Innovation and Diversity

in Marine Design

Model-Based Structural Design (MBSD)

Designing in 3D to collaborate and save time

2D Structural Design

From the earliest days of naval architecture, designers have relied on drawings and scale models to communicate the design of a new vessel. When it comes to a vessel’s structure, most design offices still prepare two-dimensional (2D) drawings for the basic, or contract, design stage before creating the kind of 3D CAD models used by shipyards for detailed production design work.

Although 2D CAD tools like AutoCAD replaced pencil drawing in 1980s and 90s, the way a structure is shown in 2D drawings has remained virtually unchanged. While 2D drawings have stood the test of time in many respects, they do suffer from limitations. For example, 2D designs are not able to clearly convey complicated three-dimensional structural geometries in a way that highlights interferences or weld accessibility issues. Designing in 2D before moving to 3D also adds a step, affecting how quickly projects on tight timelines can move. Additionally, because some marine classification societies now accept 3D structural models, which can streamline the plan review process, designing in 2D slows the process.


3D Model Based Structural Design (3D-MBSD) is a modern design approach offered by Robert Allan Ltd. Developed to enhance opportunities for collaboration, optimization, and design improvements, the 3D-MBSD approach opens the door to better information sharing and collaboration between the design team and with the client early in the design process.

This is achieved by leveraging the advantages of a single source of truth that a 3D structural model offers during the contract design stage. With 3D-MBSD, all parties can view the structural model as it is being developed—since a 3D model of a ship’s structure is far easier to interpret and discuss in an online meeting situation (using free 3D viewers) than traditional 2D designs are.

Other significant advantages with 3D-MBSD approach include:

  • Clear, visual representations of structure with less need to review multiple drawings
  • Earlier opportunity to route piping, ducting and major cableways by shipyard. The shipyard can use the 3D structural model as it is being developed for preliminary routing instead of waiting for traditional 2D drawings which then still need to be converted into the shipyard’s Production Design model. This can save significant time!
  • More accurate early-stage estimates of structural materials and weights
  • Faster Class approval (since a 3D model is easier for Class to interpret than 2D drawings)

How it works

For 3D-MBSD, a comprehensive 3D structural model called the Vessel Structure Assembly serves as the single source of truth throughout the basic design process. Along with Key Plans (described below) and underlying subassembly models, it is ultimately submitted to the marine classification society (Class societies) for review and approval. Therefore, 3D-MBSD option is offered for Class societies, including ABS, that have processes in place to conduct plan review of 3D models.

Vessel Structure Assembly

The Vessel Structure Assembly conveys the basic geometry, structural layout and scantling details required for class approval. It is made up of a collection of separately developed, self-contained 3D models of the hull, deckhouse, wheelhouse, skeg, bulwarks, mast, equipment foundations and other major sub-assemblies. Each subassembly model is packaged with a Key Plan.

As a 3D representation of the basic structural design at the contract design stage, the Vessel Structure Assembly does not replace the production design model but serves as an excellent foundation for its development. A separate production design model would still typically be prepared by the shipyard (or Robert Allan Ltd if so contracted) to add details, define modules for construction and to generate individual parts drawings for nesting/cutting. However, with the Vessel Structure Assembly as a starting point, instead of traditional 2D structural drawings, significant time savings are possible as 3D-MBSD eliminates typical issues (including interference and accessibility challenges) that crop up in the translation from 2D to 3D.

Key Plans

Key Plans serve as conventional looking 2D ‘cover pages’ for underlying 3D structural subassembly models that include design notes, equipment seating details, moulded line conventions, welding-related details, a simplified view of the structural philosophy and other information that support the associated 3D model. Since most of the design information is in the 3D model itself, each Key Plan is typically only a few pages long. Each Key Plan has a 3D model linked to it, thereby making the combined file – Key Plan pdf plus 3D model file – robust and easy to manage alongside other design documents.

For your next project with Robert Allan Ltd, consider the 3D Model-Based Structural Design option to collaborate more easily with us as we develop your vessel’s structure and to save time getting to production design. Contact us to discuss the possibilities.