Engineering Options for More Fuel Efficient Ships
Karsten Hochkirch, FutureShip GmbH, karsten.hochkirch@GL-group.com
Volker Bertram, FutureShip GmbH, volker.bertram@GL-group.com
The paper surveys engineering options to save fuel in ships, both in design and operation. Both propul-
sion and on-board consumers are discussed. Propulsion power depends on resistance and propulsive
efficiency. Here, the main options are given, following a systematic breakdown of the individual resis-
tance components and the efficiency losses at the propellers. For machinery and onboard consumers, a
general discussion is followed by a description of simulation tools for design and operational guidance
towards more fuel efficient designs and operations.
Mid-term and long-term fuel prices are expected to range from 500 to 1000 $/t including expected future
surcharges for CO
(carbon-dioxide) emissions. Therefore ship operators will put higher pressure on ship
owners to obtain fuel efficient ships. These in turn will put pressure on ship yards to supply fuel efficient
ships. As a result, we expect to see a paradigm shift in designs and refits to improve the fuel consumption
There are any many ways to reduce fuel consumption.
- reduce required power for propulsion
- reduce required power for equipment on board
- use fuel energy more efficiently for propulsion and on-board equipment
- substitute fuel power (partially) by renewable energies like wind and solar energy
Surveys on partial aspects of fuel saving options have been published before. Several HSVA (Hamburg
Ship Model Basin publications, Hollenbach et al. (2007), Mewis and Hollenbach (2007), Hollenbach and
Friesch (2007), give rather comprehensive overviews of hydrodynamic options in design and operation of
ships. Hochhaus (2007) discusses various approaches to recuperate energy losses from the main engine to
use them for on-board equipment. New hull form features are developed to improve the fuel consumption
for given payload, Harries et. Al (2007). We will discuss more comprehensively the available options in
the following, but recommend them nevertheless for further studies.
2. Reduce required power for propulsion
We may use traditional hydrodynamic approaches to decompose the power requirements into resistance
and propulsion aspects. While propulsor and ship hull should be regarded as systems, the structure may
help to understand where savings may be (largely) cumulative and where different devices work on the
same energy loss and are thus mutually excluding alternative.
2.1. Reduce resistance
There are many ways to reduce the resistance of a ship. On the most global level, there are two (almost
- Reduce ship size: The lightship weight may be reduced for example by (expensive) lightweight
materials, more sophisticated structural design involving possibly formal optimization and
reducing the ship length. None of these options is straightforward. The ship length should
consider hydrodynamic aspect as well as production and weight aspects. However, reducing the
required power during the design stage by the assorted measures discussed below will reduce in
turn the weight of engines, power trains and fuel tanks and yield considerable secondary savings
due to smaller ship size.
- Reduce speed: Speed reduction is a very effective way to reduce fuel consumption and emission.
Isensee et al. (1997) pointed already out that transport efficiency increases drastically with
decreasing speed, Fig.1. HSVA reports fuel savings of typically 13% for bulkers or tankers, 16-
19% for containerships, for a speed reduction by 5%, Mewis and Hollenbach (2007). Slow
steaming reduces in itself fuel consumption significantly. However, the ship is then operated in
off-design, thus sub-optimal condition. This offers assorted potential improvements to reduce the
fuel consumption further: electronically controlled main engines allowed better efficiencies at
slow steaming and reduce also lubrication oil consumption; controllable pitch propellers allow
better propeller efficiency over a wider range of rpm; adapted new bulbous bows may reduce
wave resistance considerably. On the other hand, waste heat from exhausts and cooling water is
considerably reduced and may require reconfiguration of auxiliary engine systems for slow
steaming. In sum, a supporting engineering analysis is recommended when deciding on slow
steaming for a longer time.
Fig.1: Transport efficiency vs speed for various vessels (modified Karman-Gabrielli diagram)
The largest levers in ship design lie in the proper selection of main dimensions and the ship lines. Ship
model basins should be consulted to assess the impact of main dimensions based on their experience and
data bases. On a more detailed level, for a given speed and ship weight, all components of the ship
resistance, Bertram (2000a), may offer fuel saving potential:
- Frictional resistance of bare hull: The frictional resistance (for given speed) depends mainly on
the wetted surface (main dimensions and trim) and the surface roughness of the hull (average hull
roughness of coating, added roughness due to fouling). Ships with severe fouling may require
twice the power as with a smooth surface. The battle against marine fouling is as old as seafaring,
Bertram (2000b). Silicone-based coatings create non-stick surfaces similar to those known in
Teflon coated pans. In addition to preventing marine fouling effectively, these smooth surfaces
may result in additional fuel savings. Figures of up to 6% are quoted by shipping companies. An
average hull roughness (AHR) of 65 μm is very good, AHR = 150 μm standard, and AHR > 200
μm sub-standard, Hollenbach and Friesch (2007). As a rule of thumb, every 25 μm of hull
roughness corresponds to 0.7-1% of propulsion power, N.N. (2008c). As a more exotic approach,
a film of air on part of the hull reduces friction and in turn fuel consumption. The air cavity ship
uses compressors to constantly pump air under the ship. However, the technical effort is
considerable. Researchers work on fuzzy acrylic paints that will contain thin air films. The air
film may even inhibit bio-fouling, preventing barnacles and other organisms from attaching
- Wave resistance of bare hull: For given main dimensions, wave resistance offers large design
potential. Moderate changes in lines can result in considerable changes of wave resistance. As the
length of the created waves depends quadratically on speed, the interaction of bulbous bow and
forebody of the ship changes with speed. Thus a bulbous bow changes effectiveness with speed.
Bulbous bows should be designed based on CFD (computational fluid dynamics), but in most
cases fast codes based on simplified potential flow models suffice, Bertram (2000a). A formal
optimization is recommended as this may offer substantial savings on typical designs, Hutchison
and Hochkirch (2007), typically 4-5% can easily be gained and 1-2% improvement are feasible
even on hulls that are deemed already highly ‘optimized’ in limited form variations with CFD and
model tests in model basins, Fig.2, Abt and Harries (2007). Optimization of the aftbody lines
requires considerably higher computer resources due to the dominant effects of viscosity and
turbulence. However, pilot applications show the feasibility of the approach and formal
optimization of aftbody lines is expected to appear soon as a standard option in ship design. Hull
optimization, whether based on potential flow models or viscous flow models, is particularly
attractive for new designs where the ship owner can and should specify that such an optimization
is performed. For existing ships, refits of bulbous bows may have payback times of less than a
year, Hochkirch and Bertram (2009), but it is frequently problematic to obtain original hull
descriptions. Service providers (classification societies, model basins, consultants) cannot divulge
proprietary lines of one client (shipyard) to another (ship owner).
- Residual resistance of bare hull (mainly due to flow separation): Flow separation occurs when the
velocity gradients become too large in a flow. Large curvature in flow direction should then be
avoided. Flow separation in the aftbody is delayed by the flow acceleration due to the propeller
and different in model scale and full scale. CFD simulations may help in finding suitable
compromises between hydrodynamic and other design aspects.
- Resistance of appendages: Appendages contribute disproportionately to the resistance of a ship.
CFD simulations can determine proper alignment of appendages and design of high-performance
rudders, Fig.3. Rudders offer an often underestimated potential for fuel savings. Improving the
profile or changing to a highly efficient flap rudder allows reducing rudder size, thus weight and
resistance. Due to the rotational component of the propeller, conventional straight rudders at zero
rudder angle encounter oblique flow angles to one side at the upper part and to the other side in
the lower part. This creates opposing lift forces which cancel each other, but the associated
induced drag forces add. By twisting the rudder the
se unnecessary drag forces can be reduced.
Compared to a conventional semi-balanced rudder, a twisted rudder with Costa bulb may have
4% lower power consumption, Hollenbach and Friesch (2007). High-efficiency rudders combine
various approaches to save fuel: twisted rudders are combined with a bulb on the rudder as a
streamlined continuation of the propeller hub, e.g. Beek (2004), Lehmann (2007). In theory, the
gap between the hubcap and the forward part of the bulb should be as small as possible. In
practice there has to be gap sufficient to allow for structural deflection under load and propeller
aperture and rudder and also tolerances that can be realistically achieved under real shipbuilding
conditions. Savings of 2-8% are claimed by the manufacturers.
- Added resistance due to seaway: Intelligent routing (i.e. optimization of a ship’s course and
speed) may reduce the average added resistance in seaways. For example, the Ship Routing
Assistance system, Rathje and Beiersdorf (2005), was originally developed to avoid problems
with slamming and parametric roll, but may also be used for fuel-optimal routing. However, GL
experts estimate the saving potential to less than 1% for most realistic scenarios. In any case,
routing systems for fuel optimization should not only consider the added resistance to motions in
waves, but also the higher rudder resistance due compensation of drift forces.
- Added resistance due to shallow water: Routing systems may also consider shallow water and the
associated increased resistance, Friedhoff (2006).
- Added resistance due to wind: Wind adds power requirements in two ways: (a) direct
aerodynamic resistance on the ship and (b) indirect power demand due to drift in side winds. The
effect can be evaluated in wind tunnel tests and CFD simulations. Proposals for wind resistance
reductions include frontal spoilers, optimized container stowage and awnings. Savings of 1-1.5%
on the overall power demand have been estimated, Hollenbach et al. (2007). However,
operational constraints hinder practical applications so far.
For each draft and speed, there is a fuel-optimum trim. For ships with large transom sterns and bulbous
bows, the power requirements for the best and worst trim may differ by more than 10%, Mewis and Hol-
lenbach (2007). Systematic CFD simulations are recommended to assess the best trim and the effect of
different trim conditions. Decision support systems for fuel-optimum trim based on such simulations have
been proven to result in considerable fuel savings (typically 5% as compared to even keel) for relatively
low investment, Hansen and Freund (2010). They are expected to become a standard feature on larger
cargo ships within the next decade.
Fig.2: Hull lines optimization Fig.3: CFD for fuel efficient rudders
2.2. Improve propulsion
The propeller transforms the power delivered from the main engine via the shaft into a thrust power to
propel the ship. Typically, only 2/3 of the delivered power is converted into thrust power. A special
committee of the ITTC (1999) discussed extensively assorted unconventional options to improve
propulsion of ships and the associated problems in model tests. In short, model tests for these devices
suffer from scaling errors, making quantification of savings for the full-scale ship at least doubtful.
- Operate propeller in optimum efficiency point: The propeller efficiency depends among others on
rpm and pitch. Fixed pitch propellers are cheaper and have for a given operating point a better
efficiency than controllable pitch propellers (CPPs). They may be replaced if the operator decides
to operate the ship long-term at lower speeds. CPPs can adapt its pitch and thus offer advantages
for ships operating over wider ranges of operational points. Several refit projects have been
reported, with savings up to 17% quoted due to new blades on CPPs, N.N. (2008a).
- Reduce rotational losses: For most ships, there is substantial rotation energy lost in the propeller
slipstream. Many devices have been proposed to recover some of this energy. These can be
categorized into pre-swirl (upstream of the propeller) and post-swirl (downstream of the
propeller) devices. Pre-swirl devices are generally easier to integrate with the hull structure.
Rudders behind the propeller recover automatically some of the rotational energy. Therefore
potential gains should always be considered with rudder behind the propeller to avoid overly
optimistic estimates. Pre-swirl devices include the SVA Potsdam (Potsdam model basin) pre-
swirl fin, pre-swirl stator blades, Liljenberg (2006), and asymmetric aftbodies, Schneekluth and
Bertram (1998). Probably the best known post-swirl device is the Grim vane wheel, Schneekluth
and Bertram (1998). The original Grim vane wheel is located immediately behind the propeller
generating extra thrust. The vane wheel is composed of a turbine section inside the propeller
slipstream and a propeller section (vane tips) outside the propeller slipstream. The vane wheel
became unpopular after several reports of mechanical failures, most notably for the ‘Queen
Elizabeth 2’. IHI and Lips BV developed a modified vane wheel supported on the rudder,
overcoming the mechanical problems of the original Grim vane wheel, Fig.3, N.N. (1992). Other
post-swirl devices are stator fins and rudder thrust fins. Stator fins are fixed on the rudder and
intended for slender, high-speed ships like car carriers, Hoshino et al. (2004). Rudder thrust fins
are single foils attached at the rudder, proposed by Hyundai H.I. Typically 4% fuel savings are
claimed for all these devices by manufacturers. As all these devices target at the same energy
loss, only one of them should be considered. Gains are certainly not cumulative. CFD simulations
are the suitable tool to evaluate effects of these devices at full scale and aid their detailed design.
Contra-rotating propellers are a traditional device to recover the rotational energy losses,
Schneekluth and Bertram (1998). More recently, podded drives and conventional propellers have
been combined to hybrid CRP-POD propulsion, Ueda and Numaguchi (2006), claiming 13% fuel
- Reduce frictional losses: Smaller blades with higher blade loading decrease frictional losses,
albeit at the expense of increased cavitation problems. A suitable tradeoff should be found using
experienced propeller designers and numerical analyses.
- Reduce tip vortex losses: The pressure difference between suction side and pressure side of the
propeller blade induces a vortex at the tip of the propeller. This vortex (and the associated energy
losses) can be suppressed (at least partially) by tip fins similar to those often seen on aircraft
wings. The general idea has resulted in various implementations, differing in the actual geometric
form of the tip fin, ITTC (1999), namely contracted and loaded tip (CLT) propellers (with blade
tips bent sharply towards the rudder), Sparenberg-DeJong pr
opellers (with two-sided shifted end
plates), or Kappel propellers (with integrated fins in the tip region).
- Reduce hub vortex losses: Devices added to the propeller hub may offer cost effective fuel
savings. Propeller boss cap fins (PBCF) were developed in Japan, ITTC (1999), N.N. (1991).
Publications of the patent holders report 3-7% gains in propeller efficiency in model test and 4%
for the power output of a full-scale vessel. Reported gains have to be considered with caution,
Junglewitz (1996). “The presence of the rudder significantly reduces the strength of the hub
vortex and hence the gain in propeller efficiency due to PBCF can be reduced by 10-30%”, ITTC
(1999). The Hub Vortex Vane (HVV), jointly developed by SVA Potsdam and Schottel, offers an
alternative to PBCF. The HVV is a small vane propeller fixed to the tip of a cone shaped boss
cap. It may have more blades than the propeller. The vendors claim increases of 3% in propeller
- Operate propeller in better wake: The propeller operates in an inhomogeneous wake behind the
ship. This induces pressure fluctuations on the propeller and the ship hull above the propeller,
which in turn excite vibrations. The magnitude of these vibrations poses more or less restrictive
constraints for the propeller design. A more homogeneous wake translates then into potentially
better propeller efficiency, for example by a larger propeller diameter or larger blade loading on
the outer radii. For new designs, wake equalizing devices like Schneekluth nozzles (a.k.a. wake
equalizing ducts (WED)), Grothues spoilers, vortex generators, Schneekluth and Bertram (1998),
may therefore improve propulsion and save fuel. For existing ships, despite several refits more
recent independent analyses shed doubts concerning the effectiveness of WEDs, Ok (2005). “In
conclusion, partial ducts [like WED] may result in energy saving at full scale, but this was not,
and probably cannot be proven by model tests […]”, ITTC (1999). The Mewis duct combines pre-
swirl fins and wake-equalizing duct, Fig.5. 4% savings appear realistic for full hulls like tankers
Fig.4: CFD for wake and propulsion improvement
Fig.5: Mewis duct
2.3. Other aspects
Resistance and propulsion and main engine interact. Partial improvements of individual components as
possible as discussed so far, but the system analyses considering the interaction of the components offers
additional saving potential.
Ships are frequently hydrodynamically tuned for a design speed, but later operated most of the time at
lower speeds, even when they are not “slow-steaming”. If designed for a more realistic mix of operational
speeds, ships are estimated to exploit further fuel saving potential. Similarly, an even speed profile in
operation saves fuel. This is largely a question of awareness. Fuel monitoring systems have proven to be
effective in instigating more balanced ship operation with fuel (and emission) savings of up to 2%.
3. Reduce required power for equipment on board
There are various options to save power in the assorted energy consuming equipment onboard ferries. The
saving potential depends on the ship type. Examples are in more efficient electronically controlled pumps,
HVAC (heat, ventilation and air conditioning) ventilation systems, and energy saving lighting. Energy-
saving lamps not only reduce the energy requirements for lighting, they also reduce the waste heat from
the lamps and thus the energy needed by air conditioning systems to cool lighted rooms down again.
Avoid oversized main engines. Sea margins should be adapted to ship type, ship size and intended opera-
tional trade. This is especially true for fast ships. Sea margins should be selected based on simulations or
experience for specific ship types, but not globally imposed. Margins for rare high-speed operation are
expensive and may be better covered by falling back on the auxiliary engine power (power take-in (PTI)
via shaft generator). Detailed engineering analyses can be used to assess feasibility and cost aspects of
alternative configurations, Fig.6. For slow-steaming ships with controllable pitch propeller, it is better to
reduce the brake mean effective pressure than the rpm. Intelligent monitoring and simulation software can
combine engine supplier data and standard onboard monitoring data for a given operational profile to
determine optimum combinations of propeller pitch and rpm.
Fig.6: Machinery simulation tool, Freund et al. (2009)
Avoid oversized auxiliary engines. Better overall energy management systems may balance the energy
demand of the consumers on board reducing peak demands allowing in turn a reduction of the generator
capacity. This in turn reduces the weight of the ship. Simulations of the overall machinery system are able
to predict fuel consumptions for provided energy consumer profile. These simulations allow assessment
of alternatives and ultimately better balanced energy profiles.
Our simulations are based on the software ITI SimulationX. The simulations can be adapted easily to
different ships using a library of predefined machinery components. The simulations were validated for
two ships, Freund et al. (2009). The fuel consumption was calculated within 2% deviation of the reported
noon data over periods of 4-8 weeks. Installed onboard, the current consumption of mechanical and elec-
trical energy can be displayed in combination with the fuel consumption of the engines and their effi-
ciency of power generation, Hansen and Freund (2010). In conjunction with the displayed time lines, the
crew can evaluate their actions with regard to energy consumption, e.g. avoiding unnecessary peak loads
requiring a higher number of running engines. An example is displayed in Fig.7, with the current values
of the main engine displayed on the left with the related timelines on the right.
Fig.7: Energy Efficiency Monitoring for main engine
4. Increase use of renewable energies
Wind has been the predominant power source for ships until the late 19
century. Wind-assistance has
enjoyed a recent renaissance. Wind-assisted ships use predominantly other means of power (typically
diesel engines) and wind power plays only a secondary role. With increasing ship speed, wind assistance
makes less sense as increasingly efficient sails are needed. Constraints are initial investment, space re-
quirements, stability and required man-power for operation and maintenance. Despite these constraints,
several industrial projects have been realized in the past decade. Wind kites have been brought to com-
mercial maturity by the company Skysails, Fig.8, drawing also on expert advice from Germanischer
Lloyd. Kites harness wind power at larger heights without the stability penalties of high masts. The de-
velopment has enjoyed large media attention, and in 2007 the first prototype was tested successfully on
the MS “Beluga Skysails” and the “Michael A”, N.N. (2008b). Fuel savings in excess of 10% quoted by
the manufacturer apply for slower ships. Flettner rotors are another technology harnessing wind energy
for ship propulsion. After 80 years of obscurity, they have resurfaced in 2008 when Lindenau shipyards
delivered a GL-class freighter equipped with Flettner rotors. These four cylinders, each 27 m tall and 4 m
in diameter, are predicted to save nearly half of the conventional fuel needed by the ship.
Fig.8: Towing kite harnessing wind energy, source:
Fig.9: SolarSailor catamaran ferry,
Solar energy may supply an environmentally friendly part to the total energy balance of a ship. For inland
ferries, solar power and fuel cells are an attractive option to have zero-emission ships. For other ships,
diesel and solar energy may be combined. Diesel-electric drive systems are already quite common. Future
ships may combine then diesel generators for 50% of the total power consumed, fuel cells providing 30%
and a solar generator accounting for the remaining 20%. Solar-power and wind-power can be combined,
using fixed sails equipped with solar panels. This option is employed successfully on the SolarSailor fer-
ries operated in Sydney and San Francisco, Fig.9.
There are many technical levers to save fuel and thus emissions for ships. Unfortunately, there is large
scatter in saving potential and quoted saving potential is unreliable. Manufacturers frequently quote best
cases and sometimes extrapolate erroneously results from model tests to full scale ships. Despite these
uncertainties, the compiled information may serve for a first assessment on a case by case basis and
identification of most promising options. This requires interdisciplinary team work of clients and
consulting experts. For a more quantitative assessment, dedicated analyses often based on simulations are
Despite these words of caution, there is wide consensus that significant potential for fuel saving exists and
dedicated consultancy companies can support ship owners and operators in tapping into these potentials.
Many colleagues at Germanischer Lloyd have supported this paper with their special exper
(in alphabetical order) Bettar El Moctar, Malte Freund, Volker Höppner, Andreas Junglewitz, Ralf Plump,
Abt, C., Harries, S. (2007
), A new approach to integration of CAD and CFD for naval architects, 6
Conf. Computer and IT Applications in the Maritime Industries (COMPIT), Cortona, pp.467-479.
Beek, T. van (2004), Technology Guidelines for Efficient Design and Operation of Ship Propulsors, Ma-
rine News, Wärtsilä.
Bertram, V. (2000a), Practical Ship Hyrodynamics, Butterworth and Heinemann, Oxford.
Bertram, V. (2000b), Past, present and prospects of antifouling methods, 32
WEGEMT School, Ply-
Freund, M., Würsig, G.M., Kabelac, S. (2009), Simulation tool to evaluate fuel and energy consumption,
Conf. Computer and IT Applications in the Maritime Industries (COMPIT), Budapest, pp.364-373
Friedhoff, B. (2006), Optimierung des Treibstoffverbrauchs und Simulation des Betriebs von RoRo-
Schiffen auf Routen mit geringen Wassertiefen, Jahrbuch der Schiffbautechnischen Gesellschaft, Springer,
Hansen, H., Freund, M. (2010), Assistance tools for operational fuel efficiency, 9
Conf. Computer and
IT Applications in the Maritime Industries (COMPIT), Gubbio
Harries, S., Hinrichsen, H., Hochkirch, K. (2007), Development and application of a new form feature to
enhance the transport efficiency of ships, Jahrbuch Schiffbautechnische Gesellschaft, Springer
Harries, S., Abt, C., Heimann, J., Hochkirch, K. (2006), Advanced hydrodynamic design of container
carriers for improved transport efficiency, RINA Conf. Design & Operation of
Container Ships, London
Hochhaus, K.H. (2007), Umweltbetrachtungen zur Schiffahrt, Hansa 144/6, pp.70-76.
Hochkirch, K.; Bertram, V.: Slow Steaming Bulbouws Bow Optimization for a Large Containership,
Conf. Computer and IT Applications in the Maritime Industries (COMPIT), Budapest, pp.390-398.
Hollenbach, U., Friesch, J. (2007), Efficient hull forms – What can be gained, 1
Int. Conf. on Ship Effi-
ciency, Hamburg, http://www.ship-efficiency.org/2007/PDF/HOLL
Hollenbach, U., Klug, H., Mewis, F. (2007), Container vessels – Potential for improvements in hydrody-
namic performance, 10
Int. Symp. Practical Design of Ships and Other Floating Structures (PRADS),
Hoshino, T., Oshima, A., Fujita, K., Kuroiwa, T., Hayashi, F., Yamazaki, E. (2004), Development of
High-performance Stator Fin by Using Advanced Panel Method, MHI Technical Review 41/6, pp.1-4.
Hutchison, B., Hochkirch, K. (2007), CFD Hull Form Optimization of a 12,000 cu.yd. (9175 m3) Dredge,
Isensee, J.; Bertram, V.; Keil, H. (1997), Energy efficiency and air pollution: A comparison of ships and
other vehicles, FAST'97, Sydney
ITTC (1999), The specialist committee on unconventional propulsors, 22
Int. Towing Tank Conf.,
Junglewitz, A. (1996), Der Nabeneinfluß beim Schraubenpropeller, PhD thesis, Univ. Rostock.
Mewis, F., Hollenbach, U. (2007), Hydrodynamische Maßnahmen zur Verringerung des Energiever-
brauches im Schiffsbetrieb, Hansa 144/5, pp.49-58.
Lehmann, D. (2007), Improved Propulsion with Tuned Rudder Systems, 1
Int. Conf. on Ship Efficiency,
Liljenberg, H. (2006), Utilising Pre-swirl Flow – Reducing Fuel Costs, SSPA Highlights 2,
N.N. (1991), Propeller boss cap with fins (PBCF) allows more efficient ship propulsion, CADDET Result
N.N. (1992), Rudder horn-installed grim vane wheel reduces ship’s energy consumption, CADDET Re-
sult 116, http://lib.kier.re.kr/caddet/ee/R116.pdf
N.N. (2008a), Foul-release smoothes hull efficiency, Marine Propulsion, August/September, p.287.
N.N. (2008b), SkySails hails latest data, The Naval Architect , September, pp.55-57.
N.N. (2008c), Reblading to enhance economy and comfort, Marine Propulsion Feb/Mar, pp.54-55.
Ok, J.P. (2005), Numerical investigation of scale effects of a wake-equalizing duct, Ship Technology Re-
search 52, pp.34-53.
Rathje, H., Beiersdorf, C. (2005), Decision support for container ship operation in heavy seas – Ship-
board routing assistance, 4
Conf. Computer and IT Applications in the Maritime Industries (COMPIT),
Hamburg, pp.455-467. http://www.ssi.tu-harburg.de/doc/co
Schneekluth, H., Bertram, V. (1998), Design for Efficiency and Economy, Butterworth & Heinemann,
Ueda, N., Numaguchi, H. (2006), The first hybrid CRP-POD driven fast ROPAX ferry in the world, J.
Japan Inst. Marine Eng. 40/2, translated English version:
Van Oossanen, P., Heimann, J., Henrichs, J., Hochkirch, K. (2009), Motor yacht hull form design for the
displacement to semi-displacement speed range, 10
Int. Conf. Fast Sea Transportation (FAST), Athens