Flettner rotor vessel design optimisation

Abstract

One of the most promising methods to reduce harmful emissions in shipping is to apply wind-assisted propulsion on ships. Uncertainty about the potential fuel savings makes ship owners reluctant apply wind-assisted propulsion on a large scale. The goal of this thesis is to develop a method that identifies the aspects of a vessel design, that can be optimised to minimise the payback period of Flettner rotors.
This research identifies all cost aspects that are affected by Flettner rotors. Of these cost aspects the fuel costs have the largest influence on the payback period of a Flettner rotor investment. However, these costs are also the hardest to predict in an early design stage. Therefore, this research focusses on determining the fuel savings from Flettner rotors.
To determine the fuel consumption of a ship with Flettner rotors, the Performance Prediction Program (PPP) has been developed. The PPP solves the force and moment balance equations in surge, sway, roll and yaw directions, including the physical effects from Flettner rotors. The physical phenomena that are a result of Flettner rotors lead to several operational characteristics whose occurrence could affect the benefits of Flettner rotors: throttling back Flettner rotors, applying constant rudder angles and changing the propeller operating point It is shown that the PPP provides accurate results, in close agreement with on-board measurements. The average savings that are predicted by the PPP differ slightly from the measured savings.
The Weather Routing Program (WRP) has been developed to obtain an operational profile of a ship with Flettner rotors. This operational profile is used to determine annual fuel savings, and it determines the occurrence of the operational characteristics.
The WRP simulates a ship's operational conditions using historical weather data. It combines the Flettner rotor performance from the PPP and actual sailing schedules as input for voyage simulations. In the voyage simulations the optimal route is calculated with the lowest fuel consumption.
If analysis of the WRP results shows that an operational characteristic is significantly affected by Flettner rotors, related design aspects should be optimised. A case study that was performed on a case ship with Flettner rotors. The study demonstrates how the developed methods are used to identify aspects of a vessel design that are interesting to optimise, when Flettner rotors are applied. It was shown that the position of the Flettner rotor on the case ship has significant influence on the operational occurrence of large rudder angles and the corresponding rudder resistance. Choosing the optimal Flettner rotor location ensures adequate manoeuvring capabilities for the ship. With the Flettner rotor on its optimal position, no other measures are required to increase manoeuvring capabilities; no larger or more effective rudders are required, additional appendages do not have to be considered. The operational analysis in the case study also showed that the average engine load is significantly reduced as a result of Flettner rotors. This possibly allows to install a smaller main engine. This could reduce the Flettner rotor investment cost and decrease the Flettner rotor payback time.