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For instance, the Wind Challenger project aims to
achieve a 50% reduction in fuel consumption by
equipping a capsize bulk carrier with nine telescopic
sails, while route-specific simulations (Yokohama–
Seattle) suggest savings in the range of 20–30%. Single-
sail installations, such as on the Shofu Maru, have
demonstrated fuel reductions of 5% and 8% on the
Japan–Australia and Japan–North America routes,
respectively [15]. Tests conducted on Ro-Pax vessels,
such as Ciudad de Mahón, indicated potential fuel
savings ranging from 7% to 22%, depending on the
operational scenario. These findings stem from a case
study based on simulations involving two 35×12 m²
wing sails and the assumption that the vessel operates
in the Mediterranean Sea at a design speed of 21 knots
[16].
A manufacturer of suction wings reports that their
systems could reduce fuel consumption by up to 20%
and 40%, respectively, depending on the number and
size of wings installed, as well as the vessel type [17].
However, only limited performance data is currently
available for suction wings. Speed trials were
conducted on the multi-purpose dry cargo vessel M/V
Frisian Sea, which was fitted with two suction wings,
each measuring 10 × 3 metres [18]. During testing, the
vessel maintained a constant speed of 10 knots, with
wind energy partially replacing engine output. Data
from these trials was used to estimate power savings
across a range of wind conditions, with calculated
savings on specific routes ranging from 0.7% to 4%, and
an average of 2.2%.
During 2022–2023, several speed trials were
conducted with the general cargo vessel M/V Ankie,
which was equipped with two suction wings, each
measuring 13 × 2.1 metres, to verify their power-saving
potential. During testing, the true wind speed was 10
m/s and the vessel maintained a speed of 9.5 knots.
Power savings reached up to 15% at the most
favourable wind angle, while the estimated average
power reduction on typical routes was approximately
3.5%, corresponding to a saving of around 40 kW [19].
One of the strongest commercial incentives for
adopting WASP technologies is their potential to
deliver immediate and measurable fuel cost
reductions. However, the lack of robust empirical data
confirming the predicted savings remains a barrier to
the wider adoption of WASP systems. Further research
on these technologies is therefore of significant
importance. Nevertheless, all savings achieved to date
translate directly into lower operational expenditures,
thereby enhancing the competitiveness of WASP-
equipped vessels.
5 OVERVIEW OF WIND PROPULSION
TECHNOLOGIES
Wind-Assisted Ship Propulsion systems, which are
recognised as a promising solution to reduce, and in
some cases replace, conventional fuel use in shipping,
convert wind energy into propulsion power, allowing
ships to partially, or depending on the design,
significantly substitute main engine output with wind
power. When properly applied and appropriately
designed to suit a vessel’s operational profile, WASP
can reduce greenhouse gas (GHG) emissions, air
pollution, fuel consumption, and underwater noise
[20]. While all Wind Propulsion Systems operate based
on the same fundamental physical principles, the
specific technologies differ in terms of their
mechanisms and performance characteristics. Selecting
the most suitable WASP for a particular vessel depends
on multiple factors, including average sailing speed,
operational routes, prevailing weather conditions, and
practical considerations such as available deck space
and compatibility with cargo operations [21].
Optimising ship design and navigation strategies to
align with the dynamics of wind propulsion is essential
for maximising the effectiveness of WASP.
Furthermore, ship structure and weather routing play
a critical role in the overall system performance.
Up to January 2025, 52 vessels registered in DNV
[2,22] have been equipped with modern wind-assisted
propulsion systems. While this represents only a small
fraction of the global fleet, adoption is expected to
increase significantly. The recent acceleration in uptake
is clearly evident, with 44 of these installations
occurring on ships built or retrofitted after 2020. Larger
vessels dominate this trend, accounting for a combined
total of 3.4 million deadweight tons (DWT) equipped
with WASP. As illustrated in Figure 1, the adoption of
WASP in the global fleet is currently concentrated
around four main technologies: rotor sails, suction
sails, wing sails and kites [22]. Therefore, this section of
the article will focus on and describe only these
technologies.
Flettner rotors, also known as rotor sails, were first
applied on a merchant vessel in 1924. These are
rotating cylindrical sails that harness wind energy to
assist with ship propulsion. Their operation is based on
the Magnus effect, a phenomenon in which a spinning
cylinder generates lift perpendicular to the airflow.
While the initial trial was technically successful, it
lacked economic viability, and as a result, the concept
remained largely dormant for nearly a century.
However, in recent years, renewed interest has
emerged, driven by the push for more sustainable
shipping solutions [23]. A major advantage of this
technology is that the sails can be installed on
newbuilds or retrofitted to existing ships, provided
there is sufficient deck space and unobstructed airflow,
even if the vessel was not originally designed to
accommodate sails. However, newbuilds offer better
optimisation by integrating WASP from the start. Rotor
sails are particularly suited to vessel types such as
tankers, LNG carriers, RoRos, RoPaxes, general cargo
ships, bulk carriers, as well as cruise ships and ferries
[24]. Currently, bulk carriers and tankers dominate the
use of rotor sails, accounting for 54% of all WASP
technologies installed on vessels in operation.
Rotors offer the advantage of being easily adjusted
to the wind direction by varying their rotational speed,
enabling effective wind utilization on both legs of a
voyage—something that is not always achievable with
other wind-assisted propulsion technologies.
However, a key drawback is the additional drag they
generate when not in operation, particularly when
sailing close to the wind. This added resistance can
increase engine power demand and fuel consumption.
In response, recent innovations, such as folding rotors,
have been developed to reduce this drag penalty when
the system is inactive.