Quantification of efficiency gains due to controllable-pitch propellers on wind-assisted vessels

Kurzfassung

Maritime regulations are driving innovative technologies to meet stricter environmental standards. In this context, the provision of decision support to ship owners and operators in their consideration of corresponding measures becomes important. Wind-assisted propulsion systems (WAPS) present a suitable solution to enable fuel consumption and emission reductions. Depending on the environmental conditions, commercial vessels equipped with WAPS rely on simultaneous utilization of WAPS and the ship propeller for operation. Conventional fixed-pitch propellers (FPP) are tailored to a specific design point. For a vessel with WAPS, the operation point of the propeller depends on the level of wind assistance, leading to off-design conditions and altered efficiency. Both FPP and controllable-pitch propellers (CPP) can be utilized to leverage this behaviour, however at this point the effect has not been quantified. Furthermore, the pairing of engine type and propeller is of great importance in the context of WAPS, as diesel engines can not easily be operated below a certain minimum power threshold. In this paper, a sailing bulk carrier vessel equipped with WAPS is investigated. Utilizing a set of voyage simulations, the impact of CPP / FPP usage, paired with a diesel or a diesel-electric engine, on propulsion efficiency is investigated. The ship behaviour is captured by means of discrete event equilibrium state calculations accounting for all relevant forces and moments. Voyage simulations are enabled by performing individual calculations along the route, while accounting for the respective environmental conditions. The results suggest that CPP enable overall efficiency gains in the range of up to 10 percent. The impact of engine type is more pronounced, resulting in an increase in energy demand of up to 30 percent for a diesel engine with respect to a diesel-electric configuration.