General Information 

Type of Project: Bow thruster coupling replacement and alignment for passenger ferry
Customer Name: Danish ferry operator
Location: North Shields 

Summary 

• New coupling sourced.

• Attended vessel to remove old coupling.

• Drilled and tapped M22 holes into face of couplings.

• Removed both couplings with 50-ton jack.

• Delivered old couplings to machine shop for sizing.

• Collected parts from machine shop once complete.

• Reinstalled new couplings by way of heating to 120°C+ then installing onto the motor and thruster shaft, using original spacer pieces and keys.

• Assisted with lifting the motor in place, and reinstalling the coupling bolts and accessories.

• Checked alignment and adjustments made as appropriate.

• Confirmed thruster operation and chief engineer acceptance.

Initial Enquiry 

The chief engineer of the Danish ferry operator reached out to our team with an urgent request. One of their passenger ferries, was experiencing issues with its bow thruster coupling. The ferry was scheduled to depart soon, and the malfunctioning coupling posed a significant risk to its operational efficiency. Our sales team quickly sourced a suitable replacement coupling, but there was a catch—the new coupling didn’t come with a stopper plate, which was essential for the installation.

After some brainstorming, we suggested reusing the stopper plate from the existing gear coupling. The chief engineer agreed, and we proceeded with the plan. The new coupling measured up the same as the old one, requiring only minor adjustments such as line boring to the final size, slotting the keyways, and balancing both pieces. With the new coupling ready, our team set out to North Shields to carry out the installation and alignment.

Project Description 

Coupling Removal 

Upon arrival at the vessel, we found the motor already removed, making both couplings easily accessible. The crew began drilling holes in the jacking plate we had prepared, while the 1st Engineer and I drilled and tapped two holes in each coupling using the vessel’s Mag drill. 

With the holes drilled and tapped, we set up the jacking rig and removed both couplings using a 50-ton jack. The motor coupling came off at around 200 bar (approximately 15 tons) without the need for heat. The thruster coupling required a bit more force, coming off at around 300 bar (approximately 20 tons), but again, no heat was needed. Both couplings and shafts were in excellent condition, with no scores from the removal process. 

The spacer pieces and keys were also removed; they were a loose sliding fit, and the keys tapped out easily. We marked all components and, along with the stopper plate and bolts, took them to the machine shop for sampling the new coupling. 

Machining the New Coupling 

At the machine shop, the new coupling was measured against the old one. The only work necessary was to line bore to the final size, slot the keyways, and balance both pieces. The original stopper plate was in good condition, so no rework or replacement was needed, and the original bolts could be reused. The hubs were bored to 110mm J7 as per the drawings and the old couplings as reference, then balanced to ISO 1940-1 G2.5. 

New Coupling Installation 

Back on the vessel, the crew had cleaned and prepared all working areas for the installation. We heated the couplings using SKF induction heaters, preparing them for installation. The keyways and spacer pieces were placed onto the shaft along with the outer piece of the couplings. Once at the required temperature, the couplings were installed onto the shafts and secured until the temperature between the coupling and shaft equalised. 

Reinstallation of Motor, Final Alignment, and Connection/Greasing of Coupling 

The vessel’s crew lifted the motor into place, seating it within the spigot of the framework. We placed laser alignment gear onto either shaft and took an initial reading. Using various jacks, we adjusted the alignment closer to zero. However, due to the limits of the spigot, the final readings were the best we could achieve. 

The coupling was then bolted together with the intermediate plate and gaskets, torqued to 250nm. We removed one grease nipple from either side of the coupling and pumped grease into the chamber until it was filled. Routine greasing will be required as part of PPM to ensure the coupling does not fail again. 

Start Up 

With everything in place, we conducted a small test with the crew present. The motor was run up, and we monitored temperatures while checking for any vibration or erratic noises. Everything appeared to be in good working order, and the crew was advised to check again once more load could be put on the thruster when the ferry was out in the river. 

Conclusion 

The project to replace and align the bow thruster coupling on the Danish ferry operator’s passenger ferry was successfully completed. The new coupling was sourced and installed with precision, ensuring the vessel’s operational efficiency. The removal of the old coupling and installation of the new one was carried out smoothly, with no damage to the shafts or other components. The machining of the new coupling was done to exact specifications, and the reinstallation process was meticulously executed, including the final alignment and greasing of the coupling. 

The crew’s cooperation and readiness played a significant role in the project’s success, allowing for efficient handling of the motor and alignment tasks. The initial test run confirmed the proper functioning of the thruster, with no vibrations or erratic noises detected. The chief engineer’s acceptance of the thruster operation marked the completion of the project. 

The job demonstrated our team’s expertise in handling urgent and complex marine engineering tasks, ensuring the ferry’s readiness for its scheduled departure. Regular monitoring and maintenance will be essential to maintain the coupling’s performance and prevent future issues.