Vanguard Magazine

ficiency. Larger improvements are possible in running diesels at lower loads, where ef- ficiency has traditionally fallen off consid- erably. For most ship types, this represents a fairly small fraction of energy consump- tion. transmission Power developed has to be applied in some way to provide motive force. In a sailing ship this transmission is directly through the rigging. For any vessel propelled by a thermal engine, the path is more complex. The simplest systems, and amongst the most efficient, involve slow-speed diesels driving a large propeller through a direct shaft. In this and most other ship applica- tions, the largest energy losses are at the propulsor. Propeller efficiencies reach up to 70 per cent with good inflow and well- adapted designs, and it is difficult to im- prove on this for theoretical and practical reasons. Wake improvement devices can help improve poor forms, and contra-ro- tating propulsors can reduce energy losses in the water flow. Such devices are becom- ing increasingly popular. Adding any transmission component between the engine and propulsor intro- duces energy losses. Mechanical transmis- sions with gearboxes and shafts can be 98+ per cent efficient. Electrical transmissions, with generators, converters, motors, etc., lose up to 10 per cent efficiency, and add- ing battery storage systems reduces this considerably through charging and dis- charging losses. Therefore, while modern hybrid systems can offer a great deal of operational flexibility for many ship types, they will not help with overall energy ef- ficiency for most deep-sea vessels. Decarbonization Considering all the factors discussed above, there is limited potential to reduce the energy requirements for most shipping operations, other than by reducing speed. Reaching IMO 2050 goals will therefore require decarbonization of the energy sup- ply, possibly in combination with a use of renewal hydrocarbons. Methane, the main component of natural gas (NG), has the lowest carbon content of any hydrocarbon. This, plus the current low prices of natural gas, is a major factor in the decision of many ship operators to invest heavily in NG-fueled ships, gener- ally with the fuel in liquid form (LNG) at cryogenic temperatures. Using LNG can reduce the EEDI by 15 per cent or more compared with conventional fuels, and is very effective in helping achieve compli- ance with IMO's phase 1, 2 and 3 reduc- tion targets. However, it cannot reach the 2050 targets and may be best considered as a transitional fuel, as is methanol. Hydrogen is receiving increased atten- tion as a potential transportation fuel. Some means of generating hydrogen (e.g. with renewable electricity sources) emit no greenhouse gases, and consuming hy- drogen leads to few undesirable emissions. Like methane, hydrogen can be burnt in thermal engines using the Diesel or Otto cycles, and engines and systems developed for LNG are reasonably readily adaptable to hydrogen and to liquid or compressed hydrogen storage. Hydrogen is also a pre- ferred fuel for fuel cells, in which chemical reactions, rather than combustion, gen- erate energy. However, hydrogen is cur- rently more expensive than hydrocarbon fuels, and cryogenic or compressed hy- drogen systems are more expensive than those for LNG. Storage densities are very low, and fuel cell life expectancy is another drawback. Current projects are technol- ogy demonstrators rather than being com- mercially viable. Other potential zero carbon fuels in- clude ammonia, which does not need cryogenic or high pressure tanks, but which is toxic and corrosive. Used in ther- mal engines, it tends to create significant www.vanguardcanada.com FEBRUARY/MARCH 2020 15 Marine industry Figure 2: Norsepower Rotor on Maersk Tanker (courtesy Norsepower) There are no obvious complete solutions currently available that will allow commercial shipping to meet the IMO 2050 targets without fundamentally changing the nature of shipping operations. A group of leading industry orga- nizations has proposed the set-up of a $5 billion research and development fund for work in this area, with a $2/tonne tax on all marine fuel to drive this.

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