Caution and a close assessment of the structural integrity of the Hoegh Osaka are key to re-floating the 51,000-tonne car carrier safely, according to a maritime expert.

Simon Boxall, oceanographer at the University of Southampton's National Oceanography Centre, said a close inspection would have to be carried out to establish whether the ship had been damaged and whether the cargo of 1,400 cars had shifted inside.

This would help to establish whether the ship was capable of being re-floated.

He said: ''The key thing is take things gently. There were reports of trying to re-float it yesterday but they weren't planning to. The reason is they want to know if the structure is still together. They don't want to just drag it off and it splits in two, causing the major disaster that they have so far avoided.

''They need to make sure it is capable of floating first and establish the best time and best way of doing this.''

Mr Boxall explained that because the ship was listing prior to being grounded on the Bramble Bank sandbank, it was unclear whether it was stable enough to stay upright unaided once it had been re-floated.

He said: ''This was the case with the Costa Concordia, which they welded a large float to the side which they filled with hot air to keep it upright. They effectively gave it water wings so it didn't tip over.''

Mr Boxall said that if this more extreme scenario was not required, the ship would most probably be righted using a combination of winches and either large airbags or steel props to push it upright.

He said this was the standard method of righting vessels in similar circumstances.

He added: ''Chances are they will probably take some of the fuel oil out first, mainly to lighten the ship as it has 500 tonnes of fuel on board at the moment.''

He said the cargo of cars would also probably have to be removed because, if they had shifted, they could be adding to the destabilisation of the vessel. He said this would probably happen once the ship had been righted and the cargo doors at the rear could be opened.

Mr Boxall said: ''Removing the cargo is very tricky, very slow. It is a question of bringing heavy lifting gear in and getting stuff by simply pulling it out or redistributing it inside using winches.

''The first job is to get it upright and if the cargo hasn't moved, then it shouldn't be a major problem. They will need to carefully drag it off the sandbank using a series of tugs. It's not a trivial job but it's well in the capability of the salvage companies. Then they can simply tow it into Southampton or Portsmouth.''

Mr Boxall said weather and tides would be a key factor for when the righting operation would take place. He said the Bramble Bank is in a fairly sheltered section of the Solent and the sea conditions should not affect a vessel of its size.

He added: ''A spring tide is the best time as they would have a reasonable amount of water underneath it, so they may have to wait a couple of weeks. The conditions are ideal at the moment but the key thing is caution. What you don't want is to put lives at risk or make it worse by causing a spillage or as you tow it off, it sinks and blocks the navigation channels.''