Low Carbon Shipping Conference 2012 Speed Optimisation for Liquefied Natural Gas Carriers: A Techno- Economic Model

The effect of a ship’s speed on its propulsion power requirements is of importance primarily due to their well-known cubic relationship. The ship’s speed also plays a fundamental role in its profitability; higher speeds are attractive to shipping’s customers but costly to the owner, both in capex and opex. Revenue and costs are dynamic and largely influenced by freight rates and bunker prices which fluctuate according to market conditions. This is further complicated in the LNG carrier sector where chemical and thermodynamic interactions contribute to the rate of LNG boil-off in the tanks. This affects revenue either directly at the LNG import terminal, or indirectly through on board reliquefaction plant power requirements. This paper investigates the ‘optimum speed’ problem in the LNG carrier fleet from a technical perspective that describes boil off, fuel consumption and CO2 emissions as a function of vessel speed, and from an economic angle whereby revenue and costs are evaluated with respect to speed by means of a profit optimisation and cost minimisation function.