For a large offshore wind farm, the project owner rarely relies on a single contract. Instead, the project is divided into work packages—turbines, foundations, cables, installation—entrusted to different contractors. The setup is decided early on. Once the contracts are signed, another issue occupies the teams on a daily basis: getting work packages that don't communicate with each other to work together.
It is at the contact points between contracts—the interfaces—that most delays and disputes in an offshore project arise. This article explains why interface risk is inherent to multi-contracting, how to manage it with the right tools, and which roles are responsible for overseeing it day-to-day.
Why offshore multi-contracting creates interface risk
As soon as a wind farm is divided into several contracts, the project owner becomes responsible for their consistency. Each contractor is accountable for their own scope, and theirs alone. The areas where these scopes meet are not covered by any specific contract: these are the interfaces, and their management remains the responsibility of the project owner.
The four work packages of an offshore wind farm: turbines, foundations, cables, installation
An offshore wind farm is typically structured around a few major work packages: turbine supply, foundations, cables (inter-array and export), and offshore installation. Each involves specialized players—shipowners, installers, turbine manufacturers, cable suppliers—with their own schedules, vessels, and constraints. The more granular the breakdown, the more the contact points multiply.
Balance of plant (BoP) and turbine supply agreement (TSA): the contractual breakdown
The most common breakdown separates the supply of wind turbines, governed by a turbine supply agreement (TSA), from the rest of the farm, grouped under the term balance of plant (BoP): foundations, cables, substation, and installation. Between these two blocks, and within the BoP itself, every boundary of scope is an interface that must be defined. The model chosen at the outset mechanically determines the number of interfaces the project will have to manage.
What exactly is an interface between work packages, and why can it cost millions?
An interface is the boundary between two scopes of work, the precise point where one contractor's scope meets another's. A cable that must connect to a foundation, a turbine being placed on a transition piece: every physical junction is also a contractual junction.
The three types of project interfaces: technical, organizational, and contractual
There are three distinct levels. The technical interface, when two pieces of equipment must fit together according to shared specifications. The organizational interface, when two teams must coordinate in time and space, for example, by sharing an installation window. The contractual interface, when it must be decided who bears the responsibility and cost of an issue occurring at the boundary. Managing the first requires monitoring what suppliers are manufacturing, a subject we cover separately. You can find more information in this article: Supplier oversight and nuclear equipment qualification: what the prime contractor must manage.
Why interfaces are the primary source of unforeseen disputes
When a scope of responsibility is not clearly defined, each contractor assumes it belongs to the other. Delays set in, followed by disputes. While interface disputes are sometimes settled by an arbitrator, they originate much earlier on the ground, in a gray area that no one has taken ownership of. This is far from a marginal issue: according to AXA XL, subsea cables—one of the packages most exposed to interface issues—account for nearly 80% of insurance claims for an offshore wind farm, despite representing only about 10% of its cost. A missed interface clause can cost millions. You can find more information in this article: Why cost estimates for major energy projects go off track and how to make them more reliable.
The interface matrix: a management tool
To avoid these gray areas, mature projects identify all their interfaces during the design phase and track them through to commissioning.
Interface matrix and interface register: two complementary tools
The interface matrix provides the big picture: it cross-references work packages to highlight every contact point and identify who interfaces with whom. The interface register provides more detail: for each interface, it records the nature of the exchange, the required information, deadlines, the person responsible, and the status. The matrix provides the map, while the register keeps the log.
Lead contractor and interface contractor: designating who is in charge
For every interface, a simple rule prevents blind spots: designate a lead. The contract can assign a lead contractor or an interface contractor the responsibility of coordinating a specific junction, providing information on time, and raising alerts in the event of slippage. Without a designated lead, an interface belongs to no one.
Interface meetings and early warning: keeping the matrix alive
A tool is only as good as its maintenance. Regular interface meetings, combined with an early warning mechanism that alerts you as soon as a delay threatens a junction, turn the matrix into a steering device. It is this discipline, more than the document itself, that prevents drift.
The package manager: coordinating packages, resolving conflicts
On a major offshore project, the project director often delegates the operational coordination of packages to a package manager. They are the key point of contact between management and the field: they track the progress of each package, manage interdependencies, and identify interface risks before they escalate into disputes.
When subcontractors blame each other for delays
The critical moment arrives when a delay affects an interface and each contractor blames the other. The cable installer is waiting for a foundation they deem non-compliant, while the foundation contractor disputes the cable installer's schedule. Without rapid, documented arbitration, the dispute hardens. The package manager makes decisions based on facts, records responsibilities, and maintains the schedule before the issue reaches the contractual level.
The offshore contract manager: managing the contract before legal gets involved
While the package manager coordinates operations, the contract manager watches over the contract. As the project director's right-hand person, they manage the agreement on a daily basis to ensure it remains a steering tool until the very end.
Pre-claims, claims, variations, and amendments: the contractual chain
The contract manager's work is continuous. When a planner reports a delay, they formally notify the contractor involved, request explanations and corrective actions, and document the situation. This documentation builds the pre-claim, the written record that prepares for a potential claim. In parallel, they negotiate the variations and amendments that adapt the contract to the project's evolution. On an offshore wind farm, these adjustments are constant.
When legal steps in: arbitration as a last resort
Contract management intervenes before legal. As long as the contract is actively managed, documented, and negotiated, litigation remains avoidable. It only arises when the situation reaches a stalemate: everyone has reserved their rights, and the file goes to arbitration, where legal experts take over. A common difficulty stems from the scarcity of negotiators after the signing: present to conclude the initial contract, they are then missing to manage it over the long term. You can find more information in this article: Securing rare talent for a major offshore wind project.
Tailoring contractual clauses to the geographic zone
An offshore contract is not a one-size-fits-all template. Sea, wind, and soil conditions vary significantly from one area to another, and clauses that work for one site may become unsuitable for another.
Weather downtime and vessel standby regimes: why these clauses cannot be copied
Certain clauses govern vessel usage and the sharing of weather-related risks: the mechanisms for weather downtime and standby/idle time define the windows and conditions under which a resource is mobilized, held, and invoiced. Calibrated initially for the conditions of a specific site, they lose their relevance if copied from one zone to another. A contract designed for the English Channel or the Mediterranean rarely holds up in the Atlantic, where weather windows and sea states change the game.
Weather, weather downtime, and maritime force majeure
Weather downtime (weather downtime) is primarily a contractual issue: the real question is who pays for the downtime when the sea prevents operations. Contracts provide mechanisms for sharing this risk, distinguishing between routine hazards, which are already covered, and maritime force majeure, which triggers different rights. If handled poorly, a missed weather window can delay a project by an entire season. You can find more information in this article: Offshore wind vessel standby compensation: why CFOs discover it too late.
FIDIC and the role of the "Engineer": the reference contractual framework
To structure these contracts, stakeholders often rely on international standards, primarily FIDIC model contracts, which are widely used in construction and energy.
Why offshore wind still lacks a standard contract
FIDIC model contracts, such as the Yellow Book are designed for more traditional projects and require extensive amendments for offshore work, to the point of becoming bespoke. In July 2023, FIDIC launched a working group tasked with creating a standard contract dedicated to offshore wind (FIDIC, TG14 working group), a sign that the sector is still searching for its standard. These frameworks also provide for a third party, the "Engineer," responsible for administering the contract and issuing an initial decision in the event of a disagreement, prior to any arbitration. This role acts as a buffer, which is particularly useful where interfaces create disputes.
Mastering offshore interfaces: a design decision
On an offshore wind farm, interfaces must be mapped, assigned, and managed from the design phase, before construction reveals them during a critical weather window. This work sits at the intersection of engineering, coordination, and law, and relies on rare profiles—package managers and contract managers—capable of being operational from day one.
Renergy strengthens the execution control of major projects through two complementary levers: the deployment of experts in contract management and project control and the training of internal teams.
If these issues resonate with your own, you can book an appointment with a Renergy consultant to discuss them. The conversation is confidential and aims to identify solutions tailored to your specific exposure.
To learn more, discover the four engineering phase decisions that save the construction of a major energy project.
