Helix Express: as-built 3D CAD modelling of a vessel tower and shallow water work deck

Helix Express: as-built 3D CAD modelling of a vessel tower and shallow water work deck

Working with Saipem, Helix and Utec, Luminous (then trading as Digital Surveys) was asked to provide as-built 3D CAD modelling services for the Helix Express vessel.

Project at a glance

  • Client: Saipem, with Helix and Utec
  • Sector: Offshore energy, subsea construction vessels
  • Location: Vessel scanned at berth in the Gulf of Mexico. Modelling carried out in the UK
  • Date: Not recorded in the archive. Delivered under our Digital Surveys trading name, so pre-2016
  • Services: As-built 3D CAD modelling from third-party scan data, clash mitigation support, point cloud and TruView deliverables

The brief

Working with Saipem, Helix and Utec, Luminous (then trading as Digital Surveys) was asked to provide as-built 3D CAD modelling services for the Helix Express vessel from a 3D laser Scanning survey.

The Helix Express is a reel pipeline construction vessel which can reach transit speeds up to 12 knots. The 520 foot long ship can efficiently reach any ocean in the world. Two reels hold 3,000 tons of pipe up to 14 inches in diameter. A huge, open deck allows the vessel to carry multiple 8.6 and 9.6 metre reels of additional product. The vessel features a 500 metric ton deck crane capable of reaching 600 foot depths, and a 150 metric ton deepwater crane capable of reaching 10,000 ft.

To prepare it for the Katy Field cable project, a custom shallow water work deck was to be fabricated to fit at the base of the tower. Our part was to turn measured reality at the stern into a 3D CAD model that Saipem’s designers could build against. As-built means exactly that: a record of the ship as she is now, not as she was drawn.

The challenge

Helix were not in possession of up to date plans or records. That is not unusual, and it is the core problem this service exists to solve. Most subsea projects require vessel modifications, with the addition of a-frames, carousels, new decks and similar. Due to the high turnaround of projects and modifications, most vessels bear little resemblance to the design plans the owners have.

A working construction vessel accumulates change. Equipment is added, moved, reinforced and removed across successive campaigns, and the drawing set rarely keeps pace. By the time a new deck structure needs to fit at the base of the tower, the only reliable description of that area is the area itself.

The second constraint was geography. The ship was in the Gulf of Mexico. The design team and the fabricators were in the UK. A new deck was to be built on one side of the Atlantic to fit a structure on the other, and the fit had to be right before the steel was cut.

The third was fit. A shallow water work deck sits into an arrangement already crowded with equipment, supports and services. Anything the design assumed but did not verify becomes a clash, and a clash on a mobilised construction vessel is measured in days of vessel time.

Our approach

On the advice of Saipem, Helix decided to 3D laser scan the rear of the ship.

The ship was 3D laser scanned by Utec Surveys while at berth in the Gulf of Mexico. Scanning was carried out with an HDS7000 laser scanner and the data, in the form of an .imp file, was sent across to us in the UK. Scanning at berth is what makes this practical: capture happens in normal port time, rather than taking the vessel out of programme.

The .imp file is Leica’s native point cloud format. Registration is the step where scans taken from different vantage points are joined into a single coordinate system. Our own standard method is cloud-to-cloud registration, in which software optimises and aligns the overlapping regions of neighbouring scans, with at least 30% overlap accommodated from each scan. Once registered, data is optimised through a process called unification, which can take 6 to 24 hours depending on the size of the dataset.

To assist with the design of the new shallow water work deck, and to mitigate any clashes, we converted the point cloud into an accurate as-built 3D CAD model. This was then fed back to Saipem’s design team to allow design and fabrication to take place in the UK.

A point cloud and a CAD model do different jobs. The cloud is the measured evidence, dense and exact but not editable as engineering geometry. The model is the surface a designer can snap to, dimension from and clash against. By using 3D laser scanning, an exact 3D snapshot of the vessel can be captured and turned into an accurate 3D CAD model, allowing project engineers to design customisations that they know will fit first time, reducing the need for costly rework at the time of installation.

What we found

The survey established what was actually at the base of the tower, which was the one thing the project could not otherwise know. With no up to date plans or records, the scan replaced an unknown with a measured baseline.

The as-built model then let the new work deck be tested against the existing structure during design, in the UK, rather than at the point of installation. Every conflict resolved on screen is a conflict that never becomes a modification on deck.

Deliverables

The deliverables for this scope, recorded verbatim in our offshore capability material, were: point cloud, TruView and 3D .dwg, for 3D laser scanning and as-built modelling of a vessel tower and shallow water work deck.

Models are supplied in a generic format, 3D .dwg, unless otherwise specified. The point cloud is issued alongside the model so the measured evidence stays with the client. Leica TruView is the 360 viewer: from every laser scan created, a 360 spherical image is also generated at that spot, and those images can be used to create a very high resolution virtual tour of a site, similar to Google street view. For a design team in the UK, that is the next best thing to standing at the base of the tower.

The outcome

Saipem’s design team received an accurate as-built 3D CAD model of the stern arrangement and used it to design the custom shallow water work deck. Design and fabrication took place in the UK against measured geometry from a vessel thousands of miles away, ahead of the Katy Field cable project.

An accurate survey of the vessel makes the whole modification process run a lot smoother. It is the reason a new deck can be built to fit first time.

Pointcloud, TruView, 3D.dwg. 3D laser scanning and as-built modelling of a vessel tower and shallow water work deck.

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