Project at a glance
- Client: Technip, commissioned through global survey company Utec
- Sector: Offshore oil and gas, marine construction
- Location: Gulf of Mexico, with modelling carried out in the UK
- Date: 2012
- Services: As-built 3D CAD modelling from third-party scan data, point cloud delivery, Leica TruView virtual tour, 3D animation
The brief
Working with global survey company Utec, we were asked to provide an as-built 3D CAD modelling service for the Chickasaw vessel. “As-built” means a model that records the asset exactly as it stands today, rather than as it was drawn. Technip, the barge’s owner, wanted an accurate record of the deck to support ongoing documentation and refurbishment.
The Chickasaw is a horizontal reel barge with an extensive history of installing 12-inch diameter pipelines in the Gulf of Mexico using the reel method. During 1994 its water depth capabilities were upgraded with a new dynamic positioning system, increased pipelay tension and a high departure angle stinger. That work enabled the vessel to install small diameter pipelines in water depths to 1,800m.
Luminous (then trading as Digital Surveys) took the role of the modelling contractor. Utec captured the reality data offshore. We turned it into engineering geometry.
The challenge
No as-built plans were available. That is the normal condition for a working construction barge rather than the exception. Most vessels of this type see a high turnaround of projects and modifications, and over time bear little resemblance to the design plans the owners hold. Every reel change, every deck strengthening job and every temporary spread that never came off adds another difference between the drawing and the steel.
The Chickasaw had also been through a substantial capability upgrade, which changed the aft end of the vessel and the loads it was built to take. Refurbishment planning on that basis needs a current record, not a historic one.
The second challenge was geography. The vessel was in the Gulf of Mexico. Our modelling team was in the UK. That split is now routine for us: we work regularly with survey companies across the US and Canada who capture on site and hand the data to us for as-built modelling. It works because a registered point cloud is a self-contained deliverable. Once scans are aligned and unified, the dataset carries its own geometry and needs no further site access to interpret.
Our approach
Utec carried out the 3D laser scanning of the Chickasaw in the Gulf of Mexico. The data was then relayed back to our modelling team in the UK.
The principle behind that capture is the same wherever we run it. Multiple laser scans are taken across the work site from a range of locations and vantage points, with at least 30% overlap between each scan. That overlap is what allows cloud-to-cloud registration, the technique in which software optimises and aligns the separate scans into one coherent dataset by matching the shared geometry between them. It removes the need to place physical targets everywhere on a congested working deck. On average one technician can register 40 to 50 scans a day. The registered data is then optimised through a process called unification, which takes between 6 and 24 hours depending on the size of the dataset.
3D Modelling
For the modelling itself we worked with the assistance of Leica TruView. From every laser scan a 360 degree spherical image is also generated at that exact spot, which can be published as a very high resolution virtual tour of the site, similar to Google Street View. For a modeller who has never walked the deck, that is the difference between guessing and knowing. A modeller can stand at any scan position, look around the vessel as the scanner saw it, and confirm what a cluster of points actually represents before drawing it. Assisted by TruView, our experienced modelling team were able to very quickly convert the point data into an accurate as-built 3D CAD model.
Modelling covered the whole of the Chickasaw barge, not a single work area. That gives the client one continuous geometric record rather than a set of disconnected local surveys that have to be stitched together later.
Deliverables
The issued package was: the registered point cloud, a Leica TruView virtual tour, and a 3D .dwg as-built model of the whole barge. We supply models in a generic 3D .dwg format as standard unless a client specifies otherwise, so the geometry drops straight into whichever CAD system the design office already runs.
A 3D animation of the vessel was also produced from the model, giving Technip a presentation-quality asset alongside the engineering one.
The point cloud matters as much as the model. A model is an interpretation, simplified to what the engineering task requires. The cloud is the measurement. Keeping both means any dimension that was not modelled can still be recovered later from the original data without going back to the vessel.
The outcome
Technip ended the project with an accurate record of the Chickasaw’s deck where previously there had been none, delivered in three issues across June and July 2012 under job number 1508.
That record supports refurbishment work directly. Engineers designing modifications can develop them against measured geometry and check for clashes before anything is cut, which is how you make new steel fit first time and reduce the need for costly rework at the time of installation. It also functions as a permanent record: a snapshot of the vessel at a known date that any future project can be measured against.
Traditional survey methods would have struggled to document a deck of this size and congestion within a working window. Laser scanning is rapidly replacing them because of its fast data capture rates and superior accuracy, and because the resulting dataset can be reused indefinitely by people who were never on site.
No as-built plans were available, so Technip looked to 3D laser scan the vessel to create an accurate record of the deck.
