The introduction of the EEDI more than a decade ago, slow steaming, and the wish to reduce bunkering costs have resulted in a trend to install less powerful engines in ships. To avoid vessels becoming underpowered and thus unsafe, the International Maritime Organization (IMO) has published a guideline regarding the “Minimum Propulsion Power to Maintain the Manoeuvrability of Ships in Adverse Conditions”. This report presents a case study that follows the IMO-guideline step by step and works out the minimum engine size for the KVLCC2 tanker. Using a combination of Computational Fluid Dynamics and model tests, the parameters and assumptions behind the guideline are discussed in some detail. Results show that it is particularly important to determine the added resistance in waves correctly because it dominates the power prediction. It becomes clear, that the selection of the propulsive factors, particularly the “thrust deduction factor” has a significant influence on results. The work summarised here is part of a wider project that aims to provide experimental benchmarking data for added resistance predictions. It has been sponsored by the Swedish Transport Administration (Trafikverket) under grant number TRV 2021/53938.

The need to reduce green-house gas emissions has renewed the interest in wind propulsion for commercial cargo vessels. When designing such modern “sailing” ships, naval architects often lean on methods and tools originally developed for the design of sailing yachts. The most common tool today is the steady-state Performance Prediction Program (PPP), typically used to predict quantities like speed, leeway, heel of the vessel when sailing in a range of wind directions and wind speeds. Steady state PPPs are very efficient and can be used to rapidly assess a large number of design alternatives. PPPs are, however, not able to consider dynamic effects such as unsteady sail forces due to ship motions in waves or the turbulent structure of the natural wind. In this paper we present time-domain simulations with a Dynamic Performance Prediction Program (DPPP) that can take the “unsteadiness” of the natural environment into account. The program is based on coupling an unsteady 3D fully nonlinear potential flow hydrodynamic solver to an efficient lifting-line aerodynamic model. Particular attention is paid to a recently implemented unsteady aerodynamic model that employs an indicial response method based on Wagner’s function. The usefulness of such advanced simulations for performance prediction in moderate environmental conditions is investigated for a wind-powered cargo vessel with wing sails. Control system strategies such as sheeting of the wing sails close to stall are studied.

Wind propulsion has emerged as one out of many possible solutions to reduce GHG emissions from ships. The industry for wind propulsion solutions develops rapidly. This calls for some industry standardisation. A committee under ITTC is currently working on recommended procedures for performance indicators, performance prediction methods and sea trial procedures for wind powered ships. This paper proposes indicators that can enable fair comparison and facilitate the investment decision. A new sea trial procedures for wind propulsion solution verification is also proposed. Finally, the application of performance models in cost-saving split agreements, monitoring and weather routing of wind powered ships are discussed.

The need to reduce green-house gas emissions from shipping has reborn the interest in wind propulsion for commercial cargo vessels. This places new requirements on the tools used in ship design, as well as the methods usually applied in sailing yacht design. A range of design tools are used by designers at various stages in the design of wind-assisted ships and for different purposes. One important tool is the steady-state velocity prediction program (VPP) which is typically used to predict the speed of the vessel when sailing in a range of wind directions and wind speeds. Steady-state VPPs can be very efficient and fast and may be used to rapidly assess a large number of design alternatives. However, steady-state VPPs are not able to consider dynamic effects such as unsteady wave forces on the hull which may require the rudder to be active to control the heading and course of the vessel. This, in turn, leads to different mean forces than those predicted by a static VPP and therefore the sailing performance may be reduced compared to the predictions of a static VPP. Another effect of the ship’s motions in a seaway is that the angles of attack of the sails fluctuate, which can lead to different optimum sheeting angles and possibly a loss of performance. This study uses an unsteady 3D fully nonlinear potential flow hydrodynamic model coupled with an efficient lifting-line aerodynamic model to investigate the differences in sailing performance of a vessel sailing in steady conditions to the performance when sailing in a seaway and gusty wind based on a spatio-temporal wind model. The analysis shows clearly that the unsteady wind model affects the predicted performance. This is especially the case when sailing close-hauled and on a beam reach, where large changes in the local sail angles of attack can be observed.

Wind propulsion systems (WPS) are major investments and the decision to install them requires careful consideration of many complex questions. One of the recurring and challenging issues for ship owners is the choice of a suitable WPS for a specific ship and a specific operational pattern. Today most WPS providers offer on-demand case studies, but obviously the underlying performance prediction methodologies differ from provider to provider. This makes comparing different technologies from competing suppliers next to impossible. In this paper we present a numerical platform to compare different WPS of different makes, sizes, and costs in a fair way. The fundamental idea is to use aerodynamic WPS datasets that are independently verified by SSPA through wind tunnel test, sea trials or extensive CFD. This is combined with a hydrodynamic dataset from SSPAs database of tank tests. The same performance prediction method, identical routes and weather statistics are then used to determine Key Performance Indicators and financial metrics of the competing wind propulsion technologies. The purpose is to provide guidance for shipowners at the early concept stage of a vessel and help them select a system that suits their particular requirements.

Before the background of the internationl Maritime Organization's 2050 emission reducation targets, the largest sailing ship in the world is currently being developed in Sweden. This wind powered car carrier, called Oceanbird, will have four 80-metre-high wing sails targeting CO2savings in the order of 90%. The prediction and analysis of the seakeeping performance of such a ship is of importance, not only in terms of sailing dynamics, but also when it comes to the structural design of the rig. To this end, a numerical method for predicting a ship's motions and loads on its rigid wing sails is described in this paper and a demonstration of how the method can be used to obtain such loads is presented. The numerical method is based on an unsteady 3D fully nonlinear potential flow hydrodynamic model coupled with a hybrid 2D RANS/3D lifting-line aerodynamic model. Simulations in a seaway with short-crested irregular waves and corresponding wind conditions are conducted, resulting in time histories of the aerodynamic and inertial forces acting on the rig. Possible applications of the method include fatigue analysis of the wing sails, where the accumulated fatigue damage over the lifespan of the rig structure depends on the sum of aerodynamic forces and motion induced inertial forces. Other potential applications include sail dynamics, parametric roll, sheeting strategies and appendage configuration studies. 

This paper presents a comparative study of wave-induced motion responses and the added resistance of a ship. Four representative types of ships are adopted as test models: LNG carrier, tanker, containership, and bulk carrier. Two experimental techniques—captive and free-running model tests—are conducted under regular head and oblique wave conditions to create benchmark data. Several numerical computation methods (asymptotic formula, 2D strip theory, 3D panel method, and CFD) are applied to perform the seakeeping analysis. The comparison results indicate that the accuracy and reliability of each analysis technique are validated, and its characteristics and limitations are investigated with respect to the physical aspects of the added resistance caused by a wave. The analysis results are compared based on how steady flow-induced coupling effects are considered. Further, the sensitivities of seakeeping quantities with respect to wave steepness were examined based on the results of linear and fully nonlinear computations. The overall tendency of the added resistance in accordance with the incident direction of a wave is discussed. © 2021 The Author(s)

Wind propulsion systems (WPS) are major investments and the decision to install them requires careful consideration of many complex questions. In this paper we present a systematic, scientific methodology to assess the benefits and drawbacks of such systems at the early concept stage of a vessel. The purpose is to provide guidance for shipowners and operators and help them make informed decisions. The proposed method was developed into a Software tool called ‘SEAMAN Winds’ and has been correlated to full scale results. The program draws on our large database of model tests, and CFD of hulls and wind propulsion technologies. It uses the intended trading routes of the vessel as an important input, typical output data are: a) performance values (ship speed, power requirements etc.) b) environmental parameters (CO2 avoided, EEDI and EEXI reduction, carbon intensity indicator) c) financial metrics (bunker savings, payback time for installation of WPS) Potential applications of the method include making the business case for one particular WPS or investigating in how far certain systems are more suited for a specific route than others.

Assessing seakeeping performance at an early stage is even more important for wind powered vesselsthan for conventional ships, since there is little design experience to lean on. When the driving force comes from sails instead of a propeller, ship dynamics change considerably. Course keeping, turning ability, motions and acceleration in waves are just some of the properties that must be assessed. Including wind propulsion devices in a model test is however not straight forward. In this paper we present a methodology for model testing wind powered vessels. Rpm and azimuth-controlled fans/airscrews are used to mimic the aerodynamic forces from the sails. Results from model tests with a car carrier are presented and discussed while particular attention is paid to possible improvements of the test methodology.

In this study, a comparative study on motion response and added resistance of a Supramax bulk carrier (K-Supramax Original) in regular waves was carried out to evaluate the reliabilities and accuracies of experimental and numerical simulation techniques. Two kinds of experiments were performed; one is the towing tank model testing for head wave conditions conducted at Seoul National University, and the other is the free-running model test for head and oblique wave conditions conducted at SSPA Sweden AB. Also, nine numerical computation results submitted by seven institutions were compared with the experimental data. The computation results were obtained by various seakeeping analysis methods such as the 2D strip theory, 3D Rankine panel method, and Computational Fluid Dynamics (CFD) based analysis. Based on the comparison, the characteristics of each numerical technique and resultant accuracies of seakeeping analyses were investigated. It was also confirmed that different results were obtained although the same program was used because of the user dependencies; setting for computation parameters, numerical schemes, and mesh generations, etc. Furthermore, the sensitivities of seakeeping quantities with respect to wave amplitudes were examined by conducting both model tests and nonlinear numerical simulations for different wave slopes. Lastly, the tendencies of ship motion and added resistance depending on the heading angle were identified, and the reliabilities of experiments and numerical computations for oblique waves were discussed.