Classification society DNV GL has launched a joint development project (JDP) in cooperation with marine insurers Swedish Club, Norwegian Hull Club, Gard and Skuld to test the potential influence of Environmentally Acceptable Lubricants (EALs) on failures in stern tube bearings. DNV GL will oversee laboratory testing of EALs by Leonardo Testing Services Ltd at the University of Sheffield, UK.
DNV GL said that the JDP had been prompted by an increase in stern tube bearing failures over the past few years. This had coincided with the increased uptake of EALs after the introduction of regulations in 2013 requiring their use in commercial vessels trading in US waters. Also there had been an introduction of new propulsion system designs, such as single stern tube bearing installations and larger and heavier propellers, operating at lower RPM.
DNV GL principal engineer Øystein Åsheim Alnes said that “very few studies have been conducted to compare the lubrication performance of EALs with that of traditional mineral oils in stern tube applications”, adding that “with this new study we hope to gain a better understanding of factors influencing the lubrication performance of EALs”.
The test programme will investigate such aspects as hydrodynamic oil film formation, oil film thickness under varying loads and temperatures, and potential shear thinning effects at high shear rates. State-of-the-art non-invasive ultrasonic techniques developed by the University of Sheffield will be utilized to examine lubricant film behaviour in real-time.
The first phase of testing will be completed in the first quarter of 2018, with the results scheduled for publication later in the year.