from the September 1999 issue of Marine Log
Excerpted from, "3D Modeling
Helps Make American Shipbuilding More Competitive,"
by John Ryba, Design Manager, Bender Shipbuilding & Repair
Co., Inc.
Upgrading to a new 3D modeling approach has helped Bender Shipbuilding & Repair Co., Inc., Mobile, Ala., substantially reduce the time and cost involved in building ships, by providing enhanced design products to be used in construction.
Bender Shipbuilding is pioneering a method originally developed by the National Shipbuilding Research Program, a cost-shared government and industry program whose mission is to assist the U.S. shipbuilding and repair industry in achieving global competitiveness with respect to quality, time, cost and customer satisfaction. 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. The elimination of the need to measure interferences and finish each piece at the assembly site dramatically improves productivity.
This new approach produces 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 ft 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. Bender evaluated a wide range of software packages before selecting AutoPLANT 97, plant engineering software from Rebis, Walnut Creek, Calif., to do the pipe and equipment modeling.
Automatic updates
The design process went well, considering this was the first time the designers had ever used the software. Ittook 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. ISOs produced by this approach require minimal checking because the software ensures they will be consistent with the 3D model. The program also generated and inserted the bill of materials. The result was a dramatic reduction in the normally lengthy time required to produce ISOs.
Producing reports
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 bills of material, or valve and instrument lists. Producing lists for a project of this size is normally a considerable job. On this project, they were produced in a few hours simply by checking a few options to format the document and printing it.
CADLink 97 from Albacore Research Ltd., Victoria, British Columbia, 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. And, rather than trying to decipher 2D drawings, the customer was able to provide input at a point in the design process when the cost of changes was minimal.Improved Manufacturing
The real test of the 3D modeling approach came during the manufacturing process. The 3D model was used to create drawings that made it possible to manufacture structural subassemblies, pipe ISOs and equipment foundations in the best possible environment, and then bring them together for assembly into the unit. And because the cutouts are defined in the model and precut in the steel, piping and other items were able to penetrate the structure without the need for cutting in the assembly area. This greatly reduced congestion and made for a cleaner, less cluttered workplace. With four ships being built at once, Bender developed a continuous flow approach that was far more productive than the traditional handwork methods. The model was also used to generate 3D perspective drawings and exploded views that were much easier to understand than traditional 2D drawings and helped further speed up the assembly process.
The new manufacturing approach greatly improved labor management. Traditionally, labor requirements vary greatly over the life of a project because so much manufacturing has to be carried out during the assembly process. The ability of the software to provide detailed drawings for all components enabled Bender to manufacture the components of the offshore supply vessels whenever they wished.
This made it possible to maintain a relatively stable workforce throughout the project. The availability of 3D perspective drawings also greatly simplified many assembly tasks, allowing them to be performed by workers with less experience and reducing the amount of rework.
As one might expect with the dramatic change in engineering and manufacturing methods on this project, there was a considerable learning curve to overcome. Despite that fact, the design time on the first ship on which this approach was used was less than the previous 2D approach would require, even though the design documentation was greatly improved. Manufacturing and assembly time are on track to end up at about 25% less than the previous approach. Management expects substantially greater savings on future programs, as the designers and shipbuilders become more accustomed to the 3D approach. ML
