Leeway Angle Research Articles

A new validated open-source numerical tool for the evaluation of the performance of wind-assisted ship propulsion systems

Wind propulsion is envisioned as one of the solutions for the decarbonisation of maritime transport, as it offers high efficiency in terms of primary energy comsumption. Many wind propulsion systems already exist at various development stages, but the uncertainties over their performance is a strong obstacle to their adoption by ship owners. This paper presents a general method for the assessment of steady and unsteady performances of wind- propelled ships with 6 degrees of freedom, as implemented in the open-source program xWASP_CN. Inspired by system-based modelling, the method consists in the independent modelling of the forces acting on the ship, as functions of the ship’s 6 degrees of freedom and environmental conditions. An original root-finding algorithm that leverages the specifics of the physical problem to find the steady equilibrium is presented. The method works either like a Power Prediction Program (PPP) or like a Velocity Prediction Program (VPP). As a PPP, the forward speed and course are fixed while the required propulsive power, leeway angle, heel, trim and sinkage are solved. As a VPP, only the course is fixed and the attained forward speed, leeway angle, heel, trim and sinkage are solved. This makes the method suitable for both hybrid propulsion and pure wind propulsion. The force models can be semi-empirical (usually requiring very little input data), based on preliminary experimental or numerical results (such as forward resistance curves, lift/drag coefficients and frequency-domain sea-keeping coefficients), or full-fledged flow solvers (e.g. potential theory, CFD). Thus the method is suitable for all design stages as each force can be modelled with several levels of accuracy depending on the input data available. Comparisons of an intermediate-level model with experiments on a 18-ft catamaran fitted with a Flettner rotor and a water turbine show good agreement for steady-state results.

High Froude Number Experimental Investigation of the 2 DOF Behavior of a Multihull Float in Head Waves

Dynamic Velocity Prediction Programs are taking an increasingly prominent role in high performance yacht design, as they allow to deal with seakeeping abilities and stability issues. Their validation is however often neglected for lack of time and data. This paper presents an experimental campaign carried out in the towing tank of the Ecole Centrale de Nantes, France, to validate the hull modeling in use in a previously presented Dynamic Velocity Prediction Program. Even though with foils, hulls are less frequently immersed, a reliable hull modeling is necessary to properly simulate the critical transient phases such as touchdowns and takeoffs. The model is a multihull float with a waterline length of 2.5 m. Measurements were made in head waves in both captive and semi-captive conditions (free to heave and pitch), with the model towed at constant yaw and speed. To get as close as possible to real sailing conditions, experiments were made at both zero and non-zero leeway angles, sweeping a wide range of speed values, with Froude numbers up to 1.2. Both linear and nonlinear wave conditions were studied in order to test the limits of the modeling approach, with wave steepness reaching up to 7% in captive conditions and 3.5% in semi-captive ones. The paper presents the design and methodology of the experiments, as well as comparisons of measured loads and motions with simulations. Loads are shown to be consistent, with a good representation of the sustained non-linearities. Pitch and heave motions depict an encouraging correlation which confirms that the modeling approach is valid.

Part 2: Simulation methodology and numerical uncertainty for RANS-CFD for the hydrodynamics of wind-assisted ships operating at leeway angles

A Reynolds-averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for wind-assisted commercial ships. This paper describes the simulation verification exercise, performed in support of the experimental validation presented in Part 1 of this two-part series describing the RANS-CFD method employed in this research. The predominance of large-scale separated flow structures in the wake of the sailing ship, an artefact of sideforce production necessary for sailing, points to a careful verification exercise and estimate for the numerical uncertainty to support the systematic investigation of wind-assisted ship hydromechanics and meshing guidelines within the available computer resources. Methods for CFD uncertainty quantification are defined and implemented for verification cases at leeway angles equal to 0ᵒ, 6ᵒ, and 9ᵒ. Analysis for four sets of grids with different meshing strategies and for varying time steps results in a grid definition and time step for simulation validation. Numerical uncertainty as adopted in Part 1 for validation is defined. Finally, the meshing strategy for full-scale simulation is described, as used for the production runs of the Delft Wind Assist Series.

THE EFFECT OF LEEWAY ANGLE ON THE PROPELLER PERFORMANCE

One of the aspects influencing the performance of wind assisted vessels is the effect of leeway (drift) angle on the propeller performance. It is known that due to leeway the delivered propeller power and propulsive efficiency can vary significantly from the straight sailing condition. This effect of leeway angle is studied using a combination of viscous flow calculations and captive model tests for one twin screw and three single screw vessels. It is observed that the changes in mean axial velocity and pre-swirl rotation in the wakefield due to a combination of leeway angle and propeller suction are sufficient to describe the trends observed in captive model tests. This knowledge is used in a proposed prediction method to model the changes in propeller thrust and torque due to leeway angle at the design stage. The prediction model combined with a fit of the average wake parameters for the studied vessel types is finally used the show the trends in propulsive efficiency and delivered propeller power at constant propeller rotation rate and ship speed for small leeway angles.

Part 1: Experimental validation of a RANS-CFD methodology for the hydrodynamics of wind-assisted ships operating at leeway angles

A Reynolds-averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for wind-assisted commercial ships. This paper is Part 1 of a two-part series describing the RANS-CFD method adopted for this study. The modelling challenge presented by large separated flow structures in the wake of a sailing ship points to a conscientious validation study. A validation data set, consisting of hydrodynamic forces acting on the ships sailing with a leeway angle, was collected at the Delft University of Technology towing tank facility, for bare-hull and appended cases. Appended cases were designed to represent a broad range of appendage typologies: Rudder, Bilge-keels, Skeg, and Barkeel. A validation statement is made for simulations for the entire bare-hull series and for appended geometries, excepting the Bilge-keel case. The simulation method is described in Part 2, including the assessment of the numerical uncertainty.

Numerical Simulations of a Surface Piercing A- Class Catamaran Hydrofoil and Comparison Against Model Tests

Hydrofoil supported sailing vessels gained more and more importance within the last years. Due to new processes of manufacturing, it is possible to build slender section foils with low drag coefficients and heave stable hydrofoil geometries are becoming possible to construct. These surface piercing foils often tend to ventilate and cause cavitation at high speeds. The aim of this work is to define a setup to calculate the hydrodynamic forces on such foils with RANS CFD and to investigate whether the onset of ventilation and cavitation can be predicted with sufficient accuracy. Therefore, a surface piercing hydrofoil of an A-Class catamaran is simulated by using the RANS software FineMarine with its volume of fluid method. The C-shaped hydrofoil is analyzed for one speed at Froude Number 7.9 and various angles of attack (AoA) by varying rake and leeway angle in ranges actually used while sailing. In addition, model tests were carried out in the K27 cavitation tunnel of TU-Berlin, for the given hydrofoil and in the same conditions as simulated with CFD to provide data for validation. Based on the CFD calculations this paper presents how the rake and leeway angles influence the foil's lift to drag ratio. The simulations have been verified by extensive analyses, including domain size verification for unrestricted water, mesh refinement and y+ verification. The influence of the dimensions of the K27 (cavitation tunnel of the Technical University of Berlin) on the flow around the hydrofoil and the wave system is also considered, as the test section of the K27 significantly influences the flow around the foil, the forces and the wave elevation. Finally the CFD results are compared against the experiments conducted in the K27.

Optimization of upwind sailing applying a canting rudder device

The research explained in this paper was carried out to investigate the efficiency of different steering systems on sailing yachts. The steering system of a sailing yacht mostly includes a simple steering system and a hydrodynamic shaped single rudder, or multiple rudders, depending on boat characteristics. One of the basic design guidelines for fast sailing yachts involves reducing the wetted surface to the minimum allowed by the dynamic stability while maintaining the optimal sailing performances. Deficiencies of different steering systems are discussed and their influences on total lift and yaw moments; yacht manoeuvrability in different sailing directions is also analysed. The discussion is focused on steering systems applicable in practice and accepted by the yacht-building industry, although several innovations may be found that remained in their development stage because of their complexity in construction, maintenance, use itself and reliability. The canting rudder is analysed applying an uncommon approach for ship building. All measurements have been conducted at sea applying on board sensors for position and acceleration acquirements. The purpose of the research is to demonstrate that the use of the bended rudder can reduce the leeway angle, the upwind sailing angle and increase the velocity made good to windward.

Research on the Wing's Thrust of “Wenzhuhai” Ship with Install Wing

In this paper the resistance of one ship with installing wing and wing’s thrust have been studied in both theory and simulation by fluent software. The influence of ship resistance which from leeway angle and down helm was analyzed on the basis of the examination result of ship model test.

On predicting boat drift for search and rescue

A theoretical model for predicting boat drift for search and rescue missions is presented in this work. The drift model is based on the law of physics which govern the motion of a floating body in a given wind and surface current field. In terms of the empirical aerodynamics force coefficients of the boat or any other drifting object, external wind field, and current field, the drift velocity of the boat being searched for can be obtained. The uncertainty of the characteristics of the boat’s drift is evaluated by interval analysis of the uncertainties of the characteristics of the drifting boat and external forcing fields. The search area expansion and the source of uncertainty are systematically evaluated. The current statistical model-based operational definitions of leeway drift, leeway rate, leeway angle, divergence angle, leeway divergence, downwind component of leeway, and crosswind component of leeway are clarified in light of the presented theoretical model. The divergence angle and leeway divergence are evaluated through the interval analysis of the uncertainty of the parameters involved.

실습선 한바다호의 강풍시 항내 어프로칭 조선 및 예인선 사용 기준에 관한 연구

실습선 한바다호는 수면 상부의 구조물이 상대적으로 큰 선형으로 풍압력의 영향을 크게 받아 압류나 회두와 같은 현상이 비교적 크게 나타나고, 특히 접이안 또는 항내에서 저속으로 운항할 경우 이러한 외력의 영향이 현저하게 작용한다. 본 논문에서는 파도가 충분히 발달되지 않은 항내 조선을 전제로 한바다호의 풍압력과 풍압모우멘트를 산출하여 상대 풍향과 풍속에 따른 표류각과 대응 타각을 분석하였다. 또한, 실습선 한바다호의 접이안시 예인선의 소요마력 결정을 선체에 작용하는 풍압력을 기초로 산출하였고, Bow Thruster를 이용한 접이안 가능 최대 풍속을 제시하였다. 연구 결과는 풍압력이 크게 작용하는 대형선의 항내조선과 예인선 운용에 큰 도움이 될 것으로 판단된다. T.S. HANBADA has a relatively large hull and superstructures above the water line, so she has much of leeway or turning of bow with the effect of winds. Especially on berthing, unberthing and/or sailing on low speed, these effects take place more significant. Therefore, it was carried out the numerical calculation of the wind force and moments acting on the T.S. HANBADA, and then calculated the leeway angle and counter rudder angle with the relative wind direction and velocity. Also, it was suggested the maximum wind velocity which could be berthed or unberthed used by bow thruster and the tugboat operations in strong winds. These results will be great helpful to the vessels with large superstructures on ship's handling in harbour or tugboat operations.

요트 킬의 형상에 따른 유체력 및 유동특성 연구

Yacht is operated by wind-driven thrust on the saii, but also experiencing the side force. Thus the keel attached on the bottom of main hull prevents it from flowing sideway. Since the keel affects the stability and thrust of yacht, its selection is one of the most important factor in design. In the present paper the correlation between yacht hull and keel was investigated. through comparison of forces measured at various combinations of heeling and leeway angles with and without keel. Keel-only test was also performed to find out the drag and lift characteristics of keel itself. finally three different types of keel, i.e. fin keel, bulb keel and winglet keel were tested to compare their advantages and drawbacks.

부산항 연안해역에서의 소형선박 표류 거동특성 관측 및 분석

표류지점 추정 모델의 환경 입력자료를 확보하기 위해 부산항 연근해에서 표류실험을 실시하였다. 실험에는 크기가 다른 4척의 선박(10, 20, 50, 90톤급)이 사용되었다. 그중 50톤급 선박에는 해류, 바람, 위치를 자동적으로 기록하는 계기들을 장착하였고, 나머지 선박들에서는 분산각 추정 연구를 위해 위치자료만 기록하였다. 각 선박들의 위치는 DGPS와 자동위치발신기(APRS)를 사용하여 기록하였다. 실험은 풍속 2~10m/s, 유속 0.5~1.5m/s의 환경에서 행하여졌으며, leeway는 선박 표류속도에서 표층의 유속성분을 제거하여 구하였다. 50톤급 선박의 leeway rate는 풍속의 약 3.6%인 것으로 분석되었으며, leeway 방정식은 <TEX>$U_L$</TEX> =0.042W -0.034로 표현되었고 leeway angle은 <TEX>$-30^{\circ}$</TEX>~<TEX>$40^{\circ}$</TEX>의 범위였다. To provide reliable data for drift prediction models, field experiments were carried out in the coastal region off Busan port. Four different size of vessels(10, 30, 50, 90G/T ton) were deployed for the experiment. Among them G/T 50ton class vessel was equipped with instruments measuring the currents, winds, headings and trajectory data. In the rest of vessels only the position data were recorded for the purpose of target divergence study. The trajectories of each vessel were measured by DGPS(Differential Global Positioning System) and collected by APRS(Automatic Position Reporting System). The experiment was done in wind of 2~10m/s and current of 0.5~1.5m/s. The leeway was derived by subtracting surface current velocity from target drifting velocity. The leeway rate of G/T 50ton vessel was found to be about 3.6% and the computed leeway speed equation was <TEX>$U_L$</TEX>=0.042 W - 0.034. The processed leeway angle data were deflected by <TEX>$-30^{\circ}$</TEX>~<TEX>$40^{\circ}$</TEX> from the direction of ship drift.

Computation of Hydrodynamic Forces Acting on Sailing Yacht by Means of Surface Panel Method

Predictions of hydrodynamic forces acting on a sailing yacht are very important, especially in the hull form design of racing yachts as used in America's cup. However those accurate predictions are very difficult, because the sailing yacht has complex geometry with a large fin keel, and the free surface problem must be solved under the condition with leeway angles.In the present study, hydrodynamic forces acting on sailing yachts are computed by means of a surface panel method. Morino's method, which is well known as one of the useful surface panel methods for lifting bodies, can be extended to the free surface problem around an advancing body with leeway angles under the linearized free surface condition. According to this formulation, numerical examples are given for two sailing yacht hull forms, KIT 34 and NCAC 12 m class, in which computed results of wave making resistance without leeway, hydrodynamic forces with leeway and side wave profiles with and without leeway are compared with the experimental results. In order to investigate the wave making effect of the fin keel, these computations are shown for both conditions with and without the fin keel.

Turbulence Effects on the Design and Performance of Low-Drag Keels

Achievement of laminar boundary-layer flow over the keel of sailing yachts offers great potential for increased boat speed resulting from the reduction in viscous drag. The intensity and the spectral energy distribution of small-scale turbulence in the upper layer of the ocean can have a large effect on the extent of laminar flow and, hence, the drag reduction. A detailed summary and interpretation is provided of measured turbulent intensities and length scales in the upper ocean. An analysis is given of the effect of small-scale turbulence on boundary-layer transition and profile drag for two laminar-flow foils at zero and moderate leeway angles. Using the modified en-transition criterion it is shown that the level of small-scale oceanic turbulence is an important parameter in the design of a laminar-flow foil. At high turbulence levels, the foil with a more forward location of the minimum-pressure point generates less drag than the foil with a more aft location of the minimum-pressure point at the same flow conditions.

Sailing Performance of Ocean Cruising Yacht by Full-Scale Sea Test

The sailing performance of a 10.6 m-LOA ocean cruising yacht was measured by sea test and the results were compared with calculated values. The sea test was carried out to examine the steady sailing performance as well as the dynamic performance in waves.First, the steady sailing performance was estimated by calculating the velocity prediction program (VPP). The VPP calculates the equilibrium sailing state of the boat considering the balance of X, Y forces and K, N moments, respectively. The hydrodynamic force coefficients of hull were derived by the towing tank test using 1/4.275 scale model, and the aerodynamic force coefficients of sail were calculated using the results of a wind tunnel test.Then, the sailing state parameters of the full-scale were measured under various wind conditions. The measured items were wind velocity, wind direction, boat velocity, leeway angle, heel angle and rudder angle. These values were compared with the results of VPP. The both results were in good agreement and this indicates that the calculating method and fluid dynamic coefficients for VPP were adequate.Next, The motion of the boat was measured in conjunction with wave measurement using a throw-in type wave meter. A vertical gyro and accelerometers were used for measurement of rolling, pitching and heaving motion of the boat. These data were analyzed by means of spectral analysis, and compared with both model test and numerical calculations. The model test was performed in regular wave conditions at the towing tank. The analyzed results indicated the sail damping effect on the rolling motion quantitatively and the distinctive feature of motion for the sailing cruiser in waves.

練習帆船日本丸の帆の空力特性について

The authors have carried out wind tunnel experiments on a 1/75 scale model of the sail training ship NIPPON MARU at Osaka University. The experiments consisted of two parts, one is flow visualization around wind speed vanes located on the top of jigger mast and the other is measurement of aerodynamic forces of the model. In visualization experiments, the wind has been getting over her sails. Particularly we have measured the angle of attack to the wind speed vane. As the propeller vane decrease measured wind velocity by the vertical angle of attack, we have corrected wind speeds and directions that had measured in 1986 on board experiments of the NIPPON MARU. Using those data we have identified aerodynamic coefficients, these are thrust force coefficient C_X, lateral force coefficient C_Y, yaw moment coefficient C_N and heeling moment coefficient C_K. We have compared them with wind tunnel tests results. And both results have coincided well in the thrust force coefficient C_X. But wind tunnel results are smaller than on board results in another three coefficients. It may be caused by the estimation of lateral water resistance that was fully depend on the leeway angle which was indicated with integer numbers by D.S. log.

Keel Design for Low Viscous Drag

Foil and planform parameters which govern the level of viscous drag produced by the keel of a sailing yacht are discussed. It is shown that the application of laminar boundary-layer flow offers great potential for increased boat speed resulting from the reduction in viscous drag. Three foil shapes have been designed and it is shown that their hydrodynamic characteristics are very much dependent on location and mode of boundary-layer transition. The planform parameter which strongly affects the capabilities of the keel to achieve laminar flow is leading-edge sweep angle. The two significant phenomena related to keel sweep angle which can cause premature transition of the laminar boundary layer are crossflow instability and turbulent contamination of the leading-edge attachment line. These flow phenomena and methods to control them are discussed in detail. The remaining factors that affect the maintainability of laminar flow include surface roughness, surface waviness, and freestream turbulence. Recommended limits for these factors are given to insure achievability of laminar flow on the keel. In addition, the application of a simple trailing-edge flap to improve the hydrodynamic characteristics of a foil at moderate-to-high leeway angles is studied.

Performance of Light-and Heavy-Displacement Sailing Yachts in Waves

Experiments with light-and moderate-displacement sailing yacht models have been carried out in the Delft Ship Hydromechanics Laboratory to investigate heave, pitch, and added resistance in regular waves. The experiments included conditions with and without heel and leeway angles. The results are analyzed and compared with calculations based on a strip theory method. Numerical methods are used to predict and to compare the performance of sailing yachts in realistic irregular-wave conditions.

An experimental investigation of the flow past hulls at leeway

When a ship is sailing, the hull moves obliquely through the water at a greater angle of leeway than when under power alone. A wind tunnel is used to investigate the flow past a Mariner type hull for the range of leeway angles expected when sailing. Flow visualisation experiments are conducted, and the non-wave-making components of hydrodynamic hull forces are measured. The hull is a very low aspect ratio lifting body which develops (horizontal) lift to balance sail side force; it does this at the expense of considerable induced drag. The body is slender and fairly streamlined, but flow separation occurs at the bilges and shed vortex sheets roll up to form longitudinal vortices. These vortices, associated with much of the drag penalty, trail downstream near to the hull; they generally maintain their identities, at least for flow distances of the order of the ship's length. There is, however, some merging of vorticity between proximate vortices. A systematic series of hull-like blocks is similarly tested to investigate the influence of certain parameters such as beam, draft and trim. The flow about these simplified hulls shows the same general features as that about realistic hulls. Specific conclusions for the block hulls indicate that the hydrodynamic repercussions on sailing ship performance of various changes are as follows — An increase in beam is marginally detrimental — An increase in draft is beneficial — Allowing the vessel to heel is beneficial — Trimming the vessel by the stern is beneficial.

Performance of a Hydrofoil Sailing Boat (1 St Report)

The performance of a hydrofoil sailing boat, which has dihedral-angled and surface-piercing foils, at high speed is described.A simple method of performance prediction was devised, which considered two important factors for sailing boats as follows : (i) variation of hydrodynamic drag caused by change of heel and leeway angles ; (ii) limitation of sailing performance due to capsizing.For the present study one typical sailing hydrofoil configuration was used, i. e. a 5. 08m long catamaran, with a pair of surface-piercing front (main) foils having 40 degree dihedral angles, and one horizontal rear foil, which formed an inverted “T” in combination with the rudder.The calculations aimed to predict the effect of dihedral angles, width between the foils, and weight of the boat on performance.The results obtained were as follows : (1) the present method gives good estimated values for the performance of a hydrofoil sailing boat with dihedral-angled and surface-piercing foils ; (2) the sails should be trimmed to produce the maximum thrust force, but the performance of a boat to a beam reach is subject to limitation due to capsizing, and to windward, due to leeway angle ; (3) although the true wind angle varies extensively, the apparent wind angle at high speed varies much less, so that the aerodynamic drag angle of the sail can be regarded approximately constant; (4) the predicted heel angle is between 0 and-6 degrees at high speed (heel to weather-side); (5) the aerodynamic force coefficients of the sail estimated from the seatrial are smaller than the wind tunnel test data ; (6) there are small differences between the predicted and measured immersion of the hydrofoils ; (7) the weight of a boat has an appreciable effect on the light wind performance ; (8) the dihedral angles and width between the foils have a considerable effect of the boat performance. The optimum dihedral angle is between 40 and 45 degrees, and the optimum width between foils is around 1. 21. 6 hs, hs beeing the height of C. E., the centre of sail force, above the foil bottom.