Initial stages of the design process have the greatest impact on energy efficiency since all major decisions, such as machinery and main dimension definitions, are made then. However, in vessel efficiency the operation of the vessel plays the largest role. It should guide the design process from the very start, so defining the operating profile of the vessel at the beginning of a newbuilding process is crucial.
Hull Form Optimization:
The hull of a ship is a key piece of the ship efficiency puzzle. The physical ability of the ship to cut through the waves in a streamlined manner is of paramount importance to achieve fuel economy.
Therefore, improving hull performance plays a pivotal role, because a smooth and a streamlined hull is an optimally hydrodynamic hull. In essence, creating a hydrodynamic ship is to create a shape and texture that is able to manipulate the flow of water around the vessel to allow for maximum ease of movement and manoeuvrability. As mentioned, there are two ways to do this:
a) Hull form and dimension optimisation: The shape of the ship itself is arguably the most important element of ensuring the ship’s hydrodynamics because it is also one of the few choices that will stay with the ship for the duration of the ship’s life-cycle; once the ship has been built, whilst some parts of the ship can be integrated, automated and retrofitted for further efficiency savings, you cannot change the shape of your hull. Few examples are: Axe box design, M-Hull (for small sized vessels) , etc.
b) Aerodynamic shaped Accommodation: This technology introduces a streamlined and aerodynamic shape to a ship’s superstructure and other advances in the vessel’s accommodation block, engine room, and funnel casing. The exterior design was developed through extensive wind tunnel testing which could potentially lead to a reduction in wind pressure and drag by up to 25 or 30% and also 2% reduction in fuel consumption.
c) Coatings and hull roughness: Hull coatings and the circumvention of hull roughness play a key role in ensuring optimal hydrodynamics of the hull and ship. The preservation of hull smoothness can represent significant fuel savings however, when comparing this figure to the fuel penalties involved when the hull becomes rough from either physical abrasion or biological fouling, the potential fuel savings become much more.
Examples – Self-polishing copolymer (SPC) paints, Enzyme-based coating systems, Nano antifouling coating, etc.
Additional installations like Marine Growth Prevention system (MGPS), Impressed current cathodic protection (ICCP), Sacrificial anodes, etc, will extend the life of Hull performance.
Energy Saving devices:
- LED Lights: Installation of LED lights to reduce energy consumption and lower carbon footprint, it has a longer lifetime, which is not affected by vibrations and does not cause interference with Navigational equipment. LEDs use much less energy than incandescent bulbs because diode light is much more efficient, power-wise than filament light. LED bulbs use almost 75% less energy than incandescent lighting. At low power levels, the difference is even larger. Bright LED flood lamps use only 11 to 12 watts while creating a light output comparable to a 50-watt incandescent bulb.
- Variable Frequency Drive Motors (VFD): As per recent energy report, 60 percent of the power produced on board ship is used to operate motors pumps. These pumps are controlled
by traditional control valve, hydraulic and turbine methods. The average pumping efficiency is less than 40%. Hence there is much room for improving energy efficiency in pumping systems.
VFD is a device which is used to vary the speed of a 3-phase induction motor. It works by changing the frequency of the power supply to the motor, the motor speed being directly proportional to the supply frequency. VFD provides precise control of pressure, speed and flow and can save up to 50% of energy. There are many ways to save energy by using variable frequency drives, depending on the type of application. For variable torque applications, like fans and pumps, simply reducing the speed will lead to a significant reduction of energy consumption. Fans and pumps are variable torque applications. As speed
increases, the torque increases exponentially. If we can run the motor at a reduced speed, we will need less torque, which would mean less current and less energy. VFD (Variable frequency Drives) can be installed for:
- Scrubber Pumps
- Steering Gear motors
- Engine Room fans
- Sea water pumps
Waste Heat Recovery Optimazation:
Waste heat recovery systems recover the thermal energy from the exhaust gas and convert it into electrical energy, while the residual heat can further be used for ship services (such as hot water and steam). The system can consist of an exhaust gas boiler (or combined with oil fired boiler), a power turbine and/or a steam turbine with alternator. Redesigning the ship layout can efficiently accommodate the boilers on the ship to better fit these systems.
Below we have discussed the five main types of waste energy utilisation systems which are fitted on
ships and which use the residual energy from the machinery systems to perform other productive
work, increasing the overall efficiency of the ship as a whole.
- Turbocharger
- Economiser
- Steam Turbine Generator
- Fresh water Generator
- Shaft Generator
Waste Reduction Equipment:
Proper waste handling is crucial to the safety and security of ship’s staff, the environment and the shipping industry. Whenever ship’s staff handle, store and dispose of harmful chemicals, biohazardous materials, paints, solvents, and any other products, do it by the book.
- Operating ships generates various amounts of hazardous waste, such as batteries, light bulbs, medical waste and chemicals. This waste should be segregated and disposed of in a safe and environmentally responsible manner.
- Solid waste should be processed and incinerated on the ship or sent to an approved facility on
shore. Make sure these facilities are compliant with environmental regulations. - Lamp-crushers allow for onboard separation of glass, mercury and metal caps.
- Installing Garbage Compactors, which can offer great reduction in waste disposal costs by
reducing the volume of waste generated onboard during a vessel’s voyage.
VOC Saving arrangements: ( for LPG tankers):
VOC saving arrangements:
- Use of COP and Economiser modes. Plants handling upto 8%mol Ethane.
- Has helped the vessels reduce the number of compressors from 4 to 3, which in turn has saved power consumption and running hrs of AE.
- Use of Propylene as a coolant in cascade plants instead of Green House Gases (GHG) like R- 404a & R-507
New Generation Engines:
Electronic controlled engine:
The intelligent engine concept widens the reliability of traditional engines to facilitate new applications and concepts. The initial cost of such engine is quite high but the operational cost is lower than other engine used with proper operating procedure and trained crew.
Few advantages of Electronic controlled Engines are:
- Fully integrated electronic control
- Low SFOC
- Superior performance parameters
- Appropriate fuel injection pressure and rate shaping at any load
- Improved emission characteristics
- Smokeless operation at any load
- Lower NOx on command.
These advantages are gained by the use of variable, electronically controlled timing of fuel injection
and exhaust valves during operation. Additionally, all software and hardware are upgradable for the
lifetime of the engine.
Dual-Fuel Engine:
In gas mode, the ME-LGIP engine operates on just 3% pilot oil and down to 10% load. Ultimately, we expect the engine to operate without the need for pilot oil. The ME-LGIP can also burn liquid volatile organic compounds, a deliberate move on industry part since the IMO will inevitably turn its focus towards the reduction of volatile organic compounds in the future. Accordingly, we view the ME-LGIP
as also ideally suited to the propulsion of shuttle tankers and very large gas tankers.
LPG is an eminently environmentally friendly fuel, in much the same class as liquefied natural gas (LNG), and an LPG-fuelled engine significantly reduces emissions, enabling vessels to meet the stringent IMO SOx emission regulations. As well as being an important step towards reaching the 2050 IMO GHG targets, use of LPG also gives credit towards IMO EEDI compliance requirements.
Furthermore, LPG is traditionally a cheaper fuel than MGO yet delivers the same performance and efficiency. Importantly, the ability to use LPG cargo as a supplemental fuel source provides significant
cost savings for LPGC owners or charterers, including reduced time and fees for fuel bunkering.
Derated Engines:
De-rating the engine offers the possibility to lower the vessel’s maximum speed, specified maximum continuous rating (MCR), and thereby optimize actual load point with design load point. This results in higher efficiency with reduced specific fuel oil consumption (SFOC) at the new optimum design point.
De-rating of the main engine, be it permanent or temporary, can be done by different methods varying in cost, flexibility and effort needed. The measure is especially relevant in today’s slow steaming markets.
Flexible and reversible de-ratings already exist and can be very attractive, keeping the option easy, and with low cost, speed up again if the market changes.
Measures to achieve this includes, but are not limited to:
- installing shims between the crosshead and piston rod to reduce stroke length
- cutting out one or several turbochargers, either with permanent or flexible flanges
- cutting out / deactivating cylinders
- various tuning methods / settings of the engine, including slow steaming kits
The main principle behind the fuel saving benefits from de-rating an engine is derived from maximizing the engine’s maximum cylinder pressure (Pmax) ratio to their cylinders’ mean effective pressure (MEP). A de-rated engine can also be further tuned to optimize the efficiency at the lower operating points. This may be complemented by reduction in cooling capacity of auxiliary systems, or by installing variable frequency drives on pumps, etc.
It is possible to achieve a reduced RPM with the same power output for certain load ranges when derating, enabling a larger and slower propeller, which typically increases the propulsion efficiency.
The reduction potential is estimated at 2% to 10% of main engine total fuel consumption.
Following is some of the significant methods adopted onboard on new build vessels, by fitting
simple monitoring and metering components in the fuel oil system and on hull and on propeller to
obtain fuel savings.
Mewis Duct(MD).
The Mewis Duct consists of two strong fixed elements mounted on the vessel’s stern boss, without removing the propeller. The duct is positioned ahead of the propeller together with an integrated fin system within. The duct straightens and accelerates the hull wake into the propeller and also produces a net ahead thrust. The fin system provides a pre-swirl to the ship wake which reduces losses in propeller slipstream, resulting in an increase in propeller thrust at given propulsive power.
Both effects mutually contribute to each other. The achievable power savings from the Becker Mewis Duct are strongly dependent on propeller thrust loading, from 3% for multi-purpose ships up to 8% for tankers and bulkers. The power savings is virtually independent of ship draught and speed.
The Becker Mewis Duct is ideally suited to both new-build and retrofit applications (e.g. Tankers, Bulkers and MPCs).
- Improved propulsion
- Proven fuel savings up to 8%
- Reduced greenhouse gases (GHG)
- No moving parts, no service necessary
- Reduced vibrations & pressure pulses
- Return on investment in approx. 1 year
- Installation time approx. 4 days
Emulsified fuel system (EFS).
The emulsified fuel system provides proven fuel savings of 2 ~ 5 % and Nox reduction of 10 ~ 15% with 10% of water emulsion. The system has been tested on both medium and slow speed engine and on multiple fuels such as heavy fuel oil, intermediate fuel oil, diesel oil and Gas oils.
The invention of Blue Ocean Solutions (BOS) dynamic mixing emulsifier is one of the key developments in emulsified fuel technology. It is developed specifically for producing the optimal water-in-fuel emulsions for achieving the best fuel savings. BOS emulsifier has no mechanical moving parts and produces emulsions on demand at the consumption rate demanded by the ship engine in ever changing sea conditions.
The advantages of the EFS are as follows:
- Fuel savings of about 2 – 5 %.
- Reduced Emissions.
- No chemical additives.
- Simple installation, easy and safe operation.
Catalytic Combustion additive dosing (CC).
This method involves uses an organo-metallic combustion catalyst to achieve fuel savings and to reduce exhaust emissions was developed by Applied Energy Solutions. The Combustion Catalyst additive, contains organo-metallic irono and magnesium which is miscible and soluble in the fuel is continuously and uniformly injected into the engine based on the flow rate of the fuel to the engine. Catalyst injection pump installation near fuel transfer pump and pipe lines laid out to connect in the fuel oil system. Further the flywheel detection device is to be mounted on the flywheel to monitor parameters related to crank angles. The catalyst is mixed into the fuel with the static mixer in the fuel line below. This device resulted in good mixing into the fuel.
The combustion catalyst is yielding 11% fuel savings with significant reductions of CO2, CO, and Nox in the exhaust gases. The reduction of Sox is based on reduction of sulphur due to less fuel consumption. The engine fuel efficiency has been observed improved to 89.5% with use of catalyst from engine fuel efficiency of 78% without combustion catalyst.
Propeller Boss Cap Fin (PBCF):
The PBCF is an energy-saving device attached to the propeller of a vessel. The effect of PBCF is achieved
by eliminating the hub vortex which is generated behind the rotating propeller for all kinds of vessels
from VLCC to small fishing boat. The PBCF improves propeller efficiency itself and the expected energy saving effect by PBCF is almost the same regardless of ship type, size, RPM, speed, etc. Also, the PBCF has no drag effect on the ship even during a slow steaming.
Features of PBCF are as follows:
- Reduced rudder erosion
- A reduction in propeller torque. Reduced vibration in the stern less underwater noise
- The PBCF is an integral part of the propeller, with no other moving parts.
- It is maintenance free after installation, requiring only inspection and polishing when thevessel is in drydock, and performance does not decline over time
Rudder Bulb:
Ship rudders are generally situated in complex, highly turbulent flow fields. This offers opportunities for significant power savings by recovering some of the associated flow energy losses through customised design of the propulsion and steering system. The Rudder Bulb provides such an optimised solution.
The streamlined bulb is positioned at the leading edge of the full spade rudder, situated aft of the propeller hub. The transition between bulb and propeller hub is bridged by a fairing cap. The Rudder Bulb minimises energy losses behind the propeller hub by eliminating flow separation and reducing wasteful fluid turbulence.
In addition, careful design of both the bulb geometry and twisted rudder leading edge ensures optimal
energy recovery from the propeller slipstream.