Investigators could be months from knowing precisely what happened before and after the Costa Concordia crashed into rocks leading to at least six deaths.

There are countless questions, general and technical, that maritime investigators will want answers to.

Karen Jacques, chief operating officer, of Dryad Maritime, which provides risk forecasts and advice to mariners, said key questions included what speed the cruiser was doing and why it took a different route.

Investigators also need to know whether there was a problem below the water level that allowed the Concordia to list so quickly.

They will want to find out what decisions Captain Francesco Schettino took and where he was before the collision; what his role was during the evacuation and when he left the vessel, and an inquiry into the evacuation itself.

Ms Jacques, who worked in the Royal Navy for 14 years in roles including navigator, boarding officer and warfare officer, said: “The first question I would ask is what speed the vessel was going.”

She said good seamanship dictates speed is reduced by proximity to land but she was concerned by the huge hole in the hull.

She said it would be assessed and measured in the same way police measure the length of skid marks at the scene of a road crash.

The maritime expert stressed it was important to give the captain some leeway and time to explain certain decisions. She said the collision could have been down to human error or equipment failure but it was likely there was a chain of events possibly involving both.

“My greatest concern as a sea-goer is that it seems to have begun listing quite quickly,” said Ms Jacques.

It suggests a possible problem below the water line, she said, and investigators need to study whether compartments were locked down properly or if there was a problem with the bulk heads – which are cavities – like an ice cube tray – in the outer walls.