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World's OFFSHORE VESSELS

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    Here is the latest and best American built Offshore vessels, the MPSV Harvey Blue Sea:
    https://www.youtube.com/watch?time_c...&v=tvrXVEkoa8U
    Designed by VARD Marine in Vancouver BC with a lot of foreign equipment, but somehow Jones Act compliant as long as it is built in USA, owned by an American company and crewed by Americans.
    These vessels are trying to compete with foreign vessels like the Normand Maximus for work in the US Gulf of Mexico.

    PS> The Harvey Blue Sea was named "Boat of the Year" at the Workboat Show in New Orleans recently: http://gcaptain.com/harvey-gulfs-new...eid=4674ba0fbe

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      I havn't been involved with pipe laying for quite some time and never with J-lay System in DP mode, but the principles for positioning are not that different from the old style S-lay system and anchors to move the barge along a planned trajectory. In both cases tensioners are key. The difference is how tension is maintained for a controlled lay down and touch point.
      Max. Tensioner capacity is always specified on the marketing brochure for any pipe layer.

      Difference between S-lay and J-lay systems:
      https://anakkelautan.wordpress.com/2...s-lay-methods/
      PS> Nice to see that the pictures used to illustrate the two systems are barges I have spent some time on board; LB 200 (now defunct) and Micoperi 7000 (Now Saipem 7000)

      But the question was about the way to ensure that the pipelay vessel move as required (IOW: maintain tension in the pipe to avoid buckling) and the method used for positioning:
      In case of Vertical Lay System (J-Lay) laying spooled pipe or cable from reel(s) the vessel maintain tension using engine power, DPS to maintain trajectory and DGPS to check position at all times. A second vessel may be used to check the "right-of-way" ahead of the pipelayer, or to ensure that the pipe/cable has been positioned correctly on the seabed, especially if there are prepared ditches for burrowing, or free-span that has been filled in.

      The speed of movement and engine power required to maintain tension is dependent on several factors. If laying spooled pipe/cable it is a continuous process, but if sections of pipes have to be welded in "on the fly" it is more dependent on the skills of the welders and whether "single jointing" or "double jointing".
      The LB 200 used double jointing, where 2 x 40' pipes (joints) were welded together and checked "off-line", than transferred to the "firing line" to be welded onto the completed pipeline, before going out over the stinger. When the Pipe Foreman sounded an alarm that he was ready to move, the Tower Operator would engage the 12 anchor winches and move the barge ahead 80', always maintaining tension, while the Tensioner Operator would ease up to allow the pipe to move. This would be repeated abt. every 15 min. on a good day with few repairs due to faulty welds.

      How they keep the right tension in the string of pipe/cable when J-laying in deep water? I'm not entirely familiar with this, but with all the computer power available on such vessels, I assume that the required tension is continuously calculated based on water depth and weather conditions etc. and monitored at the tensioners.
      The DP system ensure that the propulsion power required to maintain tension is always applied.
      Side thrusters ensure that the vessel maintain position and move along a predetermined line.
      A ROV may be deployed to check that the route ahead is free from obstruction.
      A second ROV may be deployed to check that the touchdown point is as per plan, if required.
      The DP system have a "Follow me" function, with the ROVs either following the ship, or the ship following the ROV, whichever is best.

      Some detail of the various NOV supplied Pipe Lay Systems:

      J-lay System:
      https://www.nov.com/Segments/Rig_Sys...ay_System.aspx

      Reel-lay System:
      https://www.nov.com/Segments/Rig_Sys...ay_System.aspx

      Vertical Lay System:
      https://www.nov.com/Segments/Rig_Sys...ay_System.aspx

      Horizontal Lay System:
      https://www.nov.com/Segments/Rig_Sys...ay_System.aspx

      The key component in all the above systems, Tensioners:
      https://www.nov.com/Segments/Rig_Sys...ensioners.aspx

      PS> The Normand Maximus has a Huisman system, but the principles are the same.

      Comment


      • Clipper
        Clipper commented
        Editing a comment
        Thanks Ombugge. I've had a quick read and will come back to do some more learning after Christmas when I'm significantly less busy.
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