The concept of Flettner rotor, a rotating cylinder immersed in a fluid current, with a top-mounted disk, has been analyzed by means of unsteady Reynolds averaged Navier-Stokes simulations, with the aim of creating a suitable tool for the preliminary design of the Flettner rotor as a ship’s auxiliary propulsion system. The simulation has been executed to evaluate the performance sensitivity of the Flettner rotor with respect to systematic variations of several parameters, that is, the spin ratio, the rotor aspect ratio, the effect of the end plates, and their dimensions. The Flettner rotor device has been characterized in terms of lift and drag coefficients, and these data were compared with experimental trends available in literature. A verification study has been conducted in order to evaluate the accuracy of the simulation results and the main sources of numerical uncertainty. All the simulation results were used to achieve a surrogate model of lift and drag coefficients. This model is an effective mathematical tool for the preliminary design of Flettner rotor. Finally, an example of assessment of the Flettner rotor performance as an auxiliary propulsion device on a real tanker ship is reported.

In recent years, research into ships has focused on reducing emissions, consuming less energy, and being more efficient. As a result, the maritime industry has been continuing in a green and sustainable direction. Improving the fuel efficiency of ships and the decarbonization of shipping are important issues to reduce fuel consumption and emitted Greenhouse Gas (GHG) amounts. Decarbonization in the shipping industry could be achieved through technical and operational strategies such as Energy Saving Devices (ESDs) to reduce the fuel consumption of new and existing ships. According to the makers, ESDs can optimize fuel efficiency by up to 15%. This paper reviews the current literature on stern hydrodynamic ESDs, which are mainly used on typical merchant vessels, i.e., bulkers, tankers, and carriers. A comprehensive review is carried out analysing the different available solutions for stern hydrodynamic ESDs, the working principles, the methods used for the design, optimization, and evaluation of the performance improvements, and the relevant issues of these specific ESDs.

Computational Fluid Dynamics simulations of planing hulls are generally considered less reliable than simulations of displacement hulls. This is due to the flow complexity around planing hulls, especially in the bow region, where the sprays are formed. The recent and constant increasing of computational capabilities allows simulating planing hull features, with more accurate turbulence models and advanced meshing procedures. However, mesh-based approaches based on the finite volume methods have shown to be limited in capturing all the phenomena around a planing hull. As such, the focus of this study is on evaluating the ability of the Smoothed Particle Hydrodynamics mesh-less method to numerically solve the 3-D flow around a planing hull and simulate more accurately the spray structures, which is a rather challenging task to be performed with mesh-based tools. A novel application of the DualSPHysics code for simulating a planing hull resistance test has been proposed and applied to the parent hull of the Naples warped planing hull Systematic Series. The drag and the running attitudes (heave and dynamic trim angle) are computed for a wide range of Froude’s numbers and discussed concerning experimental values.

Change in body shape characteristics is one of the ways to reduce the resistance and thereby increasing the speed of planing hulls. Creating the transverse steps is one of these variations. The main reason to use the steps in high-speed planing craft is that the wetted surface of the vessel is divided into small parts with higher width-length ratio in high velocities and in this situation, the generated lift force is more efficient. In this article, by performing a three-dimensional numerical solution, motion characteristics of a two-stepped planing hull with transverse steps in calm water have been examined. For this purpose, the vessel is free to trim and sinkage, and by using the morphing mesh approach, the numerical simulation continued until the equilibrium condition of the two-stepped planing hull is satisfied. Resistance, lift, trim angle, and wetted surface in various velocities have been computed and compared against existing experimental data. Analysis of considered two-stepped hull in calm water shows that the numerical solution for resistance, trim, and lift are relatively precise in comparison to model test data. Furthermore, various hull characteristics such as wetted length of keel, chine wetted length, spray angle and, ventilation length have been investigated. 1. Introduction: In recent years, naval architectures have proposed significant modifications in planing hulls' design by creating steps, tunnel, and other geometric features. By considering these geometric variations, the hull wetted surface and, consequently, its resistance have been reduced and planing hulls velocity can be increased. In this regard, the step is one of the main hull's modifications which can lead to resistance reduction. Generally, lift of stepped planing hulls is distributed over the forward, middle, and stern plane of the hull (Fig. 1), and therefore, its ride quality will also be improved. Moreover, planing hulls with various step configurations have been used in high-speed craft since 1910, and various types of step with different shapes and arrangements have been used in planing hulls.