Safety Alert Issued On Towing Vessel Steering Rams
The Coast Guard Office of Investigations and Analysis has released an alert regarding risk of steering loss from defective steering rams on towing vessels.
Improperly machined threads can lead to steering ram failure, the Coast Guard said in its Safety Alert 06-21 issued October 20.
An inspected towing vessel recently experienced a reduction in steering when the port hydraulic steering ram failed, the Coast Guard said in the alert. Technicians replaced the ram with a spare part on-scene, but the cause of the failure was undetermined. Within 24 hours, the vessel experienced a second steering reduction when the starboard ram failed. Both rams were installed during the vessel’s construction in 2018, so based on the timeline failure may not occur immediately, the Coast Guard said.
Due to the failures, the rams were sent to the manufacturer for inspection. Testing revealed the threads on the rod studs for both rams were machined out of specifications. Specifically, the rod stud threads were not properly machined to measure the required 0.995 inch outside diameter but instead measured 0.950 inch in outside diameter. The rod stud is the portion of the rod that is turned down and threaded for the piston and retaining nut.
“The improperly sized threads reduced the surface contact with the lock-nut threads and the fastener’s holding ability,” the Coast Guard said via a blog post at mariners.coastguard.blog.
The manufacturer said approximately 36 ram units were produced in 2017. It is unknown how many of those units were created with improper thread sizes.
The potentially defective ram units were made by All Phase Hydraulics of Hudsonville, Mich. They are Model No. 59091, Serial No. ABC 4024-S3 and have a serial number range from 155451 to 155486.
“The cylinders will be able to perform without incident if normal maintenance of setting stops is executed,” the manufacturer told the Coast Guard. However, the vessel that experienced the casualties had limit switches installed, indicating these stops may not completely prevent steering casualties over time, the Coast Guard said. It also noted in the blog post that because not all vessels are required to have setting stops, not all will have this type of defense in place to counteract this specific failure. Also, limit switches and associated linkage components can wear set points, which reduces protection against excessive force and exerts pressure on the steering rams.
The Coast Guard strongly recommended that vessel owners and operators:
• Periodically ensure set points are still within acceptable parameters for steering systems.
• Conduct checks of all installed and spare ram information for any of the manufacturer information listed in this alert.
• Regularly observe steering gear operation and inspect for signs of hydraulic oil leakage and excessive pump noise, which could indicate impending problems or failure.
• Contact the manufacturer for further guidance if any of the above referenced rams are identified.
At this time, the manufacturer has not issued a recall.