This study presents the effect of ortho-para conversion on the economics of transoceanic shipping of liquid hydrogen (LH2) based on an LH2 tanker. Four representative ortho concentrations of 30%, 20%, 10% and 2% were considered for estimating the energy consumption, pressurisation behaviour, pressure cargo tank design, cargo mass, and ultimately the supply chain economics involving the liquefaction and transportation with a 15-day voyage times. The liquefaction energy consumption was inversely proportional to the ortho concentration. The simulation of the pressurisation in an prismatic pressure vessel showed that the design pressure increased with the ortho concentration: 5.1, 5.7, 7.9 and 11.5 bara for the ortho concentrations of 2%, 10%, 20% and 30%, respectively. This trend caused the loading limit to decrease at higher ortho concentrations, thus critically affecting the LH2 shipping economics. Consequently, the optimal ortho concentration would minimise the total supply chain cost. A sensitivity study was conducted for possible ranges of voyage distance.