Fuel Saving Options for Ships

Volker BERTRAM, Germanischer Lloyd, Germany, volker.bertram@GL-group.com

Volker HPPNER, FutureShip, Germany, volker.hoeppner@GL-group.com

Abstract This paper gives a rather comprehensive survey on options for fuel savings for ships. The paper compiles and discusses options in hydrodynamics, machinery and operation as a guideline for designers, ship owners and charterers. Selected industry and research projects serve to illustrate the scope of options. 1. Introduction The present market is characterized by ship owners having to accept ship yards pursuing minimum building costs, rather than minimum life-cycle costs. For decades, ships have been designed for much lower fuel costs. In addition, the fuel bill is often paid by the charterer, the indirect costs due to the larger environmental impact is paid by the public, Isensee and Bertram (1999,2004). However, mid-term and long-term fuel prices are expected to range between 500 $/t and 1000 $/t and IMO (International Maritime Organization) is expected to pass regula-tions on CO2 (carbon-dioxide) ship emissions after 2012, adding pressure to reduce fuel consumptions. Ship operators will put pressure on ship owners to obtain fuel efficient ships. These in turn will put pressure on ship yards to supply fuel sufficient ships. As a result, we expect to see a paradigm shift in designs and refits to reduce fuel consumption in ships. 2. Reduce Emissions There are essentially two levers to reduce emissions: reduce emissions by using cleaner fuel and reduce fuel consumption as such. MARPOL Annex VI is aimed at controlling air pollution from gaseous emissions by ships. The sulfur limit for fuel oil currently lies at 4.5%, and in special emission control zones (SECA = sulfur oxides emission control area) like the North Sea and the Baltic Sea at 1.5%. MEPC58 agreed to a long-term plan to cut sulfur oxide emissions even further, and the sulfur content of fuel will be lowered gradually to 0.5% globally by 2020 and 0.1% in SECAs by 2015. The ships masters therefore have to keep a watchful eye on where they use what kind of fuel. Specifi-cally for single-fuel ships with one settling and one service tank, timely conversion from a fuel type with a high sulfur content to one with a maximum sulfur content of 1.5% before entering a SECA is essential, Krapp and Wilken (2007). Another possibility to fulfill SECA requirements is the use of an approved technology to reduce the ships total sulfur oxide emissions to below 6 g/kWh. Such a technology may evolve in the form of exhaust gas scrubbing which has been under investigation on P&O ferries since 2007. However, scrubbing results in carbon dioxide and adds acidity to the sea water, even if the concentration is very low. Generally, we believe that sulfur removal at the source (e.g. in the form of low-sulfur fuel) is preferable. In European waters, ships at berth will be required to use fuel with maximum 0.1% sulfur content starting from 1 January 2010. This could result in three types of fuel for ships in worldwide operation calling at European ports. More SECAs and low sulfur re-quirements for engine operation in port are likely to come. Emissions may be reduced by a variety of cleaner fuels. Apart from cleaner diesel fuels, the following options are at present under discussion:

Gas (particularly LNG) may be used in gas motors or dual fuel engines. Bio-fuels reduce sulfur oxide emissions.

Bio fuels and synthetic fuels would reduce sulfur oxide emissions. Hydrogen burnt in fuel cells may eventually lead to zero-emission ships. A technology demonstrator for

this future technology is the Alsterwasser, a zero-emission ship operated on the lake Alster in Ham-burg for tourist transport.

Fig.1: Concept study of gas fuelled cargoship Fig.2: Alsterwasser Hydrogen fuelled For newbuildings, ship design should already consider corresponding additional equipment like tanks, equipment for shore-supplied electrical power in port, etc. In the Fuel Change-over Manual developed by GL, the individual technical characteristics of a ship are considered and the crew and management are supported with the planning and execution of the fuel change-over. 3. Reduce Fuel Consumption There are 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, Klug and Mewis (2006), 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. We will discuss more comprehensively the available options in the following, but recommend them nevertheless for further studies. 3.1. 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. 3.1.1. Reduce resistance There are many ways to reduce the resistance of a ship. On the most global level, there are two (almost trivial) options:

- 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. 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.

B/5 B/5hold partially used for gas tanks

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 pith 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.

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, Fig.3, 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, Fig.4. 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 m is very good, AHR = 150 m standard, and AHR > 200 m sub-standard, Hollenbach and Friesch (2007). As a rule of thumb, every 25 m 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. The super micro bubbles are small enough to have negligible buoyancy. In 2008, sea trial with the ACS Demonstrator, a 2550 tdw cargo ship, commenced, NN (2009a). The considerable technical effort is most attractive for large, slow ships. Subsequently, Germanischer Lloyd and DK Group have announced a project to develop jointly an energy-efficient 200000 tdw bulk carrier. 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 themselves.

Fig.3: Massive fouling on ship Fig.4: Low surface energy coating under the microscope

- 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 (2000). A formal optimization is recommended as this may offer 1-2% improvement even on hulls that are deemed already optimized in limited form variations with CFD and model tests in model basins, Fig.1, Abt and Harries (2007). This option 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 based on a fuel price of 500 $/t, but it is frequently problematic to obtain original hull

descriptions. Service providers such as classification societies or model basins cannot divulge proprietary lines of one client (shipyard) to another (ship owner).

Fig.5: Bulb optimization by CFD, source: www.fsopt.com Fig.6: Modified lines to reduce flow

separation, source: HSVA

- 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.

Fig.7: Oblique flow at rudder creating drag Fig.8: Twisted rudders (continuous, discrete)

- Rudder resistance: 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 degree rudder angle) encounter oblique flow angles to one side at the upper part and to the other side in the lower part, Fig.7. This creates opposing lift forces which cancel each other, but the associated induced drag forces add. By twisting the rudder these unnecessary drag forces can be reduced, Fig.8. Compared to a conventional semi-balanced rudder, a twisted rudder with Costa bulb may have 4% lower power consumption, Fig.9, 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, Fig.10, e.g. N.N. (2004), 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.

Fig.9: Twist-rudder with Costa bulb, Source: HSVA Fig.10: High-efficiency rudder, Source: Wrtsil

- Added resistance due to seaway: Intelligent routing (i.e. optimization of a ships course and speed) may reduce the average added resistance in seaways. For example, the Ship Routing Assistance system, Rathje and Beiersdorf (2004), 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, Fig.11. 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.

Fig.11: Wind tunnel and CFD investigation of containership configurations

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 Hollenbach (2007). Systematic model tests or CFD simulations are recommended to assess the best trim and the effect of different trim conditions.

3.1.2. 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, 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), Fig.12. 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).

Fig.12: Controllable pitch propeller Source: Schottel

Fig.13: Hub vortex and tip vortex showing rotational losses and

- Reduce rotational losses: For most ships, there is substantial rotation energy lost in the propeller slipstream, Fig.13. 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, Fig.14, 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, Fig.15, Grim (1980), 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, Fig.16, and rudder thrust fins, Fig.17. 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.

Fig.14: SVA pre-swirl devices: Pre-swirl fin (left), pre-swirl stator blades (center), asymmetric aftbody (right)

Fig.15: Grim vane wheel; original (left) and modified (right)

Fig.16: Post-swirl stator fins Fig.17: Rudder thrust fins 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, Fig.18, Schneekluth and Bertram (1998). More recently, podded drives and conventional propellers have been combined to hybrid CRP-POD propulsion, Fig.19, Ueda and Numaguchi (2006), claiming 13% fuel savings.

Fig.18: Contra-rotating propeller (CRP) Fig.19: CRP pod arrangement

- 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. The propeller surface should be kept smooth to keep the frictional resistance of the blades low. Propeller polishing and edge repair, Fig.20, may save up to 5% in fuel consumption.

Fig.20: Propeller before (left) and after (right) polishing and edge repair

- 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, Fig.13. 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 geometry of the tip fin, ITTC (1999), namely contracted and loaded tip (CLT) propellers (with blade tips bent sharply towards the rudder), Hollstein et al. (1997), Fig.21, Sparenberg-DeJong propellers (with two-sided shifted end plates), Sparenberg and De Vries (1987), Jong et al. (1992), or Kappel propellers (with integrated fins in the tip region), Andersen (1996), Andersen et al. (2002). For the CLT, 16% fuel savings were reported for refitted tankers and bulkers.

Fig.21: Tip-fin propellers: CLT (left), Sparenberg-DeJong (ceneter), Kappel (right)

- Reduce hub vortex losses: Devices may be added to the propeller hub to suppress the hub vortex, Fig.22. These devices may offer cost effective fuel savings, Atlar and Patience (1998). Propeller boss cap fins (PBCF) were developed in Japan, Fig.23, Gearhart and McBride (1989), 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, Ouchi (1988,1989), Ouchi and Tamashima (1989), Ouchi et al. (1988,1989,1992). 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), Fig.24, jointly developed by SVA Potsdam and Schottel, offers an alternative to PBCF, Schulze (1995). 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 efficiency.

Fig.22: Tip vortex on conventional propeller (left) and suppressed by PBCF (right)

Fig.23: Propeller Boss Cap Fins Fig.24: Hub Vortex Vane

- 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)), Fig.25, Schneekluth (1986), Sumitomo Integrated Lammeren Duct (SILD), Fig.26, Grothues spoilers, Fig.27, vortex generators, Schneekluth and Bertram (1998), may therefore improve propulsion and save fuel.

Fig.25: Wake-equalizing duct (Schneekluth) Fig.26: SILD

For existing ships, despite several refits more recent independent analyses come to contradicting evaluations of the effectiveness of WEDs, Ok (2005), Celik (2007). 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). Mewis (2008) proposes to combine a wake equalizing duct with a pre-swirl fin, Fig.28.

Fig.27: Grothues spoilers Fig.28: Pre-swirl duct

3.1.3. 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%. 3.2. Reduce required power for equipment on board There are various options to save power in the assorted energy consuming equipment onboard ships. The sav-ing 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 lighting rooms down again. 3.3. Use fuel energy more efficiently for propulsion and on-board equipment Ship engines convert only up to 50% of the fuel energy into propulsive power, Fig.29. Approximately 25% of the fuel energy is lost in the exhaust heat and another 25% in the cooling water. There are various approaches to recuperate some of these energy losses, Hochhaus (2007). Exhaust heat may be used for steam generation or to fuel deep-freeze absorption chillers. Hot coolant may be used to produce fresh water from sea water. Avoid oversized main engines. Sea margins should be adapted to ship type, ship size and intended operational trade. For example, 7-8% sea margin may suffice for large containerships. The sea margin may be selected based on standard seakeeping analyses or in standard cases also based on experience. The frequently added engine margin may be omitted altogether. Ships are often operated at considerably lower speeds than the design speed, but operators want to keep the capability for occasional high speed. The required margins for such occa-sional high-speed operator are expensive and may be better covered by falling back on the auxiliary engine

power (power take-in (PTI) via shaft generator) on the rare occasion when high speed is needed. Detailed engi-neering analyses can be used to assess feasibility and cost aspects of alternative configurations, Fig.30. For slow-steaming ships with controllable pitch propeller, it is better to reduce the brake mean effective pressure than the rpm. If the ship shall be operated at lower speeds for a longer period the engine may be adapted to the mean effective pressure by changing the fuel injection system or installing an exhaust turbocharger. Intelligent monitor-ing 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.29: Sankey diagram for main engine, source: Wrtsil

Fig.30: Simulation model of engine configura- tion to assess fuel consumption based on operational profile

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 con-sumptions for provided energy consumer profile, Fig.30. These simulations allow assessment of alternatives and ultimately better balanced energy profiles. 3.4. Substitute fuel power (partially) by renewable energies like wind and solar energy Wind has been the predominant power source for ships until the late 19th century. Wind-assistance has enjoyed a recent renaissance. Wind-assisted ships, Fig.30, 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 requirements, 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 commercial maturity by the company Skysails, Fig.31, drawing also on expert advice from Germanischer Lloyd. Kites harness wind power at larger heights without the stability penalties of high masts. The development 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. (2008). 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

G 1

Qdot_ab

P_e

P_mech Messwerte_P_e

G 5

Qdot_ab

P_e

P_mech Messwerte_P_e

Leistung

Leistung

Engine

T_ER

P_ER

Skalar1

Skalar3

Skalar2

VektorOut

T_See

Tu

Pu

sTX_9L_1

Library

sTX_9L_1

LibraryP_Nutz

T_nt

mdot_L Qdot_Abgas

T_KW

mdot_Br

Qdot_KW

T_in

sTX_7L_5

Library

sTX_7L_5

LibraryP_Nutz

T_nt

mdot_L Qdot_Abgas

T_KW

mdot_Br

Qdot_KW

T_in

HFOmdot_Br1

mdot_Br2

mdot_Br3

mdot_Br4

mdot_Br5

mdot_Br6

n_HM

Leistung

P_ER

T_nt

n_HM

P_Nutzmdot_Br

Q_Abgas

mdot_L

T_HT_KW

mdotAbgas

Qdot_HT_KW

T_in

Qdot_LT_KW

Skalar1

Skalar2 VektorOut

sTX_9L_2

Library

sTX_9L_2

LibraryP_Nutz

T_nt

mdot_L Qdot_Abgas

T_KW

mdot_Br

Qdot_KW

T_in

G 2

Qdot_ab

P_e

P_mech Messwerte_P_e

G 3

Qdot_ab

P_e

P_mech Messwerte_P_e

G 4

Qdot_ab

P_e

P_mech Messwerte_P_esTX_7L_4

Library

sTX_7L_4

LibraryP_Nutz

T_nt

mdot_L Qdot_AbgasT_KW

mdot_Br

Qdot_KW

T_in

sTX_7L_3

Library

sTX_7L_3

LibraryP_Nutz

T_nt

mdot_L Qdot_Abgas

T_KW

mdot_Br

Qdot_KW

T_in

Leistung

Leistung

Leistung

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.30: Wind-assisted cargo ship Fig.31: Towing kite harnessing wind energy, source: www.skysails.de

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, Fig.7. For other ships, diesel and solar energy may be combined. In 2009, a Japanese car carrier was equipped with solar panels covering around one quarter of the ships open deck, but producing just 40 kW of the power (as compared to 13240 kW of the main engines), NN (2009b). However, the installation is seen as a test and more efficient solar panels could contribute larger shares of on-board power in the future. 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 ferry operated in Sydney, Fig.33.

Fig.32: Solar catamaran Alstersonne, Source: www.kopf-solarschiff.de

Fig.33 : SolarSailor, source : www.solarsailor.com

4. Conclusion 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 required.

Despite these words of caution, there is wide consensus that significant potential for fuel saving exists and service providers like Classification societies can support ship owners and operators in tapping into these potentials. ACKNOWLEDGEMENTS

Many colleagues at Germanischer Lloyd have supported this paper with their special expertise, namely (in al-phabetical order) Bettar El Moctar, Malte Freund, Andreas Junglewitz, Reinhard Krapp, Ralf Plump, Gerd-Michael Wrsig. References ABT, C.; HARRIES, S. (2007), A new approach to integration of CAD and CFD for naval architects, 6th Conf. Computer and IT Applications in the Maritime Industries (COMPIT), Cortona, pp.467-479. http://www.ssi.tu-harburg.de/doc/compit/compit2007_cortona.pdf ANDERSEN, P. (1996), A comparative study of conventional and tip-fin propeller performance, 21st Symp. Naval Hydrodynamics, Trondheim ANDERSEN, P.; FRIESCH, J.; KAPPEL, J. (2002), Development and full-scale evaluation of a new marine pro-peller type, Jahrbuch Schiffbautechnische Gesellschaft, Springer ATLAR, M.; PATIENCE, G. (1998), An investigation into effective boss cap designs to eliminate hub vortex cavi-tation, PRADS, The Hague BEEK, T. van (2004), Technology Guidelines for Efficient Design and Operation of Ship Propulsors, Marine News, Wrtsil. http://www.wartsila.com/Wartsila/global/docs/en/ship_power/media_publications/marine_news/2004_1/technology.pdf BERTRAM, V. (2000a), Practical Ship Hyrodynamics, Butterworth and Heinemann, Oxford. BERTRAM, V. (2000b), Past, present and prospects of antifouling methods, 32nd WEGEMT School, Plymouth, pp.85-97. CELIK, F. (2007), A numerical study for effectiveness of a wake equalizing duct, Ocean Engineering 34, pp.2138-2145. http://202.114.89.60/resource/pdf/642.pdf FRIEDHOFF, B. (2006), Optimierung des Treibstoffverbrauchs und Simulation des Betriebs von RoRo-Schiffen auf Routen mit geringen Wassertiefen, Jahrbuch der Schiffbautechnischen Gesellschaft, Springer, pp.46-48. GEARHART, W.S.; McBRIDE, M.W. (1989), Performance assessment of propeller boss cap fin type device, 22nd ATTC, St. Johns GRIM, O. (1980), Propeller and vane wheel, J. Ship Research 24/4, pp.203-226. HOCHHAUS, K.H. (2007), Umweltbetrachtungen zur Schiffahrt, Hansa 144/6, pp.70-76. HOLLENBACH, U.; FRIESCH, J. (2007), Efficient hull forms What can be gained, 1st Int. Conf. on Ship Effi-ciency, Hamburg.http://www.ship-efficiency.org/2007/PDF/HOLLENBACH_FRIESCH.pdf HOLLENBACH, U.; KLUG, H.; MEWIS, F. (2007), Container vessels Potential for improvements in hydrody-namic performance, 10th Int. Symp. Practical Design of Ships and Other Floating Structures (PRADS), Houston.

HOLLSTEIN, H.J.; GOMEZ, G.P.; GONZALEZ-ADALID, J. (1997), Bulk carrier speed trials with a Sistemar CLT propeller, The Naval Architect, February, pp.33-36. 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. http://www.mhi.co.jp/en/technology/review/pdf/e416/e416334.pdf ISENSEE, J.; BERTRAM, V. (1999), Environmental impact of fast ships, High-Performance Marine Vehicles Conf. (HIPER), Zevenwacht, pp.102-110. ISENSEE, J.; BERTRAM, V. (2004), Quantifying external costs of emissions due to ship operation, J. Eng. Mari-time Environment 218, pp.41-51. ITTC (1999), The specialist committee on unconventional propulsors, 22nd Int. Towing Tank Conf., Seoul, http://ittc.sname.org/Unconventional_Propulsion.pdf JONG, K. de; SPARENBERG, J.A.; FALCAO de CAMPOS, J.A.C.; GENT, W. van (1992), Model testing of an optimally designed propeller with tow-sided shifted end plates on the blades, 19th Symp. Naval Hydrodynamics, Seoul, pp.461-475. JUNGLEWITZ, A. (1996), Der Nabeneinflu beim Schraubenpropeller, PhD thesis, Univ. Rostock. KLUG, H.; MEWIS, F: (2006), Minimising fuel consumption, Shipping World & Shipbuilder, pp.42-46. KRAPP, R.; WILKEN, M. (2007), The influence of regional and local fuel quality requirements on ship operation, Hansa 144/2, pp.40-42. LEHMANN, D. (2007), Improved Propulsion with Tuned Rudder Systems, 1st Int. Conf. on Ship Efficiency, Ham-burg. http://www.ship-efficiency.org/2007/PDF/LEHMANN.pdf LILJENBERG, H. (2006), Utilising Pre-swirl Flow Reducing Fuel Costs, SSPA Highlights 2, http://www.sspa.se/sites/www.sspa.se/files/hl2-06.pdf MEWIS, F. (2008), Development of a novel power-saving device for full-form vessels, Hansa 145/11, pp.46-50 MEWIS, F.; HOLLENBACH, U. (2007), Hydrodynamische Manahmen zur Verringerung des Energiever-brauches im Schiffsbetrieb, Hansa 144/5, pp.49-58. N.N. (1991), Propeller boss cap with fins (PBCF) allows more efficient ship propulsion, CADDET Result 84, http://lib.kier.re.kr/caddet/ee/R084.pdf N.N. (1992), Rudder horn-installed grim vane wheel reduces ships energy consumption, CADDET Result 116, http://lib.kier.re.kr/caddet/ee/R116.pdf N.N. (2004), Efficiency rudder, Wrtsil http://www.wartsila.com/Wartsila/global/docs/en/ship_power/media_publications/brochures/product/propulsors/efficiency_rudder.pdf N.N. (2008a), Reblading to enhance economy and comfort, Marine Propulsion Feb/Mar, pp.54-55. N.N. (2008b), SkySails hails latest data, The Naval Architect , September, pp.55-57. N.N. (2008c), Foul-release smoothes hull efficiency, Marine Propulsion, August/September, p.287. N.N. (2009a), Feel it coming in the air, The Naval Architect , January, pp.26-27.

N.N. (2009b), A little ray of sunshine, The Naval Architect , January, pp.26-27. OK, J.P. (2005), Numerical investigation of scale effects of a wake-equalizing duct, Ship Technology Research 52, pp.34-53. OUCHI, K. (1988), Research and development of PBCF (propeller boss cap fins) to enhance propeller efficiency, The Motor Ship 10th Int. Marine Propulsion Conf., London OUCHI, K. (1989), Research and development of PBCF Improvement of flow from propeller boss, Int. Symp. Ship resistance and Powering performance (ISRP), Shanghai OUCHI, K.; TAMASHIMA, M. (1989), Research and development of PBCF New and practical device to en-hance propeller efficiency, PRADS89, Varna OUCHI, K.; OGURA, M.; KONO, Y.; ORITO, H.; SHIOTSU, T.; TAMASHIMA, M.; KOIZUKA, H. (1988), A re-search and development of PBCF (propeller boss cap fins) Improvement of flow from propeller boss, J. Soc. Naval Arch. Japan 163 OUCHI, K.; TAMASHIMA, M.; KAWASAKI, T.; KOIZUKA, H. (1989), A research and development of PBCF (pro-peller boss cap fins) 2nd report: Study on propeller slipstream and actual ship performance, J. Soc. Naval Arch. Japan 165 OUCHI, K.; TAMASHIMA, M.; KAWASAKI, T.; KOIZUKA, H. (1992), Research and development of PBCF (pro-peller boss cap fins) Novel energy-saving device to enhance propeller efficiency, Naval Arch. And Ocean Eng. 28, Ship and Ocean Foundation RATHJE, H.; BEIERSDORF, C. (2005), Decision support for container ship operation in heavy seas Shipboard routing assistance, 4th Conf. Computer and IT Applications in the Maritime Industries (COMPIT), Hamburg, pp.455-467. http://www.ssi.tu-harburg.de/doc/compit/compit2005_hamburg.pdf SCHNEEKLUTH, H. (1986), Wake equalizing duct, The Naval Architect 103, April, pp.147-150. SCHNEEKLUTH, H.; BERTRAM, V. (1998), Design for Efficiency and Economy, Butterworth & Heinemann, Oxford. SCHULZE, R. (1995), SVA-Nabenkappenflossen fr Schiffspropeller, Report 2218, SVA Potsdam. SPARENBERG, J.A.; de VRIES, J. (1987), An optimum screw propeller with endplates, Int. Shipbuilding Pro-gress 34/395, pp.124-133. 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: www.mesj.or.jp/mesj_e/english/pub/ap_papers/pdf/2006AP4.pdf