Offshore developments often face tight constraints during design stages, due to underestimating topsides’ sizes and weights early in the project. The keys to success are to harness what we know and what we can find out and to maintain open lines of communication during the design process.
ANGELIQUE SPIES, Wood Plc.
Weight management is critical to all offshore developments. Many developments often face tight constraints during the design development and follow-on stages, due to underestimating the topsides’ sizes and weights during early stages of a project. However, an overly conservative approach during early stages can lead to an over-designed support system (hull, jacket, etc.), wasted capital resources (CAPEX) or termination of the project altogether.
Developing early weight estimates is an iterative process, the ultimate goal of which is to set realistic control weights (Not-to-exceed, Budget) for the facility’s critical loading conditions that will remain constant throughout the life of the project, Fig. 1. For floating facilities, the critical conditions are often associated with stability. As with fixed structures, there may also be limitations related to the fabrication and integration stages of the project. The objective of the control weights is to enable the engineering teams to proceed with their work—independent of the day-to-day fluctuations of design development.
Inaccuracies or a lack of true project definition during the early stages of project development can increase costly risks, such as constrained layouts, which may require additional secondary areas to accommodate equipment or to meet human factors or safety guidelines. Other risks include excessive weight increases, which require last-minute mitigation strategies or re-engineering; changes to construction sequences, due to limited crane capacities; quayside or water channel depth limitations and center-of-gravity issues that impact facility stability or transportation arrangements.
Three key questions come into play when developing early weight estimates: what do we know, what can we find out and who are we talking to?
WHAT DO WE KNOW?
Past project information is the basis by which we can predict the future.
As a client, we can use internal data to ensure we have a ballpark figure of what we are expecting a facility to weigh. If early estimates from the contractor don’t align with our expectations, this should spark conversations to ensure they have considered all factors. If there are multiple contractors and bids being considered, it also helps identify any unreasonably high or low estimates and mitigate surprises after a bid is signed.
As a contractor, we should be able to back up any estimates with historical data and statistical averages, Fig. 2. Do we understand the outliers and the drivers behind them? Once we’ve identified and understand the outliers, we can decide what should be filtered out to reduce the statistical noise. Requirements, such as high pressures, extreme temperatures, new technologies, fabrication yards, quantities of skidded equipment, installation techniques and operator requirements should all be considered when selecting the pool of benchmarks to apply and determining how to skew them to meet the current project needs. Additional consideration should be given to project location and specific regulatory requirements. Often, factors that affect schedule and man-hour estimates also have an impact on weight estimates.
Similarly, a thorough understanding of the current project is required to confidently develop the preliminary weight estimates. Major project requirements (scope of work, basis of design, operator requirements, environmental studies, etc.) should be well-defined, and any unknowns should be addressed as quickly as possible. With major project requirements in hand, the contractor’s project team can identify the needed systems and begin developing critical project documents, such as block flow diagrams and process flow diagrams, Fig. 3. This information is then picked up by the facilities team to create a preliminary equipment list, pulling from past project data and technical expertise to estimate weights and sizes. With a preliminary equipment list, the design team can create a preliminary layout, which is shared with the hull/jacket design team to start their development.
The structural and weight management teams use the preliminary layouts to apply historical project data (benchmarks) to develop a base weight estimate, with appropriate levels of design allowance, and an initial margin that will mitigate risks involved with the lack of detailed development. This early weight estimate is shared with the hull/jacket team so they can review impacts on stability, adjust the hull/jacket sizing as needed, and settle on the facility Not-to-exceed (NTE) weights used for both topsides and hull/jacket engineering analyses, Fig. 4.
Additional iterations may be required to settle on a facility configuration that meets the project’s immediate needs, accommodates any management and future reserves, has a reasonable installation and fabrication goal, and is a justifiable use of the client’s CAPEX.
It is imperative to have these critical project documents and control weights frozen in place and tied to management of change process by the end of FEED. Depending on the deliverable requirements and project schedule, these items would be ideally set by the beginning of FEED. Changes beyond FEED are likely to have significant impacts to project schedules and engineering costs.
WHAT CAN WE FIND OUT?
We’ve done our best to come up with an accurate estimate, but the work isn’t done. Now we must figure out how to accurately track the design process. There is no reason the same tools being used for engineering and deliverable generation work can’t also be harnessed to also track facility weight and center of gravity (CoG) data. Ideally, the majority of the reported weight information should come from the project 3D model.
This is where standardization of processes comes in handy. Setting up standard processes for data entry and extraction across all projects makes information sharing between disciplines easy and automatic; and it removes dependency on person-to-person data transfer and ensures all parties are working with the same information. Ideally, we want to make each discipline responsible for their own weight reporting, so the weight management team knows who to ask when questions arise. The information that disciplines use to generate material take-offs (MTO) and other deliverables is usually the same data needed to generate weight and CoG data.
To start, a standard hierarchy should be created for all project 3D models. Each discipline should be set up to work within its own silos, with an understanding of what data need to be entered and how. Project- or client-specific modifications to the hierarchy should be within the standard framework. Setting up standard catalogue data that can be used during the early stages of project modelling, then modified and improved as specifications are set, should also be considered. Each discipline should also be thinking about fabrication and installation sequences when setting up their hierarchy, to make it easier for the weight management team to isolate items from certain load conditions.
Discipline databases should be standardized for the items and information not modelled. This includes the weight database. If the information coming from our modelling and reporting tools is standardized, then the weight database structure can be standardized as well, to extract information efficiently and consistently. Being able to periodically verify detailed information lends confidence in the reported numbers. This may require building in-house tools, versus using industry products that may not work as well with other in-house reporting tools. A standardized weight database also has the benefit of making it easier to generate project metrics and add to the project database used for those early estimates.
When it comes to equipment lists and vendor data, automation may not be the most efficient way to track data. The weight management team likely needs to be more involved in interpreting and directly managing vendor weight data. How incoming vendor information is handled often varies wildly between projects and is harder to standardize. However, the requested format of vendor weight data can be standardized across projects, and this should be communicated to vendors during the bid and purchase order phases.
Of course, automation of weight data does not excuse the weight management team from taking responsibility for the data they are presenting. It is important for everyone on the weight management team to understand discipline scopes and ask questions when something doesn’t look right. There should be a project Weight Management Procedure, so all parties reviewing weight data understand the basis of the information being presented and the process used to progress weight information throughout the life of the project.
WHO ARE WE TALKING TO?
None of this works unless there are open lines of communication, and clients must clearly communicate their expectations for facility requirements. While micromanagement of weight information should not be necessary, it’s important for clients to take an active interest in weight reporting: both means and methods, as well as the results. Someone at a project management level should be designated to sit in on periodic weight reviews, so information isn’t being received third or fourth-hand. There will likely be periods of discomfort, as well as frequent discussions around weight and CoG trends, weight risks and opportunities and possible mitigation plans, to allow a more logical approach to solutions.
Attention should be paid not just to the overall weight of the facility but also to the individual components. Topsides tend to have more moving parts and opportunities for weight savings (and increases). Project changes and decision registers should consider weight impacts—not just cost and schedule impacts—because unchecked weight changes can have other significant impacts. Vendor selection should be based on technical qualifications, cost and weight, and that should be emphasized both with the project team and pool of vendors from the beginning. Input should be provided on vendor selection or, if another party is responsible for the selection process, oversight should be provided, Fig. 5.
Everyone involved with the project, on both sides of the table—from upper management down to individual discipline players—should be a weight champion. Most importantly, the weight management team should be invited to the conversation to be an active participant, not just the accountant or reporter.
FINAL THOUGHTS
Although we primarily addressed greenfield facilities, the same strategies can be applied to brownfield work. Understanding the drivers behind limits on operating and installation conditions makes it easier to address the special set of challenges brownfield work presents. As with greenfield work, a well-defined, practicable process should be developed and implemented for brownfield work. This process should address how weight changes will be tracked and documented, as well as what the governing body’s requirements are for maintaining vessel classification and operating permits. WO
ACKNOWLEDGMENT
This article is derived from the presentation, “Strategies for improved topsides weight management for floating offshore developments,” presented by Angelique Spies, Wood plc, at World Oil’s/Gulf Energy Information’s Deepwater Development Conference, Madrid, Spain, March 27, 2025.
ANGELIQUE SPIES is a Topsides Weight Management specialist with more than 14 years of experience at Wood, a global leader in consulting and engineering. Throughout her tenure, Ms. Spies has helped develop and implement effective weight management techniques for more than 15 worldwide offshore projects, from pre-FEED through follow-on and brownfield stages