Wind, together with human energy, has been the first energy source to be exploited
for vessel traction over the sea.
As wind is a renewable and virtually endless energy source, it is foreseeable that,
as long as the energy problem will continue to rise and become more and more urgent,
wind could be destined to be the future of navigation.
Traditional sail traction evolution over the years allowed increasing performances,
mainly thanks to new materials fabrication. However, traditional sailboats only
exploit low altitude wind. Considering pure wind traction solutions, direct traction
realised by airfoils has already been patented by BP in 1982 and adopted by SkySails
as a possible solution. Such solutions are not particularly efficient, as vessels
have no drift and the airfoil traction causes leeways, unless it is running downwind.
But running downwind, besides being an inefficient point of sail for modern boats,
is also inefficient for airfoil traction, as the vessel velocity has to be subtracted
to the wind velocity. The SkySails solution has recently been adopted by Beluga
Group, which equipped a carrier In 1924 a large two-rotor ship named Buchau was
finished.
It was equipped with two propulsion cylinders put in rotation by individual motors.
According to the sense of the rotation impressed to those cylinders, the wind incident
on them allowed the ship to move towards the desired direction. It was discovered
that the rotors did not give the slightest cause for concern in even the stormiest
weather, and that the rotor ship could tack (sail into the wind) at 20-30 degrees,
while the vessel with its original sail rig could not tack closer than 45 degrees
to the wind. However, the rotor system was less efficient than conventional engines,
and Flettner turned his attention to other projects and the rotors were dismantled.
Another direct wind traction system has been developed in the 80s by Cousteau, Malavard
and Charrier, who designed and prototyped the first wind-propulsion cylinder based
on the savonius principle, the Turbosail system, which equipped the experimental
ship Alcyone (Patent n° US4630997).
The two 10,21 m high streamlined and rotating wingmasts are perforated with thousand
of little holes to allow the air to enter and escape.
Fans moved by engines are placed at the top of the two Turbosails to accelerate
the flow around the wingmasts and increase the lift, producing the driving force
forward. The Turbosail is a Savonius turbine, whose maximum efficiency is 13%. The
low performance of such solution, confirmed by the experimental results, can be
easily measured considering that the whole intercepted wind front is around 50 m2.
With a 10 m/s wind the power subtracted from the wind could be approximately 4 kW.
The wind energy harvested by the KITVES solution is not used for direct traction.
Such solution allows to design a brand new concept of on board electric generator
whose generation capabilities are essentially independent from the navigation conditions,
allowing the vessel to navigate in any direction without compromising the system
operativity.
The KSU (Kite Steering Unit) represents the basic element of the implementation
of the KITVES Proposal.
The KSU can autonomously perform a cyclic two-phase wings array manoeuvre, simply
acting on the two lines that connect the wings array to the fixed steering unit.
The lines are connected to two alterno-motors by means of wrapping drums. In the
traction phase, when the array of wings is lifted by the wind (properly driven in
the most efficient way by the control), the lines unroll, the drums are put in rotation
and the alterno-motors produce energy.
When the maximal length of the lines is reached, the control enters into the recovery
phase, where the wing is driven to a region where the lines can be pulled by the
motors until the minimal length is reached, spending a small fraction of the energy
generated in the traction phase and a new traction phase is undertaken.
The following pictures show the trajectory of the wing as it results from some controlled
flight simulations:
