Fishing interaction study

Our client was developing a gas export system in water depths of up to 1300 m. This system involved several pipelines with varying dimensions and properties, and was in an area where trawlers were known to operate.

Data on vessel and gear types was limited, however.  Jee was requested to assess the need for protection of several pipelines by considering the damage which could potentially be caused by trawl gear impact, hooking and pull-over loads.

The scope of work involved the following:

• Gathering of fishing data to ascertain the trawl gear types and speeds which would be encountered
• Calculation of the resulting loads on the pipelines due to trawl gear interaction
• Calculation of the strains induced as a result of trawl gear interaction, according to OTH 561
• Determining the dent sizes which could be caused by the trawl gear, and what effect these dents would have on the pipelines
• A comparison of DNV’s Guideline 13 and RP-F111
• A comparison of the predictions of OTH 561 and RP-F111

We were able to find data on vessels fishing in the area, and determine the types of fishing gear that they were using.  We concluded that the pipelines would be safe for operation for the known and likely future trawler types in the area and no extra protection was needed.  The study concluded that strains due to hooking and pullover would be within acceptable limits and that dent sizes were likely to be acceptable.  Predictions of OTH 561 and RP-F111 were found to be in good agreement.