Siberia explorers fail on the Thames

Tomorrow they will embark on one of the world's most treacherous journeys, across 56 miles of shifting ice.

But today the two British explorers who will attempt to cross the dangerous divide between Alaska and Siberia failed to negotiate the gentle tides of the Thames.

The Snowbird 6, which leaves for its voyage across the Bering Strait tomorrow, had to be pushed along the river to meet the media. On its "final test" today the vehicle, which is built for land and sea, turned up an hour and a half late.

Explorers Steve Brooks, 40, and Graham Stratford, 39, will attempt to take Snowbird 6 through winds of 40 knots and a vast mass of constantly shifting ice on the crossing, at the beginning of March. But on a calm, clear day on the Thames their chances of making the journey, which could take up to 10 days, did not look good.

The pair have already failed once. Last year their craft was designed to be able to mount broken ice floes from the sea. But when they left it was too low in the water to succeed.

This time the 3.5 metre machine has been fitted with two huge screws, 3.5metres long and 1.2metres wide which will double up as flotation cylinders as well as turning to push the Snowbird 6 on to the ice floes. The screws, which look like giant pencils, are mounted on either side of the craft and lowered when necessary.

On the journey to Siberia temperatures are so low that if human skin is exposed for even a few seconds it will freeze solid.