How to make an empty shell expansion drawing

Making a shell expansion drawing is an important step in the ship design process, following the import and potential modification of your shape data in MasterShip. This drawing lays the groundwork for defining the basic construction elements and defining seams and butts. 

In essence, this step involves transforming the 3D hull shape into a 2D representation. This is achieved by dividing the hull into sections called ordinates, and then measuring and mapping out these ordinates on a flat plane.

A shell expansion is used for hull models. Making a shell expansion can be skipped for other shape data, such a superstructures.

Fun fact: Did you know that the concept of shell expansion drawings dates back centuries? Early shipbuilders used similar techniques, often relying on physical models and hand calculations to achieve the same goal. The advent of computer-aided design (CAD) software has significantly streamlined this process, but the core principles of shell expansion remain essential for ensuring the structural integrity and functionality of any vessel.

How to make an empty shell expansion in MasterShip

This video shows how to make a shell expansion drawing in MasterShip from the software perspective. Next to that, we have listed some of the best practices in the shipbuilding industry from the engineering perspective, and how MasterShip functionalities apply below. 

• Mapping out the centerline: Begin by setting up the center line of the ship's shape model on the x,y plane. In MasterShip, the SHIPSESETUP function automates this process. This function also guides you through the creation of the entire shell expansion. To select the centerline, you can use the following AutoCAD functionalities to make the selection of the centerline easier: Duplicate your hull surface using COPY and then EXPLODE it to extract its contours.

Tip: Make use of AutoCAD drawing templates before mapping out the centerline. In MasterShip they can be found in the general settings folder. 

• Defining the ordinates: Ordinates are vertical lines that divide the shell model into sections. The SHIPSESETUP function also automates the process of mapping out the ordinates. You can specify the positions of the ordinates using absolute values or intervals to create multiple ordinates at once.
  Define intervals using MasterShip standards. For example: [-1200..15000,500] defines an interval between -1200 and 15000 with a 500 mm spacing.
• Matching ordinate spacing to frame spacing: This practice improves the clarity of the shell expansion drawing.
• Positioning the shell expansion drawing: Having the shell expansion displayed alongside the 3D model improves visualization and understanding of the relationship between the flattened view and the 3D representation in MasterShip.

Output and next steps

The final output of this process is an empty shell expansion drawing, which serves as the foundation for the subsequent definition of the basic construction elements in the shell expansion.