Still image extracted from video on board the Monte Alegre, showing the Chembulk Houston’s starboard-side bow and anchor in contact with the Monte Alegre’s port side. The initial contact occurred farther aft on the Monte Alegre.
On March 5, 2015, tanker Chembulk Houston and container ship Monte Alegre collided and grounded in the Houston Ship Channel, after the pilots agreed to let the Chembulk Houston overtake the Monte Alegre. Both ships were inbound in the channel. No injuries or pollution resulted from the accident, but both vessels sustained damage above their waterlines, totaling more than $1.7 million.
Summary:
In the morning on March 5, 2015, the tank vessel Chembulk Houston and the containership Monte Alegre were inbound in the Houston Ship Channel. A pilot was at the conn of the Monte Alegre, while a deputy pilot―an apprentice in training to become a full pilot―was at the conn of the Chembulk Houston.
Around noon, both vessels were proceeding north with the Monte Alegre more than 2 miles ahead of the Chembulk Houston. About that time, the Monte Alegre pilot learned that the tugboats at his destination would be delayed. He therefore reduced the ship’s speed.
Still image extracted from the PPU used on board the Chembulk Houston, showing the approximate position of the two vessels at 1320 when the overtaking situation was aborted. (Image provided by the Houston Pilots Association)
At 1249, the Chembulk Houston deputy pilot contacted the Monte Alegre pilot suggesting that the tanker overtake the containership. The Monte Alegre pilot agreed. By 1307, the Monte Alegre was about one-half mile ahead of the Chembulk Houston and transiting at about 6.5 knots. The Chembulk Houston was transiting at 10.5 knots. At 1310, the Chembulk Houston deputy pilot informed the Monte Alegre pilot that he was initiating the overtaking maneuver.
As the Chembulk Houston’s bow began overtaking the Monte Alegre’s stern, the Monte Alegre pilot ordered a speed increase from slow ahead to half ahead, and the velocity of the containership increased about 2 knots. At 1318, the Chembulk Houston deputy pilot radioed the Monte Alegre pilot stating, “I’m losing speed all the time.” The Monte Alegre pilot then ordered the speed reduced from half ahead to slow ahead, and replied, “I am only making 8 knots.” The Chembulk Houston deputy pilot replied that he would continue his attempt to overtake the Monte Alegre, but he might have to abort the maneuver. At 1319, the Monte Alegre pilot ordered the speed reduced further, from slow ahead to dead slow ahead.
Photo showing the first point of contact on the Monte Alegre, where the starboard-side anchor of the Chembulk Houston punctured the hull.
About 1320, the Chembulk Houston deputy pilot informed the Monte Alegre pilot that he was still losing speed, and the pilots agreed to abort the overtaking. The Monte Alegre pilot issued a series of commands intended to increase speed, while the Chembulk Houston deputy pilot issued a series of commands intended to slow his vessel. Nevertheless, the Chembulk Houston’s speed actually increased.
The Chembulk Houston deputy pilot then issued several helm and throttle commands that were intended to prevent the tanker from making contact with the Monte Alegre. Despite these efforts, the Chembulk Houston starboard bow collided with the Monte Alegre aft portside hull. Both vessels veered to port and grounded on the soft bottom of the Houston Ship Channel.
Ships maneuvering in confined and shallow waters are subjected to hydrodynamic forces for which pilots and ship crews must account. Two vessels transiting in close proximity in a channel can create even more intense hydrodynamic forces acting on one or both vessels. Overtaking maneuvers are inherently higher risk than meeting situations because of the longer time during which the hydrodynamic forces can affect each vessel.
The Chembulk Houston, as the give-way vessel, had the responsibility to keep clear of the Monte Alegre. In turn, the Monte Alegre, as the stand-on vessel, was required to maintain its course and speed, unless it became necessary to alter either to avoid collision. The Monte Alegre pilot’s order to increase speed―without informing the overtaking vessel―departed from expectations for the stand-on vessel. The increased time and distance needed for overtaking allowed the hydrodynamic forces acting on both vessels to build. The increased hydrodynamic forces ultimately prevented the Chembulk Houston from developing enough speed to push through the bow pressure wave of the Monte Alegre.
Cross-sectional view of the Houston Ship Channel in the accident area. (Image provided by the Houston Pilots Association)
If the Monte Alegre pilot had informed the Chembulk Houston deputy pilot of the speed increase, the deputy pilot would have realized that he could not safely complete the overtaking. By not providing this essential information, the Monte Alegre pilot contributed significantly to the deputy pilot’s decision that the best course of action was to abort the overtaking. Had the information about the speed increase been provided in a timely manner, the deputy pilot would likely have chosen a different course of action.
Probable Cause
The National Transportation Safety Board determines that the probable cause of the collision between the Chembulk Houston and the Monte Alegre was the pilot’s decision to increase speed on the Monte Alegre without informing the deputy pilot on the overtaking Chembulk Houston.
Did you subscribe for our daily newsletter?
It’s Free! Click here to Subscribe!
Source: NTSB
