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Guild sailings
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The preparation It wasn't until May 1999 that the boat was ready to be launched. However, planning had already begun in the autumn of 1998. Teachers from a local school, Hjortspringskolen, had suggested that a couple of classes should take part in the celebrations at the official launch. A local theatre enthusiast had volunteered to be the organiser. The guild set up a celebration committee and the planning and preparations began.The main plan was to roll the boat down to Dyvig in a procession, with the performers dressed in Iron Age costumes.The winter was spent sewing costumes for the school classes and for those guild members who wanted to participate in the festivities. Plans evolved and a choir of singers would participate in priest-like costumes. A song was written to an old Celtic tune from the Isle of Man and it was decided to have the goddess Nerthus participate in a two-wheeled cart pulled by four slaves. (White oxen were not available). It is a well-known fact (at least in the parish of Holm, where Lindeværftet is located) that a bog at the northern tip of Als called Hellesø is the place where Nerthus rises once a year with his cart.The front page of the parish magazine shows this. The front page of the parish magazine Holmboen, showing the goddess Nerthus in her cart. Sources Hvad Haanden former er Aandens Spor. Language The text in this article has been translated from Danish to English using the free DeepL translation programme.
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As mentioned in the section on the organisation of the guild, it was natural to utilise the professional skills and interests of the members. The aim was to gain as much knowledge as possible about the Hjortspring boat, its original shipbuilders and finally, through them, about the community that had created the boat.We were fortunate to have some members who had experience in fluid mechanics, strength calculations and computerised geometry, so already during the preparation of the boat building, the design group started analysing the boat as mentioned earlier. Here we will show some of the calculations that are important for assessing the sailing characteristics. As a starting point, the design team used the drawing that the Norwegian marine engineer Fr. Johannessen had made in connection with the publication of Rosenberg's book about the Hjortspring find. The curve shows the relationship between the amount of water displaced, which corresponds to weight and draught. For example, if the boat is loaded with 2.5 tonnes, it will sink 30 cm. Drawing: HSBL. The wetted surface of the boat, a quantity used when calculating boat speed, was also calculated. The curve shows the relationship between wetted surface and draught. At a draught of 30 cm, corresponding to the weight of 2.5 tonnes mentioned above, the wetted surface of the boat will be 15 m². Drawing: HSBL. By calculating the centre of buoyancy and centre of gravity, the boat's sensitivity to uneven loading was calculated. It turned out that the boat could be expected to be very unstable, a fact that proved to be true in the sailing tests.The power required to propel the boat at different speeds was also calculated. This power is particularly dependent on the wetted surface, its roughness and the length of the boat's waterline. The achievable speed of the boat had been the subject of a heated discussion at a couple of member meetings. Only the president of the guild trusted the abilities of our predecessors so much that he claimed the boat could reach a speed of 8 knots (15 km/hour). A bet was made. However, the calculations could not settle it. Sailing was needed.But back to the calculations. Here we see the power required as a function of speed. At 8 knots, the 20 paddlers need a net power of 2.5 kW or 125 watts each. This equates to 0.2 hp per paddle. Drawing: HSBL. Strength calculations It was also interesting to calculate the load on the boat from the load, buoyancy and wave action. However, a structure as complicated as a boat with its double-curved surfaces is difficult to analyse without using very extensive computer calculations. As we did not have access to a large enough computer, we had to simplify the starting point for the calculations.We therefore considered the boat as a beam tapered at both ends without taking into account that a boat, when loaded, can expand or contract the width of the hull (like a pea pod).The boat is loaded by external forces from the weight of the boat itself, the weight of the cargo (crew with equipment) and finally from the buoyancy forces. The first two act downwards, while the last one acts upwards. These external forces will be in equilibrium. These forces were considered to be single forces attacking the boat from a distance of 1 metre above it.When considering the strength of ships, it is common practice to calculate it in three different modes: It was also interesting to calculate the load on the boat from the load, buoyancy and wave action. However, a structure as complicated as a boat with its double-curved surfaces is difficult to analyse without using very extensive computer calculations. As we did not have access to a large enough computer, we had to simplify the starting point for the calculations.We therefore considered the boat as a beam tapered at both ends without taking into account that a boat, when loaded, can expand or contract the width of the hull (like a pea pod).The boat is loaded by external forces from the weight of the boat itself, the weight of the cargo (crew with equipment) and finally from the buoyancy forces. The first two act downwards, while the last one acts upwards. These external forces will be in equilibrium. These forces were considered to be single forces attacking the boat from a distance of 1 metre above it.When considering the strength of ships, it is common practice to calculate it in three different modes:In still watersRiding a wave amidshipsRiding on two waves with the tops at the bow and stern You use a standard wave with a length equal to the water length of the boat and a height of 1/10 of the wavelength. The boat riding on a standard wave amidships. The resulting forces from weight, load and buoyancy are shown below. It can be seen that in such a wave the boat will be loaded to keel hogging. Drawing: HSBL. For the three load cases, in calm water, with the top of the standard wave amidships and with the two tops of the standard wave at each end of the boat, the tensile, compressive and shear stresses were calculated. The latter were greater at the bottom seam than the seam's permissible displacement when the boat was travelling in standard waves (13 m wave length and a wave height of 0.65 m).Wear and tear on the seam was therefore to be expected when travelling in waves. At the same wave size, the bows would vibrate in the vertical direction with a movement of 30 mm. These calculations do not take into account the expected favourable effect of the tension rope but also the weak sewing seams.We must remember that the calculations are based on the shape of the boat as described by Johannessen. However, Tilia had a slightly shorter waterline due to the more curved keel line. The impact of this change on the stresses was not assessed in these calculations. Fakta Newton, (after Isaac Newton), unit of force in the SI system with the symbol N.The unit newton is derived from the basic units kilogram (kg), metre (m) and second (s) as follows:1 N = 1 kg x m/s²Source: Lex.dk Sources Hvad Haanden former er Aandens Spor.Symposiums: Paper 2: Theoretical Performance and initial Test Results Language The text in this article has been translated from Danish to English using the free DeepL translation programme.
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Axes For splitting the logs, steel wedges and Club hammer were used. Slim beechwood wedges with a top angle of 15º were also used when the steel wedges had opened a large enough gap.Ordinary straight axes, both large forest axes and smaller axes, were used immediately. The axe angle was adapted to linden wood, 25º.The statutes stated that contemporary tools should be used as much as possible in the construction of the boat. However, finds of tools from the Celtic Iron Age are very scarce in Scandinavia.The tool group therefore worked on the philosophy that in a craft like woodworking in boat building, tools have largely only changed with the advent of new tool materials. Accordingly, the group started with tools used for boatbuilding in the nineteenth century. Through literature studies, they then sought to identify similar tool designs from times as close as possible to the Celtic Iron Age.Finds in Denmark from the Roman Iron Age contained several tools that seemed relevant to shipbuilding, tools such as axes, azdes and chisels.In the rest of Europe, tool finds were frequent, especially in the Celtic settlements north of the Alps. As craftsmanship and trade were well developed in Celtic culture, one would expect such tools to have spread northwards.From the Bronze Age, many finds of small bronze carving axes have been found in Denmark.From the first reconstruction of the Hjortspring boat, we became aware of a azde that had been found in a shipwright's toolbox on Gotland. The find is called Mästermyr after the site and was dated to 900 AD. The blacksmith group forged the first Mästermyr axes, which proved to be very useful for removing large shavings during rough levelling of the boards. Den venstre skarøkse er en kopi af en økse fra et vikingfund på Gotland. Foto: H.P. Rasmussen "Hjortspringjern" For fine machining of surfaces, replicas of the Roman Iron Age axes that were found proved to be very useful, especially when shanked as chisels. When shafted as azdes, as indicated by S. Nielsen and J. Lund, they worked less well, perhaps because their shafted form did not provide sufficient weight.As chisels, they became so popular that they were labelled ‘Hjortspringjern’ by boat builders. Facts A bull axe found at Overbygård east of Nørresundby close to the Limfjord in 1977. The find was made in a storage cellar, together with two swords. The period is the earliest Iron Age.Source:Skalk 1978 nbr. 1 p. 3 - 10.Foto: P. Dehlholm Flat and hollow ‘Hjortspringjern’ were used for fine machining. Photo: H.P. Rasmussen Finally, a heavy-duty hollow azde was forged, not because the findings indicated it, but because it was necessary for hollowing out the bottom plank and the stem pieces. Sources Hvad Haanden former er Aandens Spor. Language The text in this article has been translated from Danish to English using the free DeepL translation programme.
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How we got started We started by defining what we wanted and how: Prioritering In any project that contains unknown elements, it is necessary to prioritise a number of parameters or aspects in relation to each other. Not all can be equally important. This is an approach used in the development process at Danfoss. The typical method is to identify 5 parameters, prioritise them by importance and leave the last one as the free parameter to deviate from the plan when difficulties arise.The prioritisation should be understood in the sense that whenever two parameters were competing, the parameter with the highest importance should prevail. In this case, the following parameters were chosen to reflect the objective: to illustrate the functional value of the boat as a gateway to a better understanding of the society of the time, while contributing to the growing understanding of the evolution of boat construction in ancient times.However, it was not the case that we chose these parameters before we started. They emerged through an organic development over the first few years. Quality in all aspects of the project.Seriousness in choosing solutions.Representation of the latest interpretations.Documentation of all actions and choices.Time spent building the boat. The five parameters are prioritised and their content is illustrated below. First, however, let's show an example of the effect of prioritisation. At an early stage, we had to choose which material the boat's planks were sewn together with. True to the Seriousness parameter, we studied the literature to see what materials were typically used for cords in the Iron Age. It seemed that cords made from linden bast were widely used throughout antiquity. Conservator G. Rosenberg, who had excavated the boat in 1922 and described and interpreted the find in 1937, had suggested linden bast cords, not least because a bundle of cords made from this material had been found as part of the find. Some cords were made and a tensile test showed sufficient strength.However, the latest interpretations by the National Museum of Denmark's Marine Archaeological Survey (NMU) suggested that the use of birch roots could be a solution. However, the arguments in favour of this last solution did not seem convincing to us, which is why we ultimately retained lime bast cords as the chosen solution. An example of a different prioritisation than the one chosen here can be seen in the book ‘Roar Linde’, where a scout troop in 1971 built a replica of the Hjortspring boat together with people from Vikingeskibshallen in Roskilde. Here the prioritisation must have been (if we use the same five parameters): Schedule (and money).Tools.Documentation.Quality.Seriousness. The result was a boat that was half a metre narrower than the one the find indicates, with ‘’lamentable‘’ horns and a very rough finish, presumably made for 1/10 of the price of the Tilia. Results from the test have not been published.Differences in prioritisation result in crucial deviations in solutions. Product quality A cleat is cut from a model lying next to it on the plank. Photo: H.P. Rasmussen A lot of work went into obtaining previous descriptions of the boat and finds. These were analysed and discussed in depth. A 1:10 scale model of the boat was made. Every detail of the boat was discussed. Parts were made for the sole purpose of being the subject of discussion.The reasons for choosing solutions often came from other parts of the boat or from other boats.A few choices were so revolutionary that they were labelled hypotheses, or preliminary theories, and the value of the choice would later be examined during testing of the finished boat.Based on the literature, tools were made, tested and modified.An intensive woodworking practice period was carried out with the manufactured tools.. Representation To ensure that the replica would represent the latest interpretation, the guild liaised with various scientists at museums and universities. The guild formed what we called our ‘Scientific Network’. Throughout the project, these scientists were contacted regularly by phone and by visiting the museums.For the first few years, people from the National Museum's maritime department in Roskilde inspected the boat building twice a year to comment on the solutions. The members of the scientific network received the membership folder and regular reports. Archaeologist Flemming Rieck and Thorkild Thomasen from the National Museum of Denmark's Marine Archaeological Survey in Roskilde assess the sample of the boat's centre section. Photo: H.P. Rasmussen In accordance with our prioritisation parameter ‘Seriousness’, the scientists' statements were “taken with a grain of salt”. We were supposed to contribute to increased knowledge about the boat through our work and should therefore represent the latest truth in our interpretation.In other words, the idea was that our work should stand on the shoulders of established knowledge. Documentation From the start, it was considered essential to record all activities and results in print or on photo/video. This attitude is very important in that a finished boat without documentation is just a boat and not a piece of scientific work from which new insights could be drawn.Without documentation, much of the work and money invested would be wasted.The various media that were used as documentation are described above. Most recently, the guild has published a website describing its history and activities (the one you are reading right now).This book is also an example of documentation.The focus on documentation had a crucial impact on the quality of the work.Nobody wants to write a report describing careless choices. The design of the frame systems is discussed during a coffee break. Photo: H.P. Rasmussen Tidsforbrug The time spent building the boat was continuously recorded, so that when people arrived to work on the boat, they signed in the logbook, just as they signed out when they left the shipyard to go home.Coffee breaks were included as part of the work, as they were very much used to discuss solutions to problems.As mentioned, time consumption was counted as the free parameter. The time needed to achieve the best possible result was available. Sources Hvad Haanden former er Aandens Spor. Language The text in this article has been translated from Danish to English using the free DeepL translation programme.
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