Filter units (2, 4 and 8 tons) have been used successfully for many years in the offshore and oil & gas sector as a protection for subsea assets.
Filter Units are recognized as an advanced alternative to concrete mattress and rock dumping. They got long lasting, effective, high position stability. The net is designed to encase the stone preventing it from breaking down and migrating from its location, therefore making it a maintenance free long-term protection solution. A key feature is the high flexibility, as the structure allows them to adapt to the seabed without further preparation or flattening. Because of its porous structure, Filter Units support the settlement of organisms and marine life like in an artificial reef. Filter Units adapt to the flow on the seabed and effectively protect against scour.
The single-lifting point enables a fast and safe installation; it also facilitates a decommissioning after many years. Positioning can be done by ROV, diver or other position determining technologies. However, it should be highlighted that a diver in the water is not essential during installation, using ROV or sonar has been proven be the most efficient method of installation which significantly reduces Health and Safety risks.
Several Filter Units can be installed simultaneously using a jig. The size of the installation vessel can vary.
The nets are extremely durable due to their PET fibers. The high quality of the nets is reflected in the tensile strength, which, according to tests, after 50 years in salt water still remains up to 79.5%. This means that Filter Units can be easily removed even after long time after their installation.
The nets are filled via a specially designed filling frame. This frame reduces time, equipment and manpower to a minimum. Intermediate storage, stacking and transport of the filled nets is possible.