Excessive vessel speed and a “bank effect” contributed to the May 10th 2019 collision between LPG tanker Genesis River and barge 30015T in the Houston Ship Channel, the National Transportation Safety Board (NTSB) has found.
The 754ft tanker Genesis River collided with the 297ft tank barge in Upper Galveston Bay, Texas. The incident resulted in the release of 11,000 barrels of petrochemicals,
The collision breached two cargo tanks in the barge, spilling approximately 473,600 gallons of reformate, a gasoline blending stock. There were no injuries.
The pilot’s decision to transit the wide-beam, deep-draft Genesis River in “navigation full” mode at “sea speed” subjected the vessel to greater hydrodynamic forces than had it been traveling at slower manoeuvring speeds through the shallow and narrow lower Houston Ship Channel, the NTSB said in Marine Accident Report 21/01. These hydrodynamic forces are known as the bank effect, which was reported to have been a factor in the grounding of the Ever Given in the Suez Canal on March 23rd.
Sea speed is the maximum efficient speed of a vessel, but it is generally used in open oceans. This is because the propulsion engine mode required for this setting limits the ability to change speeds in an emergency. The manoeuvring limitations imposed by operating at sea speed prevented a rapid increase in engine speed when needed to improve rudder effectiveness. Transiting the channel at sea speed, investigators said, “left little margin for error and introduced unnecessary risk.”
“Operating at sea speed reduces the ability to manoeuvre out of a dangerous situation,” said NTSB Chairman Robert L Sumwalt. “This is especially true in the Houston Ship Channel, a challenging waterway with a long history of accidents.”
The NTSB issued three new recommendations to Houston Pilots.
It advised their members to avoid transiting large vessels at sea speed in the lower Houston Ship Channel, and to avoid any passing arrangements between large vessels in the northern and southern terminuses of the Bayport Flare. The NTSB also recommended that large vessels such as the Genesis River be sufficiently trimmed by the stern, in order to increase manoeuvring ability.
The collision occurred after the outbound Genesis River had passed an inbound ship of similar size at the southern end of the Bayport Flare. Immediately after passing the other ship, the Genesis River approached the channel’s west bank, then sheered to port, crossing over to the opposite side (east) of the channel where, in the barge lane ahead, was barge 30015T, one of two tank barges being pushed by the towing vessel Voyager.
The NTSB determined the probable cause of the collision was the hydrodynamic effects (the “bank effect”) resulting from two deep-draft vessels passing each other, and the Genesis River’s speed, which increased the hydrodynamic effects of the channel banks and reduced the pilot’s ability to regain control of the vessel.
The NTSB also reiterated two earlier recommendations made to the US Coast Guard in 2016. These urged the USCG to identify areas of increased vessel conflicts or accidents that could benefit from the use of special routing measures.
In 2017 the USCG replied to the recommendations by saying that it would implement a risk assessment program. The NTSB said that the USCG’s initial correspondence was the last it heard on the matter.