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VPS tackles stability issues of various bunker fuels and advises precautionary measures

Steve Bee of VPS highlights the different fuel management approaches required to avoid instability and de-stablization of marine fossil fuels and biofuels.

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Steve Bee, Group Marketing and Strategic Projects Director of marine fuels testing company VPS, on Tuesday (22 July) highlighted the different fuel management approaches required to avoid instability and de-stablization of marine fossil fuels and biofuels:

Today’s ships can carry a number of different marine fuel types, from High Sulphur Fuel Oils (HSFOs), to Very Low Sulphur Fuel Oils (VLSFOs), Marine Gas Oils (MGOs), Ultra Low Sulphur Fuel Oils (ULSFOs), Biofuels, LNG and Methanol. Each of these fuels have varying degrees of stability, or instability, which can be triggered by numerous causes and effects.

However, to mitigate the risks of de-stabilsation, a range of fuel management approaches can be applied to marine fuels. This paper aims to cover the more common fuels, their associated stability issues and how to monitor and potentially overcome them.

High Sulphur Fuel Oil (HSFO) & Very Low Sulphur Fuel Oil (VLSFO)

Today, residual fuel is often referred to as HSFO, whereas VLSFO is a blended fuel of mainly distillates and residual fuels, which results in a usually less stable fuel than HSFO. Yet VLSFOs are still prone to certain similar stability concerns as its 100% residual counterpart and hence the associated test parameters.

Residual fuel, is comprised of process residues where the fractions did not boil during refining. These fuels contain asphaltenes, usually between 3-10%, which are the organic part of the crude oil, or residual oil, that is not soluble in straight chain solvents, eg pentane, heptane.

Asphaltenes exist as a colloidal suspension stabilized by resin molecules (aromatic ring systems) in the oil. The stability of asphaltic dispersions depends on the ratio of resin to asphaltene molecules.

The determination of the quantity of resin is important in estimating the potential damage created by asphaltenes. Asphaltene precipitates as a result of pressure drop, temperature, acids, mixing of incompatible oils, chemical contaminants, or other conditions and/or materials that break the stability of the asphaltic dispersion. This is the sludge witnessed when marine fuels de-stabilize.

The ability to retain asphaltenes within the fuel solution is known as the “Stability Reserve” of the fuel.

Bulk residual fuel stored for long periods can become unstable, where the asphaltene content can precipitate out of solution causing the formation of sludge. This has the potential to block filters and pipes, leaving tanks with an unpumpable residue. The ‘fuel break up’ is dependent on the nature of the liquid hydrocarbons in which the asphaltenes are suspended. If the medium is aromatic then they will remain in suspension. If it’s paraffinic, the asphaltenes may have a propensity to coalesce into sludge. Once a fuel has chemically broken down there is no way to satisfactorily reverse the process. Precipitated asphaltene cannot be redissolved.

Industry best practice is to avoid mixing fuels. Arbitrary comingling can lead to incompatibility problems and a loss of stability in the resultant blend. For example, when a heavy fuel oil with a high asphaltene content is mixed with a low-gravity distillate with a predominance of paraffinic aliphatic hydrocarbons, the stability reserve can be depleted and asphaltenes can flocculate and precipitate as sludge.

Compatibility problems must be treated as a critical concern, as they can lead to fuel starvation in diesel generators, potentially resulting in power loss. Incompatibility may cause fuel system paralysis and the subsequent clean-up is often both complex and time-consuming. There is a very simple, indicative test which can be carried out to highlight a fuels compatibility, the ASTM D4740 “spot test” . Here a blend composed of representative volumes of the sample fuel and the blend stock is heated and homogenized. A drop of the blend is put on a test paper and heated to 100°C. After 1 hour, the test paper is removed from the oven and the resultant spot is examined for evidence of precipitation and rated for compatibility against D4740 reference spots.

To provide valued information regarding a residual fuel’s stability there are a series of laboratory tests to further assess stability:

Total Sediment Potential (TSP)

The measurement of sediment involves filtering the oil through a filtration medium under vacuum. The mass of sediment is reported as a percentage by mass. The test provides an indication of the stability of the fuel as asphaltenes precipitate out forming sludge, blocking filters and choking purifiers. For residual fuels, TSP involves ageing the oil at 100ºC for 24 hours. So far in 2025, 1% of all HSFO off-specifications are related to TSP, whilst 3% of all VSLFO off-specifications are related to the same parameter. 

Total Sediment Accelerated (TSA): (Chemical Aging) A sample of the fuel is heated to achieve a viscosity of approximately 50Cst. After 10 minutes, a measured amount of hexadecane is added and the sample is placed in an ageing bath at 100ºC for one hour. The sample is shaken vigorously prior to passing through a filter paper. The result of the test is reported to the nearest 0.01% m/m and is expressed as Total Sediment Accelerated (TSA). The agreed limit for both TSP and TSA is 0.10% m/m. A fuel that falls below this limit should be viewed as thermally stable and able to homogenously maintain asphaltenic phase suspension.

Total Sediment Existent (TSE): A fuel sample is heated to 100ºC and passed through a filter paper. The amount of dry sludge retained on the filter paper correlates with the amount of sludge that is likely to be separated by an on-board centrifuge.

Separability Number, or Reserve Stability Number (RSN) is a complimentary test to the hot filtration stability methods of TSP, TSA, TSE. Using this method, the fuel is mixed with toluene which is aromatic and keeps the asphaltenes in solution. If the sample has poor stability reserve, then asphaltenes will precipitate when Heptane is added- which is naphthenic. As asphaltenes fall out of solution the transmittance through the sample increases resulting in a measure of the separability number.

Separability Number is an excellent accompaniment to the routine hot filtration methods. It can identify potentially troublesome fuels (unstable) even when the HFT method is indicating a low sediment content. Conversely, it may indicate that a high sediment fuel is in fact quite stable and unlikely to form sludge. This information in combination, is extremely useful from an operational perspective, as it will indicate in advance if and what mitigation steps are appropriate.

Note: The full article on ‘How stable is your marine fuel?’ can be viewed here.  

 

Photo credit: VPS
Published: 23 July, 2025

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Alternative Fuels

Yang Ming orders six LNG dual-fuel, ammonia-ready containerships from Hanwha Ocean

Each of the six new vessels will have a capacity of up to 13,650 TEU and feature LNG dual-fuel propulsion and Ammonia Fuel Ready specifications.

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Yang Ming orders six LNG dual-fuel, ammonia-ready containerships from Hanwha Ocean

Taiwanese shipping firm Yang Ming Marine Transport Corporation (Yang Ming) and South Korean shipbuilder Hanwha Ocean on Wednesday (2 September) signed a shipbuilding contract for six 13,000 TEU class LNG dual-fuel container vessels. 

The contract was signed by Dr. Chuck Tsai, Chairman of Yang Ming, and Mr. Charles Kim, CEO of Hanwha Ocean. The vessels are scheduled for delivery between 2028 and 2029. 

They will complement Yang Ming’s existing fleet of 10,000+ TEU vessels and serve as key vessels on East-West services, with deployment flexibility across trade lanes connecting Asia with the East and West Coasts of North America, South America, and the Mediterranean. 

Each of the six new vessels will have a capacity of up to 13,650 TEU and feature LNG dual-fuel propulsion and Ammonia Fuel Ready specifications.

“As Yang Ming transitions toward net-zero emissions, LNG provides a relatively mature and economically viable alternative fuel solution, capable of reducing greenhouse gas emissions by approximately 20%,” the company said. 

“At the same time, ammonia can serve as a carbon-free fuel by utilising converted LNG storage facilities, while offering relatively lower conversion costs and comparatively well-developed supply chains and infrastructure. The Ammonia Fuel Ready design will therefore provide Yang Ming with greater flexibility in responding to increasingly stringent international regulations on greenhouse gas emissions.”

In addition, the vessels will be equipped with Type B LNG fuel tanks with a design pressure of 1.0 bar to enhance the safety and efficiency of LNG operations, together with a range of energy-saving technologies, including Wind Shields, Rudder Bulbs, Pre-Swirl Stators, and Shore Power Systems. Smart ship technologies and cybersecurity protection features will also be incorporated to enhance operational efficiency, safety, and reliability while effectively reducing fuel consumption and greenhouse gas emissions.

Deliveries under Yang Ming’s next-generation fleet optimization plan commenced earlier this year. By 2030, a total of 24 new vessels are expected to enter service. 

This includes 18 LNG dual-fuel vessels—comprising five 15,500 TEU, seven 16,000 TEU, and the six 13,000 TEU vessels under this contract—alongside six 8,000 TEU methanol dual-fuel-ready ships. 

 

Photo credit: Yang Ming Marine Transport
Published: 4 September, 2026

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Alternative Fuels

LR, China’s MARIC unveil tanker concept ready for three future bunker fuels

Both secured AiP for a new 114,000 DWT product and crude oil tanker designed to accommodate future conversion to LNG, methanol or ammonia.

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LR, China’s MARIC unveil tanker concept ready for three future bunker fuels

Lloyd’s Register (LR) and the Marine Design and Research Institute of China (MARIC) on Thursday (3 September) have secured Approval in Principle (AiP) for a new 114,000 DWT product and crude oil tanker designed to accommodate future conversion to LNG, methanol or ammonia.

Announced at SMM 2026, the concept addresses one of the biggest investment challenges facing shipping today: the need to develop vessels and capabilities that can support a range of alternative fuel options and pathways as technologies, infrastructure and regulations evolve.

While LNG is already a mature fuel pathway, methanol and ammonia remain at an earlier stage of development, with questions around global fuel availability, infrastructure development, economics and long-term adoption.

The 114,000 DWT tanker concept has been designed as a product and crude oil carrier that can accommodate future conversion to LNG, methanol or ammonia as technologies, regulations and fuel supply chains mature. By incorporating conversion readiness at the design stage, the concept aims to reduce future retrofit complexity and provide owners with greater confidence when planning long-term fleet investments.

The design concept was reviewed against LR’s July 2026 class rules and regulations, including requirements relating to ships using gases and other low-flashpoint fuels, alongside relevant IACS Common Structural Rules for oil tankers. Final classification and statutory approval remain subject to full compliance with all applicable rules and regulations.

Theo Kourmpelis, Global Business Director for Tankers, Lloyd’s Register, said: “Shipowners are being asked to make major investment decisions today despite continued uncertainty around which fuels will dominate in the decades ahead. Alternative fuel solutions each offer potential pathways to compliance, but fuel infrastructure, regulation and economics continue to evolve at different speeds around the world.

“Designs that preserve flexibility will be critical in helping owners manage risk while preparing for multiple future scenarios.”

Si Nan, Marine & Offshore Marketing Department Vice Director, MARIC, said: “As the industry explores different decarbonisation pathways, shipowners need vessel designs that can adapt alongside technological and regulatory developments. This concept was developed specifically to provide greater fuel flexibility and long-term resilience, allowing owners to respond to changing market requirements without being locked into a single fuel strategy.

“Receiving Approval in Principle from Lloyd’s Register is an important milestone that validates the design concept and supports its future development.”

 

Photo credit: Lloyd’s Register
Published: 4 September, 2026

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Alternative Fuels

DNV: Alternative-fuelled vessel orders hit highest monthly level since October 2024

LNG-fuelled vessels accounted for the vast majority of August activity while the strong summer performance marked a significant acceleration in ordering activity after a relatively slow start to the year.

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DNV: Alternative-fuelled vessel orders hit highest monthly level since October 2024

Latest data from classification society DNV’s Alternative Fuels Insight (AFI) platform alternative-fuelled vessel ordering was strong in August, with 52 new vessels added to the platform.

This is the highest monthly total since October 2024 and follows another active month in July, when 47 vessels were added to the database.

LNG-fuelled vessels accounted for the vast majority of August activity, with 46 orders recorded. The container segment led the way with 30 orders, while the car carrier segment contributed a further 12 LNG-fuelled vessels. In addition, four ethanol-fuelled bulk carriers and two hydrogen-powered bulk carriers were added during the month, as well as one LNG bunker vessel.

The strong summer performance marked a significant acceleration in ordering activity after a relatively slow start to the year. In total, 242 alternative-fuelled vessel orders have been placed in the first eight months of 2026, representing a 27% increase compared with the same period in 2025.

LNG remains the dominant fuel choice, accounting for 63% of all alternative-fuelled vessel orders registered so far this year. Container vessels represent the largest share of these LNG orders (59%), followed by car carriers (30%).

Jason Stefanatos, Global Decarbonization Director at DNV Maritime, said: “The past two months have been particularly strong for alternative-fuelled vessel ordering, with August recording the highest monthly total we’ve seen since October 2024. This has helped lift year-to-date orders to a level well above the same period last year.

“LNG remains the leading fuel choice, driven largely by activity in the container and car carrier segments. These sectors have been among the earliest adopters of alternative fuels, supported by predictable liner operations and increasing demand from cargo owners to reduce emissions across supply chains. 

“For many owners, LNG offers a combination of emissions reductions, fuel availability and future flexibility while the longer-term fuel landscape continues to evolve. 

“At the same time, the latest figures include orders for ethanol- and hydrogen-fuelled vessels, highlighting that owners continue to explore a range of decarbonization pathways. Different segments are making different fuel choices, but the overall level of activity demonstrates continued investment in lower-emission shipping.”

Screenshot 2026 09 04 at 12.29.26 PM Screenshot 2026 09 04 at 12.29.36 PM

 

Photo credit: DNV
Published: 4 September, 2026

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