The Coast Guard’s Bureau of Investigation and Analysis issued Marine Safety Alert 06-21 to notify mariners of a potentially hazardous situation involving poorly machined threads that could result in steering cylinder failure.
According to the safety alert, an inspected towing vessel recently suffered a reduction in steering when the port hydraulic steering cylinder failed. The technicians replaced the cylinder with a spare part located on site; however, the cause of the failure was undetermined. In less than 24 hours, the vessel underwent a second rudder reduction when the starboard ram failed. Due to the abnormal back-to-back failures, the cylinders were sent to the manufacturer for inspection.
Testing revealed that the rod stud threads of both cylinders were machined out of specification. Specifically, the rod stud threads were not correctly machined to measure the required outside diameter (OD) of 0.995 inch, but instead measured an OD of 0.950 inch. The rod stud is the part of the rod that faces down and is threaded for the piston and retaining nut. Incorrectly sized threads reduced surface contact with the jam nut threads and the fastener’s holding ability.
The manufacturer said that around 36 cylinder units were produced in 2017. It is not known how many of these units were created with inappropriate thread sizes.
The security alert lists manufacturer information as:
Manufacturer: All Phase Hydraulics Hudsonville, Michigan.
Model Number: 590491
Serial number: ABC 4024-S3
Serial number Range: 155451 – 155486
The two jacks that failed in the tug in question were installed during its construction in 2018. Based on this schedule, the failure may not occur immediately. If these particular cylinders are installed on ships, the absence of steering accidents does not necessarily indicate that they were manufactured to proper thread specifications.
The manufacturer said: “The cylinders will be able to function without incident if the normal maintenance of the adjustment stops is carried out. However, the vessel that suffered these accidents had limit switches installed, indicating that these stops may not completely prevent pilot accidents over time. It is important to note that not all ships are required to have tuning stops and will not have this type of fender in place to counter this specific failure. Limit switches and associated linkage components can wear out set points, reducing protection against excessive force and putting pressure on the steering cylinders.
The Coast Guard strongly recommends that vessel owners and operators:
- Periodically check that the set points are still within acceptable parameters for the steering systems.
- Perform checks of all information on installed and aftermarket cylinders for all manufacturer information listed in this alert.
- Regularly observe the operation of the steering gear and look for signs of hydraulic oil leaks and excessive pump noise, which could indicate impending problems or failure.
- Contact the manufacturer for more information if any of the cylinders referenced above are identified. At this time, the manufacturer has not issued a recall.
- Investigators and inspection staff are encouraged to remain keenly aware of these issues and take corrective action as needed.