GIANT underwater tractors are being lined up to plant wind turbine towers in
offshore energy farms off the Dutch coast. Looking a little like the enormous
caterpillar-tracked Crawler that trundles space shuttles out to their launch
pads, the subsea tractors will be able to install turbines quickly, all year
round, in any weather.
It鈥檚 no mean feat, says Henk Hutting of Kema, a Dutch engineering firm based
in Arnhem. Wind turbine towers are usually built on land and carried out to sea
by crane-equipped barges, before being lowered onto supports driven into the
seabed. Bad weather makes installation next to impossible. This process is very
slow and expensive, says Nick Goodall of the British Wind Energy Association, in
London. 鈥淭he real cost savings in offshore farms is in deployment.鈥�
Now Kema has designed a vehicle that can be driven along the seabed to make
the whole process a lot less painful. It will be built by Mammoet, the Dutch
engineering firm that鈥檚 helping raise the Russian submarine Kursk.
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The massive 20-metre-long four-tracked tractor gets its power from a
hydraulic pump. The diesel generator driving the pump is housed safely above the
water鈥檚 surface in a pilot鈥檚 cabin halfway up the turbine tower. Hydraulic
lifting mechanisms in each corner of the tractor raise the four legs of the
turbine tower a metre off the ground before the tractor takes its icy dip in the
North Sea.
Kema hopes that the U-shaped tractor will be able to position the four legs
of the tower over its support piles with an accuracy of 10 centimetres. Once the
tower is lowered, the vehicle simply backs off, and trundles back to a beach.
This way of working may extend the range of suitable wind energy sites, says
Hutting, as turbines could be installed in water deeper than the 20 metres that
is currently feasible.
Kema has further turbine developments in the pipeline. One problem with wind
turbines is fatigue caused by the waves and wind vibrating the structure in
rough weather. So the firm is designing a new type of lattice tower that can
change its stiffness and resonant frequency by using hydraulic pistons to
control the rigidity of the diagonal cross bars.