An integrated system of Allweiler frequency converters on board Stena Line’s latest fleet addition, the 62,000-gt Stena Hollandica, promise to cut energy consumption, reduce wear and tear, and improve component efficiency. And the German pump manufacturer, which celebrates its 150th birthday this year, is already in discussion with a number of other leading owners interested in the new technology, which has a typical payback period of less than two years.

Stena Line’s Dick van der Ent, Energy Saving Engineer, comments: “We are delighted with our new ferry which is performing very well so far. It is early days yet, but we are already seeing the benefits of her energy-saving features. Allweiler’s innovative systems approach to power management on board is an important factor in the ship’s overall energy equation.”

The system developed by Allweiler uses frequency converters to control the power supplied to pumps on board, enabling them to meet exactly the required output at any moment in time. Previously, components ran at constant loads and excess cooling water that wasn’t required, for example, was discarded as waste. This meant that components were running at heavier loads and faster speeds than required, resulting in wasted energy, excessive component wear, high bearing temperatures, extra pressure on shaft seals and reduced mean time between failures (MTBF). Allweiler’s new approach to power management yields savings that typically lie in the 30-40% range, but the company says that, in some cases, these can reach 60-70%, depending on the application.

According to Martin Hoffmann, Smart Solutions Manager at Allweiler, individual components can be made more efficient on a case-by-case basis, and retrofits are possible. But the greatest benefits are achieved using a systems approach, he says, as Stena has done on board the new ropax vessel, the first of two superferries which are being deployed on the Harwich – Hoek van Holland route. Built at Nordic Yards in Wismar, Germany, the 5,500-lane meter Stena Hollandica is the largest ferry in the world and will be joined by sister vessel Stena Britannica, later this year.

“Our aim is to reduce the total cost of ownership,” explains Hoffmann. “Frequency converters are key components in the control systems we provide. We like to adopt a system approach and focus on complete solutions. Our Smart Platform allows us to use and combine different intelligent building blocks as speed controls, condition monitoring and, of course, the broad range of pumps aligned to the application. Owners and operators are our end users and we want them to realise the scale of the potential savings.”

Hoffmann says that the greatest benefits are likely to be achieved by ship operators whose components have varying load requirements – for example cruise ship air-conditioning systems in tropical regions as compared with northern seas.

But standard vessels such as tankers and bulk carriers can also realise significant energy savings. Seawater cooling pumps are a good example, says Hoffmann. In tropical conditions, where seawater temperatures are high, such systems typically function at full load. In contrast, when a vessel sails into the colder waters of northern Europe, much less cooling water is required and any surplus has typically been pumped overboard.

On ships like the Stena Hollandica, which operate in constant temperature conditions, speed control of seawater cooling pumps makes good sense as well. Typically about 20% of such a vessel’s operating time is manoeuvring, when the requirement for cooling water is typically just one third of the requirement when operating at cruising speed. 

Using Allweiler’s frequency converter control system, however, optionally combined with external information, e.g. from a condition monitoring system and/or the bridge, the pump can operate using significantly less power, typically 30-40% less but perhaps as little as 20% of its maximum. Related benefits include less component wear and longer maintenance intervals. The Stena Hollandica and the Stena Brittanica both have Allweiler seawater cooling pump control systems to provide more effective power management for varying loads at sea and in port.