Hydrographic Society Benelux
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Hydrographic Society Benelux

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HSB Workshop
‘Hydrography in Deep Water’, the theme of the HSB workshop on 12th December in Delft, attracted five interesting papers and an audience of eighty. The programme aimed to provide an overview of recent achievements and near-future challenges, starting with the surveyor’s viewpoint, and on via pipe-laying engineering and rock-dumping to a climax in visualisation. The importance of the hydrographic trade is underlined by significant technological developments in deep water. Did we not reserve oceanography for deeper water? Hydrography is perhaps seen as a commercial variety of oceanographic science, at a different level of interest to man. Anyway, the five presentations are summarised below. The photograph shows all but one of the speakers.

Brian Beard of Noordhoek Offshore presented the route survey of the Blue Stream project in 1997, carried out by NeSA, later Thales Geosolutions (and, very recently, Fugro). The pipeline from Russia to Turkey, at approximate heading 210¡ across the eastern Black Sea, was installed by Saipem using J-lay. The central part of the route crosses the abyssal plane at a depth of 2150m. The slopes on either side provided even more challenges and more than 2,300 hours of ROV survey were needed to cover the route. Many ROV systems were specially developed or adapted for the project. Given the time-consuming dive and recovery of the sub (two hours each), all systems were checked with particular care prior to a dive, which resulted in 97 per cent efficiency of the time spent at sea.
Peter Aarts of Fugro Survey met ‘the challenge of nature’ by discussing the critical role AUV surveys play in integrated site investigation and geo-hazard assessment. Two interesting short films showed an experiment in which hydrates turn into gas under atmospheric conditions on deck, and the launch and recovery of the Fugro AUV respectively. Some hazards encountered in deeper waters are rugged, steep, rocky topography, shallow geo-pressures, gas and gas hydrates, faults, landslides, fluid vents, strong currents and erosion, salt tectonics and seafloor deformation. In particular for small-area site surveys in deep water, AUVs are much better suited than ROVs or towed bodies.
After two surveyors, it was time for a different perspective. Remmelt Heemskerk is, as senior naval architect at Allseas, responsible for vessel stability and movements, structural and design aspects, in particular during conversions. Many offshore surveyors came across Solitaire, Lorelay, and/or Trenchsetter, pipelay vessels designed for S-lay installation. The deepest lay was at over 1,900m. Because of their enormous day rates (for Solitaire appr. Û 0.5M) every emphasis is placed on speed. At best, installation speeds of 9 to 10km per day are possible. The speaker revealed how when any partial operation, including survey assistance, causes delays to the installation process the atmosphere immediately becomes tense. Nevertheless, installation engineers depend strongly on data provided by ‘the survey’.
Once installed, many pipes need covering by stone. Rock dumping is the specialisation of Van Oord ACZ. Clive Skelhorn showed how ever-increasing depths only marginally influence the accuracy achieved when positioning rock over pipes. The sensors are effectively at the same distance from the seabed at any depth. Sensors on the fallpipe ROV are mounted on two carefully designed frames to each side of the vehicle. The major problem is the length of steel wires on which the ROV is suspended. At depths of several hundred meters steel wires gradually turn into elastic bands. Despite some fluctuating artefacts in the presentation of flat seabeds, accuracy of 10cm at 350m has been achieved, as shown by a four-inch umbilical clearly visible crossing a long stretch of flat seabed.
Peter Stevens and Andy Smith of Sonar Reseach and Development presented the final paper. In an entertaining exchange of anecdotes and images they showed the current possibilities of 3D visualisation. Undoubtedly a requirement exists for many underwater applications to have a detailed view of what is going on in real-time. Using knowledge of shapes and forces, in combination with existing seabed data and online acoustic measurements, operating ROVs and the like turns into an arcade video game. The discussion following on the paper concerned the way in which the surveyor’s requirement for complete quality control may be satisfied while watching the scenes. This issue remains to be addressed in close detail.

It was an enjoyable afternoon. The presentations are available for downloading from www.
hydrographicsociety.nl.

Agenda


  • 13th February 2004: AGM, Delft
  • 16th April 2004: Corporate workshop Noordhoek Offshore bv. Zierikzee
  • 18th June 2004: Ecology, Environment and Hydrography, Antwerp
  • 8th September 2004: Corporate workshop Simrad bv. Rotterdam
  • 15th October 2004: Airborne survey, Delft
  • 10th December 2004: Oceanography, Delft


Contact
Hydrographic Society Benelux
Att. T.H. Heringa
Postbus 175
1970 AD IJmuiden
The Netherlands
Tel: +31 255 545 622
Fax: +31 255 545 645
[email protected]
www.hydrographicsociety.nl

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