TSB: Electrical arc, slow response led to ferry blackout, groundingApr 29, 2015 05:11 PM
Maintenance deficiencies and lack of adequate emergency procedures led to a loss of electrical power and grounding of a ferry in Nova Scotia in 2013, investigators determined.
Princess of Acadia was approaching the terminal in Digby, Nova Scotia, inbound from Saint John, New Brunswick, on Nov. 7, 2013. When the bow thruster was started, the main generator blacked out, disabling the main propeller pitch control pumps, the Transportation Safety Board of Canada (TSB) said.
When the pitch control pumps stopped, the propellers defaulted toward full astern with the engines still running, causing the vessel to slow down, stop and travel backward toward the nearby shoreline until running aground.
The TSB determined that when the bow thruster was started, a deteriorated exciter brush caused a main generator to lose power, resulting in a blackout of the electrical switchboards. As a result, the vessel continued making way but was not under command because the controllable-pitch propeller pumps had stopped and the propeller pitch had defaulted toward full astern.
“The master was not informed that engine room personnel (were) having difficulty restoring power to the main switchboard and the engine room was not aware of the urgency of the situation, which impeded an effective response to the emergency,” the TSB stated in its report.
In addition, neither the bridge nor the engine room had effective procedures to respond to the blackout of the main switchboard, the report said.
The 460-foot ferry is owned by the Canadian government and managed by Bay Ferries Ltd. of Charlottetown, Prince Edward Island.
The TSB noted specifically how the main generator failed. Certain types of generators are fitted with exciter brushes, which are used to excite the rotor and produce alternating current. Each main generator on Princess of Acadia was fitted with two pairs of brushes. The brushes were made of graphite with a Shore hardness rating of 15. Each brush fits into a metal brush holder with a spring that forces the brush to make contact with the rotor.
Exciter brushes can become jammed in the brush holder, which prevents them from making continuous contact with the rotor. This can result in the brush arcing and unstable voltage. Arcing can cause the brush to heat up and deteriorate at a faster rate, resulting in carbon buildup. Brushes are also susceptible to breaking when in use.
In 1998, the company began using a softer graphite brush in the generators in order to reduce wear on the rotor slip ring.
“A post-occurrence examination of the No. 1 generator found that one of the brushes was approximately 80 percent deteriorated and had marks that indicated that arcing had occurred,” the TSB wrote.
There were safety deficiencies noted in the report. Despite having a passenger manifest of 63 passengers on board, when the ship’s passenger services officer counted the passengers, he counted only 61. A subsequent search located the two passengers.
During the March 2006 sinking of the ferry Queen of the North, two passengers were unaccounted for following evacuation procedures and never found. TSB then recommended that the Department of Transport develop a framework that ferry operators can use to develop effective passenger accounting for each vessel and route.
In the Princess of Acadia report, the TSB wrote that “if Transport Canada oversight to ensure compliance with regulations regarding passenger safety emergency procedures is ineffective, there is a risk that these procedures will not achieve their intended purpose.”
“If maintenance and inspections of vessel equipment are not documented with detailed and complete records, there is an increased risk that tracking of equipment reliability and related maintenance will be ineffective for determining overall maintenance needs,” the investigators wrote. “If maintenance schedules are not updated when critical equipment is modified or replaced, there is a risk that this equipment will not be serviced when necessary and, as a result, will not be fully operational when needed.”
“If bridge and engine room personnel do not exchange critical information during an emergency, there is a risk that key personnel will not be fully aware of the situation and may make ineffective decisions,” the TSB added. “If crewmembers do not have formal written procedures that facilitate quick and effective action, there is a risk that they will not respond effectively in an emergency.”
The TSB advocated regular drills, timely emergency alarms and a safety management system to provide guidance for the master. The report said there was no record of an overcurrent test for the vessel’s main generator breakers, despite a Lloyd’s Register record of a survey.
Following the incident, Lloyd’s Register changed the frequency of testing for the generator breakers on Princess of Acadia to yearly, citing the age and usage of the breakers.
Bay Ferries told Professional Mariner that it has already acted on or will act on all of the TSB recommendations in response to the grounding. Those improvements include improved thruster testing on arrival at Digby, better staff deployment in the engine room during arrival and a backup battery power supply to the vessel’s navigational equipment. The company planned to install a simplified voyage data recorder, which records 12 hours of bridge audio and data from the radars, automatic identification system and other available sensors.
“We looked at what we can do better as a company and proactively took action. This report will help our company continue to act to ensure safety is at the center of everything we do at Bay Ferries,” said Don Cormier, vice president of operations.