March 14, 2007

Ship Check Data Capture 37% Cheaper, 39% Faster with 3D Laser Scanning, NSRP and Electric Boat Report


In ship check data capture and post-processing, 3D laser scanning can reduce cost by 37% and time by 39% compared with traditional methods using tape measures, plumb bobs and 2D sketches – this is the finding of a just-completed National Shipbuilding Research Program project led by Electric Boat Corporation (EB). Additional cost savings from laser scanning-based ship checks will come from cost avoidance, minimized rework, material scrap reduction and reduced return visits to ships, EB reports.

In 2005 we reported EB’s initial investigation of laser scanning in an NSRP ship check data capture project aboard a Torpedo Weapons Retriever (TWR 841) in Newport, RI, and onboard a Trident submarine (SSGN729) in Norfolk, VA. In April 2006 the NSRP funded a follow-on project to refine the process developed in the first project. Objectives of both projects were (1) to develop a process that captures as-built measurement data in digital/electronic format during ship check, (2) to create and/or validate 3D CAD models from that data cost-effectively using available commercial off-the-shelf (COTS) hardware and software, and (3) ultimately to provide a building-block process for anticipated development of capabilities to generate 3D CAD models of the as-built space envelope from the geometric measurement data captured during the ship check.

Results of the follow-on project, carried out from April 2006 through January 2007, have just been reported by NSRP in Final Report: NSRP ASE Ship Check Data Capture Follow-on Project (NSRP ASE 05-01). The project confirmed that laser scanning technology is mature enough to support the ship check process, and provides time and cost savings during ship checks for new construction, refit and modification projects. It found laser scanning also eliminates return visits to the site to obtain measurements that are normally missed using traditional ship check methods. Finally, the project validated that a significant vendor network exists to support ship checks with laser scanning-based data capture and post-processing and recommends that shipyards consider using vendor services to aid their initial use of the technology. 

Electric Boat Corporation was the lead for both the initial FY05 and follow-on FY06 projects. Participants in the FY06 follow-on project were Bender Shipbuilding and Repair Company, BitWyse Solutions, Inc. (now part of Trimble), Construction Systems Associates, Inc., Direct Dimensions, Inc., FARO Technologies, Inc., Gulf Coast Region Maritime Technology Center (GCRMTC) and Photo Measurements Solutions, LLC. Participants in the FY05 project were BitWyse, Direct Dimensions, GCRMTC, Intergraph Corporation, Leica GeoSystems HDS LLC, Photo Measurements Solutions, ShipShaper, LLP, and Woolpert, Inc.

SPAR 2007 will feature shipbuilding applications of 3D laser scanning presented by the U.S. Navy, SIS and Northrop Grumman Ship Systems.

Key findings

One of the key points to be verified by this project was the ability of the scanners to capture accurate dimensions. Another was the ability of the scanners to capture sufficient detail to support downstream uses of the data. The project found that the data captured is complete and accurate, meeting the desired +/- 3/16-inch tolerance. The accuracy was verified by comparison of scan data to survey measurements and to design drawings.

Once scan data is loaded and worked through various post-processing software applications, it can benefit shipbuilders in a variety of ways, the project validated:

  • Take measurements of component dimensions or their locations from a reference point
  • Validate as-built to as-designed component locations by overlaying existing CAD models on the scan data
  • Create 3D as-built arrangements by placing library CAD model parts on location using the scan data
  • Create 3D surface models for visualization of as-built conditions

Benefits of conducting ship checks with 3D laser scanning include: (1) creation of as-built 3D models and validation of as-built models to design models, (2) reduction of costly design changes and improved design capability, (3) reduced construction rework, (4) accurate and less costly factory fabrication in lieu of field fabrication, (5) reduced ship check costs – fewer days, fewer personnel, (6) elimination of return visits to the site to obtain measurements of missed data which can happen with traditional ship check methods, (7) obtaining measurements that are difficult or unsafe for human reach, (8) generation of scan data (point clouds and associated models) that is readily transferred between computer systems using standard methods such as IGES, STEP, STL and DXF.

As an example of the benefits for construction, repair and retrofit, Bender Shipbuilding personnel analyzed laser scan data of the moon pool door of a Candies IMR vessel compared with the design model and found that two stiffeners were installed in a wrong location. Because this was detected during the construction stage, the problem was rectified immediately by installing the stiffeners at the design locations.

The report noted that laser scan data can also be used to create as-built 3D solids models for further design work (sometimes called reverse engineering). However, time and cost evaluations conducted in the project indicated this is a labor-intensive manual effort that is not cost-effective at present.

The follow-on project resolved some issues raised in the initial FY05 ship check project, specifically:

  • Conducting a traditional total station survey during the ship checks is necessary to merge the laser scan data sets accurately.
  • Scan data measurements need to be validated on-site during the first use of a scanner.
  • Field-verifying the completeness of data collection before leaving the ship check site, through use of a software application such as Cyclone or LFM control software applications, is a must to eliminate return visits to the ship.
  • Data analyzed and processed from the 3Dguru, FARO LS 880, and Z+F Imager 5003 laser scanners in this project is accurate within the desired tolerance of +/-3/16 inch on the as-built measurements of components.

The project also found that the photogrammetry (FotoG) process may be able to be used to complement the laser scanning, and that using the two technologies together may speed up the modeling process and also validate the data collection from each process. However, complete evaluation of synergies between these two technologies was beyond the scope of this project; the investigators recommended that such an evaluation be undertaken by shipyards and NSRP in the future.

The report adds that traditional ship checks are still needed for some measurements which cannot be obtained by the data capture technology.

Work process

Two ship checks, onboard the Candies Inspection, Maintenance, and Repair (IMR) vessel at Bender Shipbuilding, and onboard the SSGN 729 submarine in Norfolk, VA, were conducted under the project. Lessons learned from the first ship check of Candies IMR were used in planning for the SSGN 729 ship check in order to improve the process in both the data capture and data processing techniques.

The first ship check onboard the Candies IMR vessel at Bender Shipbuilding was done in five spaces (Bow, Engine Room, Moon Pool, Z-Drive Recess, and Pilot House), as well as the moon pool door and Z-Drives, using two laser scanners, a digital camera, and a video camera (only used for the pilot house for future processing with Vexcel Corporation’s ImageOn software when this becomes available). The ship check of the pilot house was done only with a digital camera (for the close-range photogrammetry process) and no laser scanners.

Two phase-based scanners (FARO LS 880, Z+F Imager 5003) were used for the Bender ship check. Three phase-based scanners (Faro LS 880, Z+F Imager 5003, and 3Dguru) were used for the SSGN 729 ship check. All three of the scanners are relatively easy to use, the project found.

A Leica TDA5005A total station was also used to capture control points for registering the multiple scans to a single coordinate system for the ship check onboard the Candies IMR vessel at Bender Shipbuilding. An INCA3 8MPXL digital photogrammetry camera was used for the SSGN 729 ship check to capture control points for registering the multiple laser scans to a single coordinate system. The registration can also be done using identical features from each scan with COTS post-processing software applications, but use of the control points from the survey with a total station or a digital photogrammetry camera provides significantly more accurate results, the project reported. The control points from the survey also speed up the alignment process and enable the scans from multiple spaces to be registered to a global coordinate system. The need for the survey should be based on the accuracy requirement of the collected as-built data.

Data analysis work of the Bender ship check was done at the participants’ offices, and the data analysis results were sent to EB to be included in the final report. Photo Measurements Solutions’ (PMS) personnel were at EB to process a portion of the Bender ship check data using FotoG.

Data analysis work of the SSGN 729 ship check was done at Direct Dimensions in Baltimore, MD, at Construction Systems Associates in Atlanta, GA, and at the EB Business Lab in Groton, CT by Gulf Coast Region Maritime Technology Center (GCRMTC) personnel.

The close-range non-targeted digital photogrammetry (FotoG) process with a digital camera (6 MPXL Nikon D70) was also used for the Bender ship check. The FotoG process, like total stations, if used in tandem with the laser scanner, has the potential to assist in accurately linking multiple scans, thus avoiding the use of best-fit routines in the laser scan data post-processing software. This concept still needs to be further evaluated, according to the report.

Lessons learned

Significant lessons learned in the follow-on project include:

  • Scan data measurements from the scanner being used to collect the data during the ship check need to be validated on-site during the first use of a scanner with standard scale bars or a survey with control points to obtain accurate ship check data.
  • A survey of the area to be ship checked is required to be performed in combination with laser scanning or digital photogrammetry. In order to accurately merge multiple scans and/or match components to specific coordinates on a ship, the survey data must be used as part of the post-processing effort.
  • Scan data can be used in a variety of ways – to take measurements, to validate as-built to as-designed conditions, to create as-built arrangements and to create visualization models. Each of these uses will provide significant time and cost benefits to ship check, design and construction processes.
  • The project highlighted the need in the shipbuilding industry to have point cloud processing software that provides more automation to the process for merging multiple scans and creating 3D CAD models. Currently, most of the software application developers for point cloud processing appear to be resisting this need, the project found.
  • A capable vendor network exists and is ready and willing to support the shipbuilding industry in performing digital ship checks. Particularly for first-time or early efforts, the use of vendor services will yield better quality results, a faster learning curve, and more efficient use of resources.

Technology transfer

The ship check process developed in these projects by Electric Boat with the support of the project team is ready for use by the U.S. shipbuilding and repair industry, EB and NSRP report. This information is available to industry participants through NSRP (, via presentations at NSRP Joint Panel Meetings, and by contacting lead personnel at EB: Raj Thiyagarajan, Principal Engineer, Electric Boat Corporation, [email protected], tel. 860-433-8481; Ken Peters, Manager of CAD Infrastructure, Electric Boat Corporation, [email protected], tel. 860-433-3234.

About NSRP

The National Shipbuilding Research Program was created by U.S. shipyards at NAVSEA request to reduce the cost of building and maintaining U.S. Navy warships. NSRP is structured as a collaboration of 11 major U.S. shipyards focused on industry-wide implementation of solutions to common cost drivers. NSRP’s flagship R & D program, Advanced Shipbuilding Enterprise (ASE), targets solutions to consensus priority issues that exhibit a compelling business case to improve the efficiency of the U.S. shipbuilding and ship repair industry. Solutions include both leverage of best commercial practices and creation of industry-specific initiatives. R & D costs are jointly funded by industry and the Navy. Aggressive technology transfer to, and buy-in by, multiple U.S. shipyards is a requirement of all funded efforts.

About Electric Boat

With more than a century of experience, Electric Boat Corporation has established standards of excellence in the design, construction and lifecycle support of submarines for the U.S. Navy. Primary operations are the shipyard in Groton, CT, and the automated hull-fabrication and outfitting facility in Quonset Point, RI, with a current workforce of 10,500 employees. EB became involved with available as-built data capture technologies in the early stages of the SSGN design (November 2001) to support the design process with as-built data in digital format. EB has led the NSRP Ship Check Data Capture Project for the past two years to refine the ship check process using data capture technologies (3D laser scanning and non-targeted close range photogrammetry) to be used by the U.S. shipbuilding industry.

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