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How Screw-Drive Vehicles Work

        Auto | Unusual Cars

Screw-Drive Vehicles Performance
The Bering Strait, separating Siberia from Alaska in the North Pacific.
The Bering Strait, separating Siberia from Alaska in the North Pacific.
Photo courtesy of NASA

As you're probably figuring out, screw-drive vehicles are highly specialized machines. As such, they're extremely good at performing a narrow set of tasks. And they're pretty lousy at everything else, like going to the supermarket to get groceries (unless your supermarket happens to be in a swamp or a snow-covered wasteland).

In their natural elements of muck and slush, some screw-propelled machines can reach forward speeds of 7.5 to 10 miles per hour (12 to 16 kilometers per hour). Just as an example, the Armstead/Fordson zipped along in deep and heavy snow but struggled in the powdery stuff. It was also a notoriously ravenous consumer of fuel. On the up side, it could reportedly haul (again, on snow) 20 tons (18,144 kilograms) of cargo, such as logs, by towing it on one or more sleds. Screw drives tend to work well on heavy snow, in mud, even on ice or marshland. But they can't truly be considered "all-terrain" vehicles, because ironically, on normal roads they're pretty abysmal.

Perhaps the most celebrated use of a screw-driven vehicle in modern times was the crossing of the treacherous Bering Strait by two adventurers from the United Kingdom in 2002 (in their second attempt). This "Ice Challenger" expedition was the first crossing of the hazardous connection between the United States and Russia by a land-based vehicle.

Numerous hazards make the crossing potentially deadly -- ice floes that can severely damage ships, patchy ice that can collapse into the sea under the weight of a vehicle and even polar bears. But Steve Brooks and Graham Stratford performed the crossing in their Snowbird 6 -- an amphibious vehicle that ran on tracks while on snow and solid ice and used its outrigger-style screws to float and propel itself through water. The screws also helped the Snowbird 6 to clamber out of the water and back onto the ice.

For more information about screw-drive vehicles and other vehicles that tread off the beaten path, follow the links on the next page.