, Scottish Enterprise Tayside; equipment and members of the STUA; and equipment and students of the Department of Archaeology including Aileen Halley, Margaret Henderson, Matt Ritchie and Nevenka Vesligaj.