An Experience of Photogrammetry by Andy Spencer

It is important for SHSC to have a scientific record of the components of the ship, as part of our experimental archaeology programme.  As things progress, we need to be able to look back at the materials we used and what we did. Photogrammetry is the science of creating a three dimensional model from a series of standard two dimensional photographs.  It is clearly the right thing for us to do.

What I have learned so far is that photogrammetry can be tricky!

I was already involved in The Ship’s Company as a volunteer, and as someone with an interest in photography starting off the photogrammetry project played to my strengths.  In an initial meeting a group of interested volunteers discussed the use of photogrammetry to create 3D models of the ship, its parts and the tools we would use in constructing it.  Subsequently we were kindly given access (by Felix Pedrotti of Southampton University) to some online tutorials  about using software and how to upload and convert the images into a 3D model.  I also did some research online and contacted Julian Whitewright for advice (there is a profile of Julian in the February 2021 newsletter).

Most people would choose to start with something relatively small that could be photographed under ideal conditions – like the clamp shown at the top of this post. However, we decided that the first photogrammetry project for the SHSC records should be the log that will form the keel of the ship. The keel log is 13 metres long and currently stored in a poorly lit barn.  Our project was no small task!

In January, fellow volunteer David Keeble and I made our first attempt to record the keel log and a second log that will be used for the stem and stern.  We had to decide on the section to be covered in each picture, and on how many to take down the length of the whole log.  There would need to be a large enough overlap in each picture so that the software creating the 3D image can work out how each picture sits in relation to the next – and from that build a 3D model.  Clever software!

We marked out locations about a metre apart with white tape down the length of each log , and about the same distance from the sides. We decided that three photographs would be needed at each location: close to the floor, about 75cm above the floor and looking down onto the log as close to vertically as possible.

The image below shows the plan that I sent Julian for advice on the angles we needed to cover.

On Julian’s advice we set more locations for pictures to be taken from each end of the log that would help the software interpret the images.  So we marked 36 locations around each log and took three pictures from each one, starting off at the lower level and then going round the entire log again at the second and third heights.

The right levels of light are important so it was challenging at times – low light levels meant long exposures and in places we had to use extra lighting but too bright a light also causes problems. We ended up with 216 carefully taken photographs!

We sent all the images of to Julian to upload using the Agisoft computer programme at Southampton University.  But after all the our efforts the software couldn’t create a 3D model.  We needed even more pictures, especially at the ends and from the top.

So, we are going back to try again with more lights.  I will fix the lens on the camera so that the zoom doesn’t change and we will need to work out the maximum possible distance that we can get from the trunk where space is limited.  Hopefully second time lucky!

The photo below and video link show how well the technique can work.

Andy Spencer

R2 D2, an exercise in photogrammetry by David Matzliach

Joe Startin Speculates, ‘Did the Sutton Hoo Ship Sail?’ (Part 4)

This is the fourth in Joe’s series of speculative posts – click here for links to parts 1, 2 and 3  

Edwin Gifford built a half-length replica of the Sutton Hoo ship in 1993 – Sæ Wylfing (moored outside the Longshed in the photo above).  He was fed up with people saying that the shape of the hull meant that it could not sail in much the same way as the classic Viking ships.

He was not seeking authenticity in materials, building techniques, and so on, but he did take care over the shape of the hull. The weight of Sæ Wylfing is 675 kg. Crudely, you would then expect the full-size ship to weigh 2 x 2 x 2 = 8 times this, or nearly five and a half tonnes. The hull and the ribs of the reconstructed ship are indeed expected to come close to this, but the thwarts, other internal supports, and a deck will add further weight.  Actually we are expecting it to weigh in at about 9 tonnes.

And of course he rigged a mast, and a yard and a sail to go up it.

Gifford gave the central thwart a thicker support in the middle, and some reinforcement where the front of the mast pushed against it.  In the image below, down between the oars you can see a lengthways member, with a recess in it. This is called a keelson, and the hole is a mast step, where the bottom of the mast fits. The main force the mast exerts on the hull is downwards, and the job of the keelson is to distribute this.

Gifford recounts some of the adventures he had in Sae Wylfing between 1993 and 1995. All the pictures show him at the helm, and I suspect this was always the case. He made some small additions to the keel in the winter of 1993/4. In 1994, when he was double-reefed in a wind gusting to 22 knots, he found he could make no progress to windward. He “decided to lower mast, first time afloat, and row.” This must have been terrifying. The dedication and composure of his crew was admirable.

His best result sailing to windward was at the Maldon Festival in 1995.

“…we covered three nautical miles direct to windward in 3.5 hours, despite many short tacks and loss of ground in crowded anchorages.”

This is just under one knot for ‘course made good’. For a land lubber that’s about one mile an hour.  And the effort of enforced tacks would have been a huge task for the crew.

The full-size reconstructed ship will be eight times as big as Sae Wylfing….Rowing (and paddling) it will be our priority. The first trials will be on the Deben; then the time will come to cross the bar and go out to sea.

Sae Wylfing on the Deben 2019

When the trials in a seaway are complete, and the ship is much better understood, we can explore how the hull performs with a big sail and the wind from the side.

Joe Startin

What on earth is experimental archaeology?

In the Ship’s Company we often calmly say that “our project to re-create the Sutton Hoo Mound One Ship is the biggest experimental archaeology project in the UK/Europe/the northern hemisphere/the world” just depending on how modest we are feeling.  But what are we talking about when we say that?

Many of you will know that as well as being a current Director of the Ship’s Company and Director of the third Sutton Hoo excavation, Professor Martin Carver is just a brilliant communicator.  And, admittedly, it was off the cuff in an unscripted interview for one of the SHSC films, but he has also given the most succinct definition of experimental archaeology that I have heard.  Martin said “we try things out to see if they work”.

A lot is implied in that simple statement.  Coates et al in the paper Experimental Boat and Ship Archaeology: Principles and Methods, state “….to learn more from [excavations] than is immediately obvious ….it is necessary to formulate hypotheses about past technologies, artefacts and cultures…. In Maritime Archaeology such experiments can take the form of building, on a full or reduced scale, models, or making other simulations of ancient boats or ships and testing them in repeatable sea trials, real or simulated.”  

We have to try to build what the archaeologists found.  We can’t diverge from that – except where the data is flaky or for example the resulting boat wouldn’t float, or wouldn’t float the right way up.  And we need to have clear aims, that might be, as Professor Sean McGrail suggested  “to use authentic methods and materials to establish how an ancient craft was built and to estimate performance”. (Experimental boat archaeology some methodological considerations 1986)

That is what we are trying our best to achieve.  Of course the Anglo-Saxons didn’t build their vessels under electric light in a shed with a smooth concrete floor – and a dry shed with a hard floor is not always an advantage when working green oak with axes!

The photos below show examples of some of the tools that we are using – tools that would have been available to the Anglo-Saxons when they built the original ship.

For our project, what both saves us from blind alleys – but causes a lot of discussion in planning – is the incompleteness of the data.  The Ship cannot be re-excavated and we inevitably have to interpret the data in what is a limited record.

Digital image of the ship based on the record of where rivets were found in the original excavation – the colours indicate differing levels of certainty – black highest and blue lowest.

But we do have clear aims, stated superbly and succinctly later on in Martin’s interview:

“The construction is to be undertaken with the utmost circumspection and attention to detail.  Every action taken that relates to the materials, their assembly, and their adjustment in the ship’s structure is to be recorded so that a trail can be followed to and from every decision made by the shipwright and their advisors.

While no-one can today build an accurate representation of an ancient vessel, we propose to build an experimental craft informed by as much archeological information, previous experience, and science as we can muster.”

The data that we acquire about the implications and consequences of building such a large ship, and the feasibility of its performance on river, sea, and land [hauling between rivers] will move the collective knowledge on Anlgo-Saxon sea-faring from a level of weak generalisation to a new platform of likelihood.”

That is our grand aim.

.Philip Leech

News from the Director of the Institute for Digital Archaeology – Roger Michel

Our partnership with the SHSC continues to provide us with a steady stream of interesting and exciting work – and great opportunities for other helpful partnerships.

Our efforts in the laboratory examining rivets (courtesy of the National Trust and Sutton Hoo Society) from the 1939 dig have yielded some extraordinary results.  I won’t pre-empt my colleagues by revealing too much.  I will only say that in addition to learning more about where, when and how the rivets were produced (and how we might produce rivets of our own using traditional materials and techniques), we may also have an unexpected opportunity to uncover some very specific data about the wood used to construct the ship. Please stay tuned for more information on these important topics.

On other fronts, an unexpected collaboration has emerged over the past six months in connection with the America’s Cup races to be held in New Zealand this spring.  During the last America’s Cup in Bermuda in 2017, the IDA sponsored a regatta featuring traditional Bermudian watercraft: 25 foot pilot gigs.  It was a great day on the water and – at least in my view – a welcome diversion from the very non-traditional sight of 5mm-thick plastic boats with trick sails skimming across the waters of the Great Sound.

Racing a Bermudan Gig 2017

Flash forward 3 years.  During a wide-ranging hour long interview with Radio New Zealand over the summer on a museum initiative with Oxford, our conversation somehow turned to a Maori translation of Beowulf that I had produced in 2012. From there it was a short hop to a lengthy discussion of the Sutton Hoo reconstruction project – and the many startling parallels between the ancient sea-faring cultures of New Zealand and Britain.  Without thinking too much about the consequences, I suggested that a race between an Anglo-Saxon longboat and a waka might be an appropriate sequel to the gig races of 2017.  Suffice it to say, people in New Zealand were listening.  Offers of technical – and political – support streamed in and now it appears that a waka versus longboat may well be on the America’s Cup 2021 undercard. You can hear the original interview by clicking the link to Roger Michel Radio interview on NZ interview

Although the competition boat would be a locally sourced simulation of a clinker-built Anglo-Saxon warship, the event would provide an excellent opportunity to educate visitors about the Sutton Hoo project – and northern European boatbuilding history generally.  It would also provide us with a chance to attract allies to the SHSC project from among a strongly boat-focused population.  Again, stay tuned.

Finally, yet another potential collaboration has emerged from an unexpected source.  My Oxford contemporary, historian Charles Spencer, has written an extraordinary new book on the White Ship disaster of 1120.  A best-seller right out of the gate, Earl Spencer’s careful chronicle of one of the most tumultuous periods in English medieval history provides a wealth of information about the clinker-built Viking-style boat that lies at the heart of that infamous episode. We expect to learn even more about the White Ship’s construction during a series of recovery dives at the wreck site this spring and summer.  The area has never been subject to any professional archaeological examination, and so may yield interesting new clues about the structure, composition and cargo of the doomed ship.

Given the many physical similarities between the White Ship and the Sutton Hoo Ship, and given also the vastly better surviving information about the architecture and construction of the White Ship as compared to the earlier vessel, examination and study of the former may well help to resolve some of the persistent mysteries surrounding the latter – including possibly providing clues about the Sutton Hoo Ship’s method of propulsion and helping to determine whether it was modified when pressed into service as a burial ship.

Certainly there are differences between the two vessels – the White Ship was a little larger and the upper strakes were pierced for oars instead of being equipped with tholes like our ship.  However the similarities swamp the differences.

Image of the White Ship disaster

In anticipation of the wreck dives to come, Lord Spencer said “I look forward to discovering possible connections between these two historic British ships.” He added that he “hope[s] that learning more about the construction of the White Ship will provide some helpful insights into medieval boatbuilding practices generally.”  

Personally, I am looking forward to a summer of exciting discoveries with Lord Spencer – and bringing to bear what we learn on the beautiful ship that will be starting to emerge day by day in the Longshed.

Perhaps a reconstruction of the White Ship, as well, may be on the cards. Time will tell.

 

Joe Startin speculates – Did she sail? Part 3

Sae Wylfing - the half length replica of the Sutton Hoo Ship

Opinions about whether or not the Sutton Hoo ship sailed differ between sailors and non-sailors.  It is difficult for the sailors, whatever their views, to avoid patronising the non-sailors.  Only practised sailors, they will suggest, can understand such things as: the forces on the mast, the stays, the shrouds and the rudder; the significance of a keel, leeway and ‘weather-helm’; the fore and aft position of the mast; the usefulness of being able to sail just that bit closer to the wind; and so forth.

With a following wind , the ship can easily move forward in response.  It can quickly get up to speed without large forces on the rig.  The ship is designed to move in that direction, with the minimum drag from the water.  Once moving with the wind, the force on the sail will diminish, and there will be even less strain on the rig.

When the wind is from the side, the forces on the rig are much greater.  The ship presents a long side to the water, and naturally resists being pushed sideways.  The windward shrouds – the lines from the windward side of the hull to the upper parts of the mast – tighten.  The large force from the wind makes the ship heel.

The effect can be seen in this picture of a modern yacht.

A sailing boat heads towards the lighthouse at the end of the Needles rocks on the Isle of Wight, Hampshire, UK.

The sideways movement of the hull is resisted by a reaction force from the water.  These two large forces, from the wind and from the water, largely oppose each other.  They strain the ship internally, but for the ship as a whole they largely cancel out.  There remains a small net force that moves the ship forwards.

The rig imposes forces on the hull.  One end of each windward shroud is trying to tear itself away from the ship’s side; the other end is pulling the top of the mast downwards, resulting in a large compressive force through the mast into the bottom of the hull.

For the reconstructed Sutton Hoo ship to withstand such forces, the hull would have to be strengthened, and the downwards point force from the bottom of the mast would have to be distributed.  We have no clues from the 1939 remains how this might have been done in the original ship, if it was done at all.  The bottom of the central part of the ship was obliterated by the burial chamber, no fittings for shrouds or stays were seen, and none of the thwarts or their supports were found.

Sutton Hoo ship plan of mid-ships section looking forwards

Some people used to say the ship could not sail because she would just skid sideways over the water.  There is no keel to ‘grip’ the water.  But the side of the hull does offer a lot of resistance.  Look at the 2018 drawing, imagine some heel, and judge for yourself.

More depth to the keel might help, but it is not essential.  That is the point that Edwin Gifford wanted to make with his half-length replica, Sae Wylfing – the photo at the top of the post shows her profile.

To be continued………..

 

Joe Startin speculates – did the Sutton Hoo Ship ever sail – part 2

Did the Sutton Hoo ship ever sport a hefty mast and a big sail? It would help if we knew what the ship was used for.

An expert view is that it could have been a sort of royal barge, a means for the king to project his power and majesty throughout much of his domain.

Raedwald (Julian Illman) in the 2017 production of The King’s River

One’s subjects should be clear about who is protecting them, and who they must pay their taxes to.

As king, it is a good idea to put oneself about and let oneself be seen. But travel overland with a large entourage would have been excruciating. Much of the populace would have lived in settlements up the estuaries, creeks and rivers which permeated East Anglia.

Using a large ship of shallow draft would be a practical alternative. Your bodyguard could show their devotion by rowing you wherever you needed to go.

The coastline would have been quite different then. Land reclamation had not begun. There would have been much more inland water about (particularly when the tide came in.)

Coastline in the area of Sutton Hoo. Modern coastline in feint, bold coastline follows 10 ft. contour. Crosses show sites of medieval churches. Based on an idea by George Arnott. (Drawing: Martin Carver)

A sail would be of limited use when you were winding up and down the rivers. Your oars can shift you in any direction whenever it suits you.

Moving from one river entrance to another would require a passage along the coast. The extra sea-room might allow and encourage the effective use of a big sail. Unfortunately, a large mast does no good for your rowing. The experience of a comparable Viking ship reconstruction was that you would lose a knot because of the windage on it. It would be soul-destroying for your oarsmen if you kept the mast up all the time, but rarely used it. But taking it down while on the water, or putting it up again, would be very risky.

The two photos below show boats with masts being rowed – not difficult in very calm water with no wind against you.  It is also easier if like the Faroese boat on the right, the craft is designed to be dual purpose and your crew has experience of both sailing and rowing.

If you do have a following wind, and you do not have a big sail, all is not lost. The rowers can take a respite simply by holding out their oars. Better still, the skipper could deploy some sort of temporary rig, with a small sail – something quick to raise, and easy to stow away again. This would not be proper sailing of course, but for the oarsmen it would be a blessed relief.

None of this is to say the ship could not sail properly. It is just a way of wondering whether it was worth the bother.

 

To be continued…

 

 

Shipwright’s report – Tim Kirk

12 foot midships model

Since we returned to operations in the Longshed at the beginning of August we have continued training and preparation to begin the actual build of the ship.  Covid has restricted numbers working but we have been able to plank the lower half of the midships model on the port side, using oak from the ‘twisted’ log that we took delivery of in autumn 2019.  Jo Wood, David Turner and Dave Rowley completed the work, including testing two caulking methods – both known to have been used in Anglo-Saxon and Viking period ships. Both methods worked equally well, providing us with something of a conundrum as to which to apply in the ship.

A different team will complete the planking in order to broaden the skill-base within the Ship’s Crew.

The starboard side has been completed in mock-up by Mike Pratt and David Steptoe, using plywood and softwoods.  We are getting on with that so that we can begin the experimental part of the project – investigating the bio-mechanics of rowing the ship. Nothing is known of the internal structure and the rowing positions will have to be derived from various technical procedures.  Jacq Barnard is involving specialists from British Rowing to advise on this aspect of the build.

Oars

We now have one (prototype) oar, made using modern techniques from the ash received last spring from Suffolk Wildlife Trust.  We had to use power tools to shape this oar because the wood had seasoned, and hardened, during the lockdown.   Still, it is a work of art – thank you Simon Charlesworth.  Brian Hunt is constructing a second oar.

Keel and strakes

We have laid a false floor in the Longshed to rest the 12 metre keel log on, in preparation for working it and subsequent cleaving of the garboard strakes (the first planks of the hull).  We will work on the second, curved, log for the stem and stern and keel ends at a new site located at Hoo House Farm (a few miles from Woodbridge).  We have temporary use of a barn similar in size to the Longshed and much of the initial cutting and cleaving of logs will be done there.  We will bring the semi-finished components into to the Longshed for final finishing and assembly.

The supports and false floor ready for the keel log
1:5 model

This model is really important as a source of practical information for the full-size build.  John Cannon and Clive Cartmel have completed battening-out of the planking.  Doing so has raised issues with the layout of the planking – that’s one of the next problems to be solved.  But its much better to identify issues like that now than when we are working on the shipbuild with hefty full-size planks five times as big.

The 1:5 model battened up for planking

Next…

Research continues; very little information exists about Saxon-era anchors and mooring systems.  Vicky Fleming has written a very stimulating research paper on the subject.  Joe Startin continues to lead on our research and has gleaned nuggets of information from the folk at Nydam in Denmark.  I am excited to be writing the dissertation for my degree on the development of the side-rudder, with particular reference of the Sutton Hoo Ship.

The next stages of the build will focus on the conversion of the keel and its extensions (the ‘underlouts’), lofting of the sections of the ship and making the moulds to check the accuracy of the shape as we build.

Many thanks to all those involved and we hope that as we go forward we will again be able to involve more people in the build team. Apologies to anyone whose contribution has not been acknowledged – I really value all the contributions that you make.

Tim Kirk, Shipwright 5:11:20

 

Joe Startin speculates – did the Sutton Hoo ship sail?

Did the Sutton Hoo Ship buried in Mound 1 use a sail?  The conventional wisdom is reflected on the British Museum website. “….it is just not possible to tell if the ship had a mast and was sailed in the open sea, or if it just had oars for rowing along the coast and rivers.”

But the romance of sail is strong.  Edwin Gifford built a half-length replica, Sae Wylfing, to test some of his theories about sailing.  There is a famous (infamous?) picture of her creaming down the Deben taken by Cliff Hoppitt in 1994

Photo of Sae Wylfing on the Deben taken in 1994 (courtesy of Cliff Hoppitt)

Who would want to imagine things otherwise?  It seems unthinkable that the Anglo-Saxons would have been such spoilsports as to forego a mast.

The ‘sailing’ I am thinking of uses a sizeable mast and a big sail.  And it is more than allowing the wind to puff you along from behind.  To be a regular, practical option, you must be able to sail when the wind comes from the side too – you must be able to ‘reach’.There is nothing convincing in the written record to say whether the early Anglo-Saxons were sailing or not, let alone what our particular ship was doing. Scandinavians have plenty of evidence to show that they made brilliant use of sail from about 800CE onwards.  How and when they got to that state is the subject of endless debate.  There is some indication of earlier prowess in pictures carved on standing stones on the Baltic island of Gotland.

Fragment of a standing stone from Gotland

A simple sail, using sheets (ropes) at the corners, starts to appear around 500 or 600, depending on who you believe. The sea-faring kingdom of Dál Riata, covering the NE tip of Ireland, the Inner Hebrides, and the adjacent Scottish coast, was flourishing around 600CE.  Their naval ships were ‘seven benchers’, with two men to each oar.  But they are also said to have had a mast and a single sail as well with 28 rowers.  Alas, Dál Riatans would not have had the slightest contact with East Anglia until Irish missionaries started arriving in the 630s.

There is a strong motivation for merchants to use sail.  If they can turn up somewhere with rare and attractive goods, they might make a killing.  They cannot afford to pay and feed lots of rowers, but they are prepared to hang around waiting for a fair wind.  A shortish, tough, beamy old tub would do for a ship, so long as it could get there.

In the middle of the 6th century, the overland trade route from Byzantium to Scandinavia was interrupted.  Goods went instead via the mouth of the Rhine, and along the coast, through the Wadden Sea, to Jutland and onwards.  The trade grew, becoming dominated by the Frisians.  Emporia (trading settlements) sprouted on the continental side, and had counterparts on the English side too, not least in Ipswich – “England’s oldest  continuously inhabited town” – from about 600CE.

I think sailing would have been around in Raedwald’s time, if only for trade.  And anyway, it would be odd if it had been completely forgotten since the Romans left for good in 410CE.

To be continued…..

Joe Startin