Reichel/Pugh, a San Diego-based naval architecture and engineering firm, designed the superyacht, which was built by Southern Wind Shipyard in Cape Town, South Africa, and launched in 2016. Reichel/ Pugh relied on its 30-plus years of design experience and state-of-the-art computational tools to optimize the performance of this cruiser while delivering an uncompromised level of comfort and safety to meet its client’s needs.
One example of the firm’s engineering and optimization efforts can be found in the anchor arm. The next-generation appendage is half the assembled weight of its predecessor and actuated by two hydraulic rams at the push of a button to stow neatly out of sight when not in use.
A Lightweight, Functional Anchoring System
Since the SW-RP90 is oriented towards bluewater cruising in the Mediterranean and Caribbean, some of the systems you would not see on a race boat are necessary for safety, usability and cruising applications. Adrian Sawyer, who was involved in the structural design and materials engineering for Reichel/Pugh during the project, explains that the anchoring system is one such necessary feature.
The anchor itself fits securely inside of the anchor arm, which is able to retract cleanly under the deck to stow while sailing. When the boat goes to an anchorage, it deploys the arm off the bow at the front of the boat and drops the anchor. The anchor arm supports and guides the anchor line as it is lowered from the front of the boat and while at anchor.
“As you can imagine, there are a lot of structural loads on that arm,” says Sawyer. “In big seas, the boat will be tugging at its anchor with impressively high resistance. The anchor arm is cantilevered off the bow of the boat, so it has to be able to withstand a wide variety of loading directions. It also has to be stiff enough so that it does not deflect and interfere with other parts of the boat.”
A Point of Optimization
To ensure proper strength and stiffness, the anchor arm is built to a specific set of requirements. Its weight, however, was open to design interpretation – which is where optimization enters the picture. The design goal for any optimization application is to reduce weight while maintaining stiffness and strength.
Sawyer explains that the weight of the anchor arm is not critically important to the RP90’s systems in cruising mode. In performance racing, however, any place you can save weight in the hull structure can translate directly to increased stability, and ultimately, speed.
The owner of the SW-RP90 not only had an interest in saving weight on the boat wherever he could, but he also wanted to create an aesthetically different piece of equipment in the anchor arm. To that end, Reichel/Pugh began its optimization process by examining an anchor arm from a similar boat. It weighed 75 kg, was built out of aluminum plating, and was very boxy in shape.
Sawyer decided to use carbon composite material in the design of the anchor arm. “Using carbon,” he says, “allows for great weight savings through optimization of the size of the carbon plies and their orientation for specific load cases. It also enables the creation of much more organic and sculptural geometry.”
Detailed Evaluation
Carbon composites differ from isotropic materials, such as steel or aluminum, because the strength and stiffness of the carbon composite are different in various orientations. Along a carbon ply, there are some fibers that are extremely stiff; however, in the direction away from the fibers, the lamina is soft and weak. Having the directional stiffness allows engineers to optimize material usage by placing that strength and stiffness only in the direction where needed.
Sawyer explains that in the case of the anchor arm, he was able to optimize the placement and orientation of each individual ply. “For example,” he says, “there is a bank of material that is over 30 plies thick. Being able to orient those plies in a very specific manner allows you to get the stiffness and strength in one direction but not waste them in others.”
Sawyer used Altair OptiStruct™ optimization software, part of the Altair HyperWorks™ suite, for this analysis. “One of the benefits of this optimization soft ware,” explains Sawyer, “is that we are able to model each ply separately, which allows us to remove or change a ply, one at a time.
“You can imagine that the models can get very big and complex, but the benefit of being able to look at this component from every single ply that goes down is that you can aggressively optimize the design.” In addition to designing a lighter anchor arm, Reichel/Pugh customized its shape. The outer shape was specified by the builder and owner to achieve a certain aesthetic. Using HyperWorks, Sawyer was able to alter the shape of the inner surface to account for varying ply thicknesses.
“We took the shell elements (of the model) that had composite, individual ply properties,” Sawyer explains, “turned them into solid elements, and then extracted the inner surface for the required thickness offsets. It was a rough model, but in the preliminary stages it showed us what the inner surface of the arm would look like and aided in detailed discussions of tooling and manufacturing methods.”
A separate CAD program was used to create a high-fidelity model that could be easily machined and used for production. The final product is a 35 kg composite anchor arm that is 53% lighter than its aluminum counterpart.
Committed to Innovation
Reichel/Pugh is committed to innovation. The company has designed award-winning racing, cruising, custom and production yachts for over 30 years, including some that have competed in the America’s Cup. The firm has invested in the research and development of new ideas to stay ahead of the latest technological advances in yacht design, including pioneering the canting keel maxi racer with the iconic Wild Oats XI and the newly rejuvenated Black Jack 100.
In addition to using OptiStruct, the Altair HyperMesh™ pre-processor and Altair HyperView™ post-processor, the Reichel/ Pugh studio has other computational tools at their disposal including proprietary programs developed in-house. The combination enables the firm to deliver innovative, optimized designs, like that of the custom 130’ My Song — a 130-ft multi-role superyacht built by Baltic Yachts and launched in 2016. My Song has been the recipient of the ShowBoats Design Awards 2017 “Most Innovative Yacht of the Year” and World Superyacht Awards 2017 “Sailing Yacht of the Year.”
For the large and complex Baltic 130 hull structure, Sawyer explains, “The team was able to create an entire model of the hull structure and put it through various load cases to understand load paths and where they were being concentrated. OptiStruct was a valuable tool for conducting global analysis to define and reinforce specific highly loaded areas in ways that were not necessarily intuitive without running the simulation.” The firm’s in-house soft ware was used to define the baseline laminates for the structure.
The finite-element analysis (FEA) allowed the team to define the load paths as well as refine the stiffness of the entire boat. Sawyer notes, “One of the major gains in performing an FEA study of the entire hull structure was that we ended up with a stiffer boat. A boat that is more longitudinally stiff helps significantly with speed and sailplan efficiency as you power through the waves.”
Full Speed Ahead
Reichel/Pugh continues to push the limits in naval architecture and engineering through soft ware use. It is trying out the Altair solidThinking™ suite and Altair Inspire™ for CAD and initial optimization. In addition, it has used computational fluid dynamics programs for many years and will be utilizing Altair AcuSolve™ paired with OptiStruct to evaluate fluid structure interaction in the design of highly loaded appendages.
Reichel/Pugh optimized laminate thickness on the arm (top left) and thickness for the specific laminate orientation (right). The company also designed the arm’s manufacturing molds (bottom) to ensure that the final product would have the expected structural integrity and premium aesthetics the owner desired.
Contributing to the firm’s success is the fact that it has well-established relationships with outside research and technology specialists who are at the top of their field. The combination of design experience, state-ofthe-art tools and key industry relationships keep Riechel/Pugh on track to meet each project goal: to design a superior yacht that exceeds client expectations, and to deliver it on time.
The ultralight SW-RP90 performance cruiser is a result of thousands of hours of design, engineering, and construction spent by industry leaders and will be as at home on the race course as she will be on long ocean passages.
For more information on Altair OptiStruct and Altair HyperWorks suite, visit http://lightweight.altair.com.
Beverly A. Beckert is Editorial Director of Concept To Reality.
By Beverly A. Beckert