I ST INTERNATIONAL CONFERENCE OF MARINE ENGINEERING, 21-23 Nov. 2018, NVNA Varna, Bulgaria 86 A Study of Ship Rudders with Improved Performances Dobrin Efremov, Anton Anastasov Bulgarian Ship Hydrodynamics Centre (BSHC) Varna, Bulgaria d.efremov@bshc.bg Evgeni Milanov Bulgarian Ship Hydrodynamics Centre (BSHC) Varna, Bulgaria e.milanov@bshc.bg Abstract — The maneuverability of a ship in waves is strongly influenced by vessel’s inherent course stability and particularly by existing rudder design. The International Maritime Organization (IMO) has published a series of regulations regarding ship maneuverability in adverse conditions at low speed in the range of 4-6 knots. These new higher standard of IMO require new approaches to improve the maneuvering characteristics in waves of the ship comparing with current criteria for calm water. In the paper, to achieve higher rudder efficiency two technical solutions have been studied - traditional, by increase of rudder area with 20% and innovative – applying the effect of substitution of the trailing edge of the increased rudder design with the wedge tail. The results of aerodynamic tests performed in BSHC-Varna wind tunnel show a high efficiency in both types than original item, independently of the increased drag. The effect of wedge tail are mostly highlight in the created torque of the rudder, almost double compared to the others. This gives preconditions to analyze the ship energy efficiency of the design point of view. Keywords — maneuverability, rudder design, wedge tail, aerodynamic tests, torque. I. INTRODUCTION Maneuverability is a basic criterion for the ship's characteristics when operating in a restricted area or in seaway. IMO recently turned more attention to the maneuverability of the vessel in seaway and began discussion of introducing additional criterion for ship's characteristics. The current criteria [1] refer to the ideal case - maneuverability in calm water. In seaway conditions it is necessary to maintain the course with frequently rudder deviations at a relatively low speed. This mode of control has its own disadvantage - the loss of speed caused by the increased resistance of the rudder. This leads to the need to implement rudders with increased lifting force at small angles of deviation and low resistance [5]. Classical variant is the selection of the standard blade, but with enhanced surface - however again would lead to increased resistance. Contemporary approaches are directed to rudders with a variable shape at their rear end - fish tail type, with a back radius of curvature [4, 6]. The article presents the results of the study of variants of rudder types, namely the efficiency of a semi-balanced rudder with a preserved enlarged area and one with its replaced outward edge with a wedge tail. Previous studies have shown that rudders with a large wedge tail, providing significantly higher lifting force, but is accompanied by higher drag. The ideal option would be to determine the dimension of this wedge tail, so as to provide a higher lifting force for small angles of attack but not with higher drag. The possibility of providing the desired lifting force more quickly would result in earlier and effective execution of the specified maneuver. II. EXPERIMENTAL SET-UP AND RUDDERS GEOMETRY To obtain free-stream rudder characteristics model experiment in BSHC low speed wind tunnel were carried out (Fig.1). Fig. 1. BSHC low speed wind tunnel