Shipping is a critical component of global trade but also accounts for a substantial portion of global greenhouse gas emissions. Recognising this issue, the International Maritime Organisation (IMO) has implemented new measures aimed at determining the energy efficiency of all ships and promoting continuous improvements, such as the Energy Efficiency Existing Ship Index (EEXI). As Computational Fluid Dynamics (CFD) can be used to calculate the EEXI value, RISE-SSPA1 and Flowtech have developed a CFD-based method for predicting full-scale ship performance with SHIPFLOW v7.0, which meets the new requirements of IMO. The method is validated through an extensive comparison study that examines the delivered power and propeller rotation rate between full-scale CFD predictions and high-quality sea trials using 14 common cargo ships of varying sizes and types. The comparison between the CFD predictions and 59 sea trials shows that both delivered power and RPM can be predicted with satisfactory accuracy, with an average comparison error of about 4% and 2%, respectively. The numerical methods used in this study differ significantly from the majority of the state-of-the-art CFD codes, highlighting their potential for future applications in ship performance prediction. Thorough validation with a large number of sea trials is essential to establish confidence in CFD-based ship performance prediction methods, which is crucial for the credibility of the EEXI framework and its potential to contribute to shipping decarbonisation.

This paper presents a numerical analysis on the induced relation between hull surface roughness and ship performance and discuss how to maintain hull-surface with cost and environmental impact in mind. The analysis is based on CFD simulation of the ship performance due to change of hull surface roughness condition before/after dry-docking and in-water hull cleaning. A typical tanker ship, KVLCC2 is investigated for 14 different partial cleaning cases. The attainable reduction of propulsive power by hull surface treatment is estimated as an index, Cleaning Efficiency Index (CEI). A clear understanding is obtained how hull geometry has profound implication for the effect of roughness on the change of power. Partial hull cleaning of fore-end and stern-aft part of the hull was found to give higher relative CEI than entire hull cleaning. The present study provides guidelines which part of the hull to treat during dry-docking and hull cleaning process with better quality or higher priority if necessary

Hull surface condition plays an important role for ships performances for new-built ships as well as ships in operation since the drag penalties due to hull roughness are substantial. It is a standard practice that ship design is based on performance evaluation by model testing of ship models with hydrodynamically smooth surface and the increase of resistance for new build condition is added by roughness correlation allowance based on empirical formula. Surface roughness effects beyond the new build condition are seldom considered in the design process. The question is whether hull roughness affects the flow characteristics to such extend that it influence with the resulting design. This is especially important for propellers or energy saving devices which are operating around the stern of the ship where the roughness effects on flow characteristics are most pronounced. This paper will discuss some practical questions related to the effect of hull roughness, both in terms flow characteristics, power increase and impact on ship design and operational practice. 

This paper addresses the effects of hull roughness on pro-pulsion performance of ships and demonstrates the importance of taking full scale roughness effects into account when designing propulsion devices. The investigation of the hull roughness effect was performed numerically using SHIPFLOW with the built in roughness model based on the assumption that hull surface roughness is uniformly distributed and can be characterized by the equivalent sand roughness. The ship investigated is a SSPA VLCC with three typical energy saving devices (ESDs), which include a duct, a standard pre-swirl stator (PSS) and two SSPA generic ESDs (GKDM and GKDF). As an initial validation study, numerical simulation and model tests were carried out for the bare hull with two surface conditions: smooth and rough surface. The results from numerical simulation were validated against towing tank tests and clearly indicates a gradual change of flow characteristics/propulsion performances with hull roughness growth: thickening of boundary layer, increase of resistance and propulsion properties (T, Q and RPM). Following the model scale study, full scale simulations have been performed. The results from full scale simulations confirm the trend in increase of EHP and DHP as roughness grows, but even much faster in full scale compared to model scale.   This paper will further focus on combined hull roughness and scale effects in the design of propeller/ESD and prediction of the performance of a ship. A quite interesting finding is that the roughness is not always affecting in negative direction. The propeller can be operating in more favorable conditions with higher angle of attack due to the thickening of the boundary layer with the increase of hull roughness. This can directly lead to the improvement of propulsive efficiency and in turn result in further power reduction with the use of ESDs.      This paper will discuss additional steps needed to take into account of hull roughness in design optimization process of propeller and ESDs and present design methodology for the successful development of propellers and ESDs performing well in actual operational conditions.

SSPA experiences a growing interest in twin skeg ships as one attractive green ship solution. The twin skeg concept is well proven with obvious advantages for the design of ships with full hull forms, restricted draft or highly loaded propellers. SSPA has conducted extensive hull optimizations studies of LNG ships of different size based on an extensive hull data base with over 7,000 models tested, including over 400 twin skeg hull forms. Main hull dimensions and different hull concepts such as twin skeg and single screw were of main interest in the studies. In the present paper, one twin skeg and one single screw 170 K LNG ship were designed for optimally selected main dimension parameters. The twin skeg hull was further optimized and evaluated using SHIPFLOW FRIENDSHIP design package by performing parameter variation in order to modify the shape and positions of the skegs. The finally optimized models were then built and tested in order to confirm the lower power demand of twin skeg designed compaed with the signle screw design. This paper is a full description of one of the design developments of a LNG twin skeg hull, from early dimensional parameter study, through design optimization phase towards the confirmation by model tests.

With environmental concerns becoming one of the most important issues facing the shipping/ship-building industry today, SSPA has witnessed strong demand for the development of energy saving devices (ESD). SSPA anticipates that the demand will be greater to respond to new requirements set by the IMO regulation on energy efficient design index (EEDI). SSPA has been involved in many joint research projects in developing energy saving solutions. Daewoo Shipbuilding and Marine Engineering Co. Ltd. (DSME) has developed several ESDs in cooperation with SSPA, where SSPA has tested most of the ESDs designed by DSME over the last 10 years. The pre-swirl stator (PSS) is a device mounted on the stern boss just upstream of the propeller (see Fig. 6 or Fig. 33). It is designed to generate pre-swirl flow to the propeller in order to gain a favorable interaction with the propeller that improves the propulsive efficiency and results in a power reduction. This paper is a full description of one of the developments of PSS from the early design stage, optimization phase, and confirmation by model tests to validation through sea trial tests.