The complex art of vessel stability and loading

From U.S. Coast Guard reports

Stability tests for a 65-foot 61-gross-ton steel-hulled scalloper were conducted on Dec. 23, 2002, although they are not required for a fishing vessel shorter than 79 feet. Test results confirmed the vessel was top heavy but that more information would be required to provide a full assessment. The naval architect recommended further calculations to determine how to reduce the tenderness of the vessel. However, the owners ordered no further tests or calculations.

In early January 2003, before departing the shipyard, one of the owners added 119 100-pound bags of concrete and 2 tons of lead to the scalloper in an attempt to stabilize the vessel.

After launch, the owner skippered it from the shipyard at Thibodeaux, La., to New Bedford, Mass., and stated he had no problems. In New Bedford, the owners added port and starboard dredges, each 10 1/2 feet long, and conducted sea trials with minimal problems, which were corrected.

The vessel operated for nearly a year with no major complications. On the evening of Saturday, Dec. 13, 2003, at approximately 9:35 p.m., the scalloper was dragging with both dredges. The vessel had been underway for 10 days. The hold was loaded with approximately 9,000 pounds of scallop meat. On deck was a large mound of unpicked scallops and a smaller pile of picked scallops on the stern.

The captain was on the bridge with the mate, who was operating the dredges. Two deckhands were on the port side main deck, and another was on the starboard side cutting scallops. Two more deckhands were below deck, sleeping.

The seas were estimated to be between 3 and 4 feet with a 15- to 20-mph wind from the north. The skipper was closely monitoring the weather and was concerned that conditions were expected to deteriorate. The plan was to get two more loads and head to a lee to shuck scallops.

The vessel was proceeding at clutch speed with both dredges loaded and alongside. The mate raised the starboard dredge, which he kept loaded because there was no room on deck to dump the scallops. He then began lifting the port dredge; all the crewmen stated the port dredge had an extremely heavy load. Once the port dredge was raised out of the water, the vessel began to list dangerously to port, causing everything on deck to slide.

The mate asked the captain to take over the dredge controls, but the captain grabbed the starboard dredge controls, swinging it to port and increasing the list. Water began coming over the port rails, and the deckhand on the starboard side called to the others on deck to come over to where he was. One deckhand stated that on the way over, he yelled down below to notify the sleeping crew. On the bridge, the captain ran over to the starboard side and popped open the life raft. The mate stated that the captain ran back into the wheelhouse, but he lost sight of him as a mist was created from the hot exhaust stack hitting the water.

The deckhands moved from the port to the starboard side and got into the raft before the vessel rolled over. The mate jumped in the water and was able to get to the raft. From statements of the survivors, the two crewmembers below were able to get on deck and abandon the vessel, but the sea conditions prevented anyone from reaching them as they drifted out to sea and went under. Once safe from the sunken vessel, the survivors fired flares.

At 10:15 p.m. a vessel saw the flares and diverted to assist. When it arrived, its crew found four of the scalloper's crewmembers on top of the raft. Once all were recovered, the good Samaritan vessel headed to New Bedford. The captain's body was recovered later that evening, but the missing deckhands were not located.

Lessons learned

Based on interviews with the surviving crewmen, the vessel had an extremely large pile of scallops and debris on deck. When the investigators met with the survivors, the mate stated, "You want to know what happened? We were overloaded."

The Coast Guard concluded the vessel had a continuous port list, either loaded or unloaded. The crew claims they managed the list by filling the stern freshwater tanks, placing cargo on deck and in the fish hold and by balancing fuel tank levels.

None of the crewmen knew how severe the list was, but the vessel's stability was a concern based on the fact that the owner added 11,900 pounds of cement and 2 tons of lead in the shipyard, and an additional 5 tons of lead in July 2003. All weights were added without a naval architect's input.

Modifications and alterations such as these tend to be added higher up on the vessel (in the case of winches or other gear). As the alterations are made, the overall center of gravity of the vessel rises and the freeboard may be reduced.

These factors affect the stability of a vessel. The center of gravity is a single point mathematically derived by summing all the factors (vessel's lightship, tankage, cargo and ship's stores) that influence the weight of the vessel. If the center of gravity is high, then the vessel is top heavy. Freeboard is the vertical distance from the waterline to the lowest watertight deck. If the freeboard is reduced, then the vessel is sitting low in the water. Simply put, the higher the center of gravity and the lower the amount of freeboard the more susceptible the vessel is to instability.

The vessel was not required to have a stability test, so there is no guidance in determining if it was overloaded. We know that each dredge was estimated to weigh 2,500 pounds and each could hold up to 1,000 pounds. Surviving crewmen could not recall how many hauls they had on deck, but they did say the load was between 7 and 10 feet above the main deck at its highest point. Based on the crewmen's statements describing how the vessel behaved before rolling over, the deck load played a role in the incident.

The mate was the only one in the wheelhouse with the captain at the time of the incident and indicates that he (the mate) was operating the dredges at the time. When the port dredge was raised and the vessel started listing to port, he asked the captain to take over. The mate stated that the captain accidentally grabbed the starboard side dredge controller, raising the loaded starboard dredge off the scallop pile and shifted it to the port side. This caused the vessel to further list to port and dip below the waterline. The crewmembers on deck at the time corroborated the statement by the mate, stating they saw the starboard dredge swing to port, causing the cargo list and water to flood over the port rail.

The captain may have intended to use the starboard dredge to counter the port list. The starboard dredge was still loaded at the time, and he may have wanted to counteract the port list by trying to shift the starboard dredge outboard. However, he was unfamiliar with the equipment or likely did not understand how moving it would further affect the vessel's stability.

With both the mate and captain new to their positions and to the vessel, this situation is conceivable.

The crew's lack of experience with this scalloper and the vessel's characteristics contributed to the vessel's instability and actions taken that propelled the situation from unsafe to gravely dangerous.

However, the captain's and crew's quick reactions to launch the life raft and abandon ship saved five lives.

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