An overhead photo of a large wooden shipwreck preserved on Cefn Sidan Sands, Carmarthenshire, and surveyed by the RCAHMW in February 2023.

Modelling Maritime Archaeology

Wales has a rich and diverse set of maritime archaeological remains. From the submerged remnants of prehistoric lands to historic harbours tucked away in remote coves, and shipwrecks from across the centuries. These archaeological sites are fragile and finite. Each site is unique, whether in its physical form, or in the priceless information it holds about people in the past. Once lost, they cannot be reintroduced or regenerated, but are gone forever.

The climate emergency has greatly increased the likelihood of maritime archaeological sites being badly damaged, or even destroyed by natural processes. Accordingly, the Commission has embarked on a strategic, long-term project to enhance our records of Wales’s maritime archaeology within the inter-tidal and coastal zone. Digital survey allows us to capture the details of individual sites in high resolution, to create a corresponding 3D dataset, and to curate a permanent, digital record of our cherished maritime heritage for future generations.

The threats to Wales’s maritime archaeological sites are increasingly well documented and understood. These include the impact of severe weather events such as storms or floods, or damage from accelerated coastal erosion. Meanwhile, changing sea-levels can bring new sites into a situation where they might be deemed threatened, while changes to sediment patterns can lead to permanent burial. At the same time, our coasts and seas are facing pressures from commercial development and recreational usage at a scale not seen before. The effect of the climate emergency increases the impact of environmental-based threats, while causing understandable developmental pressures, e.g. coastal defence schemes, or offshore renewable energy projects.

Against this backdrop the Commission is seeking to ensure that in the event of damage to a site, or even catastrophic loss, we have the best available record. Fortunately, technological developments in the past decade or so mean that rapid, high-resolution documentation of sites through digital survey methods has become the norm. Laser scanning and photogrammetry offer ways of undertaking survey that mean it is now possible for a one- or two-person team to create a detailed record of a site in a few hours; this  would have taken many days, or even weeks, for a much larger team in the past. This is especially relevant on sites in the inter-tidal zone where access might only be for an hour or two, once or twice a year. For example, the large wooden shipwreck (NPRN 302164) on Cefn Sidan Sands in Carmarthenshire (pictured in the main image) was surveyed in February 2023 using an ultra-lightweight drone to capture 687 photographs in just under one hour of manually controlled, low-level flight.

A point cloud of the wooden shipwreck on Cefn Sidan Sands in Carmarthenshire. Over 70 million points have been recorded through a photogrammetry survey as a 3D digital record of the ship.

The outputs from these 3D digital surveys come in several forms. The first of these is most easily termed a ‘point-cloud’, and is quite simply a collection of points that digitally represent the surface of the object being surveyed, including archaeological sites. These points are arranged in 3D space (each with an X, Y, Z coordinate). The points in a point cloud can be derived from measuring the speed and angle at which a laser beam emitted from a scanner is reflected back to the instrument, or from feature matching in overlapping photographs during photogrammetric processing. As an example of the latter, the point cloud from the Cefn Sidan shipwreck mentioned above comprised 70,667,521 individual points (image 2). Such a point cloud can serve as the baseline record of a site, against which point clouds from future surveys can be compared to gauge site degradation, or to confirm the loss of individual parts of the ship.

An orthomosaic of the same ship at Cefn Sidan. Here, all the photos from the survey have been combined into a single image that has no distortion from perspective or camera lens warping.

Two further outputs sit alongside the point cloud as a record of the archaeological site. These are the orthomosaic (image 3) and the digital elevation model (DEM) (image 4). The orthomosaic is a highly detailed overhead image of the site, comprised of all the photographs taken during a photogrammetric survey, stitched together to remove any perspective, lens warping, etc. As such, it can be a highly effective record of a site in a visual form and can form the basis for more traditional interpretative plans. A DEM is exactly what its name suggests; a digital elevation model of the site containing real-world coordinate data and the relative heights of surfaces and features. It is often coloured using a range of colours in the same way as for example, a mountain range in an atlas. The DEM is useful for picking out features or alignments that might be very low lying, or even invisible when viewed on site or with normal photographs. It can also be used as a record of changes tofeatures like sediment levels at a site.

A digital elevation model (DEM) of the wooden shipwreck at Cefn Sidan, derived from the point cloud that was created from the photogrammetry survey.

Finally, it is possible to create a 3D model of a site. This process turns the point cloud into a ‘mesh’ of triangles by joining the dots of the point cloud. A ‘texture’ is then laid over the top of every triangle face, which in turn is derived from the photographs taken during the survey. This can result in a photo-realistic 3D model of a site that can be easily manipulated as an aid to better understand the archaeological remains. It is also possible to share the 3D model more widely through online portals like SketchFab. This allows anyone to view and explore the products of the survey work that are done using a PC, Mac, or even a smartphone. The ability to share models in this way is especially useful where sites are difficult to reach and allows people to explore archaeological remains that they might otherwise have been unable to visit. The 3D model of the wooden shipwreck at Cefn Sidan mentioned above is accessible here: https://skfb.ly/oEBvt

The process of rapid 3D documentation just described opens up the possibility of planning a survey programme on a scale that would previously have been impossible. Setting a strategic aim of enhancing the National Monuments Record of Wales through, for example, provision of a 3D digital record for all our inter-tidal shipwrecks (c.150), or every small historic harbour (c.50), is no longer unrealistic if we are prepared to think in the medium term of the next five to ten years or so. This work will ensure that future generations of archaeologists will have the baseline records at their disposal to allow the most effective monitoring and management of Wales’s inter-tidal and coastal archaeological sites in the long term.

Dr Julian Whitewright, Senior Investigator (Maritime)

25/07/2023

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Peter Richards
Peter Richards
1 month ago

What material were the bolts for the futtocks made out of? Was it copper, or more likely iron? The hull design and size of the ship would seem to suggest mid nineteenth century onwards?

Marisa Morgan
Editor
21 days ago
Reply to  Peter Richards

Hello Peter, thank you for getting in touch. Our Coflein page for this site has further information about the probable identity of the vessel which you may find helpful, it can be found here: https://coflein.gov.uk/en/site/302164/. I’m afraid we don’t know about the material of the futtocks, as when the site was last visited none were visible on the surface. I have passed on your comment to our Maritime Investigator who I’m sure will look out for the futtocks on future survey trips. Best wishes.

Deanna Groom
1 month ago

Lovely model of one of my PhD sites! Are you going to be doing any others?

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