Duplus
Duplus in the port of Rotterdam, 1972 or -73
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The Duplus was a diving support ship for the oil industry. It was designed and built in the late 1960s for use in the North Sea . Presumably she was the first ship in the world practically built in SWATH construction . After two years of testing and use, it was rebuilt and converted into a hybrid between SWATH ship and catamaran .
history
According to a design by the Dutch design office Trident Offshore, the Duplus was laid down in 1968 as hull number 1033 at Boele's Scheepswerf & Machinefabriek NV in Bolnes, the Netherlands , and put into service in 1969. The client - the NMB (Dutch Society for Offshore Work / Nederlandse Maatschappij voor Werken Buitengaats, later renamed the Netherlands Offshore Company) - hoped that the experimental concept of the ship could also be used in higher seas than was possible with monohull ships of comparable size .
From 1969 onwards, the Duplus was active in the North Sea for diving and underwater work in the oil industry for 15 years. After being sold in 1980, it was registered in Panama as Jaramac 57 . In 1984 it was sold to International Underwater Contractors and renamed Twin Drill . Under this name she was active in the Gulf of Mexico for ten years . After a lengthy lay-in period , it was canceled in 2004 .
Original plans and the original shipyard model of the Duplus are kept in the archive of the Maritime Museum Rotterdam.
description
Two floats, each with a slightly flattened bottom, were connected lengthways to the surface hull with continuous, slender supports. The floats were each connected to a wing fore and aft, which was supposed to increase the stability against pitching. The supports were slim in the waterline and widened again towards the top (towards the working deck).
The surface ship consisted of a deck with living and working rooms that was continuous lengthways and crossways. Its surface formed a largely open working deck. On the working deck above the starboard float there was a superstructure with further working spaces in the first upper deck and the bridge in the second upper deck. Above the port-side float there was a lower structure that covered the engine room. This structure also had a chimney in the middle.
Located in the center of the working deck was a moon pool with a diameter of 7 m for lowering diving equipment between the floating bodies. Above this opening the ship carried a gantry crane with a lifting capacity of 75 t. A jib crane with a lifting capacity of 18 t was located on a platform at the aft end of the starboard superstructure.
The machinery was diesel-electric . Two diesel engines above the port-floating body driven electric traction motors at the stern at the end of both floating bodies. These acted on controllable pitch propellers in Kort nozzles . In the two stabilization surfaces between the floats there were also two Voith-Schneider propellers for precise positioning.
The ship had four anchors , each with its own windlass - a system at each of the four corners of the working deck.
Performance and subsequent modifications
The actual equipment of the ship differed from the planned one. After the first test drives, more and heavier equipment than originally planned was installed on the working deck. As a result, the draft increased by 10%, the ship became more top-heavy and did not fully meet expectations in terms of stability . In particular, the ship was prone to unevenly distributed deck loads. Furthermore, the jib crane could not be used to its full extent when it was swung outboard. Therefore, the owners tried in 1971 to improve the usability through a conversion. On the outside of both supports, the hull was widened outwards so that they were 50% wider in the waterline. The total area in the waterline increased by 65% as a result of the renovation. It was hoped that this would reduce the susceptibility to uneven charge distribution. While this goal was being achieved, sea stability suffered significantly from the conversion. Basically, the conversion meant that the ship was transformed from a pure SWATH ship to a hybrid between SWATH and catamaran.
The original gantry crane over the deck opening was later replaced by a short derrick for sediment sampling and test drilling.
classification
While SWATH ships have been designed with the support of computer simulations since the turn of the millennium, this was not yet possible in 1968. Therefore, at that time the designers could only work on the model with assumptions and investigations. This explains constructive differences to today's SWATH ships, which also had the effect of practical weaknesses of the Duplus:
- the supports, which connected the main deck with the submerged floats, flow over into them at the lower end. This led to the fact that the actually undesirable influence of the wave energy near the water surface on the dynamic lift was greater than necessary. In today's SWATH ships, the supports have a constant cross-section and abruptly merge into the floating bodies.
- To stabilize against pitching movements, two wings were provided between the floating bodies - one near the bow and one near the stern. From today's perspective, these were made very large and very massive. Possibly the wings should also act as struts between the floats to protect the main deck from dynamic bending loads. In addition, the wings had to accommodate the four Voith-Schneider propellers and therefore had to have a certain minimum height. Today's SWATH ships use dynamically controlled fins that are much smaller. The large wings of the Duplus increased drag and fuel consumption, thereby limiting speed. The pictures show that a breaking wave was constantly dragged along behind both wings while driving.
While US Navy designers were still thinking about the first model studies for the SWATH concept, the Duplus was already being used in practice in the oil industry. In 1972, when the Duplus had already been rebuilt for the first time, the construction of the US Navy's first experimental SWATH device carrier, the SSP (semi-submerged platform) Kaimalimo, began . This was launched in 1973. With a displacement of 190 t, it was only about a sixth the size of the Duplus . In Japan, Mitsui Engineering and Shipbuilding built a small SWATH passenger boat in 1977. In 1979 Mitsui put the SWATH passenger ferry Seagull with 670 t displacement into service. This is likely to have been the second SWATH ship that was in productive service.
The Duplus showed both strengths and weaknesses of the SWATH concept in practice. Its strength was the superior stability in sea conditions. Their main weakness was their relatively high sensitivity to changed load configuration. Apparently this effect was underestimated by the designers. This is probably one of the reasons why an originally planned, much larger follow-up draft was never built. The SWATH concept was only implemented successfully around 35 years after the Duplus was launched .
literature
- Boele-Bolnes launch twin-hull craft for offshore work. In: Holland Shipbuilding. Vol. 17 (1968), No. 9 (November), p. 58.
- Tewaterlating catamaran "Duplus". In: Schip en Werf de Zee. No. 25, 35th year 1968, p. 577.
- Twin-hull vessel "Duplus" for Netherlands Offshore Company. In: Holland Shipbuilding. Vol. 17 (1969), No. 12 (February), pp. 54-60.
- Jan L. Arps (Trident Offshore Co.): The Role of the Semi-Submersible Work Vessel In Offshore Production Operations. Fifth Annual Offshore Technology Conference. Houston, TX., USA. April 29 - May 2, 1973.
- Oilman's support fleet. In: Design. No. 296, August 1973, London, UK, ISSN 0011-9245 , pp. 44-45.
- Hull aids Gulf Exploration. In: Popular Mechanics . August 1985, p. 65.
- R. Schönknecht, U. Laue: Unconventional Ships. Transpress, Berlin 1990, ISBN 3-344-00487-5 , p. 52.
- Duplus - the first Dutch SWATH. In: Schip en Werf de Zee. December 2004, p. 19.
