sustainable energy for the marine sector

Energy Policy 49 (2012) 333–345

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Sustainable energy for the marine sector

Julio Vergara a,n, Chris McKesson b, Magdalena Walczak c

a Pontificia Universidad Catolica de Chile, Santiago, Chileb University of New Orleans, New Orleans, LA, USAc Pontificia Universidad Catolica de Chile, Santiago, Chile

H I G H L I G H T S

c We projected CO2 emissions for different ship types by mid century.c We applied a set of technologies/policies to reduce the 2050 emissions to a 450 ppm using wedges.c Existing technologies/policies can cope with about 60% of the task.c Further technologies are needed to achieve the share of responsibility for marine CO2 reductions.

a r t i c l e i n f o

Article history:

Received 25 May 2011

Accepted 14 June 2012Available online 24 July 2012

Keywords:

Marine transportation

Propulsion

Sustainable energy

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ail address: [email protected] (J. Vergar

a b s t r a c t

Most scientists agree that climate change is affected by anthropogenic factors, and measures to reduce carbon

dioxide emissions are being considered among countries. The maritime transportation sector must bear its

share of responsibility for adopting corrective innovative measures on a global scale. The authors projected

the energy consumption and emissions of different marine transportation types in 2050 and applied the

model of stabilization wedges to explore activities and technologies to deduce policies that would lead to

sustainable marine propulsion. Three percent of the global emissions reductions -about 44 GtCO2/y- required

to stabilize the temperature under 2 1C above current levels must come from the maritime sector. To meet a

reduction target of this segment, about 1.67 GtCO2/y in 2050, we propose a range of technologies that include

mission refinement, resistance reduction, prime mover and propulsion innovation, and new fuels. The

authors find that the goal is partially attainable and proposes the balance to be delivered by dedicated land-

based synfuel refineries that use carbon dioxide from coal power plants and hydrogen produced from

sustainable sources, an approach that would extend the lifecycle of conventional prime movers. We await the

adoption of suitable technologies to reduce the emissions in the maritime sector.

& 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Although climate change has occurred since the creation of theEarth (Ramstein and Ciais, 2004), today it represents a setback toa society that grew in the last two centuries to over 7 billion (UN,2012) with an associated energy demand based primarily on theconsumption of fossil fuels. The global population is expected topeak at 9.2 billion around 2075, while social development isdesired to continue.

Climate change has been magnified by anthropogenic activ-ities (Houghton, 2004). In the latest assessment report (AR4), theIntergovernmental Panel on Climate Change (IPCC, 2008) statesthat such climate interference is mainly caused by CO2 emissions,

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ıa Mecanica y Metalurgica,

cia Universidad Catolica de

rreo 22, Santiago, Chile.

a).

among other greenhouse gas (GHG) emissions from industrialactivities. About two thirds of GHGs are due to energy relatedactivities, including transportation, while the other third is mostlylinked to land use change for food production and urbanization,and waste management practices.

According to AR4, the primary effects of climate change arerise of global temperature, variations in precipitation patterns andsea level rise. These changes may lead to international securityinstability once the effects arise, exceeding the carrying capacityof the planet and probably leading to a population disruption(Meadows et al., 2004).

Worldwide energy use has risen since the industrial revolutionto exceed 500 ExaJoules (EJ) per year, four fifths of which is basedon hydrocarbon fuels, with current per capita GHG emissions atabout 4 tCO2 per year. Since the industrial revolution, atmo-spheric CO2 concentration has risen from about 280 to 390 ppm(ppm), under a complex set of causes, mostly from burning fossil-fuel, plus deforestation and land-use change, which would reach arange from 500 to 1000 ppm by 2100 (IPCC, 2008).

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J. Vergara et al. / Energy Policy 49 (2012) 333–345334

Global GHG emissions have risen sharply since the industrialrevolution. In the past two centuries, more than 2.3 trillion tonnesof CO2 (tCO2) have been released into the atmosphere, mostly dueto fossil fuel consumption and changes in land-use, with morethan half the release accruing since the 1980’s. Canadell et al.(2007) estimated that 1.2 trillion tCO2 have been released due tofossil fuel and cement emissions in the past 150 years, with 600billion tCO2 due to land-use-change emissions, mostly by tropicaldeforestation. Baumer et al. (2005) suggested that all energyforms account for about 64% of the total emissions. The remaining36% arises from non-energy sources such as land-use change,livestock, agriculture soils and waste landfields. Fig. 1 showsenergy alternatives by primary source and use, and global GHGemissions by sector, highlighting the ship transport emissions.

A survey by Raupach et al. (2007) accounts emissions fromfossil-fuel combustion and industrial processes approaching 29billion tCO2 (GtCO2) in 2005. According to EIA (2011) energyrelated CO2 emissions exceeded 30 GtCO2 in 2008 with further5.5 GtCO2 per year from non-energy sources. Based on thesetrends energy related GHG emissions are expected to be about44 to 48 GtCO2 in 2020.

2. Marine energy and emissions

Fossil fuels have dominated in energy consumption becauseof their density, flexibility and the establishment of global trans-portation logistics, in spite of the environmental consequences.These fuels are of special relevance in the maritime sector.

Fig. 1. Primary energy sources and GHG emissions b

Fig. 2. Family of civilian and military ships (authors work integrated from IMO

Marine vehicles are typically categorized as: (a) commercialships (cargo, passenger and special purpose), (b) military ships(warships, submarines and auxiliary), and (c) other ships (pleasure,rescue, off-shore supply, etc.). Commercial ships are the largestcategory, and include both international and domestic ships, custo-marily divided into coastwise and ocean-going ships. We estimatedan overall fleet of about 103,700 ships of very different sizes andclasses, with 97.7% being civilian units of total cargo capacity ofabout 1.16 trillion tons, distributed as presented in Fig. 2.

In the civilian fleet, smaller ships typically consume diesel oil,while heavier fuel oils propel larger and slower cargo vessels.Nuclear propulsion is used in a distant second place with only afew nuclear-powered icebreakers operating in the Murmansk. Farbehind remains wind energy that once dominated the oceans. It isused in a dozen training tall ships and cruise vessels.

Energy Information Administration (EIA, 2011) estimated thatalmost 100 EJ are consumed yearly in all transportation means,96% of which are in the form of oil products. This corresponds toabout one fifth of the total primary energy supply (TPES). Lessthan 10% of the transport fuel consumption is burned in themaritime sector.

Eyring et al. (2005) estimated fuel consumption for seagoingcivilian and military ships at about 11.7 EJ for the year 2001 whileEndresen (2007) estimated this fuel consumption at approximately8.4 EJ for the same year, excluding nuclear-powered ships and wind-powered training vessels. For the year 2006, International EnergyAgency (IEA, 2009a,b) estimated 9.2 EJ of energy use for maritimetransport, with a range between 7.7 and 12.6 EJ. Later, InternationalMaritime Organization (IMO, 2009) developed a comprehensive

y energy source, including ship transportation.

(2009), Lloyd’s (2007), Equasis (2011), UNCTAD (2007) and other sources).

Fig. 3. Marine fuel oil consumption and emissions (solid line – estimated, dashed

line – projected).

J. Vergara et al. / Energy Policy 49 (2012) 333–345 335

report for international shipping accounting 13.9 EJ, with a lowerbound of 11.7 EJ and a higher bound of 16.7 EJ for the year 2007,excluding the naval sector. Based on historical data and regressionanalysis, taking into consideration the recent crisis, a value of about15.2 EJ, including the military sector, can be estimated for the year2010. This value corresponds to 3.1% of global primary energysupply and 10.7% of world oil final consumption—fractions thatappear to increase slightly every year, coincident with the risingdemand for transportation in today’s global economy. Marine fuelconsumption represents almost 17% of the entire transportationenergy and 4.6% of the total final energy consumption (TFEC).At moderate growth rates, in a business as usual mode, we estimatefuel consumption in the maritime sector of about 19.1 EJ for theyear 2020.

The challenges of emissions reduction in the maritime sectordiffer considerably from those in land based power systems.Today’s global electricity system relies mainly on base load coalplants (41%), the most intense CO2 emitters, followed by naturalgas and oil (27%), hydroelectricity (16%), nuclear power (14%) andrenewables. Improved power cycles (i.e., combined and regen-erative cycles, supercritical steam plants, etc.) would contributeto moderate carbon emissions. Advanced coal plants are expectedto include CO2 capture devices – with some thermal efficiencyloss – along with sequestration policies and possibly recycle intoliquid fuels with the addition of hydrogen. Alternatively, coal maybe substituted with low carbon technologies such as nuclearpower, hydro power and other renewables. Other energy sectorsmay improve through efficiency augments. The non-energy emis-sions could be reduced by reforestation, soil improvement, live-stock reduction and waste management. Only a few of thesetechnologies are relevant in the marine environment.

Considering emissions in the maritime sector, Fuglestvedt et al.(2008) projects that 30–50% of total CO2 emissions would comefrom the transport sector in 2050. In 2005, the transportation sectorwas responsible for about 13.5% of the total emissions, of which 8%was international marine, i.e., a value of 460 million tCO2 (MtCO2).estimated total emissions from national and international transportat about 700 MtCO2 in 2006. Eyring et al. (2005) estimated emis-sions for seagoing civilian and military ships at about 813 MtCO2 in2001, while Endresen (2007) estimated emissions for main sea-going civilian ships at 634 MtCO2 in 2002. IMO (2009) accountedemissions for international shipping as 1,054 MtCO2 for the year2007, in addition to other gases in lower quantities. This reportexcludes the naval sector, which is more diversified and innovativein hull forms and prime movers. Based on historical data andregression we estimated an overall value of about 1115 MtCO2 forthe year 2010. This value includes about 44 MtCO2/y from militaryships. The largest aircraft carriers and submarines are nuclearpowered. Had those been powered by fossil fuels, the count formilitary ships would have increased to about 63 MtCO2/y. Atbusiness as usual growth rates we estimate GHG emissions ofabout 1480 MtCO2 for 2020, as represented in Fig. 3, which maydouble current emissions by 2030.

The United Nations Framework Convention on Climate Change(UNFCCC) adopted the Kyoto Protocol, in force since 2005 andratified by 194 Parties, in which the Annex I countries agreed toreduce their emissions of several GHGs including CO2 by anaverage of 5.2% below 1990 levels in the years 2008–2012,applying various mechanisms. Although the UNFCCC deals withemissions from transport means, the Kyoto Protocol recommendsParties to arrange reductions through the International CivilAviation Organization (ICAO) for aviation and IMO for maritimetransport. In the marine side, there is a debate whether transportemissions reductions should be left to Annex I Parties or requireddirectly to ships, regardless of their origin, which is a complextask to manage.

The conference of the parties on climate change (COP-15) heldin Copenhagen in 2009, reached a limited outcome; however, itconsidered an ambitious target below 450 ppm. Although theseinitiatives are initial steps, they seem to have a limited scope andrange for the purpose of climate stabilization.

3. Marine energy options and strategy

Transportation is essential to modern society: our daily lifedepends on timely transport to work, study and other activities.The marine component is less energy intensive than a typical carper unit of payload transport, but it is responsible for activitiesthat deeply support our economies; therefore, transportationneeds to be sustainable—an attribute which is tough to define.Sustainable development was defined by the World Commissionon Environment and Development – the Brundtland Commission– as ‘‘one that meets the needs of the present without compro-mising the ability of future generations to meet their own needs’’(WCED, 1987). It is usually represented by the intersection ofsocial, economic and environmental developments, and requiresthat the energy needed for this purpose be in turn sustainable. Inthis paper, we define Sustainable Energy as an array of energysystems with a long-term resources base, in which energy isconverted with the least environmental impact during its life-cycle, and which deliver at reasonable cost for the benefit of userswith maximum energy coverage. Energy demand, includingtransportation, would be probably constrained by GHG emissions.Then, consumption should drift away from fossil fuels, creating acontinuous transition toward sustainable energy forms.

Several authors and committees have researched advancedand sustainable technologies for marine use, but not as many asfor land-based propulsion and automobiles. We noted a fewstudies: Eyring et al. (2005) has estimated fossil-fuel emissionsand the impact of technologies. The U.S. Navy delivered a reporton propulsion technologies with options for reducing oil usebefore the U.S. House Armed Services Committee (O’Rourke,2006). Hobson et al. (2007) headed a Newcastle University reporton reduced carbon commercial ships for the U.K. Department forTransport. Veldhuis (2007) analyzed the application of hydrogenpowered systems in high speed vessels. Endresen (2007) has alsomodeled on ocean shipping emissions. Vergara and McKesson(2002) analyzed nuclear powered propulsion as a GHG-freetechnology for high performance cargo ships. Jacobs (2007) and


Sawyer et al. (2008) studied the use of nuclear propulsion forconventional containership trades. Several other researchers areproducing concepts aimed to save energy or power small craftswith solar, wind and wave resources.

These studies have proposed advanced technologies for reducedemissions but have not estimated the potential impact on stabiliza-tion of climate change. The international transportation sector isparticularly complex as compared with other segments affected bythe necessity of reducing emissions. Any activity within countryborders is subject to national policies regarding cuts. Borderingcountries may also establish some related sender-user arrange-ment. However, distant transportation needs a uniquely globalapproach. We propose that international maritime cargo shouldfollow a path similar to what international agreements are sup-posed to convey at a national level. This requires the reduction ofcarbon emissions through an integrated array of options, includinglow carbon technologies and energy efficiency measures.

Pacala and Socolow (2004) have suggested a technique based onthe concept of global emissions stabilizing wedges, each one ofwhich makes a contribution to moderate global temperature,although these wedges do not refer directly to countries oreconomic sectors. At a global scale, stabilization wedges representa strategy to arrest the rise of global average temperature byapplying known technological measures. If the GHG emissions arenot limited, the average temperature is expected to rise from 1.1 to6.4 1C by 2100, with respect to the 1980–1999, depending on theIPCC SRES scenario that our society chooses (IPCC, 2008). However,one of the outcomes of the Copenhagen Accord was the politicalrecognition of the scientific view that the increase in mean globaltemperature should be kept below 2 1C thus preventing dangerousanthropogenic interference with the climate system (COP, 2010), avalue that corresponds roughly to stabilizing atmosphere GHG at amaximum concentration level of about 450 ppm, as shown theupper right box in Fig. 4. For that to happen, the yearly emissionsneed to follow a WRE (Wigley, Richels, Edmonds)-450 curve(Wigley et al., 1996), peaking around 2020 and subsequently

Fig. 4. Global CO2 emission trajectories to stabiliz

declining to about 60% of today’s level by 2050 and keep decreasingafter that, while global population and overall economic productioncontinue to increase, pushing further technological innovation inenergy systems. The strategy developed by Pacala and Socolowinvolves cutting emissions from a projected scenario, so-called BAU,to a needed stabilization scenario, in this case the WRE-450 curve.

It must be noted that achieving the 450 level is a complex task,in a field that does not have a universally accepted scientificground and that has not yet agreed a global political commitment,especially if we consider that today’s concentration level willapproach 400 ppm by this decade. Nonetheless, the stabilizationwould be accomplished by reducing annual emissions fromalmost 63 to about 18 GtCO2 by 2050, a formidable task. Con-sidering that no single action would drive the emissions level tothe target the combined effect of several different actions has tobe taken into account with each action representing one ‘‘wedge’’of the total. To illustrate the immense effort needed, nearly tenthousand photovoltaic power plants of 200 MWP each (roughlyone half of the current installed electric capacity) would representa single wedge providing only about 1/7th (Pacala and Socolowused seven identical wedges) of the global CO2 reduction.

Our goal in this paper is to describe an array of sustainablemarine energy options that could reduce operational CO2 emis-sions leading to cap the temperature increase in an amountproportional to the emission load, with focus on the operationalenergy and emissions side of marine propulsion. (A comprehen-sive assessment of sustainability issues concerning the industry isbeyond our scope and it would need to include life cycle analysisfor the sector).

Reducing emissions in the marine environment is more com-plex than in land-based power plants, both technically andeconomically due to the mobile and atomized nature of theemitters, and the space and weight restrictions in ships. There isan additional political complexity in that ships are often regis-tered under flags of convenience, independent of the countriesthat control their operations, whereas the ten major open registry

e temperature increase (adapted from IPCC).

Fig. 6. Design factors and sources of improvement for cargo ships.


flags are not Annex-I countries. In fact, less than 1/4 of the cargocapacity is currently within Annex-I countries, which hinder theapplication of GHG mitigation techniques. Our purpose in thispaper is to equip policy makers with the knowledge that viabletechnological solutions exist, so that the best implementationpolicies can be formulated.

3.1. Mitigation strategy

Our fundamental assumption is that all industrial sectors shouldcontribute proportionally to reducing global GHG emissions. Wehave chosen to adopt a modified Pacala and Socolow model of‘‘stabilization wedges’’ for the maritime sector. Therefore, thissector would be responsible for about 3% of total emissions, and3% of total emission reductions. The proposed mitigation strategy,shown in Fig. 5, uses a scale reduced to the maritime emissionsfraction. The goal is to decrease these to corresponding level of theWRE-450 ppm track of CO2 in 2050, by reducing emissions fromabout 2.2 GtCO2/y, as estimated for moderate increase rates, toabout 0.55 GtCO2/y. Several generic wedges representing differentapproaches to reduce GHG emissions could be integrated in themitigation triangle. Their relative size is the potential of advancedmaritime technologies and policies that will be dimensioned later.The expected total reduction needed in the period is about(2.20�0.55)40/2¼33 GtCO2 which is about the total emissionsfrom the global energy sector in 2010.

4. Policies and sustainable technologies for marinepropulsion

In the previous section we presented the total CO2 emissionreductions needed in the marine sector. In this section we present adescription of sustainable energy technologies that could yield thesereductions. Fig. 6 shows some of the design factors that interplay inGHG emissions and depict improvement opportunities.

Let us now consider a set of policies and technologies that canbe tuned to mitigate GHG emissions, each representing a poten-tial wedge of improvement. We have focused on the followingissues:

1.

Figstab

(20

Mission refinement (transport system integration, route plan-

ning, reduced speed, weather avoidance, port faster transfer, etc.).

. 5. Estimation of the CO2 emissions wedge needed for maritime transport to

ilize below WRE-450. Adapted from IPCC (2008) and Pacala and Socolow

04).

2.
Resistance reduction (new lift methods, new hull forms, surface,
painting, viscosity alteration, air cavity, aerodynamic profile,

bulbs, etc.).
3. Propulsor selection (counter-rotating propellers (CRP), water
jets, free wheels, ducts, nozzles, etc.).
4. Propulsor-hull-prime mover optimization (azimuthal drives,
pre and post swirl devices, electric drives, etc.).
5. Prime mover selection (advanced Rankine cycles, advanced
Brayton cycles, hybrid cycles, etc.).
6. Propulsion augments (wind energy, kite sails, flaps, solar energy,
etc.).
7. New fuels (land based H2, synfuels, biofuels,U/Th fission, etc.).
Most of these improvement elements can be applied today withcurrent state of the art knowledge to most vessel types of theworld’s fleet. Some of them have been already applied or are beingconsidered in new ship designs. Several of the policies andtechnologies need to be integrated into new vessel architectureand some of them can be applied singly to specific ships classes.This paper identifies emissions reduction potential for the industryregardless of the political restrictions discussed earlier. Technologyand cost attributes will eventually configure preferred tracks in thissector, as it did in the past when international passenger and cargotransport was almost fully done in maritime. We are not in aposition to anticipate the dynamics of the entire transport system,for example, crude-oil transport may decline as a result of wellexhaustion, price escalation and policy restraints. Energy sustain-ability issues, mainly GHG emissions and service costs may influ-ence a rearrangement of transport technologies. We have estimatedcargo transport efficiencies of different vehicles based on nominalcapacities, expressed as grams of CO2 per ton-kilometer (gCO2/km t)as shown in Fig. 7. Most of the air cargo is of high value whilemarine cargo is generally of high volume and low value. However,the low emission factor of ships compared to that of airplanesindicates a clear opportunity to transfer the air cargo of lowestvalue to maritime cargo in the mid-term, provided that this sectorimproves cargo management and reduces door-to-door deliverytimes with new maritime technologies. Costs of maritime cargotransport are already low, i.e., as a rule of thumb, the cost oftransporting a twenty-foot equivalent unit (TEU) container maybe roughly the same as an economy class air ticket for the sametrip. Although there is a potential for cargo shift we have not

Fig. 7. Range of CO2 emissions efficiency associated with ship transport in compar-

ison with other transport modes.

Fig. 8. Projected 2010 GHG emissions from different ship classes, for the year 2050.


introduced this in our work due to the complexity of evaluatingthe scope of such opportunity. Similarly, we have not consideredan eventual capture of air travelers since our focus is cargo.

The assessment procedure has been the following: We haveestimated the energy consumption and GHG emissions of ongoingvessels arranged in eight ship categories, which were broken intotwo to eight families depending on its class and size. Then weprojected the GHG emissions into the year 2050 assuming a BAUscenario at a conservative growth rate of 1.5%/y for all ship typesexcept containerships and LNG carriers, for which we projected a50% higher growth rate. The standardized form of the cargo unitvalidates the containership as the dominant design for cargo, evensuitable for certain liquids. This reference rate is in the same orderof magnitude of what Pacala and Socolow used for the overallenergy sector. We also estimated the maritime emissions atgrowth rates of 1.0%/y (1.76 in 2050) and 2.0%/y (2.80 GtCO2/yin 2050) with the results shown in Fig. 8. A recent report byInternational Council on Clean Transportation (ICCT, 2011) rangesfrom 2.45 GtCO2/y in 2050 in a B2 Scenario (regional andenvironmentally driven) to 3.6 GtCO2/y in 2050 in a A1FI Scenario(global and economically driven). Apart from containerships,these projections do not consider relative changes in number ofcargo vessels, i.e., we did not reduce the number nor volume offossil-fuel cargo vessels as it should respond accordingly to landbased usage of transport fuel.

We have deduced the potential penetration of each of the wedgeelements to each of the vessel types to find out the extent of GHGreduction, using state of the art or credible developing technologies.Those can be applied comprehensively to the fleet while others arelimited to specific vessel types. Some technologies have alreadybeen applied in a certain vessel types. The technology optionsproposed in our study are shown in Table 1, for new ships as well aspotential retrofits. Each of these technologies implied emissionsreductions that were integrated and the goal was measured.

The naval segment was included in our analysis since this sector,as a whole, exercises peacetime control of sea lines of communica-tion, contributes to maritime safety and assists merchant vesseloperations, with advanced technologies.

This study does not deal with propulsion costs since develop-ment costs of some of the proposed technologies may hinder otheroptions. It is possible, however, to follow the cost behavior of land-based innovative power technologies in the marine environment.Traditional fossil fuel technologies have shown relatively low directoperation costs. On the opposite side, with the exception of hydro-power, renewable energies are the most expensive options due totheir intermittency, and they are often unsuitable in marine applica-tions. A higher capital cost pattern would be expected for advancedhull and propulsion options, in a similar way to the higher capitalcosts of renewable or nuclear energy forms.

4.1. Mission refinement

This wedge represents radical and incremental improvementsin the employment of efficient maritime systems. Simple exam-ples are route planning and weather avoidance. Complex refine-ments include the link with other transport segments so that thecargo minimizes energy and time from origin to destination.

One contributor to reducing energy of transport is to keep thecargo moving as it enters into efficient intermodal ports. Thereduction of stop-time can be invested in a slower speed of thevessel, and thus fuel consumption and the associated environ-mental impact can be reduced for the same transit.

Essential to this wedge is the concept of agile ports, whichimplies the application of technology and business practices inmarine terminals to accommodating different cargo types andvolumes at increased throughput with minimum cargo delays ineach terminal, as well as increased productivity and security(CCDoTT, 2009). An agile port would have the capability to servedifferent vessel types such as container, general cargo, RoRo andhigh speed cargo vessels. The architecture and infrastructureelements of agile ports include:

More efficient container handling and drayage solutions.Faster inspection and clearance technologies so that delays arenot caused by security measures.Just-in-time arrival of chassis so that containers are not drayedand stored in port.Continuous-process technologies for moving cargo to inlanddistribution centers.Information technologies to coordinate the above.

Mission refinement also includes the selection of the optimumvehicle to suit the mission and transport demand. This meansmaximizing cargo capacity while minimizing energy consump-tion and time. It demands attention to all design features, fromthe market concept to the architecture of the fleet and the ships.Intuitively, commodities require low-speed high cargo capacityvehicles, probably best served with full displacement monohulls,while expensive goods that are not stocked in high volumedemand more costly high-speed vehicles at high frequency rates,better served with advanced multihulls and lighter materials. Thisis why high-value products are typically transported in jet planesat several dollars per kilogram (Gabrielli and Von Karman, 1950).

Another element of mission refinement is speed. One of thestrategies is to slightly reduce the speed of most of the fleet. Asspeed decreases the ships’ power demand shrinks proportionallyto the third power of speed. This decrease in power permitssmaller engines, which reduce the weight and size of the ship, andthis reduce further the power demand and consequently emis-sions. This opinion is strongly supported by several studies of

Table 1Applicability chart of proposed new technologies, policies and potential retrofits, by type of vessel, for the reduction of GHG emissions.

Important R: Retrofit Crude Oil

tanker

Product

tanker

Bulk

carrier

General

cargo

Container

ship

RoRo/

vehicles

Passenger Military

Acceptable N: New

Marginal R N R N R N R N R N R N R N R N

Mission refinement Reducing up to 1 kn

Incrementing speed

Integration, agile ports,

optimization

Weather avoidance, route

planning

Resistance reduction Improved hull form, smoothness

New lift methods

(advanced hulls.)

Viscosity alteration

(i.e., air injection)

New materials

Bow bulb and stern

wedge/bulb

Propulsor selection Counterrotative and free wheel

props

Water jets, surface piercing props

Ducted props, Kort nozzle, CLT

Propulsor-hull-prime mover

optimization

Azimuthal podded drives

Electric drives and fixed pitch

props

Fins, pre-swirls and equalizing

ducts

Primer mover Improved prime mover

(i.e., Cogen)

Propulsor augments Kite sails

Wind energy (Dyna rig)

Solar energy

Fins and flaps

New fuels Land-based H2

biofuels

Synfuels

U/Th fission

(PWR and HTGR)


maritime agencies (Bazari and Longva, 2011; IMO, 2011), evenstating that if speed is reduced by half in some instances it wouldcut emission by as much as 70%. However, if the speed reductionis excessive, the trip’s frequency for a given demand would beaffected, requiring extra facilities on board and perhaps extraships, offsetting the expected GHG emissions reduction. In ourapproach, we have considered a reduction up to one knot in mostvessels from their speed trend, except for a few naval vessel types.This strategy was also neglected for LNG carriers, in order to saveboil-off gas. This loss is minimized by adopting on-board relique-faction units or by consuming it in suitable propulsion plants.Furthermore, we have considered a speed increase in ferries andmid-size containerships, in order to promote a shift to maritimecargo from air cargo. Nevertheless, the success of this strategydepends on the ship and hull design, sometimes introducingradical concepts.

We estimate that mission refinements could save 209 MtCO2/yin 2050, and contribute 13% of GHG emissions reductions goal,not including the benefit of air to maritime cargo shift.

4.2. Resistance reduction

This wedge represents radical and incremental improvementsin the architecture and shape of maritime systems, mainly toreduce energy consumption. Typical measures on the incrementalside consider smoothness and, on the radical side, changing thelift mode of the vessel.

Ship resistance is a complex phenomenon that is traditionallyrepresented by a sum of fluid-related resistance elements. Thesimplest is the skin friction term that is a function of waterviscosity, fluid density, wetted surface and the third power ofspeed. Simpler measures such as fouling control and vessel skinsmoothness reduce the frictional term. Both surface manufactur-ing quality and antifouling management apply partly in Section4.1, but their benefit is rewarded as a resistance reduction. A stepfurther to self-polishing polymeric antifouling painting may bethe use of air bubbles which alter the local viscosity (Foeth, 2008).A more elaborate device to consider is an air cavity in the hull,improving vessel lift and reducing skin resistance (Sverchkov,2010). However, this alternative requires suitable compressorsand may be impaired at rough seas.

Another term considered comprises wind and air resistance,which are less important due to the lower value of air density.This component can be reduced by improving the shape andsmoothness of superstructures and exposed cargo. A lesser termin ocean-going vessels is the acceleration resistance which maybe managed better in the mission refinement area and bymachinery selection.

The trickiest term is the wave resistance component, a resultof the formation of transverse and divergent waves self-generatedby the vessel as it advances. The transverse wave tends to stick tothe hull, creating a drag that at given speeds follows a sixth powerlaw. This effect eventually imposes a technical and economicbarrier to speed in conventional hulls. Wave formation resistance is


conventionally integrated with that resulting from the formation ofeddy vortices at points of sharp geometrical discontinuities intowhat is referred to as the residual resistance.

When the ship sails at rather small speed ratios, i.e., lowFroude number (FD¼V/(gL)0.5, where V, g and L are ship’s speed,gravity acceleration and ship’s length, respectively), the waveformation energy can be reduced with simple devices such as theInui Bow, stern bulbs and certain types of surfaces. Most of themodern displacement ships include one of these fixtures, improv-ing the efficiency by 4%, although their effect may be negligible orcounter effective at low speed. Even recent aircraft carriers,frigates and destroyers, originally slender for speed, include thesedevices for economic and other reasons such as sea keeping,course-keeping, and perhaps thin ice breaking, etc. Stern bulbsand flaps have also been proven. Stern flaps were applied to FFG-7(Cave, III, Cusanelli, 1993) and DDG-51 class Navy ships with atleast a 5% efficiency gain, depending of the operation profile.A less common approach has been the use of the Axe bow or evenan inverted bow, provided seaworthiness is balanced by sufficientflare. DDG-1000 class destroyers would include this shape andtumblehome, mostly for stealth purposes and platform stabilityplus a wave piercer.

At greater speed ratios, the idea is to apply different lift modesto radically elude the wave formation (Clark et al., 2004). Thesimplest form is seen in submarines which experience reducedresidual resistance. However, the idea of submarine cargo carriershas not prospered as they would require leak-tight cargo hatchesand non-standard container shapes. Multihull use is the equiva-lent of slender hulls without the stability problem, providedstructural stiffness is met (Gee, 1998). These platforms areexpected to gain relevance in the future, as shown by the USSIndependence. Small waterplane area twin hulls (SWATHs) aresomewhat in between, i.e., submersibles connected to super-structures by slender struts. Planing or semiplaning monohulls(SPMH) are other ways to break away from the static liftcharacteristic, relevant when speed becomes important. Radicalreduction of residual resistance can be approached by a combina-tion of the classical hydrostatic lift mode with more dynamic andless resistive lift modes such as the air cushion vehicle (ACV) andthe surface effect ship (SES). Lighter structural materials are keytechnologies to enabling some of the advanced ships; therefore,converting part of the deadweight into cargo weight or allowingthe transition to more complex lift modes.

We estimate that resistance reductions, with 286 MtCO2/ynot produced, could contribute 17% to the GHG emissionsreduction goal.

4.3. Propulsor selection

This wedge represents the improvement of the design, technologyand materials of propulsors. The preferred device is the screwpropeller, a helicoidal surface applying thrust onto the water. Thehighest efficiency is achieved with the largest propeller and theslowest rotation that result in the minimum slip and fluidperturbation; however, are limited by the stern space and inducedvibrations in aft structures. Faster rotating or larger screw propsinduce higher tangential speed at blade tips, creating cross flowsand vortices that enhance drag, reduce efficiency and promoteback surface cavitation, blade erosion and eventual failure. If thepower demand is too large and stern space or manufacturing toolsare limited, then the choice is to split power into smallerpropellers and prime movers, which may also improve reliabilityat a capital cost and a loss of efficiency. A notable gain is possibleby displacing the propellers away from the hull (PNA 1989).

Another energy sink, hub vortex cavitation, can be reduced byintroducing boss cap fins or vanes that enhance thrust and reduce

torque for improved efficiency, reportedly up to 6% (Hansen et al.,2011). Heavily loaded propellers may use tip fins, i.e., contractedand loaded tip (CLT) propeller, reducing the trail vortex (De Kat,2009). However, more research is needed to precise the gain ateach screw type. Advanced blade profiles may also improveefficiency. Kappel propeller blades include a smooth winglet ortip rake towards the suction side claiming a 4% increase inpropeller efficiency.

Current subcavitating screws, permitted by automated manu-facturing tools and tougher materials, incorporate skew to reducelocal velocity and vapor bubble formation at the back surface.Supercavitating propellers force cavitation to increase the thrustarea with bubble collapse occurring well behind the blade surfaceby means of wedge shaped blades; however these are only suitableat given applications and thrust conditions. An alternative to suchpropellers is the surface piercing or ventilated propeller that cleavesthe surface and allows air to fill the void instead of water vapor,reducing energy expense and drag as compared to supercavitatingdevices. Typical surface piercing propellers employ wedge shapedblades, and can be operated in both surface piercing and super-cavitating mode, but the applications are mostly limited topleasure boats.

Complex screw arrangements have been applied. CRPs, hybridCRPs (ITTC, 2005) and free wheels (i.e., Grim wheel) enhance theefficiency by improving the wake at the propeller and collectingwasted flow energy. A Grim wheel was used at the 1987 refit ofthe former RMS Queen Elizabeth II, with improved efficiency butreduced reliability.

A similar gain for ships can be obtained with water jetpropulsors that operate by impulse and high pressure avoidingcavitation. Wider and thicker blades tolerate high tip loading andthe duct reduces circulation losses, for better efficiency at highspeeds provided there is no air ingestion at the inlet duct. Whilethese units are common in small vessels, new commercial waterjets could reach the 50 MW level. Since these propulsors offer arelative small footprint they can be arranged closed-by allowingvery large total power demands. These propulsors may be about5% more efficient than conventional screws at the high speedrange (ITTC, 2008).

We estimate that improved propulsor selection couldsave 55 MtCO2/y in 2050, and contribute 3% of GHG emissionsreductions goal.

4.4. Hull/propulsor/prime mover optimization

This wedge deals with optimizing the whole power train forminimum fuel consumption and GHG emissions. This includesaligning the wake field developed by the hull when it comes tothe propulsor in order to maximize the thrust component,yielding the highest hull efficiency. It also applies to the bestmatch between the propulsor and the prime mover at most of theoperating profiles.

For decades, the use of controllable pitch propellers hasresulted in a better match between the engine and the ship, atthe expense of efficiency due to its larger hub and the extra costsof complexity. This propeller may be the choice for ships withfrequent port calls and maneuverability requirements. Advancedcontrolled electric transmission with fixed pitch propellers alsoallows a better match between propulsors and prime movers,overcoming the typical efficiency loss of electric motors.

The most radical way to improve the wake is simply to positionthe propulsors in undistorted water flow, away from the ship’s hull.Modern azimuth thrusters and other bulbous appendages haveseparated the propeller from the hull for enhanced hull efficiencywith an additional vectoring advantage for improved maneuveringif depth allows. Ships equipped with these fixtures seldom require


tug services to dock allowing further reduction of emissions. Twovariants exist: (a) mechanical transmission, where the propeller isconnected to an engine inside the ship’s hull by reduction gear setsthrough L and Z-drives, and (b) electrical transmission, where thepropeller is directly connected to an electric motor located withinthe pod, driven remotely by a prime mover installed at anyconvenient location. Innovative pod drives are increasingly com-mon in different types of ships and these may include conventionalpropellers, contra-rotating propellers, split units, pulling devices,etc., with power output up to 25 MW per pod (Pacaste et al., 1999).Smaller retractable units are often used for hovering and portmaneuvering.

Advanced controlled electric transmission allows an optimummatch between propulsors and prime movers, overcoming thegeneric electric conversion efficiency loss.

Simpler wake improving devices include spoilers to preventflow separation and allow pre-rotation resulting in an improvedwake field into the propeller. Equalizing ducts and nozzles areoften used for this purpose. A common device is the Schneekluthwake equalizing duct, or a half duct if it is used along with anasymmetric aft body.

ITTC, in its 22nd meeting, provides a selection of pre- and post-swirl devices for energy savings and emissions reduction, cate-gorized by operating mechanism. Among others, these includepropeller inflow pre-rotation, inflow improvement, downstreamrotational energy recovery, flow separation avoidance, decrease ofviscous losses and eddies as well as production of additionalthrust. Several technologies are listed with model and trialsavings reporting a power reduction range between 2 and 12%.The most promising single energy saving devices are vane wheels,shaft brackets and equalizing ducts. Some devices can be coupledto account for as much as 15% energy savings (ITTC, 2002).

We estimate that hull/propulsor/prime mover optimization,saving 34 MtCO2/y, could contribute 2% to the GHG emissionsreduction goal.

4.5. Prime mover selection

This wedge deals with the adoption of enhanced prime moversthat minimize fuel consumption and emissions.

Conventional prime movers have been improved for decades.Their selection is typically based on fuel consumption, operatingcosts, capital cost, space and weight restrictions, maneuverability,backing capability and other choices. Large power demands (i.e.,above 100 MW) in commercial vessels were best served by steampower plants. These are still used in some applications. Higherboiler pressure, lower condenser vacuum, economizers, super-heaters, reheaters and multiregeneration are often used toimprove the cycle efficiency at an extra complexity.

Large low speed two-cycle diesel engines now exceed the80 MW level with reduced consumption of heavy fuels and arethe preferred choice in large cargo ships. Smaller medium speedfour-cycle diesel engines are typically used in medium size andhigh speed cargo ships. Diesel engines can further enhanceefficiency by optimizing the combustion process while reducingengine size to maximize cargo space.

Lighter gas turbines can cover a range of low and high powerdemands burning lighter fuels at higher costs whenever space is apremium. Gas turbines have also been improved close to theirtechnology limits but can still have a large efficiency jump by thegeneralized adoption of complex thermal cycles (i.e., regenerationand intercooling) and integration of the main propulsion plantwith the hotel or shipboard loads (i.e., integrated electric systems,shaft power take off, etc.). The supporting technologies are mostlyavailable today, restricted by issues such as space, weight andcost, and little further breakthroughs are expected. Gas turbines

and diesel engines can typically allow the use of regeneration orcogeneration to recover part of the waste heat. The most commondevices are the waste heat recovery units, of special interest withhigh hotel steam and power loads.

We estimate that improved prime mover selection, with23 MtCO2/y not produced, could contribute 1% to the GHGemissions reduction goal.

4.6. Propulsion augments

This wedge represents the incorporation of a variety ofpropulsion augments being experimented with, along the linesof sails, kite sails, fins, etc., with the majority of the currentinnovations intended to harness wind energy. These devicesrange from classic sail rig through modern square sails on masts(i.e., Dyna rigs, currently used in luxury yachts), to hybrid devicessuch as rigid wing sails with photovoltaic cells. Compact Savoniusor Darrieus wind power turbines can be easily adopted forcollecting wind power for hotel demands. Magnus effect devicessuch as the Flettner rotor are additional power systems suitablefor on board use, either for assisting propulsion or providingelectricity for hotel demand (Craft et al., 2011).

Kite sails are worthy of a little more definition, because theyare unique in not being attached to the ship except by controllines or cables, so that their implementation is relatively simple.They are deployed and recovered as free-flying kites; therefore,they may be adaptable to a wide range of existing vessels, sincethey require very little in the way of permanent features aboardthe ship. Their developers claim that they may result in fuelsavings and emission reductions on the order of 10–35% in typicalservice in medium sized vessels.

A different class of propulsive augments are sets of fins or flapswhich attempt to harness energy from the sea waves, propellingthe ship by ‘flapping’ in response to excitation by the waves. Suchpropulsors have been successfully employed in at least one trans-Pacific crossing by a small craft. These flaps were also proposedfor the concept vessel ‘‘Orcelle’’ (O’Rourke, 2006), a pentamaranhull ferry designed by the Scandinavian shipping companyWallenius Wilhelmsen, with several of the devices listed beforebeing powered by renewable (solar, wind and wave) energysources directly or through fuel cells.

These devices, whether sail or flap, are only augments to theprimary mechanical propulsion of the ship and as augments itappears that they can yield energy and emissions savings. The lastmakes them viable contributors to the concept of maritimesustainability.

We estimate that propulsion augments, with 44 MtCO2/y notproduced, could contribute 3% to the GHG emissions wedgereduction goal.

4.7. New fuels

This wedge represents the transition to low or carbon-free fuels,with current or foreseeable technologies. We foresee the use ofrenewable sources, synthetic fuels, hydrogen and nuclear fuels.

Renewable sources are common in land based power systems,experiencing a large growth rate, especially photovoltaic, althoughfrom a very small starting point. Among several technologies, theone with the largest market penetration is wind, the resource thatdominated in marine propulsion up to the nineteenth century.However, the intermittency and low density makes most of thesesources unsuitable to supply the relatively large energy require-ment for propulsion. Similarly, solar power has been applied tosupply basic hotel needs and propulsion, the latter in an experi-mental catamaran. However, energy density in current collectors


for commercial applications is still too distant to supply timelyrelief to climate change and other sustainability issues.

A few ship types can be configured to produce synthetichydrocarbon fuels, i.e., from coal or oil cargo, provided that itsproduction has mechanisms to capture and store on board theCO2 produced in the conversion or combustion processes. Syn-fuels could be mixed with the main fuel or used for hotel powergeneration in conventional thermal machinery. The waste gaswould be collected and managed at the next port. Although thereis a possibility that the CO2 could be dumped into the bottom ofthe ocean at predetermined deep locations to form CO2 lagoons, itis unlikely that the regulations would allow such alternative.Land-based synfuels are feasible for ship propulsion; however,their emissions are not balanced within the maritime sectorunless these are produced by GHG-free sources. These could bemade part of a major commodity supply system similar to currentfossil fuels which would indeed serve other transportation seg-ments, i.e., cars and airplanes. In fact, GHG-free sources canproduce, collect and transform energy into a fuel suitable forocean-based propulsion. These energy forms can be synthetichydrogen-rich fuels to be used in fuel cells or thermal machinery.

Biofuels of first generation are produced by fermentation,anaerobic digestion, distillation and other processes applied tofoodstocks, biological wastes and municipal wastes, and theproduct is then mixed and burned with fossil fuels without majorchanges to engines or used in larger fractions with modifiedmachinery. However, foodstock-based alternatives entail a ‘‘foodfor fuel’’ dilemma that needs clarification. Second generationbiofuels are produced by gasification, pyrolysis and depolymer-ization from forestry and food wastes, with another dilemmaregarding the role of forests and land-use change in climatechange. Third generation biofuels can be extracted from algaewith advanced biochemical processes yet to be tested. Severalparties are already experimenting and prototyping with biofuelsfor transportation, for cars, ships and airplanes. These fuels can beadopted in the maritime sector (O’Rourke, 2006). In fact, it ispossible that the large slow-turning engines of merchant shipsmay be the best place to introduce such fuels. However, distribu-tion issues and public awareness may drive cars and airplanes tobe disproportionate users of such new fuels and thus lessavailable or more expensive for marine transport. We are notable to choose between these paths and have assumed a middlecourse. Biofuel combustion does emit CO2, so its usefulness restson a sustainable management and restoration of the resources,including land use change.

Hydrogen is an energy carrier that could experience a symbiosiswith electricity, only if it is produced from low carbon sources suchas advanced fossil technologies, high temperature nuclear systemsand renewable energy forms. through electricity, heat, light orbiological reactions. Solutions to its low volumetric energy densityinclude compression or liquefaction, both demanding expensivestorage systems. Advanced submarines already use this fuel forstealth propulsion.

The usefulness of any of these alternative sources relies on:(a) the endurance and intermittency of the original energy source,(b) the GHG emission levels of their life-cycle energy conversionprocesses, and (c) the internal and external costs of the appliedresource-technology systems.

The last alternative, fission fuels, produce nuclear heat withoutemitting GHGs, although very small emissions could be linked tothe fuel and parts manufacturing, if electricity or heat required forthose activities comes from fossil sources. A few navies operateabout two hundred pressurized water reactors (PWR), of tens ofMWs, and have operated several liquid metal reactors (LMR).Three unique nuclear merchant ships were independently devel-oped in the sixties for technology demonstration which failed to

prosper due to unsuitable mission selection (cargo and routes).A dozen nuclear powered icebreakers operate in the RussianMurmansk fjord. Potential marine reactors are expected to besimilar to a new line of simpler and safer integral designs that arebeing developed for land use (IAEA, 2011), in a power rangecoherent to marine propulsion reactors. We visualize integratedPWRs and the high temperature gas cooled reactors (HTGR)standardized around the following sizes: 25, 50 and 100 MW.The low-end is about the power of an attack submarine and thehigh-end is close to the power of a reactor unit size in a largeaircraft carrier. A few major issues arise regarding safety, securityand waste management in addition to industrial requirementssuch as development risks, standardization needs, regulatoryflexibility, operation culture, etc. Resources for this technologycould be low enriched uranium and elements bred from naturaluranium and thorium. Regulations for suitable safety would haveto be provided jointly by the International Maritime Organization(IMO) and the International Atomic Energy Agency (IAEA), byconvention agreements with participating States. Although con-troversial at the present time, we visualize a nuclear contributionof almost one half of this wedge, restricted to certain types oflarge ships and suitable ports, subject to public acceptance in theoperating States. If this contributing wedge should prove to bepolitically difficult, then the other wedges would have to beinflated to make up the resulting stabilization deficit. This optionis followed by biofuels and on-board synfuels.

We estimate that new fuels, with 370 MtCO2/y not produced,could contribute 22% to the GHG emissions reduction goal.

5. Summary of results and comments

The above strategies, or wedges, sum up to the total of about1 GtCO2/y, a value similar to today’s maritime transport emissionslevel, but insufficient to attain the reduction from 2.22 to0.55 GtCO2/y needed by 2050. The accumulated reduction foreach ship class is shown in Fig. 9, highlighting the role of anenhanced fleet of containerships. The gains that relate to propel-lers have been added in a single block. This result is coherent withrecent studies by Pew Center (McCollum et al., 2009) that attain a62% reduction from their 2050 BAU emissions that are 23%steeper than ours, i.e., more aggressive in the assumed growthrate, but do not consider advanced hull designs that by allowinghigher speeds would facilitate a comfortable shift from air cargo.Regarding alternative fuels, their study is biased toward replacingheavy fuel oil with marine diesel oil and LNG, in addition to windpower. Our range of technologies is also more extensive than theone considered by ICCT (2011), which restricts new fuels to windand solar power and does not incorporate advanced hulls.

The impact of each category of emissions reduction is shown inFig. 10 for each ship type. The initial and final emissions include arange of marine transportation growth rates. The reduction level isequivalent to about 62% of the task at the assumed growth rate ofshipping industry. The remaining gap is about 0.63 GtCO2/y in theyear 2050, which is equivalent to 57% of today’s emissions or morethan twice the emissions of the current containership fleet. Even ifthe assumed reference maritime transport growth rate was only1.0%/y, the reduction level would not cover the full share ofresponsibility of this sector showing a gap of 0.40 GtCO2/y in theyear 2050. If such rate had been 2.0%/y, the gap would have beenincreased to 0.95 GtCO2/y by then.

Therefore, the remaining 38% needs to be drawn from else-where. The simplest option is to provide additional fuels like theuse of nuclear propulsion in smaller ships; however, this wouldrequire thousands of small nuclear reactors that would impose asafety and security concern along with the requirement of qualified

Fig. 9. Accumulated yearly reduction of CO2 emissions by class of ship.

Fig. 10. Impact of the stabilization areas in CO2 emissions reduction.

Fig. 11. Reference concept of a synfuel refinery serving the maritime sector.

Fig. 12. Quantified CO2 emissions of marine transport wedges and their impact on

stabilizing at about WRE-450.


operating crews. Another alternative is to enhance the use ofbiofuels; however, this option is risky due to the expectations ofthis fuel for land-based uses at much larger quantities. Hydrogen isa further option; however, storage technologies make this unsui-table for massive use beyond the level that has already beenconsidered. One remaining option is the massive use of synfuelsderived from CO2 waste streams from land-based coal-fired powerplants, especially from integrated coal gasification combined cycle(IGCC) power plants. The benefit of using these fuels is that primemovers can evolve from current engines without breakthroughinnovations, based on a ubiquitous long term energy source suchas coal.

A synfuel similar to crude oil with the simplest bonds wouldbe alkene (CH2)n that can be drawn from well-known Fischer–Tropsch (F–T) chemical plants fed with carbon monoxide (CO)and hydrogen (H2). CO can be produced at reversed water gasshift (RWGS) units, a reversed form of a common chemical step,as proposes by Uhrig et al. (2007) which would combine CO2 –captured from fossil-fueled power plants – with hydrogen. Withthis alternative, the maritime sector would become pseudo-neutral by removing GHG produced at fossil fueled power plants.In this concept, hydrogen is produced from GHG-free sources anddelivered on-site directly to the RWGS and F–T plants withoutstorage facilities. Such refineries would distribute a manageableliquid fuel similar to the current hydrocarbon fuels.

The size of the additional wedge is not trivial to estimate. Thegap in maritime emissions reduction equals 650 MtCO2 per year,which corresponds to 206 MtCH2 per year. In order to producethat amount, 235 refineries with a capacity of 3000 m3 per dayneed to collect CO2 at 90% efficiency from coal fired power plantsof 570 MW per refinery, and 88 MtH2 per year, which in turn canbe produced by electrolysis with power supplied from more than5700 average size wind power turbines or conventional powerplants (four large Francis hydro turbines, seven standard com-bined cycle gas turbines or two large PWRs), per refinery.Alternatively it could be produced by direct heat from forty largeconcentrated solar power stations or four land-based HTGRs of770 thermal MW, per refinery. The HTGR is a low energy densityconcept cooled by helium whose fuel would not melt if thecooling function fails. The concept is shown graphically in Fig. 11.

The relative magnitudes of GHG emission reduction strategiesidentified earlier are summarized in Fig. 12. Naval architecturalmeasures including new hulls and propellers as well as newfuels can provide more than 60% of the goal while the rest can becovered by dedicated synfuel refineries located near the mostdemanded ports.

We can infer that sustained increase of conventional fuel costsand emissions constraints would result in a systematic shift of aircargo transport of lowest value or highest volume to sea trans-port. Eventually, we visualize a similar transport shift of certain


passenger segments demanding a slightly faster service in certainferries, which would necessarily mean an emissions enhancement.This needs to be counterbalanced by advanced high performanceships with hull forms that reduce the residual resistance to allowsuch speed boost. These ships are not just a dream, but a realisticgoal for the present.

Although maritime cargo transport is more energy efficient thanits land counterpart, we visualize a very limited shift from land to seatransport. We do foresee an improved integration in modal transportfor faster door-to-door service, which requires an increased share ofcontainerized cargo in lieu of other cargo forms.

Today’s demand for maritime transport is driven by lowmanufacturing costs at locations like China or India, distant fromend markets. The wages in these countries will eventually becomemore expensive provoking a manufacturing transfer back todeveloped countries or the appearance of poorer countries willingto take such activities. This consideration would of course affectthe growth rate of maritime transport, but here again we are notable to predict this effect.

We reiterate that none of the technologies we are proposingare necessarily new or untried. In fact, most of them exist in someform in the marine industry, generally in a small sector. Indeed, itis this very fact that makes us comfortable stating that thesetechnologies are individually realistic.

6. Policy recommendations

We believe that our analysis indicates certain policy directions.First, we acknowledge the difficulty of imposing policy on shipsthat are not controlled by Annex I countries. Changes to such shipswould be implementable via mechanisms such as port fees. Wehave shown that a substantial fraction of the needed stabilizationexists within technologies that are available today and we invitepolicymaking that would incentivize ship owners to adopt them inthe near term.

Second, we adhere to the need of further research to supportthe introduction of advanced hulls suitable for different maritimevehicles that would facilitate cargo shift from other segments.

Third, we have identified the need for an aggressive campaignof synfuel production specifically targeted to maritime consump-tion. Since synfuel plants of this size are necessarily land-based,and most feasible in Annex I countries, it seems to us that policycould be developed to encourage their development.

Lastly, we support the need to conduct studies to determinethe suitable technologies, the regulations and the minimuminfrastructure needed to implement nuclear propulsion in certaincivilian ship types and identify suitable ports.

7. Conclusions

Maritime transport is relatively energy efficient due to the lowspeed service and the larger space. The authors have describedand quantified the complex issue of sustainability for this trans-port sector.

We quantified the CO2 emission reductions that could beachieved to a target level under the WRE-450 line from the projectedemissions by the year 2050. Thus, maritime transport could con-tribute its stake to constrain the increase of global temperaturesunder 2 1C.

The identified emission reduction strategies are turned intostabilization wedges based on current or foreseeable vessel andpropulsion technologies. The use of alternative fuels, includinguranium or thorium, becomes an important wedge followed byresistance reduction and mission refinement measures. However,

we admit the introduction of nuclear fuels in commercial maritimeoperation remains controversial.

The proposed management and technical solutions reducedabout 1 GtCO2/y, a large value that is only 62% of the task. Theremaining 38% could be delivered in a nearly neutral form withdedicated land-based synfuel refineries that subtract CO2 fromcoal-fired power plants and H2 produced from low carbon poweror heat stations. Therefore, synfuel becomes the most relevantalternative fuel and the largest stabilization wedge.

We believe that most of the aforementioned naval technolo-gies can be adopted in short term, while others need refinementsand adjustment of production capacity to lower their costs. Then,it is not the lack of technology that impedes the development ofsustainability for maritime transport, but the lack of appropriateincentives to provoke a steady implementation of existing andevolving technologies worldwide.

Considering that the operation of commercial maritime vehi-cles beyond the territorial seas is not as easy to tie to a givennation as with terrestrial passenger and cargo transportation, theimplementation of commitments in emissions reduction wouldneed to be accounted for under new international rules. Wesuggest that IMO adopts the mission to develop such rules andpursue the accomplishment.

The maritime segment, in particular high performance cargoships, could take higher value cargo currently being served by lessefficient air cargo, and thus contribute to a sustainable transpor-tation sector. Therefore, we expect the maritime transport seg-ment, technologically more sophisticated, to acquire relevance inthe future.

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sustainable energy for the marine sector

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