In-depth | Sail-aSSiSted propulSion
a full-scale instrumented rotor on land high levels of thrust and efficiency. A wing large vessels, such as NYK’s conceptual ‘Super
and, from the results, along with wind sail powers one of the contenders for the Eco Ship 2030’, and could be engineered for
records derived from ships’ logs extending 2010 America’s Cup series, being held during smaller commercial vessels too.
back several years, predicted the fuel and February off Valencia, Spain. Another approach, midway between
emission savings for a notional cargo vessel A wing sail has less drag and exerts more wing and Magnus rotor, is the turbo sail,
undertaking representative voyages. This thrust than conventional sails, but raises developed in the 1980s by French marine
work has reinforced confidence in the 13% structural challenges. It must be light and scientist Jacques Cousteau and colleagues.
savings figure, even allowing for times when strong, and must be mounted via a ball Convinced that it was possible to better
there is minimal wind or alternatively wind race so that it can be rotated according to Flettner’s concept, they conceived a fixed
so strong that the rotors have to be closed the direction of the wind. Typically, wing vertical tube somewhat flattened to an ovoid,
down (about 35-40kts on the intended sails are rotated by servo flap actuators on that has air pulled into it by motor-driven
full-scale device). Greenwave argues that this their trailing edges, these being electrically axial fans so as to accentuate the suction
level of saving is ample to justify the use of operated under computer control. At created by the passing air stream. The device
wind assistance, and that the figure could be low wind speeds, the weight penalty due can be regarded as a rudimentary wing with
boosted further if rotors were to be combined to the ‘hard’ structural sail can put them boundary layer control. Experience with a
with other means of harnessing renewable at a disadvantage compared with lighter purpose-built vessel, Alcyone, including a
energy. Moreover, the rotors can be used to traditional sails. However, wing sails could circumnavigation, demonstrated impressive
assist maneuvering and even as air brakes to experience resurgence as energy-saving propulsion potential and ability in wind-assist
help decelerate the vessel. Whybrow claims a devices rather than as primary propulsors. mode (i.e. with complementary use of diesel
system would be easy to install, without dry They are more controllable than soft rigs and engines) to reduce fuel consumption by
docking, and could achieve a payback in as require negligible crewing input. up to a third, while a larger commercial
little as three years. Walker-type wing sails are symmetrical vessel demonstrated a 15% increase in fuel
in section, but a cambered asymmetrical efficiency over a three-year study. Although
Winging it section, as in an aircraft wing, can produce work on the concept stalled, again due to
Another way to generate differential pressure more lift. That is the basis of a design by easing of fuel price concerns, the turbo-sail
and derive forward thrust is to use a vertical Boatek, for example. However, a vertical could be a candidate for revival, despite the
wing. In 1986 Walker Wingsail Systems wing on a vessel has to be able to generate lift extra power required to drive the fans.
demonstrated an 8tonnes; 13m tall wingsail in either direction, unlike an aircraft wing,
fitted to the 6500tonnes MV Ashington, and and this requires the cambered surface to be Kiting
showed that use of the sail could cut fuel changed from one side to the other whenever Kite-propelled surf boarders have become a
usage by 10%-15%. Wing sails failed to catch the vessel changes tack. There are means to familiar sight in coastal locations, but could
on at the time because oil producing nations accomplish this, for instance by moving kites help propel sizeable ships? A company
relaxed a previous squeeze on supplies that the main spar laterally within a sufficiently that believes they can is SkySails GmbH of
had caused a price hike. However, several flexible envelope – though not without extra Hamburg. Founder Stephan Wrage asserts
wing sail yachts, notably Blue Nova and complication. Alternatively, the sail must that kites could save 10-35% of fuel – even
Zefyr went on to make significant voyages be rotated through 180degs at each tack. 50% in optimum wind conditions.
including a circumnavigation, demonstrating Wing-type assist sails have been proposed for Kites need no masts and, flying at 100m
to 500m altitude, they are in winds up to
50% stronger than at sea level. Computer
control ensures that a SkySails kite remains
aloft in optimum configuration and an
integrated launch and recovery module
facilitates deployment.
A large kite reportedly saved 20% of fuel
when towing the 132m heavy-lift ship Beluga
SkySails across the Atlantic in 2008. Recently,
the system was commissioned on the cargo
ship MV Theseus, first of a series of new-builds
for the Wessels Shipping Company. A leading
European fishing company, Parlevliet & Van
der Plas is retrofitting the system to a 141m
fishing vessel.
KiteShip in San Francisco is also developing
kite propulsion for commercial vessels,
Greenwave’s technical director, Spiros Contopoulos (left) and aerodynamicist richard having already provided yachting solutions.
Karn (right) put the wind engines through their paces at Warsash Maritime academy Kite propulsion has been covered in previous
(Credit: Warsash Maritime academy). issues of Ship & Boat International. SBI
22 Ship & Boat International March/April 2010
SBI_MarApr10_p20-21-22.indd 22 26/02/2010 12:21:18
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60