Despite the low fuel prices, energy efficiency is a key differentiator for shipping companies competing for cargo.
The Canada-based owner Seaspan has worked with DNV GL on a series of projects aimed at investigating possible efficiency gains through retrofits. “We are constantly trying to improve the performance of our fleet, in order to meet current market requirements. DNV GL’s dedicated service for retrofit projects, based on computational fluid dynamics (CFD), formal optimization and high-performance computing has made them a valued partner for us,” says Ian Robinson, Project Manager, Technology & Development at Seaspan.
“In one of the most recent projects, we looked at how a 13.100 TEU container carrier could be adjusted in order to minimize its yearly fuel consumption in slow-steaming operations,” says Karsten Hochkirch, Head of the Fluid Engineering Department at DNV GL – Maritime. “Slow steaming is the easiest and most effective way to save fuel, but the fact that this approach has become so wide spread means that large parts of the existing containership fleet operate in off-design conditions, where engine, hull – especially the bulbous bow – and propeller performance is not optimal. For these ships, retrofitting bows and propellers, which have been adjusted to suit their new operational realities, makes a lot of sense,” he explains.
To identify the ideal parameters for Seaspan’s 13.100 TEU vessel DNV GL analysed two years’ worth of operational data and condensed it to twelve representative clusters of speed-draft-combinations with associated weights reflecting their time share in operation. Experts also looked at the advantages and disadvantages of retrofitting the bow and the propeller individually or together. “The parametric model for the bow section alone employed twenty free parameters, which led to a wide range of possible bow shapes. The optimization significantly reduced the volume at the tip of the bow and the height of the bow to get better resistance at low drafts,” says Hochkirch. The new bulb alone would have led to 6.5 per cent fuel savings. The propeller optimization also resulted in a slimmer new design with 40 per cent less area and 20 per cent less weight, leading to expected savings of 7.5 per cent.
“In these retrofit projects, generally the sum is larger than its elements. An optimized bow leads to reduced power requirements and a better inflow. These in turn allow for additional propeller improvement. In this case, retrofitting both the bow and the propeller led to combined savings of 18 per cent, which was confirmed in independent model tests,” Hochkirch explains.
Such efficiency gains are not unusual. A further project between Seaspan and DNV GL, carried out on an 8500 TEU container vessel, led to combined savings of 14 per cent. “Larger ships generally have larger savings potential, especially if they often trade in lower draft,” says Hochkirch.
In addition to working with DNV GL on retrofit and design projects, Seaspan also utilizes DNV GL’s ECO Assistant for trim optimization data and has signed up part of its fleet to the ECO Insight solution to monitor and further optimize the performance of its vessels.