Considerations of Structural Design in Superyachts


How do we approach the successful structural design of superyachts when presented with a designers or owners vision? This vision is often inspired by building architecture. Do we approach it in the same way as we do for commercial or naval vessels? Can we learn anything from the design of buildings? Modern buildings have complex and unexpected shapes which are realized by using civil structural engineering expertise and knowledge. Superyachts are expected to incorporate similar complex shapes and large areas of glass with minimal obstruction from the supporting structure.

Both the physical structure of a yacht and the work carried out to define it is mostly hidden from the view of the owner. Despite this the structural work is deeply integrated into the overall design and the process of engineering that design. The structural engineer needs to understand how their work fits into this. For example, it may be that space has more importance than weight for a particular frame. This is different to most other vessels where the structure is most commonly optimized for low weight. Large windows and shell doors as well as the complex geometry mean that extensive analysis is required to prove the strength and durability of the structure.

Ship structures are flexible and move with the passing of waves which causes door and window openings to change shape and for cyclic loads to be experienced by the structure. The design of doors and windows needs to take this into account. Glass is not expected to contribute to the strength of the yacht and is mostly isolated from the movement of the structure. There is much interest at the moment for glass to be included as a structural element and so reduce the amount of steel or aluminum support. This would allow more scope for the yacht designer to create large, open and light-filled spaces.

It used to be accepted that the structure of ships and boats should be designed so that shapes were simple, aligned and orthogonal. This meant that load paths were known, and analysis of the strength straightforward. The accessibility and efficiency of analysis by finite element method has allowed this approach to be departed from and is where the yacht design process starts to diverge from commercial and naval design. The need to be ingenious and ready to take on the challenge should also be met with realism about the scale of the task in terms of effort and timescale. Where possible suggestions should be made on ways to improve the structural arrangement without compromising the design, and from there, the structural engineers should make it work.

The requirements for the structure are not limited to meeting classification rules. It must be strong, stiff, robust, and needs to provide a fair and stable surface to allow the yacht standard of finish to be achieved, plus be buildable, maintainable and repairable. Consideration for noise, vibration and sustainability should be taken into account. Some of these factors are addressed by the application of flag and classification rules but not all. The societies are primarily concerned with the safety and seaworthiness of the design. It is up to the structural engineer to make sure the design is fit for purpose as well as certified.

Considering the influence of civil architecture on yacht design we can say that yacht structures are similar to modern buildings in that complex shapes are made possible by the capability to analyse them for strength and stiffness. The difference is that yachts are much more flexible and subject to cyclic loads. The static load cases are similar to those for a building with the foundations being replaced by fluid support in the form of buoyancy. This means that the continuity of structure and the avoidance of sharp corners is much more important for seagoing structures. Windows on yachts are much thicker than those on buildings due to the higher loads and are supported by structure which constantly moves when at sea. Making the glass part of the support structure means these effects need to be taken into account. Incorporating similar features to those in buildings requires a different approach, innovative solutions and extensive analysis.

The increasing need for more sophisticated analysis means a different approach to the design process will be needed. The structural design exists within the bigger whole-ship design process and the structural engineer needs to communicate and work closely with the other design disciplines. The shared information exists largely within a 3D environment, and once a 3D model exists there is the opportunity to do sophisticated analysis and simulation. The ways of viewing, using and interacting in this 3D world is changing radically, and virtual reality will transform the way we control and interact with the model. This will have implications on the way we work with the approving authorities as well as the client. Not only will approvals happen in the 3D environment, the assessment and analysis will allow us to move away from purely prescriptive rules.

The future will encompass changes to the design and analysis tools we use, the construction materials and the way the structure is built. The need to be sustainable will open up new opportunities for composite materials and may indirectly put pressure on reducing weight and installed power. Steel and aluminum remain eminently recyclable materials. The challenge is to assess and quantify the sustainability of different materials in a way that can be used to make decisions during the design process.

In the ideal future artificial intelligence, virtual reality and real time simulation will free us from repetitive tasks and enable us to consider more innovative and creative solutions.

Andy Douglas

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