The overall energy efficiency of a vessel is determined by the choices made throughout its lifecycle, from the planning and new build phases to the final recycling phase, and is measured by the total amount of energy consumed in relation to a specific output, the total energy or fuel consumed per nautical mile.
Improving energy efficiency is one of the strategic plans of most shipping companies because the benefits include: lower fuel costs, which have risen significantly in recent years and are expected to rise further in the future, environmental protection, and compliance with current and future regulations.
The IMO has introduced mandatory requirements to encourage energy savings and reduce greenhouse emissions, which are currently centered on the SEEMP – the Ship Energy Efficiency Management Plan. The SEEMP’s goal is to create a mechanism for a company and a ship to improve the energy efficiency of ship operations.
The SEEMP aims to increase a ship’s energy efficiency in four steps: planning, implementation, monitoring, and self-evaluation and improvement.
These components are essential in the continuous cycle of improving ship energy management. The pursuit of energy efficiency requires more responsibility than the ship owner and operator can provide.
The list of all the parties involved in the efficiency of a single voyage is lengthy. Designers, shipyards, and engine manufacturers for optimal ship design, charterers, ports, and vessel traffic management services, and, of course, the crew for the specific voyage are obvious parties. All parties involved should consider incorporating efficiency measures into their operations, both individually and collectively.
Everyone onboard is responsible for using the least amount of energy necessary to do their job effectively and safely, because increasing energy efficiency benefits the ship, the operator, and the environment.
Key development areas should be identified and considered early in the business planning process. Comparing the performance benefits and lifetime costs of different investment opportunities can be a difficult task, and decision makers must find technically and economically optimal improvements.
It is critical to understand that a well-designed new ship can save up to 50% in operational costs when compared to an older ship. Up to 30% of this can be saved through fuel savings, as fuel consumption accounts for up to 50% of the total cost of operating a commercial cargo vessel. The easiest to assess and monitor is fuel usage reduction, as long-term forecasting of fuel price fluctuations is difficult.
Fuel prices were relatively low in the 1960s and 1970s. Many ships were built with little regard for energy efficiency. Newer vessels are designed to be more fuel efficient. The value of fuel efficiency will continue to rise and initial investments are required for energy efficiency. The profitability of this depends on a variety of factors, including the type of cargo being transported, interest rates, fuel prices, and the expected lifetime of the ship, among others.
Generally speaking, a ship’s life expectancy on regular routes is expected to be greater than that of a ship on irregular chartering in unstable financial conditions. The time it will take to recoup the initial investment should be considered when calculating the investment benefit. Short-term measures could save up to 10% of fuel consumption. Long-term measures should reduce it by at least 20% to 30%.
Ship design is the art of selecting a vessel configuration that corresponds to the mission, intended operational profile and route, as well as the operator’s performance requirements. This necessitates a thorough understanding of the vessel type, as well as new technologies and how they integrate with the vessel.
The first step toward improving energy performance is to recognize that the ship’s current performance is heavily influenced by the ship’s design. The hull shape and bow design, propeller and propulsion system, ship automation and crewing, heat recycling, and power generation are all important design factors in a vessel’s energy efficiency.
The above are normally chosen during the ship’s design and construction stages, but new developments in maritime design have made it possible for retrofitting or later design to deliver greater fuel economy.
The shape of the hull determines the ship’s water resistance and thus its fuel consumption.
A long, slim ship will provide less resistance than a short, beamy ship. Fuel consumption is also affected by the shape of the bow and stern.
The benefit of the bulbous bow has been well known for many years. Later research shows that this is also true for smaller vessels. Fuel savings of 25 to 50% can be obtained by increasing the length/beam ratio from 4.5 to 6.5. The optimal length/beam ratio is a trade-off between cargo capacity, harbor dimensions, and fuel consumption.
Experience has shown that increasing the total length of the ship has little effect on the energy required to maintain the same speed as before.
Approximately half of the energy consumed by the ship’s main engine is wasted, primarily through cooling water and exhaust gases.
Heat recovery devices reduce energy losses by passing the hot exhaust gas through a heat exchanger and converting it to steam. Steam is then used to pre-heat fuel, turbo generators, and other heating devices. The benefits of installing such devices vary depending on the type of equipment that needs to be installed. However, in most cases, the amortizing time, or time to recover costs, will be around two years.
A fuel gauge and a speed log are the bare minimum for better fuel economy. Onboard computers calculate fuel consumption in relation to the distance traveled and the vessel’s speed. Instruments used correctly can reduce fuel consumption by nearly 10%.
Many ships have relatively high propeller speeds, ranging from 300 to 400 rpm. Cutting the speed in half could reduce fuel consumption by up to 25%. Larger propellers necessitate more space. This is limited by the shape of the stern and the ship’s draught. Longening the propeller shaft and the overhanging stern is one option. A new reduction gear box should be installed in addition to the new propeller. Ships with slow speeds and high propeller loads will benefit from the use of a nozzle around the propeller. However, most cargo ships traveling long distances will benefit little, if at all.
Diesel generators, turbo generators, and main shaft generators can all generate electricity. The type of engine and the ship’s management profile will determine which type is the most energy efficient. Shaft generators should be considered for fast and continuous-running engines.
Small changes in operating conditions can result in significant changes in energy consumption, making it critical to continuously optimize operations throughout the ship’s lifecycle.
Optimal navigation can save up to 25% of fuel consumption, resulting in significant savings. Economical routing, time spent in port and at sea, speed optimization, continuous load output, optimal propeller pitch, engine efficiency, total efficiency, optimum draught and stability, reporting and computerized logging are all potential areas for efficiency improvement in ship navigation.
With such a diverse set of variables to consider, high performance in vessel navigation is possible if interrelationships are well understood and utilized.
The careful planning and execution of voyages can result in optimal routing and increased efficiency. Thorough voyage planning takes time, but there are a variety of software tools available for planning purposes. Routing is the calculation of the most efficient path. Land masses, soundings, prevailing currents, prevailing winds, and tide effects are all factors to consider. Once the route is established, it is the navigator’s responsibility to stick to it unless unusual weather conditions dictate otherwise. In general, excessive rudder use is not recommended because it slows down the vessel unnecessarily. In most cases, an autopilot will keep you on course better than manual steering.
The most significant energy savings can be achieved by reducing the ship’s speed, but unfortunately will also reduce its transportation capacity. As the ship’s speed increases so does the fuel consumption and even a small speed increase results in large increase in fuel consumption.
Based on experience operation at constant power can be more efficient than continuously adjusting the speed through engine rpm, but if the arrival time is the priority and the weather uncertain it is wise to allow for a sufficient time margin.
Harbour maneuvers should be done with progressive and moderate accelerations if the conditions allow for it, as any hard maneuver is a strain on the engine and a waste of fuel.
Some ships have a tendency to bury of lift their bow and the speed should take this into account, as in some ships it is possible to asses and adjust for optimal trim condition which will improve fuel efficiency continuously throughout the voyage.
Ballast should be adjusted taking into consideration the optimum trim and steering conditions and optimum ballast conditions should be achieved through good cargo planning. Ballast conditions have a significant impact on steering conditions and autopilot settings and it needs to be noted that less ballast water does not necessarily mean the highest efficiency.
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