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CAE

Yacht Builder Bends the Curve with 3D CAD

2 Dec, 2007 By: Cadalyst Staff

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In his 25 years of designing racing yachts, John Reichel has seen a lot of changes in a relatively short time when you consider boatbuilding is a trade that is thousands of years old. As the principal of Reichel/Pugh Yacht Design in San Diego, California, Reichel has watched a transformation in the tools, materials, and building methods of the industry.

After his graduation from the University of Michigan, Reichel followed the custom of hand drafting, just like centuries of boat designers before him. To describe a hull's complex 3D curves to builders, Reichel had to draw dozens of cross-sections on paper. "I used to spend most of my time sharpening pencils," he jokes.

Today, the curves of yacht designs are much more easily created as 3D computer models. 3D technology, however, has become more than a replacement for drafting. Through virtual models, Reichel/Pugh can simulate the effects of loads, winds, and waves to further refine the nuances of performance. Instead of functioning as a mere static drawing, 3D has taken on an active role in yacht construction.

Curve Ahead
Based in San Diego, Reichel/Pugh specializes in racing yachts custom made for competition on the world's stage. The company has also begun to expand into high-performance cruising boats. Unlike the "square" CAD seen in most architecture and engineering offices, Reichel/Pugh's designs are about curvature. The company uses surface modelers based on nonuniform rational B-splines (NURBS), which are true mathematic equations of curved surfaces. These modelers can calculate each point on a hull with extreme accuracy.

Reichel/Pugh generates its hull shapes in FastShip, a NURBS modeler from Design Systems Technologies that contains specialized templates to create such esoteric nautical objects as bossings, bulbous bows, knuckles, and twin skegs. Other components are modeled in a more general-purpose NURBS modeler, Rhinoceros. Because both programs are NURBS-based, the FastShip hullforms are imported into Rhino and all boat parts are assembled into a master 3D model. Reichel also uses Rhino to render his final designs as photorealistic examples.

Dynamic Testing
In architecture, building loads typically rest on a static foundation. In sailboat design, the structural loads are dynamic: the force of gravity, drag from water, and wind resistance fluctuate constantly while the craft is in motion.

"Before building, we run the models through simulation, analysis, and performance prediction programs that allow us to optimize our designs. Many of the new hull shapes are built as third-scale models and tested in a towing tank laboratory," Reichel explained. Forces on the model are measured, expanded to full scale, and used to validate computational fluid dynamics (CFD) experiments on the 3D NURBS models. The results from the tank tests and CFD runs are used in the velocity prediction programs to assess many aspects of the yacht's performance. Reichel uses several CFD programs, including Splash (from South Bay Simulations), Comet (from CD-adapco), and Overflow (from NASA).

"In addition to the hydrodynamics, structural efficiency is a critical consideration," Reichel said. "Lightweight and stiff structures are required to maximize performance." Using finite-element analysis (FEA) programs, Reichel/Pugh engineers can assess the structural requirements of the full-scale hull. To conduct FEA analysis, the company uses Nastran (from Noran Engineering), Algor, and Cosmos (from SolidWorks) software.

Once design and testing are completed, the 3D model is sent electronically to Reichel/Pugh's contracted boat builders around the world. Information that used to be transmitted in mailing tubes or thermal faxes is now simply emailed.

"Looking back on that era, it all seems so primitive," Reichel mused. "Builders are all now at the level where we give them data electronically, either in 2D or 3D formats. They use the electronic files directly from CNC machines and laser cutters."

More Complexity, Less Time
As a consequence of new 3D technologies, the schedule of yacht design and construction can proceed more swiftly. Reichel spends less time drawing than 25 years ago, but like so many advancements in efficiency in our technological age, time-saving software creates more complexity, rather than more leisure.

"We certainly do more work. The level of detail in the design has increased. In the past, many of the details were left to the builder. With our design capabilities now, all the geometries are defined, and every carbon ply and piece of hardware is specified," Reichel said.

For Reichel/Pugh's luxury cruisers, engineers also need to think about the internal working of their yacht designs. While racing boats are sparse on accommodations, cruisers give occupants the means to traverse oceans with all the comforts of home. Reichel/Pugh's team of designers must plan interior space economically in order to fit equipment and conduit into close quarters. Designers use the 3D model to mitigate the overlap of hydraulic systems, computer controlled systems, powered winches, generators, and air conditioning.

"You need to have a good handle on the overall project and the space required at an early stage to avoid major problems later on," Reichel said. "Computer modeling gives us the visualization and metrics needed to solve these complex problems."