Computer-Aided Engineering - March 1999 Issue

Upgrading to a new 3D modeling approach has helped Bender Shipbuilding substantially reduce the time and cost involved in building ships, by providing enhanced design products to be used in construction. The new 3D approach allows designers to define where piping and equipment exist in the structure, so all piping, equipment foundations, and structure can be pre-built in sections or subassemblies and brought together for assembly into a single unit.

Modeling the entire ship in 3D makes it possible to determine the precise geometry required for each piece so components can be built in a more efficient, factory-like manner. The 3D model also was used to generate perspective and exploded view drawings that are easier to work with and understand than 2D drawings. Bender has just completed a 220 offshore supply vessel (OSV), built with this new approach, and achieved substantial savings in both design and construction time.

For more than 75 years, Bender has been a leading ship building and repair facility in the central Gulf of Mexico region. The company builds many different types of vessels including OSVs, factory trawlers, casino vessels, excursion vessels, tuna seiners, and tugs. The company currently has three contracts to build seven similar 220-ft OSVs.

Previously, at Bender, vessels were designed in 2D. The traditional drawing boards gave way to CAD programs in recent years, but there were no major changes in drafting methods. Designers drew 2D plans, sections, and details of the structure, with manual checking for correctness and consistency on each drawing. Others drew the piping, then broke it down into convenient size isometrics (ISOs) to allow sections to be fabricated and installed later. Since each drawing was done separately, many areas of the ship were drawn multiple times, and these drawings did not always agree. Errors in consistency between these drawings left room for errors in the ISOs. And, it took an enormous amount of time to calculate the intersections of piping and structural members since piping and structural design was done separately, without being integrated with the whole ship design.

This approach restricts the shipbuilder to using the same basic manufacturing methods that were in use 50 years ago. Structure gets built first and, since piping and structure cutouts for the piping are not defined in advance, they must be added as the ship is going together. Problems arise because of the difficulty for even the most experienced workers to visualize complex layouts from 2D drawings. As a result, the designer frequently needs to visit the assembly area to provide explanations of drawings. Misunderstandings often occur and result in mistakes that need to be corrected with time-consuming rework.

Bender Shipbuilding is pioneering a method originally developed by the National Shipbuilding Research Program, a cost-shared government and industry program. The basic idea is to use a 3D CAD program to create a single model that includes all parts of the ship, structure, piping, equipment foundations, etc. Each piece of the vessel is located precisely in the model, with a common reference point. This makes it possible to define subassemblies of similar pieces, extract them from the model, build them in advance in factory-like settings, and assemble them into units with minimal fit and interference problems.

This new approach is able to produce 3D models of units weighing up to 200 tons, that can be built within the lifting and location limits of production facilities and assembled to produce the entire ship. Using AutoCAD applications, CADLink for structure and AutoPLANT 97 with ISOGEN for pipe, Bender designers divided a master model of a 220 OSV into five hull and four superstructure units to satisfy a build strategy for construction. Dividing the master model into units also allowed a faster design process, since different areas could be worked simultaneously without designers getting in each other's way.

The design process went well, considering this was the first time the designers had ever used the software. It took a large amount of time to produce the initial 3D model, with the structure, pipe, and equipment foundations, but once it was complete, the design group was able to generate ISOs automatically using ISOGEN and structural plans, sections, and details in AutoCAD's paperspace, where each drawing can be scaled as required. When changes had to be made to the model, drawings were automatically updated in all views. This eliminated what is a most time-consuming part of a 2D-design project--redrawing multiple layouts and sections to accommodate design changes.

To generate ISOs, pipe was routed in the model using AutoPLANT 97, which identified break points to mark the boundary of each ISO and tagged critical dimensions. ISOGEN was then run to automatically generate the ISO. The program also generated and inserted the bill-of-materials. Using the conventional 2D approach, after the pipe is marked for breaking into ISOs, it takes an experienced piping designer approximately 3-4 hours to produce each ISO including the bills of material (BOMs), checking, backdrafting, and issuing. Using the 3D approach, the average was about 30 secs per ISO in quantities of 10 or more.

Whenever a component is taken from a specification file and entered into the model, the contextual information is automatically saved in the program's database and linked to the model. This information can be used to create reports such as BOMs, or valve and instrument lists.

CADLink 97 from Albacore Research Ltd. was used to produce the structural model. The fact that this program is also compatible with AutoPLANT 97 made it possible to import the steel design into the master model. Working in 3D, the designers had a clear picture of the entire ship, and as the design was being completed, the customer came in to view the 3D model. The fact that the model was able to represent the actual ship, and show various views, greatly improved the quality of the review process.

Bender's upgraded 3D approach allows designers to define where piping and equipment exist in the structure, so all piping, equipment foundations, and structure can be pre-built in sections or subassemblies and brought together for assembly into a single unit.

Company: Bender Shipbuilding. Software: AutoCAD from Autodesk; CADLink 97 from Albacore Research Ltd.; AutoPLANT 97 from Rebis. Hardware: 300/400MHz Pentium II PCs.

"Copyright 1999 Penton Media, Inc."

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