Steering with wind propulsion

Although sizeable compared to other energy saving measures, the majority of present installations of wind propulsion now sailing are relatively modest. They are assisting the propulsion of the ship, corresponding to the word “Assisted” in the common acronym WASP: “Wind Assisted Ship Propulsion”. However, it is seen there is an increase in announcements of projects where the aim is that wind propulsion will on average provide a similar contribution as the propeller, or even the majority. Wind propulsion does not only deliver forward thrust, but also major contributions in side force, heeling and yaw. Theses secondary forces (and moments) influence the performance in straight line sailing, e.g. through lift induced resistance on hull and rudder. This aspect is being covered in literature. However, the impact on (dynamic) course keeping and manoeuvrability does not feature in a lot of publications yet.
Within the WiSP2 Joint Industry Project manoeuvrability and course keeping of wind propelled ships is a subject of research, focusing firstly on modelling methods. The work is also planned to start a discussion on rules and regulations. How do simulated results fare compared to criteria? Making these comparisons already highlighted that rules and regulations, such as manoeuvring standards in IMO Resolution MSC 137(76) are not geared for wind propulsion. Interpretations are required. Eggers & Kisjes, 2023, already provided results for two cases, showing results for different interpretations of the standards. The manoeuvring response showed large variations and heel in a turning circle became particularly significant for certain wind directions.
The published results so far considered Flettner rotors where the controls were fixed: the rotation rate of the rotors was set at the beginning of a manoeuvre, depending on the wind angle and speed in the approach, and was not changed thereafter. This may be a reasonable assumption in some cases. Not all wind propulsion installations have a fast response time; some of them require up to 5 minutes to decelerate. None of the installations known to the authors have an automatic control system developed for manoeuvring. Nevertheless, systems could be adapted and automatic control could be implemented. This paper extends on that previous publication by considering the potential improvement for manoeuvring that can be achieved by fast power reduction or active control.