WHY YACHT RUDDERS BREAK

For most sailing yachts, losing a rudder is probably the most catastrophic structural failure other than losing the keel. Rudder failure happens with distressing regularity. This paper examines the hypothesis that the underlying reason is design failure. There are many qualitative decisions to be taken in the design calculation process. Example calculations are presented which show that the maximum rudder force generated in steady state conditions is easily underestimated. For a typical spade rudder of a typical modern production sailing yacht, the normal rudder force should be calculated using a boat speed of at least 125% hull speed, and a force coefficient of at least 1.3. Care must be taken in selecting an appropriate value for the allowable stress of the material used for the stock.

An Improved Procedure for Strongly Coupled Prediction of Sailing Yacht Performance

In this paper, an improved procedure for strongly coupled prediction of sailing yacht performance is developed. The procedure uses 3D RANS CFD to compute the hydrodynamic forces. When coupled to a rigid body motion solver and a sail force model, along with a rudder control algorithm, this allows sailing yacht performance to be predicted within CFD software. The procedure provides improved convergence when compared to a previously published method. The grid motion scheme, partially using overset grid techniques, means that correct alignment between the free surface and the background grid is ensured even at large heel angles. The capabilities are demonstrated with performance predictions for the SYRF 14 m yacht, at one true wind speed, over a range of true wind angles, with up- and downwind sailsets. The results are compared to predictions from the ORC-VPP for a yacht with similar main particulars.

Improving the Downwind Sail Design Process by Means of a Novel FSI Approach

The process of designing a sail can be a challenging task because of the difficulties in predicting the real aerodynamic performance. This is especially true in the case of downwind sails, where the evaluation of the real shapes and aerodynamic forces can be very complex because of turbulent and detached flows and the high-deformable behavior of structures. Of course, numerical methods are very useful and reliable tools to investigate sail performances, and their use, also as a result of the exponential growth of computational resources at a very low cost, is spreading more and more, even in not highly competitive fields. This paper presents a new methodology to support sail designers in evaluating and optimizing downwind sail performance and manufacturing. A new weakly coupled fluid–structure interaction (FSI) procedure has been developed to study downwind sails. The proposed method is parametric and automated and allows for investigating multiple kinds of sails under different sailing conditions. The study of a gennaker of a small sailing yacht is presented as a case study. Based on the numerical results obtained, an analytical formulation for calculating the sail corner loads has been also proposed. The novel proposed methodology could represent a promising approach to allow for the widespread and effective use of numerical methods in the design and manufacturing of yacht sails.

Parametric Hull Design with Rational Bézier Curves and Estimation of Performances

In this paper, a tool able to support the sailing yacht designer during the early stage of the design process has been developed. Cubic Rational Bézier curves have been selected to describe the main curves defining the hull of a sailing yacht. The adopted approach is based upon the definition of a set of parameters, say the length of waterline, the beam of the waterline, canoe body draft and some dimensionless coefficients according to the traditional way of the yacht designer. Some geometrical constraints imposed on the curves (e.g., continuity, endpoint angles, curvature) have been conceived aimed to avoid unreasonable shapes. These curves can be imported into any commercial Computer Aided Design (CAD) software and used as a frame to fit with a surface. The resistance of the hull can be calculated and plotted in order to have a real time estimation of the performances. The algorithm and the related Graphical User Interface (GUI) have been written in Visual Basic for Excel. To test the usability and the precision of the tool, two existing sailboats with different characteristics have been successfully replicated and a new design, taking advantages of both the hulls, has been developed. The new design shows good performances in terms of resistance values in a wide range of Froude numbers with respect to the original hulls.

Parametric Hull Design with Rational Bézier Curves

In this paper, a tool able to support the sailing yacht designer during the early stage of the design process has been developed. Quadratic and cubic Rational Bézier curves have been selected to describe the main curves defining the hull of a sailing yacht. The adopted approach is based upon the definition of a set of parameters, say the length of water line, the beam of the waterline, canoe body draft and some dimensionless coefficients according to the traditional way of the yacht designer. Some geometrical constraints imposed on the curves (e.g. continuity, endpoint angles) have been conceived aimed to avoid unreasonable shapes. These curves can be imported in any commercial CAD software and used as a frame to fit with a surface. The algorithm and the related Graphical User Interface (GUI) have been written in Visual Basic for Excel. To test the usability and the precision of the tool, two sailboats with different characteristics have been replicated. The rebuilt version of the hulls is very close to the original ones both in terms of shape and dimensionless coefficients.

A Performance Depowering Investigation for Wind Powered Cargo Ships Along a Route

For a sailing yacht, depowering is a set of strategies used to limit the sail force magnitude by intentionally moving away from the point of maximum forward driving force, potentially reducing the ship speed. The reasons for doing this includes among others; reduction of quasi-static heeling angle, structural integrity of masts and sails and crew comfort. For a wind powered cargo ship, time spent on a route is of utmost importance. This leads to the question whether there is a performance difference between different depowering strategies and if so, how large. In this research, a wind-powered cargo vessel with rigid wings is described in a Velocity Prediction Program (VPP) with four-degrees of freedom, namely surge, sway, roll and yaw, with a maximum heel angle constraint. The resulting ship speed performance for different depowering strategies are investigated and the implications in roll and pitch-moments are discussed. The wind conditions when depowering is needed are identified. A statistical analysis on the probability of occurrence of these conditions and the impact of the different depowering strategies on the required number of days for a round-trip on a Transatlantic route is performed.

Why Yacht Rudders Break

For most sailing yachts, losing a rudder is probably the most catastrophic structural failure other than losing the keel. Rudder failure happens with distressing regularity. This paper examines the hypothesis that the underlying reason is design failure. There are many qualitative decisions to be taken in the design calculation process. Example calculations are presented which show that the maximum rudder force generated in steady state conditions is easily underestimated. For a typical spade rudder of a typical modern production sailing yacht, the normal rudder force should be calculated using a boat speed of at least 125% hull speed, and a force coefficient of at least 1.3. Care must be taken in selecting an appropriate value for the allowable stress of the material used for the stock.

Optimising Rig Design for Sailing Yachts with Evolutionary Multi-Objective Algorithm

The paper presents a framework for optimising a sailing yacht rig using Multi-objective Evolutionary Algorithms and for filtering obtained solutions by means of a Multi-criteria Decision Making method. A Bermuda sloop with discontinuous rig is taken under consideration as a model rig configuration. It has been decomposed into its elements and described by a set of control parameters to form a responsive model which can be used for optimisation purposes. Considering the contradictory nature of real optimisation objectives, a multi-objective approach has been chosen to address this issue. Once the optimisation process is over, a Multi-criteria Decision Making method based on a w-dominance relation is applied for filtering out the most interesting solutions from the obtained Pareto set. The proposed method has been implemented, and selected results are provided and discussed.

Science of the 470 Sailing Performance

This paper holds a significant place in the Journal of Sailing Technology, as the very last publication of Prof. Masuyama, published posthumously, and co-authors by Dr. Ogihara. For many decades, Prof. Masuyama has been a very influential and respected member of the sailing yacht research community world-wide, holding the chairmanship of the Sailing Yacht Research Association of Japan for close to 20 years, and being involved with the Japanese America’s Cup Challenge. His expertise and academic research have impacted generations of researchers, and his work on high performance sails, sailing yachts and velocity prediction remains at the forefront of sailing technology. It is therefore with great honour that the Journal of Sailing Technology presents the very last insights of Prof. Masuyama into the sailing performance of the 470 Olympic class dinghy.