The offshore supply vessel (OSV) Ocean Guardian was barely 30 minutes into sea trials near Seattle when its No. 3 main engine sustained a catastrophic failure and caught fire.
Crewmembers aboard the 261-foot ship quickly extinguished the fire, which happened at about 2:35 p.m. on May 27, 2022, in Shilshole Bay, just west of Seattle’s Ballard Locks. None of the 22 people on board were hurt.
The National Transportation Safety Board (NTSB) praised the crew’s firefighting response as “timely and effective.” The agency later traced the fire to an incorrectly sized crankshaft main bearing.
“The probable cause,” the NTSB said in its report, “of the mechanical failure of the No. 3 main engine and resulting fire aboard the offshore supply vessel Ocean Guardian was the replacement of a crankshaft main bearing with an incorrectly sized bearing during an engine overhaul.”
The NTSB determined the service technician who performed the overhaul did not identify the bearing’s part number to determine the correct size. Instead, the improper part was used, “which resulted in the loss of lube oil pressure in adjacent connecting rod bearings.”
Ocean Guardian Holding acquired the former Tidewater OSV Ken C. Tamblyn in March 2020, and Stabbert Maritime Group of Seattle operated the now 20-year-old vessel. Its propulsion system consisted of four 2,669-hp Caterpillar (CAT) 3516B main generator engines, which created electrical power for propulsion motors and ship service power.
Ocean Guardian arrived at Stabbert facilities in August 2021 for maintenance that included top-end overhauls and bearing inspections on its four Cat main generator engines. The sea trial held on the afternoon of May 27, 2022, represented the first significant engine test since that overhaul.
The captain led a safety briefing with the crew and technicians on board before departing Stabbert’s shipyard facility under tow. The vessels successfully locked through the Ballard Locks enroute to Shilshole Bay, in the Puget Sound. One tugboat remained close to the OSV during trials.
The trials began in earnest at about 12 p.m. with crew testing different equipment requiring increasing electrical load from the main generator engines.
At 2:35 p.m., “the trials began with the two stern thrusters about 75 percent load, and the No. 3 main engine about 30 percent load, the engineering crew in the engine control room (ECR) heard a ‘large bang’ and observed smoke in the engine room through the ECR window,” the NTSB report said. “An engineer in the engine room saw flames near the No. 3 main engine and stated they ‘looked to engulf most of the engine.’”
Crew took decisive action to extinguish the fire. The chief engineer remotely shut down the engines and their fuel supplies. The captain, meanwhile, used switches in the wheelhouse to shut ventilation into the engine room.
The chief engineer, after consulting with the captain, activated the fixed CO2 system in the engine room at 2:40 p.m. Afterward, crew wearing firefighting gear and self-contained breathing apparatus entered the engine space. They extinguished several smoldering fires near the No. 3 engine, according to the report.
The main bearing journals on the crankshaft of the No. 3 main engine had been machined down before the ship was acquired in 2020, the report said. Machining reduced its diameter by .63 millimeters, a range considered acceptable by CAT engine standards. The undersized bearing used on the engine corresponded with these changes.
“Neither the operating company (Stabbert) nor the service technicians received records of this crankshaft main journal and connecting rod journal machining,” the NTSB stated in its report.
Without service records, the part number on the shell of the bearing was the primary way of discerning the presence of the undersized bearing. But that required technicians servicing the engine to find the number and check records to verify its size. That did not happen in this case.
Ultimately, standard-sized bearings were installed on the No. 3 main engine. The NTSB, citing a report from a local CAT service company, said the engine failure stemmed from a lack of lubrication to the Nos. 9 and 10 connecting rod journal bearings.
“The failure sequence began while the engine was running,” the NTSB report said. “The incorrect sizing of the No. 6 main bearing shell allowed lube oil to leak from the larger clearances of the bearing, decreasing lube oil supply pressure to the adjacent Nos. 9 and 10 connecting rod journal bearings by about 80 percent.”
The lack of lube oil caused a rapid increase in temperature in the Nos. 9 and 10 connecting rod bearings, and the bearing caps ultimately fractured.