The net-zero ship: a revolution on the high seas by USS Disruption
Through technical innovations and refined operational paradigms the GHG emissions of the maritime sector will be drastically reduced.
Moving goods by sea is the most efficient method based on CO2 emissions per ton per mile. However, because of the great distances involved in international shipping and the amount of goods transported by ship, its contribution to global GHG emissions is important.
Ships have evolved significantly since the age of sail. The most notable advances have come in the form of improved engines and greater overall size. Operating speed is important in determining CO2 per ton per mile. For large ships the required propulsion power is proportional to the speed cubed. However, because of auxiliary loads, the cost of the crew, vessel CAPEX considerations, and the value or perishability of certain cargos, optimizing purely for minimal energy consumption and least emissions is not generally done. It must also be realized that large ships tend to burn low-grade bunker fuel, which increases the GHG consequences of the resulting emissions. One trends in the maritime sector to reduce freight rates is the use of larger ships but those advantages can be deceiving as it restricts ports of call, shifting energy expenditures to other modes of transport such as coastal barge, rail, or truck.
Innovation is called for that brings ship design and operation into alignment with societal goals of minimizing our dependence of fossil energy and a stable climate. These innovations can come in the form of optimized propulsion systems, autonomy that reduces or eliminates crew, and a rethinking of how the movement of goods over the high seas can approach net-zero energy.
The net-zero ship represents a revolution on the high seas; one where vessels optimized for particular cargoes and trade routes can operate with little or no fossil energy. The outcomes of the initiative will extend beyond high seas shipping and improve coastal commerce, ferries, fishing vessels, and tugboats.
What actions do you propose?
“A Plan for Action on Climate Change” put forth by MIT President Rafael Reif, recognized that a 2°C rise in average global temperatures was unacceptable and that human-driven emissions must decrease greatly by 2050 and eventually reach zero. The plan’s objective is to minimize emission of carbon dioxide, methane and other global warming agents by engaging MIT alumni, the greater MIT community, industry and other stakeholders. The plan further states that MIT must accelerate progress towards low- and zero-carbon energy technologies.
This initiative seeks to mobilize alumni, particularly graduates of Course 13 with expertise in naval architecture and marine engineering, hydrodynamics, ship building and international shipping, many of who are already credited with advancements in this field. By combining that expertise with others skilled in renewable energy, biofuels, advanced manufacturing and other disciplines we hope to go beyond incremental improvements of the present state of the art to revolutionizing how we use the oceans to support a strong and sustainable economy.
Through the miracle of buoyancy and the combined density and low viscosity of water, boats and ships are remarkably efficient inventions. Indeed, until the advent of flight, vessels were the only option when traveling among islands or to another continent. Until recently, they did that using only human power or wind power, spreading civilization over the planet.
With the development of propulsion based on fossil energy, the size, speed, and punctuality of shipping enabled a global marketplace for raw materials and manufactured goods. Today, international shipping carries roughly 90% of world trade and is essential to the global economy and, compared to other modes of transport, it does this very efficiently.
mode (kg of CO2 per ton per nautical mile)
Sea freight 0.0403
From this we can see that on average, moving cargo by ship is 20 times more efficient than by air, four times more efficient than by truck, and 2.6 times more efficient than by train. In spite of this and because of the great distances involved and the amount of goods being transported international shipping is responsible for roughly 3% of GHG global emissions. Such emissions exceed those from many industrialized countries, rivaling those of India and Russia http://www.vox.com/2015/11/30/9818582/paris-cop21-climate-talks.
Shipping emissions are predicted to increase between 50% and 250% by 2050, depending on future economic and energy developments. It is equally important to note the International Maritime Organization (IMO) estimates these emissions could reach 12-18% of global emissions by 2050 if no action is taken and assuming other emission sources follow GHG reduction strategies - see: Second IMO GHG Study 2009. This same study suggests ship emissions could be reduced by up to 75% through operational measures and the use of existing technologies.
The question is, will such measures and technologies be adopted under the present maritime shipping paradigm or will it require disruptive policies or technological innovation to realize the needed progress. We believe MIT alumni ingenuity applied to both these areas are the solution.
Maritime Game Changing
There is no shortage of ideas aimed at reducing shipping emissions. They range from solar-powered vessels (http://www.planetsolar.ch/#) to using silicate rock to capture the CO2 in ship emissions and turn it into a carbonate that could be released into the ocean to the remove even more amounts of CO2 from seawater http://www.theguardian.com/books/2015/nov/20/climate-crisis-future-brighter-tim-flannery. Even a return to wind power has been proposed through the use of kites http://www.skysails.info/english/ and automated sailing rigs http://www.nytimes.com/2012/08/28/science/earth/cargo-ship-designers-turn-to-wind-to-cut-cost-and-emissions.html?_r=1
More modest approaches relate to propulsion system improvements largely centered on incremental technology improvements such as more efficient propulsion configurations http://gcaptain.com/part-propel-efficient-ship/#.VmWmOcrSifA, better auxiliary machinery http://gcaptain.com/part-marine-engineering-technology/?36541#.VmWni8rSifA, operational changes http://gcaptain.com/part-operations-maintenance-considerations/?36627#.VmWoYMrSifA and blue-sky ship design http://gcaptain.com/part-design-efficient-ship/?36462#.VmWousrSifA.
While the above series of four articles offers 47 suggestions which when totaled, offer over 300% potential improvements in ship efficiency, not all are practical and, more importantly, their improvements cannot be added cumulatively. Of particular interest is that sail-assist and slowing down each individually offered the greatest single advantages – 30% and 23% respectively.
The reality is that improvements are not being realized and the most obvious reason is that these improvements in retrofits do offer sufficient payback under the present way in which maritime commerce is conducted. We hope to change that situation by conceiving, evaluating, and perfecting disruptive approaches to the movement of goods at sea.
What we proposed to do.
The following is partial list of innovations in shipping that are poised to take maritime trade towards net-zero operations.
What is preventing game-changing advances in ship efficiency is the fact that the cost of fuel and the resulting GHG emissions from its combustion are a not a dominant cost of shipping operation. As a result, the lowest freight rates and the maximizing of profits are not necessarily associated with efficient operations. Instead, due to operational costs the trend is towards larger ships and faster transit speeds. The advent of unmanned vessels may change that paradigm. By removing the capital costs associated with crew support and relieving the role of speed in reducing those personnel costs, the efficiency opportunities of low-speed operation could be realized.
Many bulk or non-perishable cargos do not require high-speed transit and could exploit the V-cubed nature of ship propulsion requirements to vastly reduce fuel consumption and associated emissions.
Large-diameter, Slow-Turning Propellers
Neglecting rotational losses, the power P absorbed by a propeller can be expressed by
Pengine = T (v + ∆v/2)
where T is the thrust, v is the free-stream velocity and ∆v is the change in velocity imparted on the flow by the propeller (http://www.mh-aerotools.de/airfoils/propuls4.htm). If the thrust could be generated without imparting that change, the power would simply be thrust times velocity, implying no losses and 100% efficiency. As the propeller gets larger, the amount of water encountered by the propeller increases therefore its change in velocity becomes smaller for the same thrust. At high speed this option suffers because of frictional losses but as ship speed decreases, the advantages of large-diameter, slow-turning propellers becomes realizable.
Typically, propellers are sized to be as large as possible within the aperture available without violating the ships draft. With the recent advent of electric propulsion, more flexibility is possible in propeller placement, even to the extent that its position could be altered to suit the conditions. For example, once out of coastal shallows, a very large propeller could be lowered into position while for other conditions partial submergence of the use of a smaller maneuvering propeller could be employed temporarily.
Just as nuclear power stands as an emissions-free source of power for the electrical grid, it also stands as a viable alternative to power shipping. Though commonly associated with submarine propulsion, the US has 20 nuclear-powered cruisers and aircraft carriers. The role of nuclear power in civilian shipping has been very limited with the exception of Russia’s use of nuclear-powered icebreakers in the arctic.
The most notable of four nuclear-powered cargo ships was the NS Savannah, launched in 1962. It operated for only six years and was decommissioned in 1972, several years before the Arab oil embargo and a sudden increase in the cost of fossil fuel would have rendered the nuclear shipping economically viable.
With the advent of smaller and some argue safer nuclear plants, combined with today’s understanding of carbon-emission consequences, is it time to give nuclear-powered merchant shipping another look? See: http://www.technologyreview.com/news/512321/safer-nuclear-power-at-half-the-price/ and http://www.world-nuclear.org/info/Non-Power-Nuclear-Applications/Transport/Nuclear-Powered-Ships/
Conversions to Natural Gas
Bunker fuels are residuals from petroleum fractioning that are lower cost but suitable for use in large power plants and for medium and low-speed diesel engines. They result in 173 pounds of CO2 per MBtu as well as high rates of SOx, NOx, and fine particle emissions. Some have advocated the adoption of natural gas as a fuel in either Compressed (CNG) or liquefied (LNG) forms (http://www.lngbunkering.org/lng/). Indeed, at 117 lbs of CO2 per MBtu the result would be 32% fewer CO2 emissions.
Much of the impetus for such conversions is the potential for lower fuel costs, however, with the present price of oil, those motivations are diminished. Even the emissions advantages become unclear when the methane losses associated with natural gas exploration, production, storage, and transportation are considered – see: http://www.marinelog.com/index.php?option=com_k2&view=item&id=9793:lng-fueling-a-slam-dunk-for-local-air-quality-but&Itemid=230). Regardless, LNG conversions do offer relief in local air quality and presently are compliant in port areas where emissions are regulated,
A Return to the Age of Sail?
Today’s maritime industry offers the speed and punctuality that was unachievable when ships were propelled by sail alone. However with concerns concerns over emissions, is wind power poised for a comeback? Are there types of shipping and particular routes that lend themselves to such approaches? Does wind power become more viable in combination with other renewable sources?
A Bright Future with SunShips?
While the diffuse nature of solar power makes its adaptation to shipping a challenge, for unique vessels of low drag and sufficient surface area for PV arrays, the approach has been shown to be feasible. Do the constraints lessen in certain types of trade, when the vessel or objects in tow offer large surface areas, or in conjunction with today’s battery technologies?
These and numerous other innovations will be conceptually developed, evaluated for their potential and practicality, and brought to commercialization as appropriate.
Missing an Opportunity for Climate Action
MIT’s “Plan for Action on Climate Change” proposes eight new “Low-Carbon Energy Centers” each focused topics such as solar power, energy storage, materials, carbon capture, and nuclear. These centers are intended to stimulate industry participation and bring fresh perspectives to the table. Yet these topics are already generously funded by federal sources. More importantly, the transportation sector, which is a significant contributor to anthropogenic greenhouse gas emissions, is a sector that is going to be the most difficult sector to decarbonize. Furthermore, within the transportation sector, air transport and maritime shipping are seen as far more challenging, since land-based transport is more readily compatible with renewable energy.
This proposal is intended to reveal the possibilities of fresh thinking applied to an important contributor to climate change and find the kind of solutions sought by MIT’s plan. A secondary hope is that through demonstrated progress, the MIT Energy Initiative (MITEI) will recognize the potential and the available talent within the MIT community and convened an appropriate center to address the carbon emissions within transportation sector.