Spirit crew had minutes to avoid grounding

The Spirit of Tasmania II's bridge crew had just minutes to stop the ship running aground at a Melbourne beach after a severe thunderstorm appeared as if out of nowhere.

A preliminary report into how the ship broke free of its moorings in January found no one saw an approaching storm because the bridge was empty at the time.

The Australian Transport Safety Bureau report, released on Monday, says the Spirit caused serious damage to the vehicle loading ramp and suffered minor bow damage during the dramatic incident.

The report found the ship's master checked the weather online at 5pm and saw it was clear, so cars began loading at 5.30pm.

At 5.37pm the Bureau of Meteorology released a severe weather warning about thunderstorms in Port Phillip Bay.

The master saw that warning at 5.50pm and rushed to the bridge.

At 5.53pm the winds hit a violent 60 knots on the Port Melbourne pier.

"By then, about 120 passengers had boarded and the ship's stern had moved off the wharf," the report states.

"With the violent storm-force wind pushing the stern off, the ship's aft mooring lines failed in rapid succession."

The boat began swinging towards the Port Melbourne beach until it was at a right angle to the pier it was meant to be alongside.

The engine room got the thrusters ready by 5.55pm, with two main engines ready three minutes later.

At 6pm those two engines and the thrusters were the only thing keeping the Spirit of Tasmania II from being forced onto the beach.

A tug boat arrived at 6.09pm to stabilise the ship's stern. The ship was secured by 7.05pm.

The investigation will now focus on weather events in the Port of Melbourne area - and how the port and port users prepare for them.

It will look at the BoM's weather forecasting and warnings, distribution of weather information to port users, and the Port of Melbourne's procedures and actions.

The TT Line Company, which owns the Spirit of Tasmania I and II, will also have its preparations and procedures examined.