DNV GL issued a position paper to describe the main elements and research work towards the next generation of methods and tools for ship energy management.
Energy efficiency has always been an inherent and fundamental necessity for ships, going back to the times when our ancestors first sailed to explore and conquer the seas of our planet. Although it may not be evident at first glance, our recurring needs for ships to be faster, able to carry more goods, sail further, consume less fuel, be cost effective and/or be more environmentally friendly have all one underlying pre-requisite: an efficient energy conversion process on board.
As our technology and societies evolve, the manifestations of this underlying need change: from the slender hulls that made the Athenian triremes the fastest ships of their time; to harnessing the power of wind that enabled Magellan’s caravels to sail around the world; to steamers burning coal that linked the continents and formed sea trade; to propelling large VLCCs and containerships that made shipping the most costeffective and widespread means of global trade; to hybrid and electrified modern vessels promising near zero emissions in the imminent future.
In the current and future shipping landscape, the need for energy efficiency is ever increasing. The shipping market conditions are characterised by tonnage overcapacity in most ship segments, increasing fuel prices, and a recessive global economy. Therefore, the need for cutting costs and reducing the ship fuel bill, hence increasing efficiency, is imperative to both ship owners and charterers. The existing and impending stringent environmental legislations are also very strong drivers for efficiency.
An efficient energy conversion process on board results in better fuel utilisation and an associated reduction in emissions. Finally, there are growing sustainability concerns regarding the environmental footprint of existing and future vessels, with both the ship owners and charterers promoting and rewarding sound environmental performance. In this case as well, energy efficiency is the most important factor in ensuring the optimal utilisation and management of resources on board ships.
These interrelated shipping market characteristics and requirements result in an increased complexity of both ship systems and operations. The question now arises of how we can best navigate through this complexity. What are the necessary methodologies and tools required to map energy efficiency and losses accurately, to compare technology alternatives, and to manage operations on board ships? The answers to these questions ultimately pave the way towards further improvements in ship energy efficiency. This theme can be termed as ship energy management. In this work we describe the main elements and research needed to produce the next generation of methods and tools for ship energy management.
Ship Energy Efficiency: Challenges & Prospects
In the introduction we argued that the quest for efficient ships, both by design and during their operation, has been an underlying fundamental and constant aspect of shipping throughout the ages. In this section we aim to define the framework, basic concepts, and challenges related to ship energy efficiency and its improvement.
A ship’s operation is characterised by the energy conversion processes taking place on board. Kinetic energy is dissipated to the sea, overcoming the ship’s resistance, through the conversion of thrust energy during sailing. This thrust has been derived through a series of energy conversion processes that transform a primary energy source (today usually fuel, wind in the past – or perhaps in the future) to heat, to kinetic energy, perhaps electricity at some stage, and finally to the required propulsive thrust. A multitude of other energy conversion processes cover the ship’s needs in electricity, heat and all other forms of energy. Together, these constitute the ship’s energy conversion system. Many forms of energy are required on board to cover the vessel’s needs for propulsion, manoeuvring, cargo handling, fresh water production, space heating, cooling, passenger comfort, etc.
Indicative energy forms and demands on board ships
The set of equipment that is used to perform the required energy conversion processes and to cover its energy needs constitutes the ship’s energy system, often referred to as the marine energy system. Marine energy systems usually convert the chemical energy of the fuel (primary energy source) to those forms that are required shipboard. They are inherently complex – ships are resource-autonomous factories sailing the seas – incorporating a multitude of components and systems. Autonomy is of essence here, since all resources (including various energy forms) needed during a voyage, have to be either stored or produced on board. This is a key constraint and source of complexity.
Typical energy flow diagram of a modern tanker at sailing condition.
Thus, several constraints have to be met during the ship design and operation mandated by international regulations and design codes addressing safety of life at sea [SOLAS 2009], pollution prevention [MARPOL 2010], and rules concerning the safety and availability of the main functions of the onboard machinery in order to maintain the essential services of the vessel [DNVGL 2013]. The vessel’s mission and its operating profile are also highly variable, depending on the trading route, weather conditions, and ship loading. In addition, the hull shape, arrangement, and payload requirements impose additional constraints on the layout of the marine energy system in terms of location, volume, footprint, and weight.
Finally, in the modern shipping environment, marine energy systems have to be fuel-efficient and cost-effective, and environmentally friendly [Kakalis and Dimopoulos 2012]. Therefore, assessing and improving a ship’s energy efficiency is a far from trivial task.
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Three pathways towards efficiency improvement during a ship’s lifecycle can be recognised, as follows:
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The first pathway includes the technology alternatives, ship concepts and solutions that can be decided and implemented during the ship’s design and construction phases. These include the hull shape and various hydrodynamic improvement concepts. On the machinery side, there are also various technology alternatives such as, prime mover technology, waste heat recovery options, the ship’s electrification level, etc.
The second pathway considers ships that are already in operation. During the ship’s productive lifecycle, there are various possibilities for ensuring that operation of the individual machinery components is optimal. These include optimal tuning of components (e.g. main engine), optimal power management strategies, trim optimisation, and minor retrofitting of additional components such as propeller ducts and turbochargers.
Finally, the third pathway addresses those management changes that will ensure the fostering of an “efficiency culture” among seafarers and operators, logistics optimisation and continuous benchmarking / improvement policies. In addition, as part of the same pathway, weather routing, optimal speed selection (e.g. slow-steaming), and port/vessel synchronisation can also contribute.
Ship energy efficiency improvement solutions
As modern ships become more complex, the pathways towards improved ship efficiency also increase in complexity and become highly interrelated. In addition, new technologies and alternative fuels are gradually being introduced into shipping. Advances in ship instrumentation and sensor technologies also create new opportunities and challenges for mapping and improving the energy efficiency of components and systems.
Source and Image Credit: DNV GL
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