How to make hull plate expansions

Accurate hull plate expansions are essential for efficient and successful shipbuilding. They serve as the blueprint for cutting and shaping the steel plates that form the body of the ship. By creating precise expansions, you can ensure that the plates fit together seamlessly, minimizing construction time and material waste.

This article will guide you through the best practices for creating hull plate expansions and molds using the functionalities offered by MasterShip. While the process itself is relatively straightforward once you have your seams and butts defined, there are a few key details to consider to avoid errors and ensure a successful outcome.

Fun fact: MasterShip's software is well-known for accurate expansions. What you see in the 3D model, is what you get in the practice. Also see this blog post for the importance of good software.

Making hull plate expansions in MasterShip

This video demonstrates the functionalities involved in making hull plate expansions and molds. Here below are some of the best practices to consider from the engineering perspective, and how MasterShip and AutoCAD can support.

• Properly defining seams and butts: This is the fundamental step in creating accurate hull plate expansions. Seams and butts essentially define the plate within the 3D model. When these are precisely defined, generating the expansions becomes more or less straightforward. In the article How to define seams and butts is explained how to do it.

• Applying appropriate mathematical models: The type of mathematical model used in the expansion process depends on the curvature of the hull plate. MasterShip offers specific commands to handle both single and double curved plates: SHIPSINGLECURVEDEXPANSION and SHIPDOUBLECURVEDEXPANSION, respectively. These commands incorporate well-established shipbuilding practices and deliver highly accurate expansions.

• Expanding marking lines: When generating the expansion, it’s crucial to include the marking lines on the hull plate as well. These lines designate essential construction details like frames and horizontals, and their placement needs to be accurate on the expanded plate. MasterShip offers the SHIPDRAWINTERSECTIONS command to facilitate the process of drawing these construction lines in the 3D model. And when executing the commands above, you can simply include these lines to get them expanded. See the article "How to add markings" for further reading.

• Adding overlength to the expansion plate: Adding overlength to the expansion plate can be  necessary to account for shaping the part and ensuring that the plates connect properly during assembly. Typically this is done at the connection butts of a section, and on the sides of heavily shaped plates in the bow area.

The SHIPDOUBLECURVEDEXPANSION command in MasterShip prompts the user to specify whether to “Add excess material?”. Selecting “Yes” and providing a value guarantees sufficient material to work with.

• Checking boundary corrections: It’s vital to verify boundary corrections for pipe connections, overlaps, fore openings, areas where angles meet, and other construction details to ensure a flawless expansion. The SHIPCREATESEAMTYPE command in MasterShip aids in seam correction for various standard situations.
• Checking stretch: Stretch refers to the amount of material deformation that occurs when shaping a double curved plate. Excessive stretch can introduce high stresses in the material, increasing the likelihood of cracking. MasterShip reports the stretch data in a text file generated alongside each expansion. If the stretch value exceeds the recommended limit, it’s advisable to revisit the seams and butts in the 3D model to reduce the curvature of the plate. Consult with the supplier for the maximum stretch limits.
• Checking for industrial plate sizes: If the expanded plate cannot be accommodated within a standard size, adjusting the seams and butts in the 3D model is the recommended course of action. Common plate sizes in shipbuilding are 6x2m up to 12x3m, however these may vary. Consult with the supplier regarding their available plate sizes.
• Do not modify the plate expansions or marking lines directly: Any modifications to the plate expansions or marking lines, such as splitting, joining, or extending them, must be made within the 3D model. Directly altering the 2D expansion can lead to inconsistencies between the 2D and 3D representations. This practice is particularly crucial for double curved plates because the mathematical model used for generating the expansion relies on the 3D model for accuracy.
• Treating rounded corners separately: Rounded corner parts need to be addressed independently during the expansion process for convenience in the production process.  Also, the mathematical model for creating double curved expansions, requires a more-or-less symmetrical plate around the middle seam.
• Defining beveled edges on parts: Bevels are defined on parts where the adjacent plate thickness differs by more than 4 mm. Bevels are essential to ensure proper welding and assembly. The SHIPMARKTEXT command in MasterShip can be used to mark the bevels on the expansions. See the article titled “How to add markings” for more information on applying markings.

Making molds

Molds are necessary to shape curved plates according to the design before fitting them onto the ship. MasterShip offers the SHIPPLATEMOLDSET command to generate a mold set within the 3D model. The command SHIPPLATEMOLDSET2MOLDS then creates the 2D parts that constitute the molds, which can be cut out for use in the shaping process. Other best practices:

• Making a workshop drawing after creating the molds is helpful to prevent miscommunications and faulty shaped plates.
• Use a logical name giving for the molds that include the part id of the plate and the place or marking line where the mold is used.

Output and next steps

Following these best practices and using the functionalities offered by MasterShip will ensure that you create accurate hull plate expansions and molds and stretch data, streamlining the shipbuilding process. The next step is to apply marking to these expansions (plate parts).