Esbjerg Maritime Survey Reports 1
SURVEY REPORT Cuxhaven BSH-Nr. 1557
Cuxhaven BSH Nr. 1557 Survey Report 2012-01
University of Southern Denmark Maritime Archaeology Programme
Esbjerg Maritime Survey Reports 1
Edited by: Jens Auer
Written by: Jens Auer Massimiliano Ditta Margaret Logan
Published by: Maritime Archaeology Programme University of Southern Denmark www.maritimearchaeology.dk
Š Copyright
Maritime Archaeology Programme, University of Southern Denmark
Acknowledgements The authors would like to thank the Arch채ologisches Landesamt Schleswig Holstein (ALSH), and especially Dr Martin Segschneider for providing Maritime Archaeology Programme students with the opportunity to apply their skills in a practical recording project. Many thanks also go to Dr Jenny Sarrazin and the staff from the Shipwreck Museum Cuxhaven for taking the time to give us an exclusive tour around the shipwreck museum and providing dearly needed refreshments! Project Participants:
Jan Fischer (ALSH), Jens Auer (Lecturer USDMAP)
Massimilano Ditta, Victoria Hawley, Margaret Logan, Dominic Tomasi, Caroline Visser (Students USDMAP)
Contents 1. Introduction....................................................................................................................................................... 1 2. Methodology...................................................................................................................................................... 2 2.1 Recording by total station............................................................................................................................2 2.2 Photogrammetry.........................................................................................................................................3 2.3 Attempt at a reconstruction.........................................................................................................................6 3. Description of the timber structures................................................................................................................... 6 3.1 Section 1.....................................................................................................................................................6 3.2 Section 2.....................................................................................................................................................8 3.3 Summary.....................................................................................................................................................8 4. Conclusion.......................................................................................................................................................... 9 5. References........................................................................................................................................................ 10
v
Cuxhaven BSH Nr. 1557
vi
Introduction
1. Introduction By Jens Auer
On February 14th , 2012, the Maritime Archaeology Programme of the University of Southern Denmark (MAP) was approached by Dr Martin Segschneider from the Archäologisches landesamt Schleswig Holstein (ALSH) and asked to record and assess a number of ship timbers, which were kept in the yard of the Wasser- und Schiffahrtsamt Cuxhaven (WSA). The timbers had been lifted accidentally by the WSA during the recovery of a drifted buoy in the river Elbe near St. Margarethen (Figure 1). The ship timbers most likely stem from a known wreck site, BSH-Nr. 1557, located at river kilometer xxx, xxxxxxxxxxxx, xxxxxxxxxxxx (DDM,WGS84).
Wreck site BSH-Nr. 1557 was last surveyed using sidescan sonar and a diver in 2006 (BSH shipwreck register BSH-Nr. 1557). The wreck is described as an unknown wooden wreck with an approximate length of 35m and a width of 6m.
It is lying in a 20° (bow) - 200° (stern) orientation directly on the steep slope of the dredged shipping channel. The highest part of the wreck is the stempost at a depth of 12.1m. The stern is either destroyed or buried at a depth of 23.9m. The starboard side is well preserved with frames upstanding by 1.5m, while the portside cannot be recognized anymore. A number of wooden elements are protruding from the midship area.
A single day survey was planed for March 20th 2012. Present during the survey were a MAP lecturer (Jens Auer), five MAP students (Massimilano Ditta, Victoria Hawley, Margaret Logan, Dominic Tomasi, Caroline Visser) and an archaeological technician from the ALSH (Jan Fischer). The survey team was supported by Dr Jenny Sarrazin from the shipwreck museum in Cuxhaven and her team. The survey aimed at assessing the timbers and producing a short report. In order to do so, a written description of the wreck timbers was sup-
Figure 1: Ship timbers from wreck BSH-Nr. 1557 on deck of the WSA vessel on the river Elbe after lifting. The two separate sections encountered during recording are clearly visible. Wasser- und Schiffahrtsamt Cuxhaven 2012.
1
Cuxhaven BSH Nr. 1557 plemented with photographs. As the wreck timbers consisted of two structurally intact timber sections, it was decided to use a total station for three-dimensional recording and also carry out a photogrammetry trial (see section 2).
2. Methodology By Massimiliano Ditta
The primary aim of the present survey was to record the timber structures to a sufficient standard to allow an archaeological assessment. However, the complex timber structures were also a perfect subject for field testing and comparing different recording techniques. In addition to using the well-tested combination of total station for three-dimensional recording and sketches/ drawing and photography for the recording of technical details, an experimental photogrammetry based recording method was tested. Due to time restrictions, the heavy timber sections were recorded in situ and not moved or
turned. Although this meant that some details were hidden, the main constructional features could be recorded as one timber structure was facing withe the inside turned upwards, while the second structure was facing the opposite way.
2.1 Recording by total station
A Leica TCR 407 reflectorless red laser total station was used in combination with Rhinoceros3D 4.0 CAD software and the termite plugin (Hyttel 2011) to allow real time recording of three dimensional data.
Points recorded with the total station either in reflectorless mode or with the help of a prism, are imported into the Rhinoceros3D CAD software via the termite plugin, and can be connected to polylines and/ or processed with the standard drawing tools available in the software in real time. Data can be recorded on separate layers and annotated.
By moving part of the often laborious post-processing into the field, this method provides a fast and efficient way of recording complicated threedimensional structures with one or two operators (Figure 2).
Figure 2: Steps in the recording and modelling process. Above recording by hand and total station. Below raw total station data in Rhinoceros3D and processed results. Ditta 2012
2
Methodology To save time, technical details were recorded using photographs and sketches as well as hand written annotations.
2.2 Photogrammetry
This experimental technique is essentially based on two software technologies called SFM or Structure-from-Motion, also erroneously called Photogrammetry, and Image-Based-Modelling.
SFM aims to determine the parameters of a camera (position and orientation of the trigger points) and to produce a cloud of points at low density from a simple collection of images taken around the object in question, while Image-Based Modelling allows to obtain a reconstruction of the scene creating a cloud of high density points starting from a simple collection of images.
The combination of these two software methods provides a powerful tool, which, with the assistance of surface reconstruction software, is able to produce a high-definition 3D model of an object or a context from a collection of images. These concepts are not new and have their roots
in the 1980’s. Since then several commercial applications were developed. However, in the recent years, the development of open source software packages led to the availability of low cost alternatives to expensive proprietary software.
In this case a free open source solution running under Microsoft Windows has been chosen since the purpose was to test a free and accessible photogrammetry tool. Photosynth (http://photosynth.net) mixes techniques of Structure-from-Motion and ImageBased-Modelling to create a point cloud of the photographed object. The data resulting from the processing with Photosynth were subsequently acquired, cleaned and meshed with the help of an open-source software application called Meshlab (http://meshlab.sourceforge.net/), an application created to manage point clouds and allow surface reconstruction and texturization (Figure 3 and 4). The dataset of pictures was taken with two different digital SLR cameras, a Pentax K-5 with a 50 mm fixed prime lens and an Olympus E-500 with
Figure 3: Photosynth pointcloud of the timber fragments after cleaning in Meshlab. Ditta 2012
Figure 4: Result of the point cloud based texturized surface reconstruction in Meshlab. Ditta 2012
3
Cuxhaven BSH Nr. 1557 a zoom lens at 24 mm focal length. The pictures were taken around the timber structures in an attempt to cover every angle and blind spot.
The results obtained with the method described above are not referenced to real time measuring units although proportions are maintained. For this reason the resulting point cloud had to be scaled using known reference points, which in this case were available due to the total station recording. Overlaying both, the point cloud and the model resulting from total station recording showed a remarkable correspondence (Figure 5). Moreover, the combination of the two models provides a more understandable overview of the timber structures, as both, geometrical information and interpretation (total station) and visual
information become available to the viewer.
To conclude, the use of the open source photogrammetry methodology allowed rendering a precise 3D model of the object in question with a minimum expenditure of time and money.
Furthermore the accessible and user-friendly nature of the methodology used in Cuxhaven could enable operators with little experience to obtain excellent results. However, in order to obtain a measured model by using solely the photogrammetry methodology discussed above, reference points have to established, clearly marked and measured in relation to each other.
Figure 5: 3D surface resulting from Photogrammetry merged with the data recorded by total station. Both data sets show a remarkable correspondence. Ditta 2012
4
Methodology
Figure 6: Simple reconstruction of the original position of the timber structures in Rhinoceros3D. Ditta 2012
5
Cuxhaven BSH Nr. 1557 2.3 Attempt at a reconstruction
A simple attempt of reconstructing the original position of the timbers recovered from the river Elbe has been carried out (Figure 6). Using the information collected with the total station and the resulting 3D model, it was attempted to reposition the starboard and port side elements in Rhinoceros3D based on a first interpretation of the timber structures. The extension of the sheer line of the keel is based on the hypothetical maximum height of the keel itself given by the draft marks. Although very hypothetical, a simple reconstruction like this can help to visualize and understand elements recovered from shipwrecks.
3. Description of the timber structures By Margaret Logan & Jens Auer
The wreck remains surveyed in the yard of the WSA in Cuxhaven consist of two separate timber sections, which are referred to as section 1 (the larger of the two) and section 2. Both sections were originally joined to form part of the bow structure of a wooden vessel (Figure 8).
3.1 Section 1
Section 1 is comprised of a stem-post and apron with four framing elements attached on the star-
board side. The stem post measures 5.46 m in length and has moulded dimension of 19cm and a sided dimension of 31cm at the head and a moulded dimension of 26cm and a sided dimension of 27cm at the foot. The apron has a moulded dimension of 26cm and a sided dimension of 30.4cm.
Both, apron and stem post are cut at an angle at the head, probably to receive the bowsprit. The stem post ends with a fresh break at a scarf joint, while the foot of the apron is cut square and would have butted against another part of the apron extending further down. However, the lower part of the apron is recessed for what appears to have been a scarf joint at some point. The resulting gap has been filled in with a chock, also cut square at the bottom end. This might be the result of a repair to the apron (Figure 11). Stem post and apron are joined with iron bolts, 4cm in diameter. The stem post rabbet, which is cut to receive planks with a thickness of 7cm (top) to 10cm (bottom), starts 80cm from the head of the post. The hooding ends of the outer planks were attached with a combination of iron and copper alloy bolts, eight of which are still discernible, spaced 18cm apart. 135cm from the head of the stem post, an iron band or brace is recessed into the post (Figure 9). It measures 8cm in width and is approximately 5.46m
Hawse pipes
Section 1
Hawse pieces
Knight head Apron Stempost
Draught marks
Rabbet Metal reinforcement Hawse pieces
Knight head
Section 2
Outer planking w. hawse pipes
Figure 8: Annotated plan of the timber structures, based on the results of photogrammetry and total station recording. Not to scale. Auer 2012, based on Ditta 2012.
6
Description of the timber structures 1m long. The iron reinforcement could represent the cheek and would have served to support the chocks forming the knee of the head.
Another iron reinforcement, which extends from the stem post has an iron pulley affixed to the end. The band is 7cm wide and 1cm thick and is bent out of shape. The pulley is approximately 12cm in diameter. The pulley might be connected to the bobstays or martingale guys.
81cm from the foot of the stem post, four draught marks are discernible: the numbers 6, 7, 8, and 9. The 7 and the 8 are in good condition (Figure 10), while 6 and 9 are heavily eroded. The numbers are uniformly 16cm in height and appear to be made of lead. They are nailed to the moulded side of the stem post with round-headed copper alloy nails. The distance between the bottom of the numbers varies between a minimum of 30.8cm and a maximum of 31.5cm, probably as a result of distortion and drying of the timbers. A large broken piece of timber, measuring 32cm by 24cm, is bolted to the inner face of the apron with iron bolts. This is probably the remains of a breast hook.
On the starboard side of the stem post, a knight head and three hawse pieces remain in situ. The
Figure 9: Iron reinforcement recessed into the stem post. USDMAP 2012
Figure 10: Draught mark No 7 nailed to the stem post. USDMAP 2012
Figure 11: Foot of the stem post. The fresh break at the scarf joint is clearly visible. The apron is cut square and a possible former scarf has been filled in with a chock. USDMAP 2012
7
Cuxhaven BSH Nr. 1557 knight head, which would have supported the bowsprit, extends higher than the hawse pieces and measures 22cm moulded by 20.8cm sided. The adjoining hawse pieces measure 16cm moulded and 18cm sided on average. The heads of both hawse pieces and knight head are cut square, while the timbers are eroded or broken at the bottom (Figure 12).
Trenails and trenail holes in the hawse pieces have an average diameter of 3.5cm and are evidence of the attachment of ceiling planking and outer planking. Some of the trenails were secured with a single square wedge. Two iron hawsepipes have been set into the hawse pieces. The inner hawsepipe has an outer diameter of 32cm and a hawsehole of 12cm diameter. The outer hawsepipe has a diameter of 20cm with a hawsehole of 12cm diameter. A small iron chain concreted to the outer hawsepipe, might be related to the standing rigging of the bowsprit.
3.2 Section 2
The second assemblage of timbers originates from the port side of the vessel. It is a mirror image of the section still attached to the stem post and consists knight head and three hawse pieces, held together by planking around the hawse pipes. The two fragments of outer planking measure 42cm and 26cm in width respectively. Both
planks are 7cm in thickness, which matches the size of the stem post rabbet at the position where section 2 would attach to section 1. The dimensions measured on section 1 also apply to the timbers on section 2. However, on section 2, the lower ends of the hawse pieces are preserved. These are cut square. All timbers are made from oak and the ends of post, apron, hawse pieces and knight heads are boxed.
3.3 Summary
Section 1 and 2 form the upper part of the bow of a wooden sailing vessel built from oak. Both sections were originally joined, and a fresh break at the foot of the stem post as well as bent iron bolts and protruding intact trenails can be seen as evidence that the bow section was in situ and fairly well preserved before the forceful accidental recovery. Timbers on the port side are slightly better preserved than those on the starboard side.
Figure 12: Heads of the knight head and hawse pieces on the starboard side. The metal band with attached pulley can be seen on the right hand side. A hawse pipe is visible in the background. USDMAP 2012.
8
Conclusion
4. Conclusion By Jens Auer
The two timber sections represent the remains of the upper bow of a wooden sailing vessel built from oak. They were accidentally lifted from the site of shipwreck BSH-Nr 1557, which is described as an unknown wooden vessel with the preserved bow forming the highest, and thus also most exposed section of the wreck. It would appear that the mooring chain of buoy got entangled around the stem post, which led to the accidental recovery of the bow section. The ship timbers are generally well preserved, with slightly better preservation on the port side. The level of preservation of the lifted timber section is probably indicative for the remainder of the wreck which is described as lying on the steep slope of the dredged shipping channel with a well preserved starboard side and the stern either buried or disintegrated. The port side is said to be missing, however, judging by the preservation of the port side part of the bow section, at least the forward part of the port side must be preserved.
The scantlings of the surveyed ship section are indicative of a larger vessel with a length of around 30m or more (Auer et al. 2008; Adams et al. 1990; Mcgregor 1984). The lowest draught mark, the number 6, would have been 6 foot above the lower end of the keel, which based on the measured distance between the draught marks would have been around 1.8m. This added to the total measured length of the stem post, 5.46 would give a total height of the post of 7.26m, a substantial size. The double hawse pipes would also speak for a larger vessel size (Mcgregor 1984; Mcgregor 1986; Gardiner 1993). This corresponds well with the observations in the BSH shipwreck register, stating that the wreck has an approximate length of 35m.
The construction features provide a number of pointers as to the date of the wreck as well. The iron sleeves in the hawse holes indicate the use of chain cable, which was introduced into the Royal Navy in 1817, but in use from the beginning of the 19th Century (Goodwin 1987). The general construction with mainly wooden elements fastened with a combination of trenails, copper alloy bolts and iron bolts and strengthened with metal reinforcements is typical for the first quarter of the 19th Century as well. Throughout the 19th Century an increase in the use of iron can be noted,
finally culminating in the construction of hybrid and later iron and steel vessels (Gardiner 1993; Mcgregor 1984; Mcgregor 1986). It would seem that wreck BSH-Nr. 1557 was built in the first quarter of the 19th Century. In addition to allowing establishing the height of the stem post, the surviving draught marks also provide clues as to the origin of the shipwreck. Instead of the Roman numerals common in English shipbuilding, Arabic numbers were used. The measured spacing of 30.8 to 31.5cm between the numbers is closest to the Rhineland foot of 31.385cm, which was used in Prussia from 1816 and became the standard foot measure in the whole of Northern Germany after 1867 and until 1872 (Rabbel 1983). A similar definition of the foot also applied to Denmark and Norway. Based on the spacing of the draught marks, the most likely origin of the shipwreck is therefore either Northern German, or Danish/ Norwegian. Taking into account the location of the wreck near the Elbe pilot station Bösch, which was established in 1749, it seems unlikely that the wrecking of a large sailing vessel would go unnoticed.
A quick check of the German investigations of shipping accidents, Entscheidungen des OberSeeamts und der Seeämter des Deutschen Reiches (Reichsamt des Inneren 1879), which were published from 1878 onwards did not produce any results or likely candidates for the years 18781900. However, a more detailed archival search in Hamburg or Schleswig-Holstein might allow the identification of the wreck in question.
9
Cuxhaven BSH Nr. 1557
5. References
Adams, J., van Holk, A.F., & Maarleveld, T.J. 1990. Dredgers and Archaeology. Shipfinds from the Slufter. Alphen aan den Rijn.
Auer, J., & Belasus, M. 2008. The British Brig “Water Nymph” or ... even an Englishman cannot take the liberty to deride a civil servant on German soil. International Journal of Nautical Archaeology 37(1): p.130–141. Gardiner, R. ed. 1993. Sail’s last century: the merchant sailing ship 1830 - 1930. London: Conway Maritime Press.
Goodwin, P. 1987. The Construction and Fitting of the Sailing Man of War 1650-1850. London: Conway Maritime Press.
Hyttel, F. 2011. Digital Recording in Maritime Archaeology: Total station, Rhinoceros and Termite. Master Thesis. Esbjerg: University of Southern Denmark. Mcgregor, D. 1984. Merchant Sailing Ships 1815-1850. Supremacy of Sail. London. Mcgregor, D. 1986. Merchant Sailing Ships 1850-1875. Heyday of Sail. London. Rabbel, J. 1983. Rostocker Windjammer. Rostock: Hinstorff.
Reichsamt des Inneren. 1878-. Entscheidungen des Ober-Seeamts und der Seeämter des Deutschen Reichs. Hamburg: Friederichsen.
10