It must have been the ultimate nightmare – being trapped in a steel tube 120m below sea level. The crew of the Russian submarine Kursk could only wait to be rescued, and hope that someone heard their banging on the hull. Their wait was in vain.

The Kursk suffered two explosions and sank on 12 August in the Barents Sea, north east of Murmansk. At the surface many efforts were made to get to the submarine, but a combination of good old-fashioned cold war Russian cover up, simple inefficiency and the lack of even the simplest of means needed to rescue their comrades, made the undertaking a disaster in progress with the world watching. Contrary to statements by senior Russian officers, it took Norwegian divers just 90 minutes to get through the rear escape hatch. If these divers had been allowed in a week earlier, some of the crew of 121 might have survived.

Several months on, the question remains how to raise the submarine and the two nuclear reactors that are on board. The Kursk weighs 14,000t and is 154m long.

Possible solutions

Per Lindstrand, the balloonist behind several of Virgin millionaire Richard Branson’s stunts, and owner of the UK-based Lindstrand Balloons, has suggested that a number of heavy duty bags could be filled with gas to raise the structure from the seabed. The method has been tested and the balloons or gas bags have been designed. Made of Vectran, a high strength synthetic fabric, they are each rated at 1,000t lifting capacity.

This method may get the wreck up and rescue the reactors, but it would probably have been ineffective in a rescue bid. Not only extremely expensive, it would also be very time consuming as divers and robot drilling equipment would have to place between 14 and 16 of these bags in slings around the hull.

Other methods suggested include simply using a large semi-submersible crane. The largest of these, the Thialf, has a maximum capacity of only 14,200t using both its cranes – theoretically just enough, though the given weight of the submarine may not be entirely accurate. It is likely that more than one lifting vessel would be needed. It is possible to attach slings to the hull of the submarine, then lift it closer to the surface, stabilise it and shorten the slings, and repeat the operation until it is raised to the surface. But how to stabilise the vessel and shorten the slings is a key challenge.

Lindstrand’s balloons could help stabilise the submarine, but they would need to be adjusted for their gas content, as the pressure at the depth of the Kursk is 12 bar. This means that the content of the balloons would expand correspondingly, subsequently bursting them, if no gas was let out.

Attempts to hoist the stern piece of the Titanic some years ago ended in failure when the slings broke. And yet that load was just 65t.

The Latvian Estonia weighs about 18,000t, and all official plans for salvaging that ship have been dismissed as impossible, and the Estonia lies at a depth of ‘only’ 70m.

To use a large semi-submersible crane would probably not be a bad idea. The problem is that they are not widely available and the positioning time could be considerable.

Lifting with two cranes such as these, however, also presents some major problems. First of all, spreading the load between the two cranes could be a problem. If one crane has a lifting capacity of 12,000t and the other only 7,000t, for example, any sudden drop of the load regardless of reason, would risk sinking the smaller crane.

Secondly, the buoyancy of the vessel itself is important. When afloat and lifting something heavier than yourself, you risk sinking your ship when buoyancy is lost in the load. It may be necessary to heel the crane vessel so much that the entire hull gets flooded and sinks.

A possible solution

My own feeble attempt at a solution consists of a sort of floating dock with a hole in the bottom large enough to accept the bridge section plus the top part of the submarine.

Large slings must be positioned on the hull of the submarine, preferably in padeyes (which should be included in hull structures from the design stage).

Six large offshore tugs would then hook on to the slings and slowly start pulling away from the dock to raise the sunken vessel.

Ideally, the floating dock would adapt to the rules of establishing an equilibrium and would move sideways to position itself above the load’s centre of gravity, even though the tugs would not exert a uniform force.

Waves and currents will move the dock around, as will the lateral roll of the submarine, as one sling is pulled higher than the other. This creates a sideways force on the dock, and will induce movement.

The buoyancy of the dock must be enough to sustain the weight of the submarine, but in a rescue attempt (as opposed to a salvage operation) the aim is not to lift it right out of the water but just to gain access to the hull.

Neither of these solutions, however, give much hope to a sunken crew, for mobilisation would probably not be quick enough.