Vessel speed was a factor in the 2019 collision between an LPG tanker and a barge in the Houston Ship Channel that resulted in the release of 11,000 barrels of petrochemicals, the National Transportation Safety Board (NTSB) said on Tuesday, March 30.
The 229-metre tanker Genesis River collided with the 90-metre tank barge 30015T on the Houston Ship Channel in Texas' Upper Galveston Bay on May 10, 2019. The collision breached two cargo tanks in the barge, spilling approximately 1.79 million litres of reformate, a gasoline blending stock.
There were no injuries on either vessel.
In a recently published marine accident report, the NTSB said the pilot's decision to transit the wide-beam, deep-draught 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.
Sea speed is the maximum efficient speed of a vessel, but it is generally used in open oceans 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 "left little margin for error and introduced unnecessary risk," NTSB investigators commented.
"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, including advising their members to avoid transiting large vessels at sea speed in the lower Houston Ship Channel and avoiding 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 Genesis River be sufficiently trimmed by the stern 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, 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 resulting from two deep-draught vessels passing each other and 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. Those 2016 recommendations urged the coast guard to identify areas of increased vessel conflicts or accidents that could benefit from the use of special routing measures.
In 2017, the coast guard replied to the recommendations by saying it would implement a risk assessment program. However, the NTSB has not received further information on this initiative after the coast guard's initial correspondence.
