Slew Bearing & Gearbox Change-Out using a custom Jacking System

Alatas ServiceField Service
LocationEMEA, United Kingdom, Invergordon
Equipment TypeOffshore Cranes
Offshore Pedestal Crane
CranesLiebherr BOS 30/1100

With an extensive track record of successful Slew Bearing Changeout’s, Alatas Engineering and Design Services UK were entrusted by the client to Jack Up 2 Liebherr BOS Pedestal Cranes, in order to replace their Slew Bearing’s and overhaul both Slew Gearbox’s. To achieve this, Alatas UK designed and fabricated a custom and re-usable Jacking Frame.

It was important for the solution to work efficiently whether out at sea or in port, be re-usable and enable a quick turnaround to minimize crane downtime.


Due to being in service for an extended period of time, the case-hardened surface of the original Slew Bearing Teeth had depleted. This results in further rapid wear, potential for breakdown, and reduced control of the boom’s slewing motion. Therefore, Alatas UK assisted the client by periodically inspecting the Pinion and Slew Gear teeth to understand the structural integrity and rate of wear. This allowed the client to plan the Replacement for a time which is most convenient, and subsequent downtime has a minimal impact. 


Alatas UK managed the project right through from supply of the new Slew Bearing and Design of the Jacking System, to Commissioning and Load Testing. To ensure safe and efficient project execution, Alatas provided experienced personnel, including Senior Design and Project Engineers, Coded Welders, Rigger, Electrician, Crane Operations, Hydraulic Technician and other Crane Service Technicians.


Jacking Frame Design

  • Review crane data and select the most suitable jacking method
  • 3D Model Crane
  • Design Jacking Frame around the design and dimensions of the crane Pedestal and Chassis
  • Check Stress Valves using predicted loads
  • Design a skidding frame to allow efficient replacement of slew bearing

Jacking Frame Fabrication

  • Establish ITP and Quality Plans
  • Fabricate Jacking Frame
  • Supply of all Fixings
  • NDT and Testing
  • Provision of Manufacturing Record Book and Certification Pack

Jacking Frame Construction

  • Manage construction of Access and Load Bearing Scaffolding
  • Lift Plan and Rigging for lifting Jacking Frame Components into position
  • Assemble, Tension and Weld Jacking Frame to Crane
  • Pre and Post NDT of Welds
  • Assemble and Test Jacking System

Slew Bearing Changeout

  • Disconnect and Remove of Slip Ring
  • Remove both Slew Motors, Brake Packs and Gearboxes
  • Remove Slew Bolts
  • Controlled Trial Lift to determine Centre of Gravity
  • Jack Up Crane
  • Check Pedestal Flatness using Laser and provide condition report
  • Remove Old Slew Bearing and Install New Slew Bearing
  • Jack Crane Back Down
  • Install and Tension Inner and Outer Slew Bolts (Rotabolts)
  • Re-Connect Slip Ring

Slew Gearbox Overhaul

  • Lift Plan for Slew Gearbox Removal
  • Split Gearbox using a hydraulic press
  • Replace Pinion, Driveshaft, Seals, Bearings and Planetary gears.
  • Sleave added to Slew Gearbox Casing to remove play
  • Re-assemble


  • Full Visual Inspection
  • Backlash, Rocking Motion and Teeth Flank Contact Check completed
  • Function Test
  • Load Test using water bags and load cell
Newly Installed Slew Bearing
Load Test

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