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Jee Star Logo Overtrawlability trials of a subsea structure

Overtrawlability trials of a subsea structure

The problem

Our client required a study of the interaction between a protection structure for a wellhead and fishing gear. The structure had a protruding feature, which was designed to protect a tiein location for a number of months before the pipeline was connected to the manifold.

The final design had to meet the Norsok U-001 guidelines on overtrawlability.

The solution

We developed a scale model of the protection structure and a test procedure based on the client’s fishing gear interaction studies. Preliminary tests identified a minor snagging feature. We then re-designed the structure to avoid catching, before the flume tank trials.

Once the re-design had been implemented, scale model tests of trawl gear and nets passing over the structure were run at the flume tank. These were filmed on three cameras in different orientations around the tank to allow a detailed examination of the behaviour of each gear as it passed over the structure. To aid the analysis, the loads in the warp lines were also recorded.

During the flume tank trials, unacceptable behaviour was seen with a specific type of net. Using the video footage we were able to identify the exact snag points and re-design the affected areas. After further testing, the structure was deemed overtrawlable.

The benefits

We provided clear visual and analytical results from the scale model trials, allowing our client to understand the causes of the snagging and work with our engineers to quickly develop a solution.

We liaised with the verification agency who were on-site during the project, giving our client confidence the project would run smoothly and meet Norsok U-001 guidelines.

Our flexible and reactive approach allowed us to progress the project quickly, enabling the client to meet their time sensitive target schedule.

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