A chemical tanker in the Houston Ship Channel experienced a steering problem and ran aground, possibly as a result of a damaged rudder.
The 523-foot Isabel Knutsen had just departed Houston on July 14 when it strayed to port, exited the deep-draft shipping channel, and got stuck for almost two days. The grounding occurred near the intersection of the ship channel and the Gulf Intracoastal Waterway at Galveston, in the vicinity of buoys 25 and 26.
The United Kingdom-flagged tanker was transporting mostly cyclohexane and benzene, said Cmdr. Jim Elliott, chief of the U.S. Coast Guard Marine Safety Unit at Galveston. The vessel also carried some Hygold 100, Hyvolt I, naphtha and piperylene, plus bunker oil. None of the contents spilled.
|Three tugboats pull at the stern of Isabel Knutsen in an attempt to dislodge the vessel. The ship eventually refloated after an internal cargo transfer. (Courtesy U.S. Coast Guard)|
“It happened relatively quickly. It was heading outbound and it lost steerage,” Elliott said. “It diverted to port, crossed the Houston Ship Channel and grounded. It was pretty hard aground.”
Isabel Knutsen is operated by Knutsen OAS Shipping AS of Haugesund, Norway. The vessel’s owner is Knutsen Kjemikalie Tanker V KS of Norway. The companies initially decided to try to have the tanker pulled free after the incident, which happened at about 0540.
“They attempted to refloat it using assistance tugs, but they didn’t have enough horsepower and it was unsuccessful,” Elliott said. After trying once more at the next high tide, again without success, “they did internal cargo transfer operations and they were successful.”
After the ship was dislodged at 1920 July 15, the Coast Guard ordered it to the Galveston Fairway Anchorage, where inspectors identified a problem with the vessel’s rudder.
“The dive survey discovered damage to the Becker-type system,” Elliott said. “The top section (of) the rudder flap was damaged. The pins and the actuator link system were missing.”
A Becker-type system features a flap that extends from the outside of the main rudder that significantly increases the angle and force of a turn. The system is used for low-speed, close-quarters maneuvering in port where a tug assist might otherwise be necessary. If the flap breaks off, the master initially may not realize it and the main rudder usually still can control the vessel, unless it also has been damaged.
Elliott said investigators are still probing the origin of the damage. He said they do not believe the pieces broke off during the grounding, and they doubt the ship had struck an underway object immediately before the accident. Isabel Knutsen was en route to Lake Charles, La., from the Intercontinental Terminals Co. docks in Texas.
“It appears that the rudder had been damaged prior to the loss of steering,” Elliott said. “It appears that they did not hit something at that point. It was an existing problem. The pin was missing, and we did not recover the top flap of the rudder.”
After an attempt at temporary repairs failed, a major lightering operation emptied cargo from Isabel Knutsen in August. The vessel was sent to a dry dock in Freeport, Bahamas, for a more extensive fix.
John Einar Dalsvag, Knutsen OAS Shipping’s chartering director, said the rudder still hadn’t been repaired by late September. The tanker remained at the Freeport shipyard pending further investigation, he said. Dalsvag declined to comment on the cause of the grounding.
The Houston Ship Channel remained open to other vessels during the grounding response.