Kongsberg Maritime’s K-Sail wind-assist technology excels on Terntank’s chemical tanker, Tern Vik. By integrating nextgen suction sails with advanced digital optimization and automated propulsion systems, the solution is already exceeding theoretical fuel-efficiency benchmarks. The pilot program marks a shift toward data-driven, sustainable shipping, with plans to expand into semi-autonomous voyage planning and potential fleet-wide retrofitting.
Gothenburg | March 31, 2026 – As the maritime industry faces intensifying pressure to decarbonize, a centuries-old power source is making a high-tech comeback. Kongsberg Maritime’s K-Sail solution, a pioneering wind-assist technology, has moved from theoretical modeling to real-world validation following the successful late-summer 2025 entry into service of the chemical tanker Tern Vik.
The vessel, the first of five ordered by sustainability-focused owner Terntank, represents a critical milestone in the integration of wind-assist power with sophisticated digital optimization.
A Technical Milestone: The Suction Sail Integration
The Tern Vik, a Kongsberg NVC 615 CT design, is equipped with four advanced suction sails provided by Econowind. Unlike traditional canvas, these aerodynamic cylinders use internal fans to create a pressure difference, generating significant forward thrust even in varying wind conditions.
According to Henrik Alpo Sjöblom, Kongsberg Maritime’s K-Sail Technical Lead, the project is more than just a hardware installation; it is a live laboratory for the future of green shipping.
“This is a pilot installation. We’re developing K-Sail into a solid wind-assist solution by learning from real-world data,” Sjöblom stated. “Aerodynamics around a vessel with sails is complex. The only way to get accurate insight is to collect data during operation and refine the wind model as we go.”
Performance Exceeding Theoretical Models
Working in tandem with the Research Institute of Sweden (RISE), Kongsberg conducted a rigorous sea trial program last autumn. The objective was to pit empirical performance against the initial computational fluid dynamics (CFD) models.
The early verdict is overwhelmingly positive. Sjöblom noted that the sails are currently performing slightly better than expected. One of the primary drivers for this success is the system’s “low threshold” for use. Aside from port maneuvers where visibility is paramount, the “on/off, up/down” simplicity has allowed the crew to deploy the sails almost continuously during transit.
The Power of System Integration
The true differentiator for the K-Sail solution lies in its deep integration with the ship’s “nervous system.” The Tern Vik utilizes a comprehensive Kongsberg equipment package, including:
- K-Chief automation and propulsion control.
- AutoChief systems.
- Controllable Pitch Propellers (CPP).
By adjusting the combinator curve to match sail performance, the system automatically optimizes propeller pitch when wind conditions are strong, reducing the load on the main engines. While engine speed adjustments are currently manual, guided by K-Sail’s advisory input, the roadmap points toward full autonomy.
“The next step is to move to semi-automation, an ‘execute’ button for crew, and eventually full automation,” Sjöblom explained. “We need confidence in the system before removing the human from the loop, but optimization is already happening.”
Economic Viability and the Charterer’s Perspective
For shipowners and charterers, the bottom line remains fuel consumption. Reduced engine loads have already translated into tangible savings that track ahead of initial forecasts.
Claes Möllar, CEO of Terntank, emphasized that the data harvested from Tern Vik and its four upcoming sister ships will create a “critical mass” of information across diverse routes.
“Charterers are attracted by the potential for reductions in fuel consumption, so it is important for us to demonstrate the benefits with hard data,” Claes said. “These ships will serve as testbeds, allowing us to compare fuel savings, emissions reductions, and maintenance costs against our other vessels.”
This data will ultimately determine the feasibility of retrofitting older vessels within the global fleet, potentially accelerating the industry’s transition to wind-assist technology.
The Next Frontier: Digital Voyage Optimization
Kongsberg is already looking toward the next iteration of the technology: K-Sail Voyage. This digital tool moves beyond immediate sail trim to holistic route planning. By analyzing weather forecasts, the system can advise a vessel to slow down in the short term to intercept stronger winds later in the journey.
The ultimate goal, according to Sjöblom, is to shift the operational mindset from maintaining a constant speed to matching the ETA in port through the most energy-efficient means possible.
With five vessels currently equipped or on order, Kongsberg Maritime and Terntank are proving that wind-assist is no longer a “nice idea”, it is a practical, scalable solution for the modern energy landscape.
About Terntank Rederi
Terntank Rederi is a premier family-owned shipping company with deep roots in the Swedish maritime tradition. Now led by its fourth generation, the company remains firmly anchored in the coastal community of the Swedish west coast, carrying forward a legacy of seafaring excellence that dates back to the early 20th century.
Today, Terntank owns and operates a modern fleet of ten chemical tankers, primarily in the 15,000 dwt range. The company has distinguished itself as a global leader in sustainable shipping, operating what is widely considered one of the world’s most environmentally friendly tanker fleets.
By pioneering technologies such as the Hybrid Solution Plus® series, incorporating battery hybridization, wind-assisted propulsion, and the capability to run on fossil-free fuels, Terntank continues to push the boundaries of maritime innovation. The company remains committed to staying at the forefront of the industry’s transition toward a carbon-neutral future for many years to come.
About Kongsberg Maritime
Kongsberg Maritime (KM) is a global leader in marine technology, providing “The Full Picture” for the entire maritime lifecycle. As of April 2026, the company has transitioned into a standalone publicly listed entity on the Euronext Oslo Børs, marking a new era of independent innovation in the maritime and energy sectors.
Headquartered in Norway and with a history stretching back over 200 years, Kongsberg Maritime’s systems are currently installed on more than 30,000 vessels worldwide. The company is at the forefront of the industry’s “green shift,” developing high-tech solutions that prioritize safety, efficiency, and sustainability.
Key Facts & Specialized Areas:
- Global Presence: Operates in 35 countries with approximately 8,300 employees, more than half of whom are engineers.
- Technological Leadership: A pioneer in autonomous shipping, dynamic positioning (DP), and integrated bridge systems.
- Green Propulsion: KM offers a comprehensive portfolio of eco-friendly technologies, including the K-Sail wind-assist solution, hybrid battery systems, and ammonia-ready engine designs.
- Market Reach: Serves a diverse range of sectors including merchant shipping, offshore oil & gas, offshore wind, subsea robotics, and naval defense.
- Digital Innovation: Through its Vessel Insight and K-Sim platforms, KM leverages real-time data and simulation to optimize vessel performance and reduce the global shipping industry’s carbon footprint.
Source: Kongsberg Maritime | Terntank Rederi