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Redox flow batteries for ships

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Safe and sustainable: redox flow batteries for ships

Piet Visser’s graduation research on implementation, risks, and opportunities

Redox flow batteries (RFB) are already widespread for stationary energy reserves, but in the maritime industry their potential remains largely unexplored. Former graduation student and now full-time employee, Piet Visser, delved into the feasibility of redox flow battery for ships on board short-sea operating vessels. At Conoship, we consider full– or partly electric propulsion a crucial element for reaching the 2050 sustainability goals. 

Personal experience & transition to Conoship

Over the last academic semester, Piet has been conducting his research and integrating at the Conoship office in Groningen. He has done so with remarkable success as his degree in Maritime Technology has been concluded and he has since begun as a full-time employee. 

‘It was a wonderful experience working for Conoship due to the comfortable working environment and exciting graduation assignment. During the project I learned a lot, but I am happy to be a full-time employee right now.’ 

Studying at NHL Stenden was a resourceful experience to help delve into the fundamentals of maritime technology. However, doing a theoretical research project with clear practical implications has allowed Piet to delve into something truly unique.  

Conoship office

Understanding redox flow batteries for ships

Redox flow batteries are an innovative energy storage solution that has already gained traction in stationary applications worldwide. Unlike conventional battery systems, RFBs store energy in a liquid electrolyte and release it through electrochemical reactions. The major advantage, compared to traditional batteries, is their energy efficiency, long cycle life, and scalability. Additionally, RFBs do not run the risk of combusting like lithium batteries, providing a major safety boost for sailors.  

At the core of an RFB is an electrochemical cell divided into two chambers: one positive and one negative, separated by a membrane. The electrolyte, which contains active chemical species, is pumped through these chambers, where energy is stored or released based on the reaction taking place. The choice of electrolyte is crucial, as it determines the battery’s energy density, efficiency, and overall feasibility for marine applications. 

Schematic overview of redox flow batteries for ships

Research findings

For this research, a vanadium-based electrolyte using hydrochloric acid (HCl) as a solvent was selected due to its high energy density of 43 Wh/l (27 Wh/kg) and stable electrochemical properties. Vanadium redox flow batteries (VRFBs) are particularly attractive because they enable full charge-discharge reversibility, have a long lifespan, and are considered safer than conventional lithium-ion batteries due to their non-flammable nature. 

The study focused on the feasibility of implementing RFB technology onboard ships, identifying key challenges such as system integration, operational risks, and safety requirements. A risk-based design approach was used to assess potential hazards, including electrolyte leakage, membrane failures, and material corrosion. To mitigate these risks, design measures such as compartmentalized storage, reinforced piping, and automated leak detection were evaluated to ensure safe and reliable operation at sea. 

While the research confirms the technical viability of RFBs for maritime use, further refinement is needed to optimize efficiency and scalability. These findings provide a foundation for future development, paving the way for broader discussions on how this technology can contribute to sustainable shipping solutions. 

Implications for the maritime industry

  • Specialized chemistry expertise is essential for handling electrolytes safely and optimizing system performance. 
  • Industry collaboration is needed to develop maritime redox flow battery applications. The Digital & Green Maritime Coalition can help connect the right partners.
  • Retrofitting potential is high, especially for Conoship’s CIP-series, which is designed for future fuel adaptability. 
  • Further system design is required to refine integration, safety measures, and efficiency for real-world applications. 
  • Scalability & Modular Design – RFBs have the potential to be modular, allowing ships to scale energy storage based on operational needs. This could be particularly useful for short-sea vessels with varying energy demands. 
  • Port Infrastructure & Charging – Unlike conventional fuels, RFB electrolyte refueling and management systems need to be developed at ports. Collaboration with port authorities could accelerate adoption. 
  • Integration with Hybrid Systems – RFBs could work alongside other energy sources (e.g., methanol, wind, battery-assisted propulsion), making them part of a broader hybrid maritime energy strategy. 

Challenges and limitations of redox flow batteries for ships

Implementing redox flow batteries onboard ships presents key challenges, particularly in integrating storage tanks, pumps and piping while ensuring safety and reliability. The corrosive nature of the electrolyte demands strict containment measures to prevent leaks and maintain operational safety. 

RFBs also require significant storage volume, making them less suitable for vessels with tight space constraints. While setup costs are high, their long lifespan and cycle stability offer long-term value. 

Currently, RFBs are most viable for short-sea vessels – an area where Conoship specializes, positioning us at the forefront of this innovation. However, further design work is needed before large-scale adoption becomes feasible. 

Conoship’s approach

At Conoship, we continuously refine ideas to develop the most sustainable and efficient solutions for the maritime industry. Our CIP-series is a prime example—standardized short-sea vessels weren’t common in the market, yet we saw the potential. By focusing on modular, future-proof designs, we created ships that save time, reduce costs, and allow for easy adaptation to new technologies.

The same mindset applies to Redox Flow Batteries (RFBs). While they have yet to be adopted in shipping, their long lifespan, scalability, and safety advantages make them a compelling option. We are actively exploring how RFB technology can be integrated into our designs, particularly for future-fuel-ready vessels like the CIP-series.

To bring this innovation to life, collaboration is key. We are looking for partners in energy storage, shipbuilding, and regulation to develop practical applications for RFBs at sea. Interested in working with us? Let’s shape the future of short-sea shipping together.

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General cargo vessel converted into cable recovery vessel Maasvliet

Cable recovery vessel Maasvliet delivered

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Cable recovery vessel Maasvliet delivered

First in series of five CIP3800 vessels delivered by Holland Shipyard Group

Holland Shipyard Group has successfully delivered the cable recovery vessel Maasvliet, the first of five CIP3800 vessels, for Hudig & Veder. The first three of these will be operated by Hartel Shipping. This delivery introduces a new generation of fuel-efficient vessels to the European short-sea market, with the Maasvliet specifically designed for cable recovery operations.

Cable recovery vessel construction and delivery

The Maasvliet was launched on January 11th, 2024, at the shipyard facilities in Nantong, China. Following the launch, the vessel was transported to Rotterdam alongside her sister vessel Rijnvliet. At Hardinxveld, Giesendam, Holland Shipyard Group completed the final outfitting and commissioning work before delivery to Hartel Shipping in January 2024.

Designed as a cable recovery vessel, the Maasvliet is specifically equipped to retrieve and transport subsea cables, playing a crucial role in cable decommissioning and repurposing projects. With its fuel-efficient design and optimized cargo handling capabilities, the vessel enhances the sustainability of offshore and maritime infrastructure by facilitating the responsible removal and recycling of cables.

General cargo vessel converted into cable recovery vessel Maasvliet

Technical specifications of the vessel

Main particulars
  • Length overall: 89.43 meters
  • Breadth: 13.20 meters
  • Design draught: 4.30 meters
  • Dimensions hold: 60.9 x 10.8 x 8.5 m
  • Service speed: 10 kn
Propulsion system

The vessel features an advanced diesel-electric propulsion system, designed for optimal fuel efficiency and reduced environmental impact:

Tank capacities
  • Ballast water: 1,768 cubic meters
  • Fuel oil: 173 cubic meters
  • Potable water: 23 cubic meters

Environmental features

In addition to its role in cable recovery, the Maasvliet benefits from the Vliet series’ advanced environmental features, which focus on fuel efficiency, emission reduction, and adaptability to future propulsion technologies.

Future-proof design and standardization

The CIP3800 series demonstrates forward-thinking design principles with its future-fuel ready capabilities, allowing for potential conversion to alternative fuels. The vessel can also be prepared for battery hybrid installation, showcasing its adaptability to emerging maritime propulsion technologies. This standardized design approach offers the advantages of reduced delivery time while maintaining cost-effectiveness, making it an attractive solution for operators looking to modernize their fleet.

Fleet expansion

This delivery is part of Hartel Shipping’s fleet modernization program. The next two vessels in the series are scheduled for delivery throughout 2024, with the second vessel, Rijnvliet, expected to join the fleet in Q2 2024. Upon completion, this series will strengthen Hartel Shipping’s position in the European coastal shipping market while significantly reducing their environmental footprint.

With its specialized role in cable recovery and its future-proof design, the Maasvliet is not just the first in the Vliet series—it represents a step forward in sustainable maritime solutions. We congratulate Hartel Shipping and Hudig & Veder Group on this significant milestone and look forward to the successful delivery of the complete Vliet series.

More info on our CIP series

Stabilizing the future of beam trawlers

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Stabilizing the future of beam trawlers

Improving safety for beam trawlers: Conoship’s advances in vessel safety

Following two extensive research projects on the ‘Stability of beam trawlers’ and ‘Improving the safety of beam trawlers’ (please reach out to us to request the research papers), we visited the MARIN model testing facility last October. Our appreciation goes to MARIN for their hospitality, expertise and professionalism, the results of the testing days are invaluable to the fishing industry.  

The project, which began in 2022, was commissioned by the Dutch Ministry of Infrastructure in response to the tragic capsizing incidents involving beam trawlers UK-165 ‘’Lummetje’’ and UK-171 ‘’Spes Salutis’’. We dedicate our ongoing work to the crewmembers of the beam trawlers that were lost at sea, aiming to establish new standards in vessel stability and crew safety. 

What are beam trawlers

Beam trawlers are a type of fishing vessel introduced shortly after the second world war. They operate by dragging two large nets (called fishing trawls) through the water along the bottom of the sea.

Why this matters now

On November 28th, 2019, beam trawler UK-165 Lummetje capsized and sank, with the sad loss of two lives. While investigations by the Dutch Safety Board were still underway, in December 2020 the UK-171 Spes Salutis experienced a similar incident, fortunately the crew was rescued.

Following the results of the investigation, the Dutch Ministry of Infrastructure and Water Management was recommended to ‘Investigate the scale of the safety risk of the capsizing and sinking of trawlers as a result of dangerous asymmetric loading conditions within the entire Dutch trawler fleet. Include all fishing vessels in this investigation, irrespective of their length. Take measures to counter this safety risk’. Hence, Conoship was assigned by the ministry to follow up on the investigation and recommend the solutions necessary to improve vessel safety. 

During the first project on the stability of beam trawlers Conoship carried out, all Dutch flag beam trawlers were included in the investigation .One of the main conclusions of this project was that it was necessary to narrow down the scope to beam trawlers with a length of 24 meters and less. 

Beam trawler ‘Lummetje’ UK-165

Research findings and outlook

We are on the brink of revolutionary change in the industry. For the first time, major players from the entire Dutch fishing industry are coming together to address maritime safety and regulations for beam trawlers. By bringing together builders, fishermen and those who make the regulations we are finally looking at major breakthrough. While the project is commissioned by the Dutch Ministry of Infrastructure and Water Management and carried out by Conoship, local governments are also involved, together with:

Designers

Fishermen

Governments

Students & educational institutions

The research is relevant for all European nations as many findings can also be applied to different types of vessels. The Belgium and Germany governments have been specifically informed, as there is also a sizeable beam trawler fleet in those countries as well. Furthermore, other countries that use these types of vessels are the UK and France. 

As so often, tragedy is at the essence of regulatory breakthroughs. Right now is the time to ensure we keep moving forward. As the various stakeholders of the (beam trawler) fishing industry come together we are close to pushing new national policies that will drastically reduce the risks Dutch fishermen face. 

Looking at the second research project, it resulted in three proposals to stabilize the future of beam trawlers: 

Proposal for stability criteria during fishing operations

General stability rules apply also on beam trawlers, but adding requirements for fishing conditions with additional safety margin makes sure vessels can handle these tough situations better. The new rules focus on required vessel stability under heel at different angles and stability requirements while pulling fishing nets.

Onboard warning system

Based on the proposed new criteria, a stability module can be developed. Based on this module a warning system can be developed, to assist the crew with timely detecting of stability risks while fishing.

improve-relevance

Improved education

More practical education on vessel stability is essential to prepare skippers for tricky real-life scenarios. The conclusion of the research is to use an operational ship’s model to demonstrate and experience the effects of moving booms, rigging and other weights on stability. Additionally, the use of beam trawler simulators is also recommended. In particular, the 24-meter simulator at MARIN and the 40-meter simulator at VDAB.

Insights from MARIN beam trawler model testing

The model testing was done based on the results of Conoship’s second research project and was executed by MARIN and commissioned by the Dutch Ministry in collaboration with MARIN. The first impression seems to confirm our findings. 

MARIN simulated realistic fishing scenarios, such as the effects of fishing gear weight and derrick positions. Testing verified that these conditions ensure a more realistic evaluation of a vessel’s stability compared to traditional free-sailing criteria. Even minor design improvements for newbuilt beam trawlers and retrofitting existing ones can already play a major role in improving safety and stability. 

Ongoing steps and intended vessel safety results

MARIN will process the results of the testing, with which Conoship will assist in any way possible. At first glance, the results seem to align with the second research project, but we must eagerly await the definitive conclusion.

diagram-module-new

Working out the module upon which the warning systems can be designed. Implementation of the to-be designed warning system on new beam trawlers will be easy. On the other hand, retrofitting existing beam trawlers will likely be more challenging in the upcoming years.

Further develop the beam trawler simulations systems for the education of fishermen in close collaboration with MARIN.

Finally, the proposal to the Dutch Ministry will give national policy makers the opportunity to stabilize the future of beam trawlers. These steps mark the beginning of a safer future for the Dutch fishing industry. By addressing the challenges head-on, we aim to reduce risks at sea, protect the lives of fishermen, and ensure that beam trawlers remain a vital and viable part of our maritime heritage. 

By taking decisive action today, we ensure that tragedies like those of the recent past become a thing of history. This journey is one that requires commitment from everyone in the industry. Together, we can implement these solutions, create safer vessels, and set a global standard for fishing vessel safety. We are proud to be a part of this process! 

Do you want to know more about this topic or want to know about how you or your organization can contribute to stabilizing the future of beam trawlers? Feel free to reach out to us through the form on our website or call us directly at +31 (0)50 526 88 22. 

TSHD Ecodelta

Ecodelta – the new LNG consuming dredger

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In 2015, the project Ecodelta was initiated by Van der Kamp, a Zwolle-based dredging company and Conoship International. Ecodelta is a trailing suction hopper dredger which consumes liquified natural gas (LNG). This one of a kind dredger has two main objectives: recover valuable material from the seabed and create a greater depth of water. The vessel has a length over all of 134.10m, the breadth moulded 21.40m, a dredging draught of 7,770m, a hopper volume of 5900m3, a dredging depth below baseline of 35m and a Gross tonnage of 7560 GT. The ship has been designed by Conoship International and has been built by the Frisian shipyard Barkmeijer. Today, January 11th, the vessel will be christened. Conoship International congratulates Van der Kamp with reaching this milestone and thanks them for the pleasant cooperation throughout the project. Conoship International is very proud of the result and wishes the Ecodelta and her crew many safe journeys.

 

Environmentally friendly

Van der Kamp has signed a contract with the Port of Rotterdam Authority, in order to perform maintenance of port of Rotterdam until 2023. The final goal is to become the most sustainable port by replacing the fuel oil with LNG for shipping. Another advantage of LNG is cost-efficiency. The LNG tank of approximately 300m3, can store an energy which can be used in a period of two weeks.

Ecodelta is already meeting the upcoming regulations for emission reduction that will come in force in 2020. The usage of LNG reduces the emissions of CO2 up to 20% and NOx up to 85%. In addition, SOx is reduced to zero.

 

Read more about this ship:
Ecodelta 5,500 m3 TSHD on LNG (portfolio page)

eConowind-unit at sea

CONOSHIP DECREASES ECOLOGICAL FOOTPRINT

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CONOSHIP International decreases significantly the ecological footprint of shipping

Conoship International B.V. is in continuous innovation since 1952. The passionate team of Conoship International delivers the next level in ship design by introducing equipment which support the positive human impact on Earth’s ecosystem.

Since 2017, Conoship has been developing the eConowind-unit which is used to reduce emissions and fuel consumption. The unit has two foldable VentiFoils which create a superior thrust. Two, four or six units can be fitted on a vessel. In the case of two eConowind-units on a vessel with 5000 ton cargo, it is expected that the average fuel savings and reduction of emissions will be between 10 to 20%. The first trials of testing at sea have been successful and the results are promising. Therefore, Conoship International makes a big step towards emission free shipping.

Conoship strives to add more value to the development of new as well as future equipment which will decrease the ecological footprint. In this manner, the organization advocates the philosophy of a global citizenship by initiating a forthcoming transition to the usage of more renewable energy systems. As a result, Conoship has launched and is involved in several research projects for alternative fuels. In the next years, Conoship will present designs for a fleet that will be able to fulfil any foreseeable future demands, up to zero-emission.

Methanol as marine fuel

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The potential of methanol as alternative marine fuel:                                                                            LeanShips

As member of the LeanShips project Conoship International plays a great role in the research of the possibility to use methanol as a marine fuel.

With its simple molecule, methanol has great potential to become the future marine fuel as it is safe to handle, environmentally friendly and can be produced from a large number of available raw materials from natural gas to biomass.

Conoship International already has a wide experience with assessments for conversions on existing ships but we also developed several new ship designs where the use of methanol as main fuel has a central role. These designs are made for new builds that will be powered with methanol as main fuel from the build or are easy to convert from one type of fuel to another.

Beside the technical part Conoship International has also developed a great Economic Assessment Tool. With this program several combinations of ship types, voyages and used fuel can be analyzed to compare alternative fuel options and to get an optimal prediction of the cost and returns for these scenarios.

 

Why methanol,

No sulfur and low NOx > near to zero emission.Methanol

Still liquid under ambient circumstances so easy and safe to transport and store.

Dilutes in water so no environmental harm in case of spills.

Already adopted within the provisional rules and regulations of Lloyd’s Register.

Widely available all around the world.

Can be used as fuel for combustion engines and also with a DMFC (Direct Methanol fuel Cell)

 

Is it Green?

With methanol as a fuel you are in compliance with Tier III regulations without any further aftertreatment.

Methanol has a very small ecologic footprint as it can be produced from a variety of renewable sources.

Methanol readily dissolves in water and biodegrades rapidly.

 

Conoship International will keep on investing in new designs and knowledge and we are ready to help you with questions about new solutions for your future ship propulsion.

European Commission Horizon 2020