Testing alternative gears: otter boards in a large wind tunnel
Wind tunnels are the newest playground of BENTHIS research. In our search for less impacting fishing gear, we tested traditional and novel otter boards, the door-like devices that make the mouth of the fishing net go open.
In the Mediterranean case study of BENTHIS the focus is on gear innovations. In this area, there is a shift from the traditional demersal otter boards to semi-pelagic otter boards. The idea is that the novel otter boards have a lower impact on the seafloor than the traditional ones.
Novel semi-pelagic otter boards were developed by two small Italian companies (Grilli and Mori) participating in BENTHIS. The novel otter boards are supposed to hover over the seafloor, instead of touching it. Researchers from CNR tested the different otter boards in the wind tunnel of the University of Rostock (Germany) in October 2013. Next to the traditional and novel otter boards of each of the manufacturers, also the ‘Thyboron VF15’ otter board was tested, serving as a reference.
Wind tunnel measurements have advantages over the commonly used flume tank experiments as they are less time consuming, less expensive and provide more information. The wind tunnel tests produce detailed data on aerodynamic forces and moments of otter boards that can be translated to circumstances more relevant for fisheries: the hydrodynamic forces during fishing. The researchers tested the boards under different configurations in terms of pitch and attack angles. The pitch angle is the angle between the longitudinal axis of the otter board or chord line, and the vertical z-axis of the wind tunnel. The attack angle is the rotation of the door with respect to z-axis.
The next steps will be made in February 2014, when researchers will test the otterboards at sea. Scientist-in-charge Antonello Sala expects to present the first results at the next BENTHIS annual meeting (Rome, 30 March-4 April).
