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Global shipping contributes (2.8%) to greenhouse gas emissions and needs to find future fuels which will allow the International Maritime organisation's 2050 net zero targets to be met. There is much uncertainty as to which fuels should be used between hydrogen, ammonia or methanol as future costs are uncertain. We propose and evaluate a Wind-to-Wake ratio that provides an objective measure based on the amount of renewable energy required to propel a ship. Time domain voyage energy demand profiles are used to simulate the fuel used and emissions for a cruise ship, a research survey vessel, a container ship and a large multi-fuel Liquefied Natural Gas carrier. Alternative ship power systems are investigated using various carbon-based fuels, ammonia and hydrogen either using conventional engines or fuel cells. For all voyage and fuel scenarios the combination of hydrogen and fuel cells uses 30% less renewable energy than ammonia and 26% less than methanol. Hydrogen only emits steam whereas the other fuel scenarios still emit significant amounts of greenhouse gasses. [Display omitted] • Wind to wake ratio provides an objective measure for comparing future fuels • Time-domain energy demand allows for 4 vessel types and 12 power systems. • Quantitative comparison of methanol, ammonia and hydrogen as future marine fuels. • Hydrogen through fuel cells requires the least amount of renewable energy investment. • Methanol and ammonia combustion scenarios yield a carbon footprint and other air emissions. [ABSTRACT FROM AUTHOR]