Tugboat designers must step up their attention to safety and stability – going beyond even what present regulations require – to keep pace with burgeoning horsepower and technology demands, master tug designer Robert G. Allan said at Tuesday’s opening session of the 24th International Tug, Salvage and OSV Convention in Boston.
Allan pointed to the Jan. 17, 2015 sinking in China of a new tugboat, the 98’, 368-GT Wan Shen Zhou 67, during sea trials in the Yangtze River that left 22 dead. Chinese authorities have said an inexperienced captain, a turning maneuver and down flooding of the engine room were factors, but investigations continue.
“It’s not a single failure, but multiple failures. On that day everything went wrong,” said Govinder Singh Chopra of Sea Tech Solutions Ltd., Singapore. “This was our design, and 22 lives were lost.”
“How does our industry reach a state where that can happen?” Allan asked standing next to a screen image of rescuers around the capsized hull. “It’s certainly the worst accident in modern tug history.”
Allan’s company, Robert Allan Ltd., Vancouver, British Columbia, designs state-of-the-art tugboats. Allan said the escalating power requirements for harbor tugs capable of handling bigger ships are running up unanticipated hazards for operators.
By 2005, favored tugboat classes that would have 50 tons bollard pull in the mid-1990s were being supplanted by 60- to 65-ton bollard pull vessels, Allan said. “Today, 80 tons is not at all uncommon,” he said.
“Typically we’re putting twice as much horsepower into boats as we did 20 years ago,” Allan said. “We’re trying to cram this into less than 500 tons.”
Allan called it “a race between technology and regulation … this is not a fair race.” The industry’s demands are increasing much faster than regulatory agencies can respond, he said.
As a result, some tugs are so powerful they can be at risk of driving themselves underwater in the wrong conditions, such as running astern, Allan said.
“There have been some pretty serious accidents,” he said. “We cannot accept that operating … with decks awash is safe.”
Allan and Chopra spoke of the need for designers to step up their attention to safety and stability issues, and communicate design limitations to operators and captains.
For all the technology in the pilothouse of a modern tug, there are few warning systems that aid captains’ awareness of their vessel’s stability, Allan said. Chopra compared that to aviation, where pilots in commercial and military aircraft have a host of warning alerts and alarms to warn them of impending stalls or handling errors.
At the least, captains could have precision inclinometers to see when angles of heel are within performance parameters, or entering danger zones, Allan said.
“It’s too much to ask the (tug) master to keep track of these forces,” Chopra said. “It’s the designers’ job to give him that information.”
It’s that “limiting envelope” – mechanical forces bearing on the tug under loads, angle of heel, speed, and sea conditions with modes of operation – that captains need to understand, he said.
“If we could develop some sort of monitoring system around this limiting envelope, we would be more safe,” he said.
Both designers stressed the need for a larger goal: international standards for tug safety and stability.
“Safety has to be by design,” Chopra said, “but we need a homogenized, uniform standard.”