Choosing the ideal lubricant for a cruise ship

Cruise and ferry lines should consider the performance and environmental qualities of oils
Choosing the ideal lubricant for a cruise ship
The Polar Code specifically addresses Safety Of Life At Sea and several shipborne causes of pollution (Image: Simon Maennling)

By Rebecca Gibson |

This article was first published in the Autumn/Winter 2017 issue of International Cruise & Ferry Review. All information was correct at the time of printing, but may since have changed.

Selecting the best lubricants for a vessel is important, particularly if the ship sails in extreme climates around the globe. This has been particularly topical since the Polar Code came into force in the Arctic regions this January.

The International Maritime Organization (IMO) is concerned about the safety of ships, especially cruise vessels, sailing in the polar regions where they encounter hazards including ice, remoteness, and severe and rapidly changing weather conditions. The IMO is prioritising many issues related to safety and pollution in these regions. The Polar Code specifically addresses Safety Of Life At Sea (SOLAS) and several shipborne causes of pollution such as sewage, garbage, chemicals and oil. Discharge of oil or oily mixtures into the sea from any ship are prohibited.

According to Polar Code recommendations, vessel owners should consider using environmentally friendly lubricants. It also states that cold temperatures may reduce the effectiveness of numerous components of the ship, including deck machinery and emergency equipment.

The base oils of lubricants that are generally accepted as being environmentally friendly – or Environmentally Acceptable Lubricants (EALs) – include plant- or seed-based triglycerides, which are commonly known as vegetable oils; polyalkylene glycols (known as polyglycols); polyalphaolefins (PAOs) or synthetic hydrocarbons (man-made mineral oil); and either fully saturated, or unsaturated, synthetic esters.

Critical pieces of cruise ships’ and ro-pax vessels’ propulsion, steering, stability and deck equipment rely on the performance of EALs when they are sailing in environmentally sensitive waters and, now that expedition cruises are also venturing to polar regions, it’s essential operators select the right lubricant. But how do they decide which base oil type to select?

Reliability and long life comes from the ‘partnership’ of the base oil and additives, so operators should look at the overall operational performance characteristics of base oils. Triglycerides perform poorly in low and high temperatures, whereas polyglycols can operate well in low temperatures, but their hygroscopy raises questions about toxicity and the corrosion of metals. Plus, because polyglycols are not compatible with mineral oils, they are costly to convert to, and from, mineral oil-lubricated systems. PAOs work well in low temperatures, but require viscosity improvers to provide higher viscosity lubricants such as gear oils. These lubricants can be broken down under conditions of shear in equipment. This leaves both the unsaturated and saturated esters. Unsaturated esters are susceptible to thermal oxidation, resulting in polymerisation and an increase in viscosity. In addition, unsaturated esters (and PAOs) require frequent viscosity monitoring and offer relatively short operational life, hence they have high through-life costs compared with the more stable and better-perfoming fully saturated esters.

The base oil also needs to have good additive solubility. In arctic conditions, certain base lubricants exhibit poor additive solubility, which results in the separation (crystallisation) of additives and comprises equipment performance, potentially causing equipment failure. Fully saturated ester has excellent additive solubility. A passenger ship operator’s equipment lubricant is an asset – they should select it wisely and look after it.

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