A high-profile test of major energy efficiency improvements to four vessels managed by Hammonia Reederei has generated inconclusive results due to a lack of detailed performance data.

The retrofit aimed to prove that fuel consumption of 10-year-old, 10,536-dwt general cargoships could be cut by 25%, but data gathered in the first year of monitoring showed a definite fuel saving of only 7%, and potentially as high as 20%.