Overtrawling of large diameter pipeline trials JIP

Fishermen have been concerned in recent years about the laying of large diameter pipelines in the North Sea.

The perception is that these pipelines could provide an enhanced hazard to safety because they provide a larger obstacle and increase the likelihood of their fishing gear becoming snagged.

To address these concerns the DTI requested that instrumented overtrawling fishing trials with load cells and accelerometers be carried out over the Exxon-Mobil Skene pipeline to confirm that the pipeline did not present an increased hazard compared to existing pipelines, which are up to 40" diameter.

Jee set up a Joint Industry Programme (JIP) to:

• conduct the overtrawling trials, and
• perform model-scale tests that could be used to predict overtrawling behaviour.
• draw conclusions about the safety of overtrawling large diameter pipelines and the ability to simulate full scale results from model-scale tests

The final deliverable was a report that represents the culmination of a series of tasks that have been performed in consultation, and agreement, with the fishing industry and with the participation of the Fisheries Research Services Marine Laboratory.

The benefits to the sponsors and fishermen can be summarised as follows. The work carried out by the JIP showed that:

• There is no fundamental safety problem in overtrawling large diameter (46”) pipelines, and that the risks to fishermen are no greater than overtrawling smaller pipelines
• The pipeline provided no worse obstacle to the fishing gear than that from other natural features, debris and artefacts present on the seabed. It was not always evident from the fishing vessel when the fishing gear crossed over the pipeline.
• Model tests are representative of the full-scale behaviour and that model-scale testing can be used to conservatively estimate full-scale warp forces.