We have investigated a hybrid power train for ship crane operations, using a lithium-ion battery in conjunction with diesel gensets for auxiliary power generation, as an alternative to a conventional power train using only gensets. We have simulated crane operations in port using both solutions, in order to quantify the potential economic gains of using hybrid power generation. This study is based on a real open-hatch dry bulk vessel of 50,000dwt, which is compared with a corresponding newbuilding ship with hybrid auxiliary power generation. We have modelled the complete auxiliary power system, including diesel generators, lithium-ion batteries, cranes and ship hotel consumers. We have developed a novel hybrid control strategy that has the potential to reduce the minimal size and thereby cost of batteries for hybrid ships. Our results indicate that the hybrid solution will lead to about 30% reduced fuel consumption and CO 2 emissions while operating cranes, which amounts to annual savings of $110,000, with $450,000 savings over three years of operation, as well as reduced capital costs compared to the conventional power generation system.