TSB says steering failure cause of grounding

Dutch-owned chemical tanker Chem Norma grounded on the edge of the former Lock 23 May 30th. (The Leader/Blancher photo)

OTTAWA – The Transportation Safety Board of Canada has released its report on the May 29th grounding of the Chem Norma at the Morrisburg waterfront.

The report, issued by the TSB December 17th, said that at 4:15 a.m. that day, the ship was steaming at a speed of 11 knots when the rudder unexpectedly “went hard over to starboard”, exiting the Seaway shipping channel.

The crew regained control of the rudder with a back up system but were unable to prevent the grounding which took two minutes 23 seconds to occur.

The ship rested on the south embankment of the former Lock 23, which was flooded in 1958 as part of the St. Lawrence Seaway project.

The vessel, a bulk chemical-tanker, was carrying 11,119 tonnes of naphtha bound for Sarnia. Naphtha is used in the petroleum refining process.

The TSB could not determine a precise cause for the failure but offered a “plausible scenario”, identifying issues with the control relays for the steering system.

The report said that relay contacts were subject to large voltage and current surges when switching inductive loads and when the relay points open, it is important that any surge be absorbed to protect the relay contacts.

The agency said the relays used in the steering gear were unsuitable for the equipment.

“The Chem Norma’s steering control electrical system did not have provisions or countermeasures to protect the control relays’ contacts from voltage and current surges,” the report said.

The TSB examined the relays for failure and found heat damage on some of the contacts. The agency used scanning electron microscopes and a spectrographic examination on the relay contacts.

“All of the relays examined showed signs of damage due to electrical arcing,” the report said.

The report said that the damage on the relays was more pronounced on one certain relay, identified as 5K3 in the system.

The TSB sent a Marine Safety Information Letter to the owners of the Chem Norma, Netherlands-based ASM Maritime, identifying the failure analysis performed by the agency in late-July. The vessel is one of five of the same designed by ASM Maritime.

The Chem Norma was freed after six days of attempts by the ship to back out of the embankment, and up to three tug boats pulling. The three tug boats, along with a temporary increase in water levels on Lake St. Lawrence, freed the vessel June 3rd. The refloating attempts saw hundreds visit the Morrisburg waterfront to watch.

Once freed, an inspection revealed the ship had sustained minor damage to the hull consisting of dents to fresh water tank areas under the water line, and major damage to its propeller and rudder.

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