The oceans’ wild fish resources are limited, so it is critical that trawl nets do not catch unwanted species or small/under-sized fish. The water flow in and surrounding a trawl net’s construction is an important factor in this context. Arne Fredheim’s recently completed doctoral work at NTNU involved developing an approach for calculating the water flow in and around trawl nets. The methods can be used to design trawls that will prevent undesired catches, as well as for the design and control of water flow through nets intended for fish farming.