Engineering Replacement of Liaaen ACG CPP Shaft Coupling During Scheduled Drydocking
Oil leakage was detected from the hydraulic shaft coupling of a fishing trawler equipped with a Liaaen ACG 95/650 controllable pitch propeller system. Because replacement required drydocking and long manufacturing lead times, a complete engineering assessment, coupling selection, and tooling specification were completed before docking. This allowed the replacement to be executed during a planned maintenance window without extending vessel downtime.
Operational Condition Assessment
During normal vessel operation, oil leakage was identified within the propulsion shaft system. Technical evaluation indicated that the source of leakage was associated with the existing hydraulic shaft coupling installed on the controllable pitch propeller system. Immediate removal and inspection were not practical because the fishing trawler was in active operation, and any intervention strictly required drydocking and withdrawal of propulsion components.
Engineering Review & Replacement Strategy
To avoid an unplanned outage and long operational delays, a replacement strategy had to be developed well in advance. Since manufacturing a custom replacement hydraulic coupling requires significant lead time, all technical documentation, shaft drawings, and class records were analyzed while the vessel remained at sea. This allowed the shipowner to order the new components early and precisely align the equipment delivery with the upcoming scheduled drydocking window.
Coupling Selection & Technical Validation
The vessel is equipped with a Liaaen ACG 95/650 controllable pitch propeller system driven by a Wärtsilä main engine rated at 3,415 kW at 148 rpm. Based on these operating parameters and torsional calculations, the design torque was established at 617 kNm. A SCHAAF GripLoc Ø315 hydraulic flange coupling (Article C19750000) was selected and manufactured as the permanent replacement solution, fully validated against the shaft geometry and class requirements.
Installation Tooling Preparation
In addition to the replacement coupling, a dedicated SCHAAF Mounting Auxiliary Tool Set and a heavy-duty Hydraulic Nut (Type C19760000 with M360x4 thread) were specified and supplied. Procurement of the required hydraulic tooling was completed ahead of schedule to ensure that the installation process could proceed without a single hour of delay once the vessel entered the shipyard.
Scheduled Drydock Execution
Following the delivery of the newly manufactured GripLoc coupling and tooling to the shipyard, the vessel entered its previously scheduled drydocking period. The old leaking hydraulic coupling was successfully dismounted, and the new GripLoc Ø315 assembly was installed using controlled radial oil injection pressure up to 1,550 bar. Because all engineering work, technical validation, and manufacturing had been completed in advance, the replacement was executed seamlessly within the planned maintenance window.
Prevention
Hydraulic shaft coupling replacement projects should always be initiated based on operational monitoring before drydocking whenever long manufacturing lead times are involved. Early engineering assessment, shaft data verification, and proactive procurement of the coupling and installation tooling eliminate the risk of extended docking periods and unexpected operational downtime.
Measurable Results
- operational disruption Zero unplanned downtime — completed during scheduled drydocking
- replacement coupling SCHAAF GripLoc Ø315 hydraulic flange coupling (C19750000)
- main engine Wärtsilä — 3,415 kW @ 148 rpm
- design torque 617 kNm (Shaft torque: 220.34 kNm)
- installation tooling SCHAAF Mounting Tool Set and Hydraulic Nut M360x4 supplied in advance
- downtime optimization Perfect synchronization of manufacturing lead time and dock schedule