The Port of Hamburg announced that it is offering a 10 percent discount on port fees for cruise ships registered with the Environmental Ship Index (ESI) of the International Association for Ports and Harbours (IAPH) and performing well.

The announcement said well performing vessels would receive a 10 percent discount on port fees in the German city.

The ESI evaluates the quantity of nitrogen oxide (NOX) and sulphur oxide (SOX) released by ships as well as CO2 emissions and accounts for the potential to use shorepower as well.

This data is then presented in a score from zero to 100.

Ports with an ESI-based port fee reduction scheme attract more environmentally friendly vessels and hence reduce the environmental impact of shipping in the port, said the port, in a statement. 

About 100 cruise vessels are voluntarily registered in the ESI currently.