Electrolytic corrosion shares a common characteristic with cockroaches – see one example and there’s probably a lot more under the floorboards. The crew of the fishing vessel Velee apparently found that out the hard way to judge by the latest investigation report from the UK’s Marine Accident Investigation Branch.
Late on 5 August 2011, the 19m trawler Vellee (Figure 1) suffered catastrophic flooding when on passage from Fraserburgh to Kilkeel. The crew received no warning of the water ingress from the vessel’s three high-level bilge alarms, and by the time the flood was discovered, the sea water level was above the main engine’s gearbox.
The crew were unable to establish the source of the water ingress and, despite making attempts to pump out the water, in the early hours of 6 August they were forced to abandon to the liferaft.
Approximately 45 minutes later the vessel sank. The crew were rescued by helicopter and delivered safely ashore at Stornoway.
Says the investigation report:”Two of the vessel’s main engine cylinder liners needed to be replaced as a consequence of severe electrolytic corrosion only days before her final voyage. It is highly probable that electrolytic corrosion had also affected the vessel’s sea water piping and associated fittings, weakening their integrity and ultimately causing a failure”.
Investigation by marine electricians had identified the probable sources of the electrolytic action and repairs were made to prevent further electrolysis. However, no further inspections were made and the owners issued no instructions to identify other areas that might have also suffered from electrolytic corrosion. Furthermore, no precautions were taken to combat the increased risk of flooding resulting from electrolytic corrosion of sea water piping and fittings.