Assessing the manoeuvre of the last minute: A numerical lifting line model for wind assisted MASS

Technical development of MASS is currently mainly focusing on autonomy. Replacing the eyes, ears and brains of the crew with sensors and algorithms for path and trajectory tracking, collision avoidance, docking, etc. represents a prerequisite for successful implementation of MASS. However, there is another, equally important area of development in international shipping which is decarbonisation. Rules and regulations for decarbonisation are firmly in place and also apply to MASS. It is already known that deep sea shipping in compliance with decarbonisation regulations will only be possible with alternative fuels and power sources in the long term. Since the energy density of alternative fuels is significantly lower than for conventional fuels, the cargo capacity is reduced. One alternative power source that reduces the fuel consumption and offsets these disadvantages are wind propulsion systems. However, these systems do not only improve the fuel efficiency, but they also affect course keeping and manoeuvring performance of a vessel, which means they need to be considered in the control systems of autonomous vessels. This paper presents a numerical lifting line approach to predict the forces and moments exerted by sail assist systems as input for modelling the behaviour of the ship. The presented method can consider interaction effects of multiple wind propulsion systems and provides individual as well as total forces and moments as function of wind conditions and wind propulsion settings, which can be easily integrated in autonomous vessels control systems. Using the example of the popular Flettner rotor, the paper also discusses how wind propulsion system might be used to support automated manoeuvres and improve manoeuvrability.