Mars Report – Lessons learned
The Nautical Institute has issued Mars Report to highlight how important is to take maintenance seriously. Inspection and maintenance are not tick box exercises. Those involved need to know what they are looking for and why it matters, and have specific instructions on serviceability, replacement, renewal and adjustment.
At this Mars Report, a series of defects came to light when a slipping anchor caused significant damage to the hull of a cargo ship. The anchor windlass brake pad was worn down; the anchor was a replacement with different specifications to the original; and the inner wire strands in a wire sling used to secure the anchor at sea had corroded.
Recently, a freight ship was underway in 15 foot seas when theforepeak flood alarms activated. The crew investigated and discoveredthe starboard anchor had slipped 10-15 links, causing it to strike andpuncture the hull. As a result, seawater flooded the bow thruster andemergency fire pump compartment. The casualty resulted in excess of$1 million in vessel damage and a months lost revenues while the vesselwas out of service undergoing repair.During the repair period, it was discovered that the anchor windlassbrake pad had worn down to 2-3mm thickness. With only this amountof pad, the fully applied brake could not achieve its designed holdingpower.
The crew should have recognised the excessive wear to the brakepads and that these required replacement.It was also discovered that the anchor involved in the incident was areplacement, and had different specifications to the original anchor. Thereplacement anchors relative position in the hawse pipe was not thesame as the original, because the shank length and connecting linkageswere different. The size difference prevented the riding pawl fromproperly engaging the anchor chain.As an added safety device,a wire sling had been used tosecure the anchor while at sea.
The wire sling was threadedthrough a chain link and securedto the vessel with a pelicanhook. When the sling broke andthe brake failed, the anchorsweight and the ships movementthen caused it to drop beforethe riding pawl could properlyengage. The sling failure waslikely caused by the corrosionof the inner wire strands; the inner wire strands being exposed to theelements because of the sharp bend in the wire. Although the wire sling was inspected regularly, those performing the inspections were notinstructed on how to examine and determine its serviceability
-All preventative maintenance programmes should be up to date andinclude specific language on anchor windlass equipment, particularlyemphasising when brake assemblies must be renewed or adjusted.
|NI notes that inspection of wire rope is not an easy task andcannot be properly done without opening the lay with a spike andexamining the inner core. Even this step is not foolproof, and wire ropedegradation within the core can be hard to spot. Crew should adopt the’precautionary principle’ when using and examining wire rope – that is,if unsure, replace with new.|
Source & Image Credit :Mars Reports/ The Nautical Institute