To the untrained eye, it looks like a jumble of objects, lines and patterns — but to maritime authorities, it’s an image of catastrophic consequences.
The image shows the moment Australia’s $528 million Antarctic icebreaker “collides” into a pylon as it travels under Hobart’s Tasman Bridge.
Fortunately, it was an incident that only occurred in a computer simulation — but it wasn’t a one-off.
TasPorts’ harbour master has told the ABC that over the course of 109 computer-based trials, the virtual RSV Nuyina hit the bridge four times.
It would have impacted it a further 10 times if the test run hadn’t been called off mid-journey.
The vessel also came dangerously close to the pylons on almost 50 per cent of the remaining computer-based assessments, he said.
The tests were conducted to see if the ship, which is 35 metres wide, could safely travel between the bridge’s central pylons, which are 73 metres apart.
But following the computer assessments, the risk of a real-life collision was considered so high that in August the harbour master declined to grant permission for the transit.
“If something the size of the Nuyina even nudges against [the bridge], brushes against it even at a very slow speed, that’s going to be catastrophic,” Captain Mick Wall said this week.
His concerns were based on real-world experience after another ship collided with the pylons in 1975, causing the partial collapse of the Tasman Bridge and the deaths of 12 people.
But the decision has had significant flow-on effects.
It means that instead of refuelling just 4 kilometres away at Selfs Point, the Nuyina must now take a 660-kilometre detour to fill up in the state’s north-west.
As revealed by the ABC earlier this month, the extra mileage will add $875,000 to the Australian Antarctic Division’s fuel bill this season.
‘Dire and fatal consequences if exercised in reality’
Tasmania’s ports regulator has previously been relatively circumspect in its public messaging about the decision, saying only that the Nuyina “would exceed the safe minimum clearing distances from the bridge pylons”.
But details of the collisions and near misses during the virtual trials have been disclosed after the ABC obtained TasPorts’ final report of its “Non Standard Vessel Assessment”.
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The report — released under Right to Information laws — featured 11 simulator screen grabs, including an image that showed one of the “loss of control” events that resulted in an “allision”.
An allision is when a moving vessel strikes a fixed object, which in this case was the Tasman Bridge.
The report also warned that alternative methods — such as towing the Nuyina or using an additional tugboat to shepherd it through the navigational span of the bridge — carried unacceptably high risks.
“Exposing a tug to the side of vessel where the safe passing distance was diminishing would not only have an expectation of push at all costs but … very quickly escalate to both dire and fatal consequences if exercised in reality,” it stated.
While the ship is considered adept at cutting through ice in polar waters, the report noted that during on-water trials in Hobart, it had difficulty maintaining “directional stability”.
This was due to the icebreaker’s rounded hull and its relatively large surface area, which can be heavily affected by wind.
In constrained waters, it meant maximum rudder angles had to be applied to avoid hitting the pylons during the virtual simulations.
“Therefore, there are no in-built or redundant risk treatments available with which to apply safely at that critical transit time,” the report stated.
‘Catastrophic’ risk not worth it
The harbour master told the ABC that for ships to safely pass under the bridge, there should be a minimum gap of about 20 metres between the vessel and the pylons.
A gap of between 10 and 20 metres was considered a “marginal” risk, while anything less than 10 metres was “extreme”.
During the computer simulations, which occurred in three stages over two years, Captain Wall said the Nuyina fell into the marginal or extreme risk categories 40 times, in addition to the other actual and likely collisions.
The problematic simulation attempts were all during the return leg, when the ship was travelling south from Selfs Point back to its wharf at Macquarie Point.
While the northern passage was much simpler, Captain Wall said the southern transit required challenging turns at critical moments because of the geographical layout of the area.
“You have a very limited straight-line run before you need to get into a position of what’s called the ‘point of no return’,” he said.
“If you pass the point of no return, you can’t steer away from the hazard, ie the bridge.
“You haven’t got enough engine or tug power to stop yourself before you come to grief and have an allision.”
If a tugboat was used to counter the Nuyina’s sideways movement, Captain Wall said it would have to remain connected to the ship past the point of no return, leaving the tug without enough room once it reached the bridge.
“It would actually force the tug in most cases up …. against the pylon, and that would be catastrophic.”
As a result of the on-water and computer-based trials, the harbour master said the possibility of the Nuyina impacting the bridge was a risk he was not prepared to take.
“The consequences are you would get fatalities, let alone you’d lose a major part of Hobart’s infrastructure, being the Tasman Bridge adjoining the eastern and western shores.”
The Australian Antarctic Division (AAD) is not seeking a review of the harbour master’s decision.
The AAD has previously confirmed the ship’s “bridge wings” were extended by an additional 3.6 metres compared to its original design in 2017, although it’s not clear what impact this had on the vessel’s directional stability.
While the Nuyina failed to get clearance for a bridge transit, the AAD told a Senate inquiry in October the icebreaker had performed well during its southern missions.
“It is our main lifeline to Australia’s Antarctic and sub-Antarctic stations and the central platform of our research,” the AAD’s acting deputy secretary Robert Hanlon said.
“This combination of speed, size, strength and endurance is unparalleled in Antarctic shipping. In short, it is transformational.”
The Tasmanian government is currently assessing whether a fuel barge should be set up in Hobart.
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