SEARCH

SEARCH BY CITATION

On 15 March 1942, the British merchantman steamer SS Dago was sunk off the Peniche coast, Portugal by three bombs from a German Focke-wulf 200 Condor. Archival sources pointed towards the ship's final location (Survivors' Report: Merchant Vessels, 7 April 1942). However, during an initial survey by a volunteer team of divers in 2007, two steam-powered wrecks were located in the vicinity of the reported coordinates, at a depth of 50 m and about 500 m apart. In order to identify one as SS Dago, a specific approach was required. Similar cases at an equivalent depth were not found in the relevant literature, and only very recently the use of engine comparison in the identification of the wreck of the USCSS Robert J. Walker (Delgado, 2013: 38) came to our attention. For the terminus post quem approach, the Dry Tortugas provide classic examples (Souza, 1998: 49–83), even if a different kind of ship is discussed.

To identify one of the wrecks as SS Dago, two basic approaches were used: first, dating by chronological markers provided by the rapid evolution of steam technology in the 20th century; second, a more classical approach of comparing structural features of the wreck with archived technical documentation regarding the ship. This methodology resulted in the identification of one of the wrecks as SS Dago, and, in our view, could be used in other similar cases.

SS Dago was a 1.757 GT British Merchantman steamer operated by Ellerman's Wilson Line of Hull (Fig. 1), and built in 1902 at Dundee, Scotland, by Caledon Shipbuilding & Co (Copy of Certificate of British Registry, 26 May 1902). It joined the O.G. 80 merchant convoy that left Liverpool on 23 February 1942, set for Gibraltar (Movement Cards, 21 May 1939–9 March 1942). The convoy arrived safely at Gibraltar 8 March (Convoy O.G. 80, February–March, 1942). The ship then left Gibraltar on a solo mission, heading to Lisbon where it stood 9–15 March. On the afternoon of 15 March, it departed towards Leixões (Oporto) with 300 tonnes of general cargo, including soap and machinery, where it was planned to load cork. At 18h30, when preparing to pass Cape Carvoeiro, 3.5 miles (6.5 km) SW of Peniche, the vessel was attacked and sunk by machine-gun fire and bombs from a German Focke-wulf 200 Condor, based at the occupied French base of Bordeaux-Merignac (Survivors' Report: Merchant Vessels, 7 April 1942).

figure

Figure 1. SS Dago 1:100 scale model by Pedro Serrano. (Photograph: author)

Download figure to PowerPoint

Both local divers and members of the fishing community referred to an underwater wreck as ‘The Dago’, but as mentioned previously, in fact there are two wrecks at the site, both steamers, so both were eligible candidates (Fig. 2).

figure

Figure 2. SS Dago's last voyage and Wreck 1 and 2 locations. (Drawing: author)

Download figure to PowerPoint

As both wrecks lie at a depth of 50 m, their study requires a team of certified technical divers, preferably using Trimix and Rebreathers. A team of volunteers matching those requirements was put together to dive on the wrecks. Depth and time precluded the use of an external grid of control points on which to base a detailed survey; instead, datums were limited to those that were strictly essential and positioning was achieved using direct distances and the depth trilateration method. This data included a LAT calibrated zero reference point, in order to offset the amplitude impact of the tide on the survey data. Recording of individual features and areas was achieved using photography and HD video. By these means, and after proving that Wreck-2 was not the ship in question, a 1:100 scale model was produced of Wreck-1 (Fig. 2), that could be correlated with known technical information regarding SS Dago.

In order to define a terminus post quem, two artefacts which could serve as chronological markers based on steam technology were chosen: the boilers and the engine. Furthermore, a comparison between the structures of the wrecks and that of the SS Dago as reported in the General Arrangements and Port Registry technical documents was undertaken. Four measurable features were found which together might enable a positive identification of the SS Dago: 1) the fore cargo hold N.1 hatchway dimensions; 2) the length of the rudder, measured from the point where the main-piece of the rudder enters the hull, in the horseshoe plate, to the centre of the propeller shaft; 3) the length of the ships; 4) the relation between engine height and engine stroke proposed by John Riley (Russo, 2013).

Boilers

  1. Top of page
  2. Boilers
  3. Engine
  4. Hatchway dimensions
  5. A distinctive distance on the rudder
  6. Length
  7. Engine stroke to height ratio
  8. Conclusion
  9. Acknowledgements
  10. References

Boilers can be chronological markers for steamships, because their documented development provides a typology than can be used in relative dating. Both wrecks had two scotch boilers (Fig. 3i), which have the distinctive feature of a diameter larger than their length. Scotch boilers were first used in marine propulsion on the River Clyde (Bertin, 1906: 27), on SS McGregor Laird, built by the shipbuilder Randolf Elder (Powles, 1905: 153) in 1862, so the terminus post quem for the wrecks would be 1862. SS Dago, built in 1902, had two 200 psi scotch boilers (Copy of Certificate of British Registry, 25 November 1909: 10). Both wrecks were consistent with a possible correlation with the SS Dago.

figure

Figure 3. Wreck 1 1: 100 scale model. (Model and photograph: author); a) unidentified element (Armando Ribiero); b) Cargo hold N.1 hatchway (AR); c) and d) SS Dago General Arangements Plan (Dundee City Archive); e) rudder (AR); f) Emergency steering device (AR); g) Triple expansion steam engine (AR); h) Low-pressure cylinder mesured with bespoke callipers (AR); i) Boilers. (Manuel Leotte)

Download figure to PowerPoint

Engine

  1. Top of page
  2. Boilers
  3. Engine
  4. Hatchway dimensions
  5. A distinctive distance on the rudder
  6. Length
  7. Engine stroke to height ratio
  8. Conclusion
  9. Acknowledgements
  10. References

Archival evidence states that the SS Dago had a triple expansion steam engine (Copy of Certificate of British Registry, 25 November 1909: 10). This feature gives a terminus post quem of around 1860, the date from which the use of the compound steam engine was generalized in the shipping industry (Armstrong and Williams, 2011: 8).

Analysing the engines of both wrecks, we found our first discrepancy. Wreck-1 had a triple expansion engine (Fig. 3g), and Wreck-2, had a compound, two-cylinder steam engine. This eliminated Wreck-2 which reverted to its designation Peniche 1, as dubbed by the Portuguese Centre for Underwater and Nautical Archaeology (DANS 2012/01–CNS 33699). However, because the number of cylinders alone could not prove beyond all doubt the identity of Wreck-1 as SS Dago, further analysis was undertaken to substantiate this hypothesis.

The cylinder diameter reported in the Port Registry refers to its internal diameter, but it was only possible to measure the external upper cylinder covers, instead of an exact match the approach was to ascertain a consistent and linear difference. Because cylinder covers were convex or had pressure release valves, measuring tapes were unfit for this procedure and a large-scale calliper instrument was developed and constructed for that purpose (Fig. 3h).

The Port Registry referred to the following cylinder diameters: High-pressure cylinder 20 inches (0.50 m); Intermediate-pressure 33 inches (0.83 m); Low-pressure 56 inches (1.42 m).

Our measurements on the Wreck-1 were: 25 inches (0.63 m), 38 inches (0.96 m) and 61 inches (1.54 m) respectively. The difference was a linear 5 inches on every cylinder, which is consistent with the expected difference between the internal cylinder diameter and the external cylinder cover diameter. These findings support the case for a correspondence between Wreck-1 and SS Dago.

Hatchway dimensions

  1. Top of page
  2. Boilers
  3. Engine
  4. Hatchway dimensions
  5. A distinctive distance on the rudder
  6. Length
  7. Engine stroke to height ratio
  8. Conclusion
  9. Acknowledgements
  10. References

There was one intact hatchway on Wreck-1, a corresponding hatchway in the builder's General Arrangements Plan from the Dundee City Archives was located and compared (SS Dago General Arrangements Plan, no date). This hatchway was in the position of the fore cargo hold N. 1, in the bow near the forecastle (Fig. 3b).

Using the known length of the engine room, 42 ft (12.80 m) as a scale, it was ascertained that the hatchway marked on the general arrangements plan measures, about 18 ft 257/64 in (5.56 m) by 8 ft 75/32 in (2.62 m). The wreck's hatchway measured, 18 ft 9/64 in (5.49 m) by 8 ft 21/32 in (2.49 m), the slight difference may be accounted by ferrous metal corrosion processes or intrinsic scale error.

A distinctive distance on the rudder

  1. Top of page
  2. Boilers
  3. Engine
  4. Hatchway dimensions
  5. A distinctive distance on the rudder
  6. Length
  7. Engine stroke to height ratio
  8. Conclusion
  9. Acknowledgements
  10. References

The distance from the point where the main-piece of the rudder enters the hull in the horseshoe plate, and the centre of the propeller shaft (Fig. 3d, e), was recorded in the ship's Port Registry as 15 ft 71/64 in (4.75 m), and measured under water as 15 ft 83/16 in (4.78 m) in Wreck-1, a difference of 4%. This distance can be a very distinctive characteristic with wide variations depending on the design of the ship. For example, the 1937 SS Biddlestone was 400 ft (121.92 m) long and the propeller-shaft-to-horseshoe-plate distance measured 9 ft 10 in (2.98 m) (Capacity particulars for yard no. 450, ‘Biddlestone’, 1937).

Length

  1. Top of page
  2. Boilers
  3. Engine
  4. Hatchway dimensions
  5. A distinctive distance on the rudder
  6. Length
  7. Engine stroke to height ratio
  8. Conclusion
  9. Acknowledgements
  10. References

The ship was reported as 290 ft (88 m) and the calculated length of Wreck-1 approximates to that value. However, as the wreck is split into two pieces a precise length cannot be given (Fig. 3).

Engine stroke to height ratio

  1. Top of page
  2. Boilers
  3. Engine
  4. Hatchway dimensions
  5. A distinctive distance on the rudder
  6. Length
  7. Engine stroke to height ratio
  8. Conclusion
  9. Acknowledgements
  10. References

John Riley, an iron and steam shipwreck specialist who collaborated in many significant Australian archaeological projects and theories, such as the SS Xantho and the ‘waterline theory’ (McCarthy, 2002: 97), proposed a possible relation between engine stroke and height. According to Riley, the engine height was equal to six times the engine stroke (pers. com.). In SS Dago, the engine stroke was 39 inches (0.99 m) (Copy of Certificate of British Registry, 25 November 1909: 10), and in the Wreck 1 the engine total height was 2329/32 inches (5.9 m). Applying Riley's theory, by multiplying the stroke by 6 we should get the height of the engine: 39 × 6 = 234 inches, a very close correspondence to the wreck's engine height of 2329/32 inches. We considered this consistent with the hypothesis that Wreck 1 is SS Dago.

This correspondence, also led to The Stroke Project (Russo, 2013), which has the goal of collecting data from wrecks, both from Portugal and abroad, in order to test Riley's theory.

Conclusion

  1. Top of page
  2. Boilers
  3. Engine
  4. Hatchway dimensions
  5. A distinctive distance on the rudder
  6. Length
  7. Engine stroke to height ratio
  8. Conclusion
  9. Acknowledgements
  10. References

Chronological markers and terminus post quem, established through the analysis and characterization of technological aspects of the marine steam technology, namely the engine and boiler, used in conjunction with the comparison of technological and structural elements found on Wreck 1 and in the archival records relating to SS Dago, enabled a strong correlation to be established and thus to identify the wreck as the SS Dago.

The method developed and tested here could be used in similar cases, in which the objective is to establish physical correlations, either between a list of wrecks and a ship, as was the case here, or between a wreck and a list of candidate ships. The latter scenario is now the case of the on-going project to identify Wreck 2.

Acknowledgements

  1. Top of page
  2. Boilers
  3. Engine
  4. Hatchway dimensions
  5. A distinctive distance on the rudder
  6. Length
  7. Engine stroke to height ratio
  8. Conclusion
  9. Acknowledgements
  10. References

The author acknowledges the team (Carlos Gomes, Carlos Trindade, João Pedro Freire, Jorge Russo, Luísa Tavares, Manuel Leotte, Nuno Sousa, Paulo Carmo, Paulo Correia, Paulo Costa, Pedro Encarnação, Pedro Ivo Arriegas, and guest photographer, Armando Ribeiro), members of XploraSub and In Silence dive groups. All were volunteers, paid all their own expenses and spent weekends and holidays committed to the project, with disadvantages for their families. The author also would like to acknowledge the local diving industry that provided the team with exceptional quality services and safe dives. A special thanks to John Riley, sadly deceased, for sharing his knowledge of steam technology. And finally to Tiago Fraga for the revising this text.

References

  1. Top of page
  2. Boilers
  3. Engine
  4. Hatchway dimensions
  5. A distinctive distance on the rudder
  6. Length
  7. Engine stroke to height ratio
  8. Conclusion
  9. Acknowledgements
  10. References
  • Armstrong, J. and Williams, D. M., 2011, The Impact of The Early Steamship in Britain. International Maritime Economic History Association: St John's, Newfoundland, Canada.
  • Bertin, L. E., 1906, Marine Boilers—Their Construction and Working, Dealing More Especially With Tubulous Boilers. New York.
  • Capacity particulars for yard no. 450, ‘Biddlestone’, 1937, Short Brothers Ltd, shipbuilders, Sunderland, Collection 1861–1957, Operational Section 1870–1958, Capacity particulars series 1924–1946. Available at the Tyne & Wear Archives & Museums, archive number DS.SH/4/19/36.
  • Copy of Certificate of British Registry, 26 May 1902, Port of Hull, Archives of Ellerman's Wilson Line, First Deposit, Vessels, in Ships' Registry Book No 2: Plans, 53. Available at the Hull History Centre, archive number DEW/10/2.
  • Copy of Certificate of British Registry, 25 November 1909, Port of Hull, Archives of Ellerman's Wilson Line, First Deposit, Vessels, in Ships' Registry Book No 3: Plans, 10. Available at the Hull History Centre, archive number DEW/10/3.
  • Convoy OG 80, February–March 1942, Admiralty: Naval Staff: Operations Division: Convoy Records, Second World War. Western Approaches Convoy packs. OG 80. Available at The National Archives, Kew, archive number ADM 237/562.
  • J. P. Delgado (ed.), 2013, Identification of the Wreck of the U.S.C.S.S. Robert J. Walker off Atlantic City, New Jersey: Preliminary Archaeological Report. NOAA, Maryland.
  • McCarthy, M., 2002, Iron and Steamship Archaeology—Success and Failure on the SS Xantho. The Plenum Series in Underwater Archaeology, London.
  • Movement Cards, 21 May 1939–9 March 1942, Records of the Board of Trade and of successor and related bodies. Registry of Shipping and Seamen: War of 1939–1945; Merchant Shipping Movement Cards. British Ship Name: Dago. Gross Tonnage: 1757. Available in The National Archives, archive number BT 389/9/25.
  • Powles, H., 1905, Steam Boilers—Their History and Development. London, Philadelphia.
  • Russo, J., 2013, The Stroke Project. NAS Newsletter Winter 2013, 4. http://www.academia.edu/2398403/The_Stroke_Project, accessed 7 August 2013.
  • Souza, D. J., 1998, The Persistence of Sail in the Age of Steam. College Station, TX.
  • Survivors' Report: Merchant Vessels, 7 April 1942, Records of the Admiralty, Naval Forces, Royal Marines, Coastguard, and related bodies, Admiralty Survivors' Report: Merchant Vessels. Available at The National Archives, Kew, archive number ADM 199/2140.
  • SS Dago General Arrangements Plan, no date, Caledon Shipbuilding & Co. Available at Dundee City Archives, archive number GB251/RHP60072/112.