Finite Element Analysis (FEA) is mature technology that has been in use for several decades as a tool to optimize structures for a wide variety of applications. Its application to composite structures is not new, however the technology for modeling and analyzing the behavior of composite structures continues to evolve on several fronts. This paper provides a review of the current state-of-the-art with regard to composites FEA, with a particular emphasis on applications to yacht structures. Topics covered are divided into three categories: Pre-processing; Postprocessing; and Non-linear Solutions. Pre-processing topics include meshing, ply properties, laminate definitions, element orientations, global ply tracking and load case development. Post-processing topics include principal stresses, failure indices and strength ratios. Nonlinear solution topics include progressive ply failure. Examples are included to highlight the application of advanced finite element analysis methodologies to the optimization of composite yacht structures.

A coupled aerodynamic/structures approach is presented for predicting the flying shape and performance of yacht sails in upwind conditions. The method is incorporated in a flow simulation computer program, and is part of an ultimate objective for a simultaneous aeroelastic/hydro analysis in a Dynamic Velocity Prediction Program (DVPP), that will include a 6DOF motion solver, and at some point could include calculations in waves. The time-stepping aerodynamic module uses an advanced vortex lattice method for the sails and a panel method with special base separation treatment to represent the abovewater part of the hull and mast. A coupled inverse boundary layer analysis is applied on all surfaces including both sides of each sail membrane; this computes the skinfriction drag and the source displacement effects of the boundary layers and wakes, including bubble and leeside “trailing-edge” type separations. . At each step, the computed aerodynamic pressure and skin-friction loads are transferred to a coupled structures module that uses a network grid of tension “cords” in each sail membrane, each cord representing a collection of fiber “strings”. The solution of a structural equilibrium matrix provides the displacements needed to achieve balance between the aerodynamic and tension loads at each grid point as the shape iterations proceed. Details of the methodology used are presented and comparisons of predicted aerodynamic forces to wind tunnel results and an existing VPP sail model are provided. In addition, predictions are compared to some simple experiments to demonstrate the aerodynamic/structural coupling necessary to predict flying shape. Finally, an outline is given for incorporation of this methodology into the planned Dynamic Velocity Prediction Program.

Sandwich structures are increasingly used in marine applications where high bending specific stiffness and strength are required. So far, expanded polymeric foams such as Styrene Acrilonitrile (SAN) and Polyvinyl Chloride (PVC) have been proved to be the most suitable core materials for motor and sailing yacht sandwich constructions. ISO standards have accepted these materials and suggested design rules built around their mechanical properties. One of the main drawbacks in the application of sandwich composite structures is the fact that their load carrying ability may be significantly reduced by the presence of a local damage such as core indentation or partial face sheet delamination. Local damages usually take place in dynamic scenarios and they can be caused by indentation due to floating object impacts, interaction with mooring structures and rocks or by high deformations due to slamming loads. It should be noted that such damages usually cannot be observed from outside the sandwich construction and they may cause a serious reduction in load-bearing capacity, jeopardizing the safety of the boat and its crew. ARPRO® is an expanded polypropylene (EPP) foam extensively used in the automotive industry, where it has gained full approval due to its outstanding energy absorption characteristics. Unlike standard polymeric foams, ARPRO® foams possess a hyper-elastic stress versus strain response and recover their initial shape after having undergone very high deformations. For this reason this material is expected to enable the design of sandwich panels with an enhanced damage tolerance. In the case of an impact, the core stores the energy as it is compressed and once the load is released it will return to its original geometry preventing the skin from debonding. SAN or PVC cores would absorb the energy by destroying their cell structure leading in this way to core-skin delamination. On the other hand, ARPRO® has lower shear and compressive moduli which implies lower sandwich structures performances in static scenarios. This paper presents static and dynamic testing aimed at determining the relative mechanical performances of sandwich beams cored both with ARPRO® and SAN foams. Comparison of the static and dynamic response ofthe two materials shows that ARPRO® is a potentially competitive core material for composite sandwich construction.

Aerodynamic performance of a Japanese traditional square rig, “Bezai-ho”, and a Chinese lug rig, “Shinshi-bo” in Japanese, were studied by means of wind tunnel tests, sea trials and numerical calculations. Sail forces and sail shapes were measured in the wind tunnel tests. A sail dynamometer boat Fujin was employed for the sea trials, by which aerodynamic forces acting on sail, sail shapes, and sailing conditions of the boat can be measured at the same time. Using the measured sail shapes, sail forces are calculated by means of a vortex lattice method. Differences of sail performance of the above mentioned two types of rig were clarified in the wind tunnel tests and sea trials. The calculated sail performance shows good agreements with the measured data in upwind condition. Dynamic sail performance of the two types of rig during tacking and wearing operations was also clarified in the sea trials using the boat Fujin. Details of sail force variation in time during maneuvering can be investigated by the sail dynamometer system. For the “Bezai-ho,” the backward force acting on sail when the boat changes tacks (wind over the bow) was investigated. At this moment, the square sail falls into a “caught aback” situation, which makes the tacking operation difficult. On the other hand, “Shinshi-bo” showed good steady performance similar to that of the modern marconi rig, and good tacking performance. Obtained results of steady and dynamic sail performance in this paper provide useful information for sail trimming and maneuvering of boats equipped with the western square rigs and modern lug rig introduced by H.G. Hasler.

Improving lightweight structures is a continuous challenge for yacht hull structural components. Sandwich beams consisting of strong face sheets and a low density core have gained application as weight efficient structures subjected to bending loads. The sandwich structure provides good stiffness by keeping the face sheets at a fixed distance with considerable weight reduction over a statically equivalent monolithic panel. New fabrication technologies now allow for hybrid sandwich structures, known as X-cor to be manufactured. X-cor panels consist of carbon fiber face sheets separated by a closed cell polymer foam core reinforced with carbon fiber or metallic (Titanium or Steel) pins. The pins are inserted into the light weight foam core in the out-of-plane direction and extend from face sheet to face sheet. Pin orientation and concentration can be varied providing a large design space for scientist and designer to explore and to improve material performance. The effect of core thickness, pin reinforcing and polymer foam core on the out-of-plane axial compression response of these panel will be presented. The through thickness three- point simply supported bending behavior of these reinforced panels is used to evaluate the core shear, stretch, face sheet failure characteristics of the structures. Explicit experimental observations are used to develop and calibrate analytical energy balance models to generate failure mode maps describing the panel collapse load as a function of geometry. Multi-scale effective modeling, blurring the distinction between structural and material behavior, will enable optimization of the X-cor sandwich structures in light of Yacht hull design requirements. The mechanical response of X-cor sandwich panels will be compared to current Yacht hull materials using material selection charts, and demonstrator components presented.

Offshore-capable sail training craft (STC) specifically designed and built for the United States Naval Academy (USNA) have been a cornerstone of its seamanship training program since 1939. Currently the fourth generation of these craft is under development and this paper summarizes research projects performed by eight midshipmen in the areas of parametric design criteria, structures, appendage development and analytical tool evaluation. While the results are oriented toward the new sail training craft, they are general enough to apply to any medium-sized offshore sailing vessel.

This paper relates the results of our investigations to improve the design of "full-length" composite battens. The paper starts by describing the technologies used to manufacture battens and the role they play in sail equilibrium. A method is then proposed to help in the design of battens. It is a blend of theory and experiment that focuses on the strength of the battens. When a batten is close to rupture, it is subject to large rotations and must therefore be modeled by non-linear computations of the slender beam type. In addition, we have calculated the stress distribution in a laminated composite. As for the tricky problem of the maximum allowable stresses for composite materials, we have shown that a specific characterization test is necessary. With a series of examples, we show that stronger battens can be developed through selection of the cross-sectional areas and the materials.

The SPLASH free-surface potential flow panel code computer program is presented. The 3D flow theory and its numerical implementation are discussed. Some more conventional applications are reviewed, for steady flow past solid bodies, and for classical linearized free-surface flow. New free-surface capabilities are also described, notably, steady nonlinear solutions, and novel unsteady partially­nonlinear solutions in the frequency domain. The inviscid flow method treats both free-surface waves and lifting surfaces. The calculations yield predictions for complex interactions at heel and yaw such as wave drag due to lift, the effect of the free­surface on lift and lift-induced drag, and unsteady motions and forces in oblique or following seas. These are in addition to the usual predictions for the simpler effects considered separately, for example double-body lift and induced drag, and upright steady wave resistance or added resistance in head seas. For prediction of total resistance, the use of computed variable wetted areas and wetted lengths in a standard semi-empirical, handbook-type "viscous stripping" algorithm provides a more accurate estimation of viscous drag than is possible otherwise. Results from a variety of IACC and IMS yacht design studies, including comparisons with experimental data, support the conclusion that the free­surface panel code can be used for reliable and accurate prediction of sailboat performance.

The structural design of adequately strong, light weight yachts is studied with emphasis upon optimum strength to weight tempered by the practical considerations of cost, durability and construction capabilities. The properties and relative weights of the principal construction materials are reviewed. Design philosophy and its implementation for the hull, deck and hard points are developed. Specific examples of interest for rational design are offered. Builder's problems of materials and craftsmanship are discussed.

The purpose of this paper is to present a very general overview as to how basic concepts of aerodynamics and hydrodynamics can be utilized in the selection and trim of sails. I have used the term selection to go all the way back to the routes of designing and selecting a rig for a given boat. The paper introduces absolutely no data and, in fact, does not explore any existing data in detail. Its main purpose is to show that almost any decision on rig or sails on a sail boat is always a compromise of varying forces. Sometimes these compromises are conflicting dynamics of the hull and sails, other times the forces are man-made such as rule parameters. Perhaps I could have done a more scien­tific job by choosing just one set of parameters that are in conflict and explored these in great detail showing how a conclusion can be reached from all the varying inputs into one particular problem involving rig, sails or hull. This type of thorough analysis, which would obviously require more exacting research to prove the hypothesis once defined, is not my strength. Therefore, it would be inappropriate for me to do such an analysis. My strength is in actually applying a large range of sail­ing theory to actual on-the-water sailing conditions. What I hope to accomplish by this paper is to let sailors realize that when making a decision on a rig, a particu­lar sail, or how to trim a particular sail, they first must decide what they want to accomplish with the rig, sail or sail trim. They must think about it in general terms as to what direction they should take aerodynamically or hydrodynamically to get the forces they want to achieve. Then they must go about the task with the full realization that there is no preset answer and that they must be willing to experiment in order to hone in on the optimum. The input variables of the hydrodynamics of a pitching yacht going to weather in a moderate breeze that is constantly receding and increasing in velocity as well as direction defies simple solu­tions. Thus, the best compromise is usually the best solution.