From the magazine – Offshore walk-to-work (W2W) operations in the North Sea are increasingly challenged by rising operational costs, ambitious emission-reduction targets, and a growing shortage of skilled maintenance personnel. While W2W vessels have become an established solution for offshore access, traditional operating concepts – based on frequent port returns for crew rotation and resupply – result in significant idle time, reduced offshore productivity, and avoidable emissions.
This article first appeared in SWZ|Maritime’s January 2026 issue. It was written by Reinier Dick, Poolfleet Manager SNSPOOL, Peterson Energy Logistcs, rdick@onepeterson.com.
This article introduces a shared resourcing concept in which W2W vessels are deployed as mobile offshore assets, supported by a shared pool of supply vessels and crew transfer vessels (CTVs). Maintenance activities across multiple platforms and stakeholders are clustered using a graph-based routing approach subject to practical operational constraints. The approach increases hands-on-tool time, improves schedule robustness, and significantly reduces logistics-related costs and emissions. Case study results show cost savings exceeding fifty per cent through shared pooling, with an additional potential reduction of approximately thirty per cent through optimised supply routing.
Logistical efficiency as a prerequisite
Offshore maintenance operations in the North Sea are entering a phase where logistical efficiency is no longer merely an optimisation objective, but a prerequisite for continued operability. Ageing offshore assets demand increasing maintenance effort, while the availability of skilled and certified offshore personnel is becoming structurally constrained. This imbalance between maintenance demand and workforce capacity is rapidly emerging as one of the dominant bottlenecks in offshore operations.
W2W vessels play a key role by enabling safe and weather-resilient access to offshore installations. However, the effectiveness of W2W operations is not determined by vessel capability alone, but by how efficiently scarce offshore personnel can be deployed. Traditional, port-centric W2W concepts – characterised by frequent returns to shore for crew changes and resupply – introduce significant non-productive time, increase fuel consumption, and reduce schedule reliability. Valuable offshore working hours are consequently consumed by logistics rather than maintenance execution.
At the same time, offshore operators face increasing pressure to reduce operational expenditure and emissions while maintaining high standards of safety and reliability. Idle vessel time, fragmented logistics chains, and unnecessary sailing distances directly translate into higher costs and environmental impact. Dependence on frequent port calls further introduces sensitivity to weather, berth availability, and supply-chain disruptions, reducing overall control over project execution.
These developments call for a shift from isolated, asset-specific W2W deployment towards a shared, offshore-centric resourcing model. In such a model, W2W vessels are treated as mobile offshore production assets rather than stationary access units. Maintenance activities are coordinated across multiple platforms and stakeholders, allowing platforms to be clustered and served efficiently within defined operational cycles. By keeping W2W vessels offshore for extended periods and supplying them via a shared pool of logistics vessels, idle time is minimised and hands-on-tool time is maximised.
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Shared W2W concept and operational rationale
The shared W2W concept combines mobile W2W deployment with pooled offshore logistics. Instead of operating W2W vessels in isolation, offshore supply vessels and CTVs are used to perform resupply and personnel exchange offshore. This allows W2W vessels to remain offshore and focused on maintenance execution rather than transiting to port.
From an operational perspective, this approach fundamentally changes the utilisation profile of W2W vessels. Time previously lost to port transits and port stays is converted into productive offshore time. This directly increases hands-on-tool time (HOTT) and reduces the total duration of maintenance campaigns.
In addition, shared resourcing improves schedule robustness. Offshore supply from a pool of vessels introduces redundancy and flexibility, allowing deviations in weather, execution speed, or scope to be absorbed more effectively. The result is a more predictable and controllable maintenance process, with fewer critical dependencies on port availability or individual vessel schedules.
Routing and planning method
To identify feasible platform combinations for shared W2W operations, a graph-based routing approach is applied (Dijkstra algorithm-based). Offshore platforms are represented as nodes in a network, while sailing times between platforms form weighted connections. Platform sequences are constructed incrementally while enforcing practical offshore constraints.
Key constraints include a fixed transfer and setup time per platform, limited offshore working windows aligned with crew routines, and a maximum daily operational cycle duration. These constraints ensure that generated routes are not only efficient in theory, but also executable in practice.
An upfront feasibility screening is performed for each platform to determine whether two operational working groups can be formed within the defined constraints. Platforms failing this screening are excluded from further evaluation. For feasible platforms, a best-first routing search generates low-cost clustering alternatives, prioritising solutions with minimal sailing distance and idle time.
Although the number of possible platform combinations grows rapidly in theory, the application of strict operational constraints significantly reduces the effective search space. This ensures that the method remains computationally tractable and suitable for practical offshore planning environments.
Results and operational impact
The routing approach was applied to a dataset of 151 offshore platforms in the North Sea. Approximately thirty per cent of the evaluated platforms were found to be suitable for shared W2W clustering under the applied constraints, while the remaining seventy per cent were identified as structurally unsuitable due to spatial isolation, excessive sailing distances, or limited operational flexibility.
For the feasible platforms, a total of 1060 valid daily routes were generated. Depending on local platform density, individual platforms offered between a few and more than 100 routing alternatives. Typical route durations ranged between five and twelve hours, remaining within the imposed daily planning horizon.
Figure 1 illustrates the cost difference between traditional port-based W2W operations and shared pooling concepts. In standalone configurations, a significant portion of total cost is driven by charter time that is operationally idle when the W2W vessel returns to port. In contrast, shared pooling replaces this idle time with lower-cost offshore supply and CTV operations.
Figure 2 shows optimised sailing patterns in which W2W vessels dynamically relocate between platform clusters instead of returning to port. Blue lines represent the shared pool supply runs, while the green platforms are the W2W clusters. The yellow lines mark the CTV transfers.
Figure 3 demonstrates the resulting vessel schedule, where idle periods are largely eliminated and hands-on-tool time is significantly increased. Comparing the “return to port” mechanism with the sea supply, it can be noted that the hands-on-tool time loss for the latter is significantly less than the return to port schedule.
Case study
During 2021, a client performed W2W operations at his production platforms. During the period between June and September, it was possible to allocate the W2W vessel as a destination platform six times in the shared supply runs (approximately a four-weekly schedule). By doing this, it was possible to avoid unnecessary port calls. The combination between sea replenishment and shared pooling, reduced project times by ten days and achieved a substantial reduction of charter time, fuel consumption (emissions) and port fees.
Also read: SWZ|Maritime’s January 2026 issue: Know how
Shared W2W deployment addresses key challenges
The results presented in this article demonstrate that shared resourcing for W2W operations is not a generic optimisation exercise, but a targeted and operationally grounded approach to offshore maintenance planning. By explicitly incorporating practical offshore constraints, the method distinguishes between platforms that are structurally suitable for shared W2W deployment and those that are not.
Shared and mobile W2W deployment directly addresses several key challenges currently facing offshore operations. By reducing unnecessary port returns and idle vessel time, scarce offshore personnel can be kept productive for a larger proportion of the operational cycle. Reduced sailing distances and improved logistics coordination further contribute to lower fuel consumption and emissions, while increasing control over schedule execution.
In an offshore environment increasingly constrained by workforce availability, sustainability targets, and cost pressure, shared W2W resourcing provides a practical and scalable pathway forward. When applied selectively in geographically dense offshore areas, the approach delivers measurable operational, economic, and environmental benefits.
Picture (top): W2W ship Larissa is supplied with materials on the high seas from a supply ship.
