Berwick Bank B's Seaway7 deal is a bet on 60-metre monopiles — and a 2027 decision nobody has taken yet

SSE Renewables' appointment of Seaway7 as preferred supplier for the foundations and inter-array cables at Berwick Bank B is a useful signal precisely because it commits almost nothing. There is no contract value, no vessel reservation fee disclosed, no exclusivity or breakage terms and, most importantly, no final investment decision. What the announcement does reveal is the shape of the engineering problem SSE intends to solve — and how thin the installation supply chain is for projects of that shape.

What is actually agreed

The scope covers engineering, procurement, construction and installation (EPCI) of around 90 fixed-bottom turbine foundations and the subsea inter-array cabling for the 1.4 GW second phase of SSE's 4.1 GW Berwick Bank development, about 38 km off the Scottish Borders coast in the outer Firth of Forth.

Seaway7's own framing, echoed by SSE, is that this would be the third EPCI contract between the two companies after Beatrice and Seagreen, with Dogger Bank work ongoing in England. The agreement "remains subject to a final contract award and a final investment decision on Berwick Bank B by SSE, expected late next year" — that is, late 2027.

SSE states that Berwick Bank B would become the world's deepest fixed-bottom offshore wind farm on completion. That claim deserves scrutiny because it is the technical crux of the whole package.

Depth is the real story, not the jobs

The headline of SSE's release is employment: 465 UK roles supported, 400 of them in Scotland, comprising roughly 160 direct Seaway7 positions led from Aberdeen, 105 UK supply-chain roles and around 200 direct and indirect jobs from foundation marshalling at a Scottish port yet to be named. Adding the Montrose Port operations and maintenance base (100 long-term roles plus about 30 construction roles) brings SSE's stated Berwick Bank B total to around 600 UK jobs, more than 500 in Scotland.

The arithmetic is internally consistent — 160 + 105 + 200 = 465; 400 + 100 + 30 ≈ 530 Scottish; ≈595 UK in total. But these are modelled estimates spanning direct, indirect and induced categories, one tranche of which depends on a port that has not been selected. They are a political deliverable as much as an industrial one, and both the UK energy minister and Scotland's economy secretary welcomed them accordingly.

The more consequential fact is the 59.7 m maximum water depth. Fixed-bottom monopiles in that range move into territory where wall thickness, diameter, driveability and, above all, installation vessel capability become binding constraints rather than engineering details. Deriving turbine rating from the disclosed figures: 1.4 GW across ~90 foundation positions implies roughly 15.5 MW per position if each foundation carries one machine. SSE does not name the turbine model, so that is inference, not fact — but it places the project firmly in the current large-machine class, where monopile masses of 2,000–3,000 t are routine and the heaviest units are constrained by crane capacity worldwide.

That is why the vessel list matters more than the job count. Seaway Alfa Lift is a purpose-built foundation installation vessel with a large, shallow-draft deck for transporting and upending monopiles; Seaway Strashnov is a heavy-lift installation unit with a long track record on UK projects; Seaway Phoenix covers cable lay. Naming all three at preferred-supplier stage is an unusually specific commitment to a particular fleet configuration, and it hints at how SSE intends to de-risk a schedule that runs to 2031.

The supply-chain read-across

For steel producers and fabricators, the package is more interesting than the gigawatt figure suggests. Roughly 90 large monopiles, plus transition pieces, at the upper end of current mass ranges, is a meaningful tonnage enquiry — plausibly in the order of 200,000–300,000 t of structural steel depending on final design, though SSE has disclosed nothing on foundation type or mass and any such estimate is analytical conjecture rather than a reported figure. UK and European pipe mills and rolling mills capable of heavy-wall, large-diameter plate have been running with limited spare capacity for monopile-grade product, and the 2029–2031 installation window will collide with other North Sea and Baltic projects targeting the same fabrication slots.

The choice of a Scottish marshalling port — still unannounced — is therefore not merely a logistics detail. Marshalling requires quay length, load-bearing capacity, laydown area and dredged access for heavy transport vessels; Scotland's candidate ports have been competing for exactly this role, and the Scottish government has signalled up to £500 million of support for offshore wind port infrastructure and supply chain. Whoever wins that nomination inherits a decade of related activity; whoever loses faces a longer wait.

Reading the FID date correctly

A preferred supplier agreement 12–15 months ahead of FID is normal for a package of this complexity: it lets the installer influence foundation design before the design freezes, and it gives SSE a credible cost line for its investment case. It also transfers optionality to SSE and optionality cost to Seaway7, which will be holding vessel slots and engineering resource without a firm order. Neither party disclosed how that risk is shared.

Investors should resist the temptation to read this as backlog. Subsea7 discloses awards in sizeable/substantial/major bands under its own policy; no such announcement has appeared, which is consistent with the absence of an award. The trigger to watch is not this announcement but the FID decision in late 2027, and before that the confirmation of a CfD strike price and the marshalling port.

What to watch

• The turbine order. Foundation mass, and therefore steel tonnage, cannot be pinned down until SSE names the machine.
• The marshalling port decision. The most contested piece of Scottish industrial geography in this project.
• Seaway7's fleet allocation. Whether Alfa Lift is committed elsewhere for 2029 determines whether the schedule is achievable.
• CfD terms. SSE reports the 20-year contract was secured in January 2026 under Allocation Round 7; the strike price and administrative strike price comparison would tell us how much headroom exists for cost inflation between now and FID.

Berwick Bank B is a well-consented, subsidy-backed project with a credible delivery partner and a technically demanding foundation package. That is a stronger position than much of the UK pipeline enjoys. It is still not a contract.