The Atlantic Enterprise (AE), now fishing prawns off Canada, is the world''s first trawler with a complete electrical AC winch control system, provided by Vacon, whose liquid-cooled NX system is controlling the vessel''s 19 AC winches. This means the Danish company Ocean Prawns vessel enjoys the same towing capabilities as with hydraulic winches but smoother, silent operation and big savings in energy, space, installation, and maintenance.
Three winch motors at 315 kW each, part of three groups of smaller winches, have a 315 kW front-end system offering a bonus off spinoff, self-generated electricity.
Although hydraulic winches have been dominant in Western Europe for two decades, electric winches are not new. What is new, is the development by the Norwegian Aker Brattvaag companies Brødr, Rogne and Haram Elektro AS and their associates for the AE.
The 700-tonne storage capacity of AE can handle five weeks' catch. It has a twin rig trawl system with two trawls pulled by three cables. It uses a Scantrol 2000 auto-trawl system with a Scanmar sensor to monitor the critical middle cable.
Tension on the cables is regulated by three, 55-tonne trawl winches, each controlled by a liquid-cooled Vacon NX drive (820 A, 440 V). A constant relation is maintained between the tension on the middle cable and that on the outer cables. For 90 per cent of the time the winches are operating in constant tension mode (zero speed with full torque).
Frequency converters and fieldbus technology are the key elements that make AC electric winches superior to hydraulic ones. When towing, electric winches use only 10 per cent of the electricity required by hydraulic winches, gained through variable speed control of the motor with a frequency converter. Electric winches use only the electricity needed. They also generate electricity to be fed into vessel's batteries and electrical system. Atlantic Enterprise gets 160...180 kWh of 'free' electricity per cast. With the trawl drum at 21 revs per min, the power generated is approximately 70 kW for each motor.
Smoother starting and stopping means the frequency converter protects the electrical grid and the machinery from unnecessary load, giving more reliability and lower maintenance costs. And if one line fails, the system still keeps running, whereas the whole system would fail with hydraulic winches.
Lighter and smaller electric winches save space. The liquid-cooled drives are up to 60 per cent smaller than air cooled ones. No runs of hydraulic piping also means lower installation costs and easier maintenance. The AE's electric winches are 50 tonnes lighter than a hydraulic system and even more weight is saved as 16 cubic metres of hydraulic oil can be dispensed with, giving more bunker space and more time at sea.
Though the vessel is in active operation for approximately 17 hours per day, daily fuel consumption is now as low as 10,000 litres - a saving in fuel of a third over a similar ship with hydraulic winches. This is because a hydraulic system runs at full power when full pressure is needed to achieve full torque, whereas an electrical motor needs power in direct relation to speed.
