Fabrication of pipe bundles offshore

A method of assembling an elongate pipeline bundle offshore aboard an installation vessel, the method comprising:

• suspending the bundle from the vessel so that the bundle hangs in an upright orientation underwater beneath the vessel;
• successively attaching pre-fabricated elongate structural core sections to a corresponding uppermost core section already incorporated into the bundle, in each instance to become a newly-uppermost core section of the bundle;
• each pre-fabricated elongate structural core section comprising a core pipe a guide frame that extends radially outwardly from the core pipe, and a buoyancy block;
• and,
• after attaching each core section, lowering the bundle in a downward launch direction to suspend the bundle from the newly-uppermost core section;
• wherein the method further comprises incorporating a portion of flowline pipe into the bundle aboard the vessel, another portion of that pipe already incorporated into the bundle extending along the bundle beside the successive core sections, by feeding the flowline pipe on a feed path converging with the launch direction and engaging the flowline pipe with the guide frames and the buoyancy blocks of the core sections, that pipe being a flexible pipe, a composite pipe or a rigid pipe.