Low-energy fishing for razor shells
Ensis B.V. director Adri Bout believes that handling operations and fishing for razor shells (ensis) can be done better and more sustainably.
Razor shells hide in the sand, and they are removed using a basket, air and water. Until recently, they were then stored in wet conditions in crates on board. Those crates were located on the deck because the three compressors needed for pumping air and water took up all the space in the hold.
Adri Bout has been wanting to make improvements to both processing on board and to the fishing gear for years. He was pretty much convinced that the capacity of the compressors was excessive (8 bars overpressure). ‘At the time, I relied on expert opinion. Even so, I felt that we could manage the water column with less pressure. And those diesel compressors were costing me €40,000 in maintenance every year. That’s a lot of money.’
Adri talked to innovation consultant Willy Reijniers from Syntens about his ideas for more sustainable fishing. How much water is needed to liquefy the sandy seabed, and how much pressure is needed to bring the razor shells to the surface were important questions requiring answers. Willy Reijniers suggested getting in touch with Deltares and he pointed out that Adri could apply for a Knowledge Cheque from the Southern Netherlands Operational Programme (‘OP-Zuid’) for the research. He also knew the researcher that Adri Bout needed and he brought the two together. ‘Dick Mastbergen knows about how the soil and water interact, and he works a lot for dredging companies’, explains Willy. ‘That was exactly what Adri needed. After a few changes had been made, he could apply those data himself.’
It sounds simpler than it was in practice. Adri, who had already called in John Kramer from Kramer Machines in Colijnsplaat to look at his ideas, took samples after Dick Mastbergen advised him to do so, and ordered analyses. The next step was to calculate the volume of water and the pressure needed to liquefy the sandy bed and to bring the razor shells to the surface. John Kramer design a completely new basket with spray heads and an air lift. Using relatively low amounts of energy, it is possible to induce an eddy pattern in the bed and the shells, after which the razor shells can be lifted up on board, leaving the sand behind on the bed.
Adri Bout: ‘All the calculations were right, but we weren’t getting the shells to the surface. We spent at least the next six months getting the angle of the fishing gear right. And the electric cable snapped regularly as well. But we sorted it all out eventually.’
Once the fishing gear was working, the returns became clear. ‘We made the switch from three 68 hp diesel compressors (150 kW) to one 20 kW low-pressure blower. In combination with the low-energy (17 kW) electric underwater pump from Drive & Flow in Krabbendijke, we achieved a saving of 73 per cent(!).’
John Kramer designed a processing line – which can now be located in the hold – to ensure that the razor shells were handled as little as possible. The line sorts the shells automatically into different lengths and thicknesses before depositing them in one of the twelve refrigerated silos containing water. Small shells are returned to the sea. Storage capacity on board has increased enormously. ‘So we can now fish at the best time, we don’t need to sail out as often and we always have adequate stocks of razor shells,’ says a contented Adri Bout. ‘On top of that, the crews don’t need to lug 30-kilo crates around anymore: the silos are lifted to shore using cranes.’