Development of roll stabilization on a large zero-energy freighter-ship using sails.

Abstract

In recent years, research for creating climate-friendly solutions has become more desired. As the transport of cargo by sea is heavily utilized and will continue to be so, this is an area that can be improved. During this thesis, the main focus will be on analyzing the effect of roll motion mitigation and investigating the optimal solution to reduce roll motion for a large cargo ship using sails as means of propulsion. For the analysis, simulations will be performed using the ANSYS AQWA hydrodynamic diffraction and including an additional matrix to obtain the correct RAO (Response Amplitude Operator) values. Different alpha values are compared to showcase the potential effect of the viscous damping created by the keels. The RAO values that are obtained through the simulations will be presented and discussed. These simulations showcase that the efficiency of the keels increases when a more considerable alpha value is presented. Most of the simulations during this thesis are simulated with an alpha value of 0,01. Values of 0,02 and 0,05 are also presented as potential higher values of damping. Research is showing that utilizing bilge keels become more effective when traveling at lower speeds and will due to this be the primary solution when analyzing roll mitigation. The simulations show that the bilge keels are becoming more effective when the ship´s heeling is increased. The keel with the higher aspect ratio is more effective, yet limitations in the size of the keel could prove vital if navigating shallower water become of interest. Due to this, a less wide keel could prove beneficial, even though a wider keel mitigates more roll motion. The keels created for this study reduces the roll motion by 9% up to 30%, depending on the geometry of the keel, where the reduction increases with further heeling on the ship hull. The conclusion is that for a large freighter using sails as means of propulsion, bilge keels will be most effective as the cruising speed of the vessel will be lower than the traditional freighter ships.