On January 14, 2026, during the “2nd Study Group on Port Infrastructure for Offshore Wind Power,” a critical report was submitted by the key players responsible for the “construction” of floating offshore wind. This report came from FLOWCON (Floating Offshore Wind Construction System Technology Research Association), a consortium of 14 major marine contractors (including Penta-Ocean, Toa, and Toyo) and shipbuilders like JMU.

In this article, DeepWind provides a detailed analysis of the structural challenges and solutions revealed in this simulation report. We examine the “fatal time loss caused by typhoon evacuation,” the “shipping channel occupation issue,” and the comparative analysis of construction scenarios (“Multi-Port Collaboration [26 days] vs. Mega-Port Completion [19 days]”). This is the “inconvenient truth” that Japan must face to achieve its 15GW target.

For a structured overview of Japan’s offshore wind market—including policy, investment dynamics, costs, and supply-chain constraints—see our pillar article.
👉 Japan Offshore Wind Market Analysis (Pillar)

Contents

1. Behind the 15GW Goal: Construction Capacity and the “10-Year Overlap”

The Japanese government aims to deploy 30GW–45GW of offshore wind (including floating) by 2040. According to FLOWCON’s estimates, the formation of floating wind projects will accelerate from FY2029. Crucially, because floating projects will begin before earlier bottom-fixed projects are completed, “port usage for bottom-fixed and floating wind is expected to overlap for more than 10 years.”

In a race for limited port resources, how can “Construction Capacity (units/year)” be secured efficiently? FLOWCON decomposed construction capacity into “Construction Days,” “Availability,” and “Fleet Size,” presenting a severe reality based on Japan’s specific metocean conditions.

2. The Biggest Enemy: “Typhoons” — 10 Days Lost in a Single Evacuation

The greatest risk factor present in Japan but absent in Europe is the “Typhoon.” The most serious data in this report is the quantitative estimation of schedule loss during a typhoon.

If a typhoon develops while a wind turbine is being mounted on a floater inside a port (in a temporary floating moored state), stability cannot be guaranteed. Therefore, operations must be suspended, and the unit must be “evacuated” to a safe sea area. The process and required time are as follows:

FLOWCON calculates that for one typhoon passage, a total waiting time of “8 days for evacuation + 2 days for resumption = over 10 days” occurs. If three typhoons hit in one season, nearly a month of the construction window evaporates. To avoid this risk, the industry must either adopt designs that withstand typhoons in a grounded state (bottom-seated in port) or build massive (and costly) schedule buffers into the project plan from the start.

3. Scenario Comparison: “Multi-Port Collaboration” vs. “Mega-Port Completion”

What does the standard construction cycle look like excluding typhoon risks? The report compares the “Base Scenario” (aligned with Japan’s current status) and the ideal “Mega-Port Scenario.”

Scenario A: Base Scenario (Multi-Port Collaboration)

A model where floater manufacturing, turbine installation, and temporary storage are dispersed across multiple ports or water areas.

• Process: Tow from Fab Port → Enter Installation Port → Install/Commission → Exit → Tow to Site

• Duration (per 2 units): 26 days

• Challenge: Every port entry/exit involves “Towing (1 day)” and “Adjustment Waiting (1 day to several days),” causing cumulative time losses.

Scenario B: Mega-Port Completion Scenario

A model where movement and installation are completed within a single vast port.

• Process: Intra-port move → Install/Commission → Exit

• Duration (per 2 units): 19 days

• Benefit: Eliminates external towing and port entry adjustments, enabling a ~27% schedule reduction compared to Scenario A.

Scenario B is clearly more efficient, but it requires massive infrastructure capable of handling “manufacturing, assembly, installation, and storage” all in one place. Given that Japan must utilize existing ports for the time being, the strategy will likely be based on Scenario A (Multi-Port), with the key to success being the minimization of “Adjustment Waiting” times.

4. The Berth Dilemma and the “Channel Occupation” Wall

Operational efficiency within the port is also heavily dictated by the scale of infrastructure.

1 Berth vs. 3 Berths: A 1.5x Efficiency Gap

According to FLOWCON’s analysis, construction capacity varies significantly based on the number of quay berths used.

• 1-Berth Operation: “Material delivery” → “Tower assembly” → “Turbine installation” are done sequentially in the same spot, causing idle time between steps. Construction Capacity Ratio: 1.0.

• 3-Berth Operation: Processes are separated by location, allowing parallel execution like a production line. Construction Capacity Ratio improves to 1.5.

However, ports in Japan capable of dedicating 3 berths (entire quay sections) to wind projects are limited, highlighting another severe infrastructure constraint.

Massive Objects Blocking Channels for “Half a Day”

Even more critical is the “Shipping Channel” issue. A floater carrying a 15MW turbine occupies a channel width of 250m (including safety margins) during towing. Estimates suggest that a single entry or exit occupies the channel and anchorage for “about half a day.”

Japan’s major ports are busy with LNG carriers, coal ships, and container vessels for thermal power plants. Coordinating a request to “please clear the channel for half a day for the wind turbine” is not easy. When weather-related delays are added, the puzzle with commercial shipping schedules becomes extremely complex, creating “Adjustment Waiting (0 days to 1 week+)” as an uncertain factor that pressures the schedule.

5. 40% Availability: The Difficulty of Year-Round Construction

Grim realities were also presented regarding offshore “Availability.” Assuming a 15MW turbine on a semi-submersible floater, and adhering to crane operation limits (Wave height 1.2m, Wind speed 10m/s), availability based on Japanese metocean data is as follows:

• Year-round Average: Approx. 40%

• Summer Average (6 months): Approx. 70%

Year-round operations are impossible for more than half the days. Concentrating construction in the summer (6 months) raises availability to 70%, but this coincides perfectly with “Typhoon Season.” Constructors are forced into a difficult dilemma: “We want to work in the summer when waves are calm, but a single typhoon sets us back 10 days.”

6. The Significance of the “All-Japan” FLOWCON Team

FLOWCON, which produced this detailed report, is a newly established organization (approved Jan 2025). Its members include major marine contractors like Penta-Ocean Construction, Toa Corporation, and Toyo Construction, along with engineering firms like Nippon Steel Engineering and Sumitomo Heavy Industries, and supporting members like JFE Engineering and Japan Marine United (JMU).

This is truly an “All-Japan” construction team bringing together top players in marine civil engineering and shipbuilding. The challenges they have presented are not desk theories but a practical “SOS” based on field expertise—and simultaneously, a “prescription for solutions.” They have also concluded an agreement with FLOWRA (Technology Research Association), establishing a structure where developers and constructors collaborate on technical development.

7. DeepWind View: European Hardware, Japanese Software

If the previous FLOWRA report preached the response to “15MW Hardware Upsizing,” this FLOWCON report exposes the limits and solutions for “Software (Operations)” under Japan’s unique environment.

Simply importing European technology will not work against Japan’s typhoons and narrow port conditions. “10 days lost to typhoon evacuation,” “Days of waiting for channel adjustment”—these numbers have an impact that fundamentally overturns LCOE calculations.

The key to the solution, as FLOWCON suggests, lies in abandoning the single-port completion model and establishing “Logistics that operate multiple ports as a single unit.” To solve this complex puzzle (weather, channels, berths, vessel arrangements), it is essential not to leave it to individual developers but to have a “Port Integrator” function that oversees and coordinates the entire area.

With full-scale project formation beginning in FY2029, time is running out. The question is how the government and port authorities will respond to the “limit points” shown by the contractor alliance (FLOWCON) and the developer alliance (FLOWRA) and incorporate them into the institutional design.

[References]
This article is based on the following materials submitted at the “2nd Study Group on Port Infrastructure for Offshore Wind Power” held on January 14, 2026:
・FLOWCON (Floating Offshore Wind Construction System Technology Research Association): “Construction Cycle and Challenges in In-Port Turbine Installation”

Japan’s offshore wind market cannot be understood through a single lens. A cross-cutting view—integrating policy, investment behavior, cost structures, and execution capability—is consolidated in our pillar article.
👉 Japan Offshore Wind Market Analysis (Pillar)

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