By James Heinz
There is an ancient proverb that we have all heard. One version of it goes like this:
For want of a nail the shoe was lost.
For want of a shoe the horse was lost.
For want of a horse the rider was lost.
For want of a rider the message was lost.
For want of a message the battle was lost.
For want of a battle the kingdom was lost.
And all for the want of a horseshoe nail.
The poem refers to how failure of seemingly insignificant factor in a situation can lead to disaster. This story is about how the failure of a single screw led to a maritime accident costing over $2 million.
The website of the National Transportation Safety Board describes itself as: “an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation — highway, marine, pipeline, and railroad. We determine the probable cause of the accidents we investigate and issue safety recommendations aimed at preventing future accidents.” All of the information in this story comes from the official NTSB report.
The 23,054 ton, 736 foot Canadian-flagged bulk carrier ATLANTIC HURON was built at Collingwood Shipyards in Ontario, Canada, in 1984 as the PRAIRIE HARVESTER. She is owned by Canadian Steamship Lines (CSL) and transports products between ports in the United States and Canada.
The vessel is propelled by a single non-reversing, slow-speed, direct-drive diesel engine that was coupled to a drive shaft and controllable pitch propeller (CPP). The CPP allowed the vessel to move ahead or astern without changing the direction of the shaft.
In a CPP, the blades are not fixed in position but are fastened to the hub in a way that allows them to rotate and thereby change pitch. The blade pitch determines both the vessel’s speed and its direction (forward or astern) through the water.
On July 5 2020, at 12:48 am, the ship approached the Soo Locks in the St. Mary’s River from the west or Lake Superior side. The second mate conducted a check of the vessels systems and equipment, including the CPP system. At 1:50 am the captain reported to the bridge. The weather was good and the approach to the locks was uneventful.
According to the NTSB report: “At 0245, the captain slowed the ATLANTIC HURON and allowed the vessel to “coast” toward the South Canal and the west center pier, where he intended to land the vessel and slide it up the pier wall toward the locks. As the vessel’s speed reduced to 3.8 knots about 0.5 miles from the end of the west center pier, the captain ordered full astern to slow the vessel further. At this point, the captain noticed that the CPP pitch indicator was “erratic,” fluctuating from full ahead, to full astern, to zero, and then back to full astern. He also received a pitch differential, or wrong-way, alarm indicating that the requested propeller pitch from the helm station did not match the propeller’s actual pitch. Using the shipboard telephone, he called the engine control room (ECR) to report the inconsistent pitch indicator.”
The Engineer on Watch (EOW) checked his instruments and there were no warnings or anomalous readings, and the CPP pitch indicator showed full astern, as the captain had ordered. The captain directed the EOW to summon the Chief Engineer to the engine room.
At about the same time, the captain noticed that his ship’s forward speed was actually increasing. The chief engineer and EOW inspected the CPP control valve assembly. They noticed that the oil distribution box (OD box) that should have been fixed atop the CPP shaft had rotated out of position.
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At 2:48 am the ship continued to accelerate forward until it reached a speed of 6.5 knots. The captain then ordered the second mate to drop the stern anchor. When the ship reached a speed of 7.1 knots, the captain remotely dropped both bow anchors from the bridge. The chief engineer reported that the engine had to be shut down to avoid damage due to the displaced OD box, and this was done.
The port anchor brake held when 450 feet of anchor chain had been paid out. However, the starboard anchor brake did not hold, and the anchor paid out all the way to the bitter end. As a result, the ship sheered to the left toward the west center pier of the lock. The captain attempted to compensate by putting the helm hard to starboard, and activating the bow thruster to avoid contact with the pier.
At 2:50 am the port side of the ship impacted the west center pier of the locks. Since the engine had stopped, the ship slowed as it scraped along the side of the lock. The captain reversed the bow thruster to hold the ship against the pier. The ship was brought to a stop and secured to the pier.
Examination showed that the cribwork of the west pier had been pushed in almost six inches, causing $573,000 in damage. The ship sustained damage to the port side shell plating and longitudinal stiffeners, and the web frames of the #1 port ballast tank, costing $1,633,00 to repair. The total cost of the incident was $2.2 million.
But what caused the CPP to move in the opposite way it was set? Well, as that great marine accident investigator Yogi Bearra once said, “It’s dejavu all over again.”
On June 26, 2020, nine days earlier, under the command of another captain, the ship’s CPP had malfunctioned in exactly the same way. When the reverse command as sent, the CPP instead went full ahead and began accelerating. The crew shut down the engine and anchored.
Repair technicians found, in the words of the NTSB report, “Third-party technicians from a marine service company later discovered that a bearing within the feedback mechanism arrangements of the CPP’s OD box had come out of position and jammed against the feedback arm. This caused the arm to deflect ‘in such a way that it [the CPP pitch] went full ahead and seized in that position.’ They also discovered that the OD box was able to move axially on the shaft an ‘inch or more.’ They concluded that this movement was caused by a worn torque stay.”
“To alleviate the issues, the technicians freed up components that had become jammed, replaced the bearing that had come out of position, and checked the propeller pitch feedback arm for damage. They also temporarily shimmed the torque stay and recommended that, while shimmed, the propeller pitch should be limited to 75 percent to prevent failure.”
The ship was allowed to continue for a limited time pending further repairs. On June 30, 2020, other technicians conducted further repairs. The vessel made three transits without incident through the Soo Locks from that date until July 5, 2020.
Examination of the OD box after July 5 showed that a set screw which was supposed to hold a pin that held the feedback ring in place had backed out, enabling the feedback ring to contact the feedback arm, damaging both. This cascading chain reaction malfunction led to the misdirection of hydraulic fluid, causing the CPP to run ahead while the unit sent signals indicating that it was operating full astern as directed.
The manufacturer of the OD box specified that the set screw be installed using thread locking fluid to prevent the screw from doing exactly what it did. The last time this screw was removed and replaced was 2016. There was no evidence that the screw locking fluid had been applied then.
For want of a screw, the ship was lost.
The NTSB determined that the nature of the malfunction concealed its true cause to those who repaired the OD on and after July 26, 2020. Since their repair seemed to fix the problem, there was no reason for them to look further.
The NTSB report said that about the only thing that the captain could have done to prevent the collision would have been to shut the engine down earlier, but that given the speed of events and the fact that the ship owner did not have a policy as to what to do in a CPP malfunction of this type, the captain’s actions were understandable.
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The ATLANTIC HURON was launched as the PRAIRIE HARVEST in 1983 by the Collingwood Shipyards of Collingwood, Ontario. Built for the Canada Steamship Lines, she measured 736 feet in length and 75 feet in beam. She was scheduled to be launched on July 14th but workers at the Collingwood Shipyard went out on strike June 30th. The PRAIRIE HARVEST finally hit the water on October 18th. She was renamed ATLANTIC HURON the first time in 1989; renamed MELVIN H. BAKER II in 1994; and again ATLANTIC HURON in 1997.
Photo on top of page:
PRAIRIE HARVEST later renamed ATLANTIC HURON. Photo credit: Great Lakes Marine Collection of the Milwaukee Public Library and Wisconsin Marine Historical Society.
More photos:
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James Heinz is the Wisconsin Marine Historical Society’s acquisitions director. He became interested in maritime history as a kid watching Jacques Cousteau’s adventures on TV. He was a Great Lakes wreck diver until three episodes of the bends forced him to retire from diving. He was a University of Wisconsin – Milwaukee police officer for thirty years. He regularly flies either a Cessna 152 or 172.
