Design Methodology
The design spiral I use is much less cumbersome than the design spiral used in generic naval architecture. It is composed of three analysis tools and two design sections. The entrance to the spiral is a preliminary design section. The preliminary design should utilize a collection of software to automatically create a design based upon the buyer's requirements. Hydrostatics, structures, and peroformance analysis all take place which the design is in a "static" form. Once these analyses take place, the design is refined, and the spiral is repeated.
Preliminary design is the basic component of any design phase. The goal of the phase is to start with a set of needs for a yacht, and come up with the basic parameters. Most tools in preliminary design are spreadsheets which use parametric analysis. Some tools are used for geometric estimates, while more advanced tools can provide performance estimates. The preliminary design stage actually contains miniature tools of the full analysis components.
After a preliminary design is created, the most basic question is "does the boat float?" There are a variety of tools used for Hydrostatic analysis. Traditionally, hydrostatics are calculated by hand from a lines plan. With the development of CAD systems, many design tools include the calculations automatically. There are even more advanced tools, such as GHS, dedicated only to hydrostatics. However, even spreadsheets may be used to calculate hydrostatic analysis including iterating for sinkage and trim.
Structural Analysis for yacht design is varied based on the materials used for construction, and the amount of money and accuracy needed for the calculations. Many boats may be designed based on scantling rules to determine the arrangement and amount of material needed. Simple load estimates can be used to calculate the stresses in the hull or the rig. A more advanced method includes a direct stiffness method to subdivide the hull to solve for the stresses. Finally, finite element analysis may be performed on the yacht when precision is very important.
Performance analysis in yachts estimates the speed of the boat. The first component of performance analysis is hydrodynamics, the computation of fluid flow around the hull. The second component of performance analysis is aerodynamics, the computation of air around the sails. There are many ways of calculating fluid flow. Strip theory is a simple method of calculating fluids by calculating the flow across discrete strips of an object. Potential flow is a method to calculate flow by first assuming that fluid is inviscid. Tank and tunnel testing provide experimental results based on models. Finite volumes and even finite element analysis can calculate flow of viscous fluids and can even model turbulence. Particle based simulations show promise by calculating fluids in a meshless manner.
Once fluid calculations are performed, there are various ways to calculate the speed of a yacht through Velocity Prediction Programs (VPPs). VPPs iterate between hydrodynamic and aerodynamic forces to come to an equilibrium conditions on a moving body. This section includes a discussion on hydrodynamics, modelling, and data recovery. Also included are hydrodynamic tools, VPP tools, and many papers on the subject.
After all of the above steps have been performed, the process is repeated multiple times until all parts of the design correlate. Posted in the Final design section are some of my designs showing how the design process works.