Use of inclinometer technology to control otter board angles, filling and twist of net and cod end has added quite a new dimension to efficient trawling and reduced energy consumption.
In the new sensor generation from Scanmar all sensors are equipped with inclinometers that show pitch and roll of the otter boards, net and cod end. Patents have been obtained for the new technology.
Extensive trials have shown that there is great room for improvements in efficiency and reductions in fuel consumption:
Trawl doors are the most important part of effective fishing, and also, often together with the resistance in the net, counting for 60-90% of fuel consumption. Most fishermen have been focusing on the angle of attack, but observations conducted during recent years show that the doors' roll angles have more impact on efficiency and especially fuel consumption. Most vessels should be able to save 10-20%.
Observations of trawl nets show that many of the fish entering the trawl opening never end up in the cod end. In pelagic fisheries it is quite normal that as much as 50% disappear through the panels. The reasons for this are; bucket effect in the trawl caused by wrong towing speed and caused by fish gathering in the intermediate section. Now it has also been disclosed that most trawls are twisted, causing the meshes to be misshaped.
The result caused by the bucket effect and a misshaped net is that the meshes are wide open and the fish disappear. 'Netting' of fish is a signal that something is wrong, but the problems might even be bigger in area with bigger meshes. With the new angle sensors it is easy to control the shape of the net and at the same time observe how the fish is moving inside the trawl, and especially in what area the problem occurs (both the roll and the pitch angles will change).
Maybe the best way to save fuel is to control the fish entering the trawl opening so that it ends up in the cod end. Extra towing time doesn't only increase the fuel bill, it also ads to the cost of maintenance and repair.
