Engineering Performance of Self-adjusting Otterboards in Comparison with a Conventional Trawl Otterboard

For the purpose of improving hydrodynamic performance and reducing contact with the seabed, a new self-adjusting otter board (SAO) has been developed by MLD (https://mld.one/) for operating in demersal trawl fishery. The SAO has two flaps (upper and lower) that can be opened and closed in order to control the lift on the otter boards and thus control the horizontal and vertical position in the water. These dynamic otter boards can be controlled remotely by the skipper or by a positive feedback control system using acoustic signals. A full-scale experiment was conducted to compare the engineering performances of SAO against a conventional seabed-contacting design. There was no seabed contact when SAO was set to a target height of 5 meter above the seabed. Lift and drag coefficients at a towing speed of 1.54 m/s were calculated to be 2.25 and 0.48 for SAO and 1.48 and 1.18 for conventional door respectively. Thus, the efficiency (lift/drag ratio) of the SAO was 4.68 whereas that of the conventional otter board was 1.25. The results provide the information for fishermen to make an informed decision about the viability, engineering performance and fuel efficiency of self-adjusting otter boards.