Thicker plating may have bought more time before Lamma IV sank: expert

Passengers on the Lamma IV could have had "marginally more time" to escape if the ferry had been built with thicker side plating, a naval expert has said.

The vessel started to sink just 96 seconds after the crash with the Sea Smooth, Australian naval architect Dr Neville Armstrong yesterday told the inquiry into the October 1 accident.

Armstrong said he found it "quite extraordinary" that Marine Department officers used only professional judgment and experience - instead of making full calculations - to approve the ship without a watertight door it was designed to come with.

He said he believed that the ship was built with a side plating of 4.5mm - 0.5mm thinner than in drawings approved by the Marine Department and 0.72mm less than the standard set out in 1995.

"The thinner plating size … may have contributed to the extent of the damage," stated Armstrong in his expert report. Thicker plating would have reduced the size of the holes, he said. "[It] might have provided marginally more time for escape before the vessel sank."

The ship's bottom plating was between 0.2mm and 0.5mm thinner than the 6mm set out in the drawings, but Armstrong said that contributed little to the sinking of the vessel.

According to documents submitted to the commission, Cheoy Lee Shipyards, which built the Lamma IV, had ordered 4.83mm-thick metal sheets for the ship.

While that could be considered normal variation, it was unlikely that the decrease in thickness from 4.83mm in 1995 to 4.5mm in 2005 was caused by corrosion, Armstrong said.

The construction of the vessel hull was subcontracted to a shipyard in Guangxi .

Armstrong estimated that the deck at the stern of the Lamma IV started to go below the water 96 seconds after its collision. It then hit the seabed at a 70-degree angle 22 seconds later, before settling into the mud.

He said surveyors responsible for approving the ship should have made calculations, which were "not difficult to do, especially with software".

"I cannot see how you could use professional judgment. I wouldn't want to do that, with so many people's lives at risk," said Armstrong. "We're not talking about a situation where someone might be injured: we're talking about risk to 300 people's lives here. So I would have thought 'professional judgment' was not satisfactory."

Armstrong also remarked that the shipbuilder took a great risk by constructing the ship not in accordance with its original drawings, if it had not consulted with the Marine Department on the matter beforehand.

"I find the risk that was taken to be far larger than certainly I would be willing to take as a shipbuilder," he said.