Concordia disaster: How safe are modern cruise ships?

The capsizing of the Costa Concordia has raised many questions about the safety of modern cruise ships.

They have doubled in weight over the past decade, they sit higher in the water and are flatter underneath to enable them to enter more harbours. To the untrained eye they look top heavy, and with up to 6,000 people on board, they look difficult to evacuate quickly. But is that the case?

One maritime union, Nautilus International, thinks the regulations need looking at. It has been warning for some time that something like this might happen.

Look at this quote, which raises the spectre of the Titanic.

"The grounding of a cruise ship carrying more than 4,000 passengers and crew two weeks into the Titanic centenary year should serve as a wake-up call to the shipping industry and those who regulate it. Attention needs to be paid to existing evacuation systems and more innovative systems for abandonment."

The evacuation of the Costa Concordia didn't go well. The fact that the ship listed so quickly and so far meant they couldn't launch all the lifeboats. Passengers have complained of chaos, confused staff - some of whom didn't speak their language - and the fact they hadn't been taken through a drill.

The International Maritime Organization, which regulates ship safety across the world, sets the rules on evacuating ships and providing drills for new passengers.

Here is what they sent me:

Regulation 19: Emergency training and drills.

• 1 This regulation applies to all ships.

• 2 Familiarity with safety installations and practice musters.

• 2.1 Every crew member with assigned emergency duties shall be familiar with these duties before the voyage begins.

• 2.2 On a ship engaged on a voyage where passengers are scheduled to be on board for more than 24h, musters of the passengers shall take place within 24h after their embarkation. Passengers shall be instructed in the use of the life jackets and the action to take in an emergency.

Effectively, the company has 24 hours to take you through a drill once you are on board. The Costa Concordia was only a few hours into its voyage. Some people arriving back at Heathrow started flashing their drill cards around. They had been scheduled for a rehearsal on Saturday afternoon, by which time the ship was lying on its side.

I suspect, in the light of this accident, all cruise companies will now make sure they drill passengers before they set sail.

But what about the time it took to get everyone off?

Regulation III/21.1.3: All survival craft required to provide for abandonment by the total number of persons on board shall be capable of being launched with their full complement of persons and equipment within a period of 30 min from the time the abandon ship signal is given after all persons have been assembled, with life jackets donned.

With lifeboats unable to launch, passengers had to evacuate the ship any way they could

In practice, this means all passengers and crew are ordered to lifeboat stations first and then, when everyone is mustered, the captain orders abandon ship. So Coast Guards test to see if ships can load the boats and place them in the water within 30 minutes.

Regulations also state that a ship's systems should last for at least three hours because that is how long it is expected to take to completely abandon a large ship.

It took a good five hours to get most passengers off the ship. One former sea captain I spoke to had some sympathy with the crew in this situation. Once the ship was listing heavily, he told me, and the lifeboats were sitting on what had become the top of the boat, everyone just had to leave the ship any way they could.

The regulations work to the principle that the ship itself is the best lifeboat, and is designed to be able to limp back to port in most situations.

Prof Philip Wilson at the University of Southampton specialises in ship dynamics and we spoke alongside his 29ft (9m) testing tank.

"Modern ships are safe as they can possibly be," he told me.

"The centre of buoyancy is in the right place... instinctively it doesn't look right but it is in fact very, very stable, the beam of the boat being very large."

We have also heard a lot about watertight compartments since the Costa Concordia went down. The theory is that if one side of the hull is breached, the other side can be flooded to keep the ship upright. The big question is then, why didn't it work in this case? The truth is we won't know until the investigation is finished.

But Prof Wilson wasn't too surprised, saying: "Every ship will sink if you make the hole big enough."

Latest underwater images reveal previously unseen damage to the hull of the ship

He added, however, that something was "puzzling" him.

The hole in the hull is sticking out of the water. It should be under the sea, because that is where the water came rushing in. In other words, the ship seems to be lying on the wrong side.

"We're working on information that's incomplete so we don't know really what's happened. Potentially of course, the crew could have been pumping water to bring the ship upright, and maybe took too much water on board."

What many people are keen to stress is that cruise ships are still among the safest ways to travel. Companies emphasise that training and regulations are rigorous and that this kind of accident is very rare. But no-one argues that there isn't room for improvement.

The International Maritime Organization has not had a lot to say on this accident so far, but it has released a statement, and once again, it revives memories of the Titanic.

"IMO must not take this accident lightly," it says.

"We should seriously consider the lessons to be learnt and, if necessary, re-examine the regulations on the safety of large passenger ships in the light of the findings of the casualty investigation. In the centenary year of the Titanic, we have once again been reminded of the risks involved in maritime activities."