R Stokes, First steps towards electrification of shipping, Energy World, November 2018, p 27

In the marine world, attention is turning to hybrid systems and, more rarely, all-electric of propulsion, with an annual increase of about 30% as these two categories combine, and a current total of some 227 ships. The driving force behind this is the policy of the International Marine Organisation to order a 50% reduction in gas emissions, and a 70% improvement in energy efficiency compared with the baseline year 2008. To date, their propulsion units apply largely to small and mid-sized vessels, particularly ferries. Currently battery capacities are of the order of 4.16 to 4.7 MWh, and recharging in port is expected to take up to 7 minutes. With regard to the liquid fuel used in hybrid versions, interest is expressed in terms of LNG, ammonia, hydrogen methanol and biofuels.