Energy Efficiency Measures :
Section 1: Hull Form Optimization
This section addresses issues linked to the basic hull form design including selecting proper proportions, reducing resistance by optimizing the hull form and appendage design, & evaluating the impact on resistance of waves & wind. There is also a discussion of how the IMO Energy Efficiency Design Index (EEDI) impact ship design & efficiency.
Section 2: Energy-saving Devices
This section covers devices used to correct or improve the efficiency of propellers as well as developing technologies focused at reducing the hull frictional resistance or using renewable energy sources (such as solar & wind energy).
Section 3: Structural Optimization and Light Weight Construction
This section marks the impact of the use of high strength steel on lightship weight & energy consumption.
Section 4: Machinery Technology
This section looks at the efficiency gains that are possible in the design and operation of the ship‘s machinery and systems. It covers main & auxiliary diesel engines, waste heat recovery & other auxiliary equipment.
Section 5: Fuel Efficiency of Ships in Service
The final section addresses operational procedures that can decrease fuel consumption. These covers voyage performance management, hull & propeller condition management, optimum ship systems operation & overall energy efficiency management.
Section 1 Hull Form Optimization
Hull form optimization keep up to be identified as the growing field within the marine community as a means to enhance energy efficiency of the ships. When assessing hull form optimization the owner has three options available for the consideration:
1. Accept the standard easily available hull form & propulsion system offered by the shipyard
2. Alter the existing & preferably well optimized hull form to address the expected operating profile
3. Develop a new design
Option 1 requires the least capital expense – substantive cut in vessel construction costs are often realized by accepting the standard design offered by the shipyard. Many of these standard ships have well optimized hull forms & propulsion, though generally only optimized at the design condition & to the lesser extent at the normal ballast condition or other service conditions. Hydrodynamic performance changes significantly with changes in draft & ship speed, but
these working conditions may not be fully observed in the original design.
Option 2 enables optimization of the design for the specific service conditions (e.g. a number of expected operating draft, trim & speed combinations with their corresponding service durations). This optimization procedure normally covers alterations to the forebody design & may include alteration to the stern shape, generally when excessive transom immersion is experienced at heavy load conditions.
Option 3 allow optimization of the vessel hull particulars to be in harmony with the propulsion & power plant, but this will leads to an increase in capital cost of the vessel. However, Option 3 is typically only justified when a particularly large series is being ordered, the shipyard under consideration does not offer a suitable standard design, the recovery by decrease in operational cost is identified or the ship needs unique characteristics to suit a niche service. This section
presents basis for evaluating the efficiency, explain the procedures available to today‘s naval architect for optimizing hull form & propeller, & outlines some of the situation that owners should consider in the evaluation of the hull form aiming to improve vessel fuel efficiency. The contents of this section are as follows:
Optimizing Ship Particulars
- Ship Size – Capacity
- Service Speed
- Principal Dimensions Minimizing Hull Resistance & Increasing Propulsion Efficiency
- Optimizing the Hull Form (Lines)
- Forebody Optimization
- Aftbody Optimization
- Twin Skeg Design
- Appendage Resistance
- Maneuvering & Course keeping Considerations Added Resistance Due to Waves & Wind
- Assessing Added Resistance in Waves
- Assessing Added Resistance due to Wind
The Influence of IMO‘s EEDI on Ship Design
Optimizing Ship Particulars
Enhancements in the sophistication & ease of utilization of the analytical tools & techniques for the vessel design have authorized the designer to optimize & explore alternative solutions that were previously unavailable. These tools take into consideration a range of disciplines such as hydrodynamics, ship structures, & environmental & safety performance (e.g. stability, oil outflow assessment & fire control). Multi-objective and multidisciplinary optimization software packages are being developed where these various tools are linked. Economic studies are routinely applied in the design optimization process and are beneficial for assessing the relative merits of standard designs offered by shipyards.
Ship Size – Capacity
Service Speed for the container ships, increasing size from 4,500 TEU to 8,000 TEU decreases fuel consumption for the propulsion by about 25 percent (calculated in terms of fuel consumption per tonne-nm of cargo transported). Increasing from 8,000 to 12,500 TEU decreases consumption by about 10 percent.
Ship Type All ships. The largest savings arise for the higher speed ships & are most significant for smaller sized ships.
All Cost Increasing size from 4,500 TEU to 8,000 TEU decreases construction cost in terms by about 15 percent (measured in terms of US$ per TEU).
Savings for the container ships of 4,500 TEU & above, decreasing speed by 1 knot decreases propulsion fuel utilization by 12 to 15 percent. For oil tankers, decreasing speed by 1 knot decreases fuel consumption by 17 to 22 percent.
Ship Type All New/Existing Ships
Some cost reduction if the smaller engine is selected. Significant decrease in fuel consumption per TEU carried can be perceived through the economy of scale of using larger capacity ships. The relative improvement in fuel consumption diminishes as capacity increases and is fully realized only if the larger ships can be effectively utilized. A number of factors are considered when selecting the design speed. These include but are not limited to: the expectation of shippers; active market conditions; the speed required to keep regular service; essential sea margins for the intended service; & maximizing efficiency. The cost of fuel is a major component of operating expenses, and therefore the establishment of the optimal speed is particularly sensitive to fuel price. In addition the inventory rate of cargo (the time value of cargo shipped) is also a significant factor. For any service with the calculated cargo quantities per annum & a target fuel cost, the ideal design speed can be measured from an economic data analysis such as a required freight rate (RFR) analysis. This analysis covers the number of ships essential to meet the cargo demands at some speed, capital costs & operating costs. It is a convenient way of judging the economic efficiency of a range of designs. If someone is planning to acquire new ships, doing this RFR analysis over a range of potential fuel costs is a good way to find the most efficient speed at the outset. Designing for the right speed has other benefits as well. A hull form optimized for the slower speed generally means a fuller form & higher cargo deadweight. It is also possible to refine the hull form for multiple drafts & possibly multiple speeds if cargo quantities may change. The main engine & propeller can be optimized around the slower speed for the maximum benefit.
Section 2 Energy-saving Devices
Many different devices have been considered to either correct the energy performance of sub optimal ship designs, or to enhance on already optimal or nearly optimal standard designs by utilizing physical phenomena generally regarded as secondary in the normal design process, or not yet completely understood.
This section inspect a range of these devices, most of which historically focus on the enhancement of the propeller propulsion effectiveness. But, recent developments have led to a series of devices focused at either decreasing the hull frictional resistance or utilizing readily available natural resources, such as solar & wind energy. Some of these devices are also examined in this section.
The contents of this section are as follows:
Propulsion Improving Devices (PIDs)
- Wake Equalizing and Flow Separation Alleviating Devices
- Pre-swirl Devices
- Post-swirl Devices
- High-efficiency Propellers
Skin Friction Reduction
- Air Lubrication
- Hull Surface Texturing
- Ship Design Characteristics/Ship Type
- Mutual Compatibility
All of these devices are intended to reduce the propulsion fuel consumption. The PIDs and skin friction reduction technologies do this by reducing hull resistance and/or increasing propulsive efficiency. The renewable energy sources take the place of some portion of the purchased fuel. Many of the devices are not compatible to all ship types.
Propulsion Improving Devices (PIDs)
- Rudder Thrust Fins, Post-swirl Stators and Asymmetric Rudders
- Rudder(Costa) Bulbs, Propeller Boss Cap Fin(PBCF) & Divergent Propeller Caps
- Grim Vane Wheels
- Controllable Pitch Propellers (CPPs)
- Ducted Propellers
- Contra-rotating and Overlapping Propellers
- Podded and Azimuthing Propulsion
Skin Friction Reduction
Air Cavity Systems
In air cavity systems, a thin layer of air is formed and maintained over the flat bottom of the hull. When a stable layer can be maintained (typically for small Froude numbers) significant reductions in skin friction can be achieved, roughly linearly proportional to the decrease in wet surface area obtained.
Micro-bubbles and Hull Surface Texturing
Renewable Energy – WIND AND SOLAR
Structural Optimization and Light Weight Construction – Use of Higher Strength Steel (HTS), Composites and Other Nonferrous Materials
Prime Movers – Main and Auxiliary Engines – Electronic Control