Modeling Tankers’ Optimal Speed and Emissions

摘要

With the increased quest for greener shipping, reducing the speed of ships has obtained an important role as one ofrnthe measures to be applied toward that end. Already speed has been important for economic reasons, as it is a keyrndeterminant of fuel cost, a significant component of the operating cost of ships. However, as emissions are directlyrnproportional to fuel consumed, speed is also very much connected with the environmental dimension of shipping. Sornwhen shipping markets are in a depressed state and “slow- steaming” is the prevalent practice for economic reasons,rnan important side benefit is reduced emissions.rnEmissions estimation models typically assume fixed ship speeds. However, ships do not trade at predeterminedrnspeeds. Those who pay for the fuel may choose an operating speed as a function of the freight rate and bunker price,rnamong others. Assuming a fixed speed may thus seriously miscalculate emissions. This paper incorporates ship speedrninto the analysis, and goes one step further by investigating the impact of optimizing speed on ship emissions. Thernstudy of the paper focuses on Very Large Crude Carriers (VLCCs), but some analysis for the Suezmax, and Aframaxrncrude tanker segments is also presented, and some results for Panamax/Product, LPG, and LNG tankers are alsornreported.rnThe paper’s modeling approach has two goals: (a) the determination of the optimal operational speeds (laden andrnballast) of a tanker as a function of fuel price, freight rate and other parameters, and (b) the estimation, among otherrnoutputs, of the emissions of the global fleet of a specific tanker segment. The modeling task comprises two steps. Thernfirst one optimizes the laden and ballast leg sailing speeds over reference trade routes for a specific (single) tanker.rnIn a second step, we estimate annual emissions, and other operational attributes (e.g. fuel consumption) for therntanker fleet segment, based on the output of the previous optimization. Other outputs such as CO2 , SO2, NOx andrnPM emissions are also produced. The policy implications of our work are finally discussed.