Anchor demonstrates extreme holding power in very hard soilsEquipment & Technology // October 2, 2017
Vryhof has successfully completed extensive field tests with the STEVSHARK REX anchor in Australian waters, proving its suitability for hard soils and carbonate rocks. The new anchor has a new fluke and shank geometry.
In 2016 a total of 15 tests were successfully carried out at three locations in the North Sea known for their anchoring problems with stiff clays. In early 2017 the new anchor was used in the United Arab Emirates by a rock cutter suction dredger on cemented soils. The results received from this site were also very positive.
For the most recent test Vryhof selected test sites offshore Australia in close collaboration with Woodside Energy.
“We were very interested in getting the test results of the STEVSHARK REX anchor in remote and challenging territories such as the Angel Field in the North West Shelf of Australia with complex cemented soils of carbonite origin or calcarenite to calcilutite to limestone rocks,” explained Amy Rathmel, Geotechnical Engineer with Woodside Energy. “These geological settings can be quite brutal and very hard, so difficult for an anchor to embed.”
Over a period of several days, Deep Sea Mooring Australia coordinated and executed the test. The 18 tonnes STEVSHARK REX anchor with 7.2 tonnes ballast was tested in 100m of water at four different locations, each with their own ‘extreme’ soil characteristics. For the execution of the tests, SolstadFarstad’s Far Scorpion, having a bollard pull of 251 tonnes, was deployed.
The first test took place in a carbonate silty sand seabed, up to 4m thick and overlaying calcarenite rock. The second test was performed in a thinner sediment (1-2m), also with rocks beneath. The soil for the third test consisted of calcarenite rock with rough/irregular topography, while the last test was in calcarenite rock with a smooth bedrock surface.
Vryhof says all of the tests were successful. "The holding power of the anchor exceeded all expectations. The open geometry and the protruding fluke tips on the anchor effectively penetrated even the hard rock field at the final test site as predicted," said the company.
Leopoldo Bello, Managing Director of Vryhof Anchors, said “We are very pleased with the results of these tests offshore Australia. "We are grateful to Woodside Energy, Farstad and our Australian colleagues for the fantastic cooperation."