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Large cargo vessel travelling through an expanse of water filled with containers and powered by a propeller

Additives for stern tubes

We are world leading in the development of synthetic base oils for use in environments where oil release or spillage may occur and have developed an industry leading range of Priolube™ ester base oils. Many of our products designed for environmentally sensitive areas are made using renewable and sustainable raw materials; almost all are ultimately biodegradable and have low toxicity towards aquatic organisms. Our products are also European Ecolabel certified (on the LuSC list), suitable for formulation under Vessel General Permit (VGP) and most are USDA Biopreferred®. 

The stern tube is vital for marine propulsion and pollution prevention. The majority of the global shipping fleet operate with oil-lubricated stern tubes, which are submerged below deck and have a direct interface with seawater. Oil leakage from stern tubes is now considered to be an issue of concern and can have substantial effects on the aquatic ecosystem.  

Ship propeller and stern tube close up at the bottom of a vessel

What makes a good stern tube oil?  

Marine vessels are driven through the ocean by means of a propeller, connected to the diesel engine via a propeller shaft. Housing this assembly is the stern tube, which contains many bearings and seals as well as oil and water sealing “glands”, which aid the expulsion of seawater and maintain lubricating oil integrity.  

A stern tube oil is necessary to provide lubrication to stern tube bearings and propeller shaft seals, deliver excellent hydrolytic stability and maintain oil integrity should water ingress occur. The oil itself must also be compatible with the range of materials found inside the stern tube e.g. elastomers, paints and various metal types. 

Given that the stern tube is submerged beneath the seawater during its application, there is the potential for water to egress into the surrounding seawater, whether this be during normal use or as an accidental spillage. Lubricants lost in such a way can cause catastrophic effects to the aquatic ecosystem and so there is now a drive to use environmentally acceptable lubricants (EALs) on board vessels to protect the environment, should oil leakage occur. 

We understand it can be difficult to formulate and meet regulatory requirements around protecting the environment. Using our technical expertise and in-depth application knowledge, we develop products with regulatory challenges in mind.  

Emkarox™ VG NS 

Our most recent product innovation is Emkarox VG NS, a range of innovative, non-sheening base fluids which allow the formulation of compliant lubricants without compromising on performance, even in the presence of water. 

Available in ISO 100 and ISO 150 grades, these base fluids and possess the properties of a conventional base oil, but also have the unique ability to partition into water.

Emkarox VG NS base fluids: 

  • Have excellent inherent hydrolytic stability 
  • Are non-emulsifiable 
  • Readily disperse in sea water at low concentrations 
  • Are non-sheening. 

Marketing sheet: Emkarox™ VG NS

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Emkarox VG NS

Ideal for use in stern tubes

This video simulates what happens when a stern tube oil becomes expelled into seawater. The Static Sheen Test (EPA Method 1617) was used. Conventional stern tube oil, Emkarox VG100NS and Emkarox VG150NS were added to synthetic sea water at room temperature.

The video clearly shows that conventional oil imparts sheening on the surface on the water. Conversely, both Emkarox VG NS fluids sink and ultimately disperse in the seawater.

Recommended products

Emkarox™ VG 100 NS

Emkarox™ VG 100 NS

Our Emkarox™ VG NS range of innovative, non-sheening base fluids allow the formulation of compliant lubricants without compromising on performance, even in the presence of water.

Emkarox™ VG 150 NS

Emkarox™ VG 150 NS

Emkarox VG 150 NS is a non-emulsifying base fluid that meets the relevant Ecolabel criteria for lubricants, and is on the LuSC list.

How can we help you with your application needs?