Duplus

Duplus in the port of Rotterdam, 1972 or -73

Jaramac 57, Twin Drill

4 Voith Schneider drives, each 220 hp

4 Danforth anchor, 2.5 tonnes weight

75 t capacity

18 t capacity

The Duplus was a diving support vessel for the oil industry. It was designed and built at the end of the 1960s for use in the North Sea. She was probably the first practical built in SWATH design ship in the world. After two years of testing and use, it was rebuilt and thereby converted into a hybrid of SWATH ship and catamaran.

History

According to a draft of the Dutch design offices Trident Offshore Duplus the year 1968 as hull number 1033 at Boele 's Scheepswerf & Machinefabriek NV placed in Bolnes, Netherlands to Kiel and put into service in 1969. The client - the NMB ( Dutch Society for Maatschappij voor Offshore-Arbeiten/Nederlandse works Buitengaats, later renamed the Netherlands Offshore Company) - expected the then experimental concept of the ship, a possible application even at higher seas than in comparable Einrumpfschiffen size was possible.

From 1969 to the Duplus for 15 years in the North Sea worked for diving and underwater work in the oil industry. After a sale in 1980 it was registered as Jaramac 57 in Panama. In 1984 she was sold to International Underwater Contractors and renamed drill in Twin. Under this name, she was ten years in the Gulf of Mexico active. After a long Aufliegezeit it was canceled in 2004.

Original plans and the original model of the shipyard Duplus be kept in the archives of the Maritime Museum Rotterdam.

Description

Two floats, each with slightly lintelled floor were longitudinally associated with continuous, slender columns with the surface vessel. The floats fore and aft, respectively were connected to a supporting surface, which would increase the stability against pitching. The supports were slender in the water line and were up ( the working deck out ) again wider.

The surface vessel consisted of a continuous longitudinal and transverse deck with living and working spaces. Its surface formed a largely open working deck. On the working deck above the starboard float was a building with other work rooms on the first upper deck and the bridge in the second upper deck. Above the port side float was a lower building, which covered the engine room. This structure also contributed to the approximately central chimney.

Located centrally in the working deck there was an opening of 7 m diameter ( moon pool ) for lowering diving equipment between the floats. Above this opening the ship carried a gantry crane with a lifting capacity of 75 tonnes. At the aft end of the starboard structure was on a platform, a jib crane of 18 t capacity.

The machinery was diesel-electric. Two diesel engines above the larboard float driven electric traction motors at the aft end of both float. This seemed to pitch propellers in Kort nozzles. In the two stabilizing surfaces between the floats are still two Voith -Schneider propellers were in addition to the exact positioning.

The ship had four anchors each with its own windlass - one system at the four corners of the working deck.

Performance and later changes

The actual equipment of the ship departed from the planned. After the first test drives more and heavier equipment were as originally provided on the working deck installed. Thus, the draft increased by 10%, the ship was top heavy and did not meet fully the expectations of stability. In particular, the ship was vulnerable to unevenly distributed deck loads. Further, the jib crane could not be used to the full extent when it has been swung overboard. Therefore, the owner tried in 1971 to improve the usability by a conversion. On the outside of both support the hull has been extended outward so that they are wider in the water line by 50%. The total area in the water line increased by the conversion of 65%. Thus it was hoped that a lower susceptibility to unequal charge distribution. While this goal has been reached, the Seegangsstabilität suffered considerably under the tag. Basically, the conversion meant that the ship from a pure SWATH ship became a hybrid between SWATH and Catamaran.

The original gantry crane on the deck opening was later replaced by a short rig for sediment samples and test drilling.

Classification

Be designed during SWATH ships ever since the turn of the millennium with the help of computer simulations, this was not possible in 1968. Therefore, the designers at that time could only work with assumptions and investigations on the model. This explains differences in design to today's SWATH ships, which affected also as a practical weaknesses of Duplus:

• For stabilization against pitching two wings were provided between the floating bodies - one near the bow and near the stern. These were carried out from today's perspective, very large and very massive. Maybe the wings should also serve as struts between the floats to protect the main deck forward of dynamic bending loads. In addition, the wings had to take out the four Voith-Schneider propellers, and to have a certain minimum height. Today's SWATH vessels use dynamically controlled fins, which are much smaller. The large wing of the Duplus increased the resistance and the fuel consumption, and limited so that the speed. In paintings can be seen that momentum behind both wings continually has a breaking wave was dragged along.

While designers of the U.S. Navy still discussing first model studies on the SWATH concept that Duplus has already been used in practice in the oil industry. In 1972, when the Duplus had already been rebuilt for the first time, began in the United States, the construction of the first experimental SWATH equipment carrier of the U.S. Navy, the SSP ( Semi-submersible platform / semi- submerged platform) Kaimalimo. This was in 1973 by the stack. With its 190 t displacement, these only about one-sixth as large as the Duplus. In Japan, a small SWATH passenger boat was built in 1977 by Mitsui Engineering and Shipbuilding. In 1979, the SWATH ferry Seagull was put into service with 670 t displacement of Mitsui. This was probably the second SWATH ship, which was in productive service.

The Duplus showed both strengths and weaknesses of the SWATH concept to practical. As a strength, the superior stability proved in a seaway. Their main weakness was the relatively large sensitivity to changes in load configuration. Apparently, this effect was underestimated by the designers. Probably also because of an originally projected, much larger successor design was never built. It was not until around 35 years after the launch of the Duplus the SWATH concept was really successfully implemented.