3-D Laser Scanning for Boat Building and Marine Applications

Ensuring the as-built matches the design intent

Published: Wednesday, January 6, 2010 - 06:30

The majority of marine vessels in service today do not have digital documentation or CAD models. Despite the fact that vessels currently under construction are designed based on 3-D data, they suffer the same lack of documentation of their true as-built geometries. Due to the inherent inaccuracy of the build process and the tolerances of the engineering techniques involved, there is always a mismatch between design data and reality. The actual as-built shape of the vessel, from the hull to the layout of internal features such as piping, does not accurately reflect design prints.

When they are due for any kind of fitting or refurbishing, the process is hit or miss as to whether new parts will fit and function correctly. Long-range laser scanning’s true-to-life modeling results offer marine engineers a way to ensure their vessels are built and modified correctly and safely the first time, saving them time and money.

GKS Global Services, an international provider of scanning services since 1981, has pioneered laser scanning and other techniques for overcoming the issue of as-built structures not conforming to design prints in the aircraft industry. These methods are now common practice in that industry.

In the last decade, laser scanners have acquired the range and accuracy to capture marine-sized structures to accuracy equal to their manufacturing tolerances. Software applications that develop 3-D models of plans, such as piping and valves, by recognizing the components that make up the system now exist to dramatically reduce scanning and modeling time. GKS has expanded its area of scanning expertise to include the marine industry through GKS Marine Services.

Like all evolving technologies, many different approaches have been taken to meet the needs of reverse engineering and inspection process. All of the new technologies have their advantages and their disadvantages. Speed and ease of use often need to be balanced against accuracy and the extent to which a process can be validated. GKS is successfully using laser scanning technology to aid in both the construction and modification processes in marine environments, such as reverse engineering ship hulls for the application of new parts, engine rooms, and fuel tanks.

What is 3-D long-range scanning?

Long-range scanning for marine applications is a ground-based technique for collecting high-density 3-D data to create digital models of complex entities such as hull models, entire seagoing vessels, shipyards, engine rooms, ships’ systems, and other big structures and locations, both inside and out. Using the highly accurate 3-D scan data generated with long-range laser scanning, engineers and designers can create CAD models of as-built structures by processing the scan data into universally usable CAD models.

GKS Marine Services has performed many long-range marine scanning projects, from reverse engineering ship hulls to documenting engine rooms and calculating volumes of fuel tanks. Long-range scanning is by no means unproven or experimental as a technique. It is just not as widely used in the marine industry as it could or should be. It is now possible to perform on-site 3-D scanning of objects that are virtually unlimited in size, since the size of the specimen being scanned is no longer limited to the directional travel of the measuring instrument, or the reach of a mechanical device. The laser scanning unit records all objects within the range and sight of the scanner. Long-range scanning functions in almost any environment including broad daylight, night, indoors, and outdoors.

Since grayscale values are applied to the X, Y, and Z coordinates, the data has the appearance of a black and white photograph. Scans can also be done in color, where each measured X, Y, Z coordinate is assigned an RGB color value. The specialized scanning software offers a variety of additional options such as overlaying digital images on the top of the point cloud for enhanced realism. Laser scanning technology also saves time. Clocking in at 100 times faster than conventional scanners, laser scanners collect eight megapixels of data in less than one minute, so even the largest scan scenario is time-efficient. Noncontact laser scanning means that no detail is omitted or disturbed.

Hull modeling to aid construction

The first thing to be built on a boat is the hull skeleton. Invariably the as-built structure is not exactly the same as the plan drawings. In order to fit all the components to the hull, such as the windows, deck, cabins, various subsystems, etc., shipbuilders need very accurate data of the hull’s actual dimensions.

Long-range laser scanning of the inside and the outside of the hull structure provides scan data to an accuracy of one-eighth of an inch. Laser scanning can be performed at every stage of the construction process to make sure the hull doesn’t stray from its as-designed shape. This ensures the fit of windows, decking, cabin areas, propulsion systems, electrical systems, as well as design features on the bow and stern. With accurate scan data, a CAD model can be made to monitor that the ship’s parts will fit correctly the first time, saving time and money.

Marine simulations

3-D scan data can also be used for marine simulations and tests. Laser scanning provides high-resolution data very quickly, so digital models can be made and used to create 3-D virtual spaces and simulations at any stage of the construction process or afterward on an in-service vessel. Simulations can be run to test the stability, which of course, is a critical factor in boat design. Being able to run tests on the precise 3-D measurements saves time and ensures craft safety.

Analytical software for computational fluid dynamics (CFD) can take the CAD from the scan data gathered by GKS and analyze water flow problems, leading to improved hull and structure architecture, fuel efficiency, power transfer, craft stability, and safety. This is particularly useful when repurposing an existing vessel because simulations can be conducted on as-built data.

Hull surface modeling

Most vessels in existence today were built before CAD computer models were common, so no 3-D model exists of their structures. When it comes time to repair, test, or update a hull, shipbuilders are left without accurate dimensional data.

Boat hull designs involve complex free-form geometric shapes and are therefore very difficult to measure and model with traditional measurement methods. GKS has laser scanned the entire hull surface on many large-scale marine projects. The scan data allowed them to create precise 3-D models that can be used by interior designers and naval architects to ensure the quality of interior construction, as well as for design, simulation, and inspection purposes.

Surface analysis for fairing optimization

The accurate as-built surface of the hull can be compared to a theoretical perfect surface that has the aesthetic qualities required by a yacht. By constructing a surface with these qualities as close as possible to the as-built shape of a metal hull, the application of fairing material to achieve a smooth surface can be optimized, saving the cost and the weight of excess material that would normally be used were this technique not available.

Installing a perfect-fitting new hull feature

One such hull modeling project performed by GKS Marine was scanning a Coast Guard cutter’s hull to provide accurate data from which to install a transom platform and stern flap. A stern flap is an extension of the hull bottom surface which extends behind the transom and is designed to reduce propulsion power requirements and emissions, improve fuel efficiency, speed, and range of travel.

Engineers used the ship’s scan data to create a CAD model accurate to one eighth of an inch, a figure more accurate than the manufacturing tolerance of the fabricated parts. The CAD model allowed the engineers to determine the optimum location and geometric shape for the stern flaps and to design the new parts so that they fit with minimal fitting work. The investment in scanning when the vessel was in dry dock paid off handsomely in time savings when the parts were actually fitted.

Remote construction of systems

Another project where scanning a vessel prior to designing modifications paid off was one that involved scanning the top of a ship’s deck in preparation for the addition of cranes at the stern. The crane was built in Europe, and then shipped to China to be fitted. The hull scan data provided the crane manufacturer with precise dimensions of the future crane location so it could be built to fit perfectly straight “out of the box.”

Sometimes extremely tight tolerances must be maintained to ensure the ideal mating of diverse parts.  In such cases, GKS Marine uses a laser tracker measuring device in conjunction with the laser scanner to align large-scale scans precisely. The tracker picks up individual points to accuracies measured in thousandths of an inch, and using registration points and spheres can create precise coordinate systems upon which the scanned data can be overlaid.

Restoring or modeling a vintage or damaged boat

As noted previously, many vessels are not documented with 3-D CAD models, which is a major roadblock to performing any major restoration on a vintage or damaged boat. With the increased availability of long-range laser scanning from reputable service companies like GKS Marine, however, this lack of 3-D data can be easily remedied.

GKS has laser scanned many vintage boats, both seaworthy and damaged, for collectors who wanted to restore their prized possessions to mint condition. The free-form, complex shape of the hulls is difficult, if not impossible, to recreate by any other method because of the irregular geometry and small details. Of course, noncontact laser scanning does not damage the article being scanned, so the boat is not harmed in the scanning process and all the intricate design work is captured.

With laser scanning, the as-built, 3-D digital data is collected quickly and accurately. Once the entire surface geometry, inside and out, is captured, the preprocessed raw data contains millions of data points that adequately define the boat for reverse engineering. Without noncontact 3-D laser scanning, capturing enough data coordinates to accurately define the boat’s shapes would have taken at least 10 times longer, and would have resulted in a much less complete data set.

After GKS scans the vessel, the scanning software automatically connects the point cloud data from multiple views into a common coordinate system in a single scan file. The modelers then create a CAD model of the boat “as is” for exact replication, or if modifications or repairs are needed, the original design intent of the prismatic shapes can be extracted even if the as-built part is warped, misaligned, or broken. A boat designer can make the desired modifications or digital “repairs” in the CAD model to faithfully replicate the original or incorporate updates.

Another use for the 3-D scan data is scaling down the size of the watercraft to make smaller models with exacting details, popular with boat hobbyists.

Learn more about this exciting technology by checking out the “3D Marine Scanning” video from GKS and Laser Design’s Video Center.

About The Author

GKS Global Services

GKS Global Services is an in-house service bureau division offering complete 3-D scanning, reverse engineering, and dimensional inspection services. The company’s metrologists and engineers are experienced in the automotive, defense, electronics and many other manufacturing industries. GKS also provides terrestrial scanning services for digitizing large-scale objects, for example, bridges, buildings, power plants, mines, and ships.