In March, the National Transportation Safety Board released its Marine Accident Report detailing the May 10, 2019, collision between the liquefied gas carrier Genesis River and a tank barge pushed by the mv. Voyager on the Houston Ship Channel (HSC).
The Genesis River, stretching 754 feet, was outbound on the Houston Ship Channel that afternoon near the intersection of the Houston Ship Channel and the Bayport Ship Channel when it met the inbound tanker BW Oak at about 3:15 p.m. The two tankers passed each other on their port side, with the Genesis River’s next maneuver a 16-degree turn to port just past the southern end of the “Bayport Flare.”
As the Genesis River entered the turn, though, the ship suddenly swung hard to port, crossing the Houston Ship Channel and entering the “barge lane” on the eastern side of the HSC. That put the Genesis River in the path of the inbound mv. Voyager, which was pushing a pair of tank barges side by side. With the bank to starboard and the ship careening toward his port side, the captain aboard the Voyager attempted a turn hard to port to avoid the Genesis River. The collision, though, was unavoidable at that point. The Genesis River struck the Voyager’s starboard barge, penetrating the barge’s hull and breaching its center cargo tanks. More than 11,000 barrels of reformate, a gasoline blending stock, escaped into the ship channel.
In the cleanup that followed, the Houston Ship Channel was closed to navigation for two days and finally opened without restriction May 15. Damage to the vessels involved totaled $3.2 million. Containment and cleanup of the reformate cost $12.3 million. No one was injured in the collision.
Hydrodynamics At Work
NTSB’s report on the 2019 collision includes a lengthy section titled “Vessel Hydrodynamics” that explores the hydrodynamic effect the two passing tankers had on each other, which contributed to the incident. In that section, NTSB defines “squat” and “trim,” respectively, as the sinkage and “a tendency for its forward and aft drafts” to change as the vessel is in motion in shallow water. The report also defines “bank cushion” and “suction,” which refer to pressures near the bank that push the bow away from the bank and pull the stern toward the bank, respectively.
In addition, after the Genesis River and BW Oak passed one another, additional hydrodynamic forces were present that pushed their sterns away from each other. That repulsive force on the stern created a “yawing moment” that “tends to turn the vessels back toward the center of the channel.” Both the hydrodynamics of the pass and of bank cushion “yawed the Genesis River to port, overwhelming full starboard rudder applied to counter this port yaw. The ship continued port across the channel, where the encounter with the east bank curved the ship’s path starboard and into the Voyager’s barge,” an NTSB Kinematics Parameter Extraction Study concluded.
NTSB also examined the Genesis River pilot’s decision to travel down the Houston Ship Channel at “sea speed,” about 12 knots. At that speed, the total stopping time required to bring the Genesis River to a complete stop would have been more than seven minutes, with the vessel covering a mile. The report, though, concluded that dropping the ship’s anchors or initiating emergency full astern earlier “may not have prevented a collision” due to the hydrodynamic forces at work. Rather, NTSB concluded that traveling at sea speed “through the shallow and narrow lower Houston Ship Channel left little margin for error and introduced unnecessary risk.”
‘Go To The Greens’
NTSB noted that, while poor communications often play a contributing role in waterway incidents, good communications between the Genesis River pilot and Voyager’s on-duty relief captain likely helped prevent a more serious collision.
“Pilot 2 on the Genesis River radioed the Voyager as soon as he began having difficulty controlling his vessel, giving warning to the towing vessel’s relief captain that an emergency situation was developing,” the report stated.
As the ship veered to port, the pilot aboard Genesis River radioed the Voyager to say, “[I’m] that ship lookin’ at you. Trying to check this thing up. Just keep an eye on me.” The relief captain aboard the Voyager replied, “Roger, Roger.” At the time of the first communication, the vessels were about 0.7 miles apart.
Still unable to correct course, Pilot 2 aboard Genesis River told Voyager, “She’s not checkin’ up, Voyager.” The Voyager relief captain took the engines out of gear and asked, “What do you need me to do, Captain?” The pilot aboard the Genesis River replied, “Go to the greens,” indicating the Voyager should head to the western bank to try to avoid the collision. The Genesis River pilot said after the incident that his intention was for the vessels to pass on the two, or starboard to starboard.
The relief captain aboard the Voyager started that maneuver just after 3:13 p.m., with the two vessels 0.55 miles apart. In the minute that followed, the Genesis River’s turn to port slowed and ceased. Then the vessel began to swing back to starboard. Seconds before 3:15 p.m., Pilot 2 aboard Genesis River radioed, “Go, Voyager, go! Go, go, go!” Voyager’s relief captain replied, “I’m hooked up, hard over, there, brother.”
The Voyager was making 4 knots as it crossed the channel, with the Genesis River still swinging to starboard. Pilot 2 again radioed the Voyager: “I’m gonna be swinging’ your way real soon. She’s coming’ your way. You gotta push on it.” To which the Voyager relief captain said, “She’s all she’s got there, brother. All she’s got.”
Despite the efforts of both the pilots aboard the Genesis River and the Voyager, the ship collided with the Voyager’s starboard barge at 3:16 p.m. The force of the collision caused the port barge to capsize, with the facing and long wires parting. The Voyager heeled over to starboard “until the last face and long wires gave way,” the report stated. The captain aboard the Voyager, who had been exercising in the engineroom before he heard the general alarm, sent a deckhand to close the engineroom door just before the impact. The deckhand was able to secure the door despite the impact, with about 200 gallons of water pouring into the engineroom before the door was fully closed. One of the Voyager’s propellers was fouled by a parted wire.
No one was injured aboard either vessel. Following the incident, the Voyager was towed to a Kirby facility nearby. The Genesis River went to a lay berth in Bayport.
After conducting its investigation, the NTSB determined the probable cause of the collision was “the Genesis River pilot’s decision to transit at sea speed, out of maneuvering mode, which increased the hydrodynamic effects of the Bayport Flare’s channel banks, reduced his ability to maintain control of the vessel after meeting another deep-draft vessel and resulted in the Genesis River sheering across the channel toward the tow.”
Following the incident, NTSB issued four new recommendations for ship operations in the HSC, which included to avoid “any passing arrangements between wide-beam, deep-draft vessels in the northern and southern terminuses of the Bayport Flare” and to avoid transiting at sea speed on the lower HSC.
Caption for photo (click on picture for full image): From the NTSB report, a screenshot of when the tanker Genesis River struck the tow of the mv. Voyager in the Houston Ship Channel.