Managing the transition to Low-Sulphur fuel – not always smooth sailing?

January 29, 2021



In the latter half of 2019 we were all busy preparing our vessels to stem VLSFO as part of IMO 2020 compliance, with several questions still in our minds:

  1. Would the new regulations be postponed?
  2. Would all our ships be ready by 01 January 2020?
  3. Would compliant fuel be available, worldwide, and if so at what price?
  4. How would the new rules be enforced by port state authorities?
  5. Above all, what would be the VLSFO quality and what issues would we need to tackle?

The transition to VLSFO was largely smooth, but some issues remain and there is no room for complacency. The regulations came in on schedule and all our vessels were changed over well before the deadline. Compliant fuel is widely available, with HSFO/VLSFO price difference of about USD 80 at Rotterdam. The main thing still causing concern is VLSFO quality. Though there have been no major breakdowns so far, 2020 revealed more bunker alerts compared to previous years.

Before consumption it is important to perform fuel oil analysis at a shore-based laboratory. Some owners even allow us to carry out detailed investigative analysis to ensure that the fuel complies with Clause 5(8) of ISO 8217, i.e. fuel should not adversely affect either the machinery or the onboard personnel handling it. Despite all the possible tests, the risk of unknown adulterants always exists and there is still no way of knowing what precise contaminants or concentrations can cause damage to the ME. So efficient onboard bunker management remains vital.

Our commonest operational problems in 2020 were increased sludge deposits and the appearance of wax. VLSFO consists of a variety of blends and as a prudent ship operator we need to focus in particular on the below factors:

  1. Varying viscosity between stems;
  2. Varying density;
  3. High Total Sedimental Potential (TSP);
  4. Increased Sulphur percentage;


As there is no ISO requirement on VLSFO viscosity, efficient onboard management is critical. We have experienced viscosity as low as 30 CST, which indicates a paraffinic blend with a high possibility of  wax formation. Correct purification and injection temperature must be set, based on analysis reports and the onboard viscosity/temperature nomograms. Too high a purification temperature can cause breakdown of the blended components, resulting in excessive sludge formation and possibly even complete breakdown of the purifier. Too high an injection temperature can mean too low viscosity and even gasification of the fuel. (The photographs below show excessive sludge formation, and thus damage to the purifier casing, when the purification temperature was too great.)


First of all, whenever a new fuel is used the purifier’s specific gravity disc must be chosen using the nomogram given in the manual. 

VLSFO specific gravity varies greatly, ranging from 0.85 to 0.96. This must be considered when ordering the stem, as lower end density can mean a huge increase in volume. For example, 1,000 MT can be 1,042 cubic meters at a specific gravity of 0.96, but 1,176 cubic meters at 0.85. Failure to take this into account may mean insufficient space, cancellation of the balance and a monetary claim.

Total Sediment Potential (TSP)

Last year we had many instances where analysis showed the TSP marginally exceeding the ISO 8217 limit of 0.1% m/m. High TSP can cause heavy sludge accumulation in the purifier, and this will cause overflows and mean frequent dismantling and cleaning of the bowl assembly. In such cases the settling and service tanks must be frequently drained of water and sludge, and the purifier must be desludged as often as possible. Two or more purifiers should be operated in parallel, with a minimum feed rate and sludge dispersant added to all affected storage tanks.

In one instance the TSP was so high that the lab could not obtain the result. The sample did not pass through the filter paper in the allotted time, plainly indicating a TSP well above the relevant ISO 8217 limit, and after we had addressed the issue the entire quantity of VLSFO was pumped off.

Increased Sulphur Percentage

This is another common issue.

For example, the Bunker Delivery Note might indicate compliant fuel i.e. with the Sulphur percentage less than or equal to 0.5%, but independent testing during bunkering shows a level above that. So please consider the following whenever there is a PSC check on sulphur compliance:

(a) readings from portable devices of more than 0.53% are generally taken as clear grounds for a more detailed PSC inspection. However, such are merely indicative, and should not be treated as evidence of non-compliance;

(b) as part of any more detailed inspection, the “in-use” or “onboard” samples must be tested ashore by an accredited laboratory. If the sulphur content of these is found to be less than or equal to 0.53%, verified as an average of two tests performed at the same laboratory, the fuel should be deemed compliant.

MEPC.1/Circ.882 says that for sulphur the onboard and in-use sample limit is 0.53%, but NB this does NOT apply to samples taken on board at the time of bunkering. If analysis of any such indicates a sulphur percentage above 0.5%, to protect the vessel’s interest the Flag State should be notified, and likewise the relevant authority on arrival at the next port, according to RESOLUTION MEPC.321(74)

There are still challenges ahead for crew, owners and managers, mainly due to variability in fuel blends and continuing lack of oversight by the authorities over worldwide bunkering as a whole. However, all can be addressed by good practices, both on board and ashore.


About the author:

Mr Hariprasad is a Fleet Manager at Synergy leading a technical team managing different types of vessels. He is a Class 1 Marine Engineer with more than 28 years of experience in maritime industry including 12 years at Synergy. He is passionate about application of new technologies in Marine industry including digitalisation.