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NTSB reports sinking of 71-year-old tugboat


Written by

Nick Blenkey

The captain of the tug Proassist III decided that it was better to stay on the vessel while waiting for rescue rather than using his only life raft. [USCG photograph]

Unsecured openings in the deck of a tug led to its flooding and sinking off Puerto Rico, according to the National Transportation Safety Board.

Marine Inquiry Report 22/12 details the NTSB’s investigation into the December 24, 2020 flooding and sinking of the 1949-built tug Proassist III near Puerto Yabucoa, Puerto Rico. The tug vessel was transiting north off the coast of Puerto Rico when its aft compartments began to flood. The three crew on board were unable to pump out the water and eventually abandoned ship. No injuries were reported. The vessel was declared a total loss at $968,000.

Shortly after leaving Laguna de las Mareas, Guayama, the Proassist III encountered worsening weather conditions and the sea began to wash over the deck. More than two hours after leaving, the crew noticed the vessel had gone down the stern and found approximately three feet of water in the broadside rudder compartment. About 40 minutes after the crew discovered the water and attempted to pump it out, the rudder and rudder compartments filled with water. A disaster examination of the ship revealed openings in the ship’s watertight bulkheads and a lack of gaskets and securing mechanisms for flush hatches and door openings on deck.

NTSB investigators found no structural defects in the hull that could have allowed significant flooding and concluded that a cover for an opening in the after deck must not have been in place. Recently implemented regulations for towing vessels required that all openings be secured when operating at sea. The regulations also require that the watertightness and structural integrity of the vessel be maintained. However, the shortcomings observed during the post-disaster examination of the Proassist III indicated that the vessel was not properly maintained. The US Coast Guard’s concentrated inspection campaign uncovered three other vessels belonging to the Proassist III the owner had hull and deck integrity issues, reporting that the company did not have an effective maintenance program.

“An effective hull maintenance and inspection program would have proactively sought to minimize the wastage of steel on the Proassist III (and other company vessels) and would have made it easier to identify and report any corrosion issues,” the report said.


The NTSB has determined the probable cause of the sinking of the Proassist III had unsecured or open aft deck hatches, which resulted in the vessel’s aft compartments being flooded with water on deck and other compartments progressively flooding through openings in the watertight bulkheads. The lack of an effective hull inspection and maintenance program by the owner contributed to the flooding of the vessel.

“Over the past five years, the NTSB has investigated five accidents involving tugs that had poor decks and openings, resulting in flooding and sinkings,” the report said. “To protect vessels and the environment, good marine practice requires owners to carry out regular hull monitoring and maintenance, including between dry dock periods, regardless of inspection requirements. An effective program of Hull maintenance and inspection should proactively address potential wastage of steel, identify flaws in hull and watertight integrity and ensure that corrosion issues are repaired in a timely manner by permanent means .


As always, the NTSB’s bland summary of its findings only hints at what’s in the full report. For example, here’s what happened before, “the crew finally decided to abandon ship”.

“The crew prepared to abandon ship and donned personal flotation devices,” the NTSB’s full report reads. “The captain and deckhand/engineer threw the vessel’s only life raft container into the water and pulled the line they had attached to one of the bollards. The carbon dioxide cylinder valve opened to inflate the life raft; however, two straps around the center of the canister did not break, limiting the expansion of the liferaft. Seeing this, the captain went inside the ship to get a knife to cut the straps. During the search he stopped in the engine room to look for evidence of flooding but saw none. Meanwhile, the deckhands are coming up the hump to bring the life raft alongside the ship. After finding a knife, the captain jumped into the water and cut the two straps. Once the life raft was inflated, he entered the life raft briefly before re-boarding the Proassist IIIdeciding it was better to be on the ship waiting for help.

Subsequently, the crew was rescued by a fishing boat.


The ship itself?

“The 111.3 foot long tug Proassist III was built of welded steel by the Nashville Bridge Company in Nashville, Tennessee, in 1949. Originally built as a river transport tug on inland rivers, the vessel was converted to a harbor tug in 1989. Modifications included the rounding and the addition of a sail at the bow. the Proassist III’The hull was originally constructed with seven compartments separated by bulkheads designed to be watertight and fitted with watertight doors. The ship operated on the Mississippi River until it was purchased by Puerto Rico Operations in 1992. The Proassist III was later operated by American Tugs & Barge (ATI) and homeported in San Juan and then Puerto Yabucoa, Puerto Rico.


“Before 1992, the Proassist III was 316 gross registered tons (GRT) below the
regulatory measurement system of the United States, and, if the vessel were to operate out of port (off the coast of Puerto Rico), it would have been subject to Coast Guard inspection, as required by regulations in 46 Code of Federal Regulations 2.01- 7. Requirements for an inspected vessel would have included annual reviews and dry docking twice every five years. In 1992, the Proassist III was re-measured; the vessel was determined at 241 GT ITC according to the international convention measurement system and at 213 GRT according to the American regulatory measurement system. In 1993 the ship received a new tonnage certificate and was no longer subject to ship inspection laws for a seagoing motor vessel over 300 GRT.

“Similarly, vessels of regulation tonnage of 150 GRT or more are subject to load line regulations and must be inspected annually by inspectors from the authority issuing the load line certificate (the American Bureau of Shipping or another recognized classification society approved by the Coast Guard) and dry-docked for inspection once every 5 years. When the Proassist IIIthe regulatory tonnage was over 150 GRT, the vessel was subject to regulation, including Coast Guard inspections for single trip load line exemption certificates (the vessel received certificates in 1994, 1995 and 1996 to sail between San Juan and Guayama).

“In December 1996, deep frames (similar to a bulkhead) were added to the vessel to reduce the volume of space below the main deck used to calculate GRT using the regulation measurement system. This modification further reduced the tonnage of the vessel to 148 GRT (the GT ITC remained the same). In 2000, the owner of the Proassist III advised Coast Guard Sector San Juan that the vessel had reduced its regulation tonnage to 148 GRT on December 10, 1996 and was therefore no longer subject to load line regulations as it was a vessel existing (now) less than
150 GRT. »


The owner’s preparations for Subchapter M compliance are also informative reading in the full report.

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