Methods of installing elongate underwater structures

Abstract

The disclosure relates to a method of laying a seabed pipeline from a surface vessel. Pipe strings are assembled from their upper ends from the vessel for attachment in a pipeline extending from the vessel to the seabed. An upper end of a pipe string is attached to a trailing end of a pipeline, the pipeline is guided through a generally semi-circular curved path having an upwardly directed entry and a downwardly directed exit from where the pipeline extends to the seabed. The vessel is moved forwardly while guiding the pipeline around said curved path so that the pipe string passes around the path and is then released in a downwards direction towards the seabed until the trailing end of the pipe string is above sea level. The vessel is then stopped, an upper end of a further pipe string is aligned at the entry to the curved path, the upper end of the further pipe string is connected to the trailing end of the pipeline and then forward movement of the vessel and release of the pipeline from the vessel are resumed to lay the pipeline on the seabed.