Vanguard Magazine

14 FEBRUARY/MARCH 2020 www.vanguardcanada.com Marine industry at time of writing the full impacts of the 2020 low sulphur limit are not yet clear. The first two stages of EEDI implemen- tation, requiring up to 20 per cent GHG reduction have been achieved by ships scheduled for building this year. However, achieving further reductions is becoming progressively more difficult, and reaching the IMO 2050 goals does not appear pos- sible without more radical changes to de- sign and/or operational approaches. How Ships Use Energy It is worth revisiting some basic aspects of naval architecture and marine engineering to understand how energy is used in ships and the potential for further increases in energy efficiency. This provides context for the IMO 2050 objectives. Resistance There are three aspects to the overall prob- lem of moving a ship through the water. First is the resistance to moving the hull. There are three main components to this: friction, wave-making, and form drag. For a unit of volume that a vessel can carry, friction is reduced by reducing the sur- face area in contact with the water, which taken to the extreme would result in an impractical circle or a slightly more practi- cal square brick. Bricks unfortunately have very poor wave-making and form drag performance. Tankers and bulk carriers, optimized for transporting large volumes, are approximately rectangular bricks. They have shaped bows and stern forms to im- prove form drag and wave-making, and they move at relatively slow speeds. At the other extreme, vessels intended to optimize wave-making resistance, such as container ships, have more slender forms with hull angles and supplementary fea- tures tailored to reducing the energy trans- mitted into their radiating wave fields. However, despite this, they still have much lower transportation efficiencies than tankers and bulkers, due to the dramatic fashion in which wave-making energy loss increases with speed. This can be seen in Figure 1, which shows the IMO EEDI ref- erence baselines. Putting 100,000 tonnes of containers onto a 2010 bulker design would allow this to meet the IMO 2050 container ship target, at the cost of much longer delivery times. The bulker itself does not have this type of "simple" option available. Powering Resistance is the minimum energy required to move the vessel. This energy must be supplied from some source. For millen- nia, vessels used wind as the main energy source, but over the last two centuries this has been supplanted, initially by steam and more recently by the ubiquitous diesel. These and other types of thermal engine use stored energy in some form to provide more reliable and higher power levels than those available from wind. The stored en- ergy does not have to be a fossil fuel such as oil or coal, or indeed any form of hydro- carbon. However, the convenience of oil fuels means that these are the predominant transportation fuel source of the early 21st century. Diesels are highly efficient thermal en- gines, with up to 55 per cent of the stored energy in the fuel being turned into useful work in the best marine diesels (well above the 40-45 per cent achieved by automo- tive diesels, and actually very comparable to current fuel cells). This is still somewhat below the theoretical maximum for the cycle of around 75 per cent, but is prob- ably close to practical limits. Some of the energy lost to the engine exhaust and to cooling systems can be captured by waste heat recovery systems of various types, and these can add a few per cent to the overall energy efficiency of a ship. However, there are not huge gains to be made in peak ef- Figure 1: IMO EEDI Reference Lines (source IMO 2018) Putting 100,000 tonnes of containers onto a 2010 bulker design would allow this to meet the IMO 2050 container ship target, at the cost of much longer delivery times. The bulker itself does not have this type of "simple" option available.

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