Bronze bearings in the stern roller of the Anchor Handling Tug Supply (AHTS) Vessel ES Kestrel have been replaced with grease-free SXL bearings from Thordon Bearings while the vessel remained afloat and operational.
The replacement was undertaken in May 2024 by Thordon’s Dubai-based distributor Ocean Power International (OPI) for the AHTS owner Echo Cargo & Shipping of U.A.E. While typically checked during routine drydocking, the vessel’s stern roller was experiencing turning issues during operation. On inspection, it was found that the existing bronze stern roller bearings were seized and worn, mostly due to failed grease lubrication.
Harsh sea conditions
Stern rollers are a key feature of anchor handlers and other offshore support vessels that need to deploy and retrieve anchor chains and wires. These vessels often operate in harsh sea conditions with high bearing loads.
These vessels often operate in harsh sea conditions with high bearing loads
ES Kestrel was built in 2011 and has mostly operated in the shallow coastal waters of the Persian Gulf region. Thordon SXL bearings operate without oil or grease above and below the waterline and are approved for pressures up to 12 MPa (1740 psi). The SXL material offers high abrasion resistance and can also withstand high shock loads, improving the wear life of the bearing.
High abrasion resistance
Rafid Qureshi, President of OPI, said off-the-shelf availability and his team’s ability to undertake the engineering and installation were key to the success of the project. His team worked with the vessel’s owner and the shipyard to design, machine and install the 360mm (14.2in) long bearings that were interference fit into split housings.
The top half of the bearing housing needed to be lifted to remove the worn bushes and install the new ones. Axial installation was not possible, and the bearings had to be placed over the pin prior to positioning the stern roller. The ability to refurbish the roller bearings while the vessel was afloat saved time and money for the client.
Sustainability of stern rollers
Thordon’s Regional Manager – Southern Europe & Gulf Med, Malcolm Barratt, said, "Thordon’s bearings enhance the performance and sustainability of stern rollers on AHTS vessels."
“Our polymers feature exceptionally long wear life and offer the best combination of strength and stiffness with flexibility and elasticity, along with high abrasion resistance. Their use in this project demonstrates the shipowner’s commitment to innovation, environmental friendliness, and cost effectiveness. This upgrade was a noteworthy achievement that showcases OPI’s engineering capabilities and dedication to efficiency.”
Small machining errors
Thordon has previously supplied rudder and tail shaft bearings to other Echo Cargo & Shipping vessels
Thordon SXL bearings are easy to machine and produce no dust. In comparison, other non-metallic materials require dust extraction and tight machining tolerances that may result in product rejection or repair delays.
With Thordon SXL, machining tolerance is less critical, and because of the relatively large interference on the bearings, it is usually possible to adjust dimensions to compensate for small machining errors.
Thordon Bearings has more than 70 distributors in 100 countries who carry extensive inventories of Thordon’s common bearing sizes. This is backed up by large regional and head office inventories. Thordon has previously supplied rudder and tail shaft bearings to other Echo Cargo & Shipping vessels and now expects to refurbish the roller bearings on two more vessels. To date, more than 80 AHTS vessels worldwide have been fitted with Thordon SXL bearings in stern roller applications.