Sunday, 11 February 2018

HULL VANE- THE CONCEPT

INTRODUCTION


The history of Hull Vane can be traced back to 1992 when it was first used in full-scale trials of a catamaran. Surprisingly, the results of the test showed that the vessel had reduced bow-up trim and resistance and, this had driven interest among the engineers to further carry out research on this device.
At first, the questions that strike our mind are what actually is a Hull Vane?
How does it look like?
What is the purpose of using it in ships?
And where actually is it used on ships?

 All these questions are answered in this article to give a general idea about Hull vane, its geometry and purpose.
Model used for hull vane model test 
Image courtesy- Google Images

Hull Vane is a fixed, resistance reducing foil attached to the hull below the water line near the stern of the ship.
In order to increase the fuel efficiency of the ships, the hull resistance must decrease. The concept of hull vane first struck the mind of Dr IR. Pieter Van Oossanen of the Netherlands and the first patent was filed by him in the year 2002. Since then a number of tests, for the optimization of this device, have been carried out using model tests, CFD and full-scale trials. The results were remarkable and showed fuel reduction in excess of 20% for yachts and 5% to 10% in other vessels mostly naval vessels, merchant ships, cruise ships, etc.
Hull vane animated concept
Image courtesy- Google Images

During the trial of the catamaran in 1992, it was found that the vessel wasn’t acquiring its required speed due to excessive trim and wave generation. By placing a foil in the steepest part of the interacting wave system aft of the midship, reduced the bow-up trim and the resistance significantly. Since then a number of tests, trials were carried out for a range of vessels like container ships, Ro-Ro vessels, Supply vessels, cruise ships, etc. and the results show a decrease in resistance to 26.5% to an increase of 9.5% which clearly indicates that the device is not suitable for all kinds of vessels. 
The second application of the Hull Vane, on the 2003 IACC yacht Le Defi Areva.
Image courtesy- Google Images

In 2014, two vessels equipped with Hull Vane were launched. A 55 meter supply vessel Karina manufactured by Shipyard De Hoop in the Netherlands and 42m yacht built by Heesen Yachts. The required engine power was reduced by
15% in the former and in the latter vessel a resistance reduction of 23% was significantly observed.

HULL VANE - WORKING PRINCIPLE


In this section, we will discuss how the Hull Vane actually does what it has been designed to do. We can observe four prominent effects of hull vane on the vessel dynamics.

THE THRUST FORCE


It is based on the basic foil theory. A schematic overview of the forces on the Hull Vane is given in the below figure.
Schematic overview of the forces on the Hull Vane in a section view of the aft ship.
Image courtesy- Google Images

Ξ± is defined as the hull vane inflow angle ( the angle between the inflow and the chord line), Ξ² is defined as the hull vane angle ( the angle between the chord and the body fixed x-axis). The vessel displayed in the figure is at zero trim.
The foil creates a lift force vector LHV which is by definition perpendicular to the direction of flow of water, and a drag force vector DHV in the direction of the flow. The sum of these vectors FHV can be decomposed into an x-component and a z-component:
LHV + DHV = FHV = Fx,HV + Fz,HV
If the x-component of the lift vector is larger than the x-component of drag vector, the resulting force in x-direction provides thrust. The lift and Drag Forces can be estimated using:
LHV = CL * ½πœŒV2A
DHV = CD * ½πœŒV2A
If ΞΈ is defined as the trim angle (the angle between the body fixed x-axis and the inertial x-axis) the thrust force that is generated by the Hull Vane can be derived by the equation:
F x, HV = sin (𝛼+𝛽+πœƒ) LHV – cos (𝛼+𝛽+πœƒ) DHV

TRIM CORRECTION


The force in the z-direction affects the trim, and especially at higher speeds, this trim reduction proves to have a large influence on the total resistance of the vessel. This effect can also be achieved with interceptors, trim tabs, trim wedges or ballasting. Similarly, to the force in the x-direction, the force in the z-direction can be estimated using:
 F z, HV = cos (𝛼+𝛽+πœƒ) LHV + sin (𝛼+𝛽+πœƒ) DHV
With this, the influence of the hull vane on the running trim can be derived using:
π›Ώπœƒ = tπ‘Ÿπ‘–π‘šπ‘šπ‘–π‘›π‘” π‘šπ‘œπ‘šπ‘’π‘›π‘‘ / π‘Ÿπ‘–π‘”β„Žπ‘‘π‘–π‘›π‘” π‘šπ‘œπ‘šπ‘’π‘›π‘‘ π‘π‘’π‘Ÿ π‘‘π‘’π‘”π‘Ÿπ‘’π‘’ π‘œπ‘“ π‘‘π‘Ÿπ‘–π‘š
≈ FZ π‘Žπ‘Ÿπ‘š / 𝐺𝑀L π›₯ 𝑔 sin (1°)
Not only the trim reduction itself has a positive influence on the hull’s performance, but the trim also affects the angle of attack of the water flow on the hull vane.

REDUCTION IN WAVES FORMATION


The flow along the hull vane creates a low-pressure region on the top surface of the hull vane. This low-pressure region interferes favourably with the transom wave, resulting in a significantly lower wave profile. The wave reduction is so significant that it can be observed by eye. The reduction of waves not only leads to a more beneficial resistance, it also leads to less noise on the aft deck, and to a lower wake. The former is mainly beneficial for yachts and the latter for inland shipping, where wake restrictions limit ship speeds in ports or other enclosed areas.
 Wave pattern on the 55 meter supply vessel without Hull Vane (top) and with Hull Vane (bottom) at 20 knots
Image courtesy- Google Images

 Comparison of the wave profile of the 55 meter supply vessel without Hull Vane (left) and with Hull Vane (right) at 13 knots.
Image courtesy- Google Images

Image courtesy- Google Images

REDUCTION OF VESSEL MOTIONS IN WAVES


Another significant effect of the hull vane is that it dampens the heave and pitch motions of the vessel. When the vessel is pitching bow-down the stern of the vessel is lifted and the vertical lift on the hull vane is reduced by the reduced angle of attack of the flow. This counteracts the pitching motion. Similarly, during the part of pitching motion in which the stern is depressed into the water, the vertical lift on the hull vane is increased. This again counteracts the pitching motions and similarly, it also dampens the heave motions.
 Image courtesy- Google Images


The advantage of reduction in motions is that the added resistance due to waves is reduced, which makes the hull vane even more effective in rough waters. As the motions are reduced, it increases the comfort levels onboard the vessel, safety and range of operability in various sea states.

 INFLUENCE OF POSITION OF THE HULL VANE


According to Moerke, if the Hull vane is fitted too close to the hull, it might lie in the boundary layer thus reducing the lift it generates. In addition to it, the low-pressure region on the upper side of the hull vane is reflected on to the hull and additional pressure resistance is created on the hull. Hence, the resistance of the combination of the hull and hull vane increases. After carrying a number of CFD analyses, it was found out that if the hull vane is placed behind the transom of the vessel, the pressure reflection can be reduced along with a slight reduction in the thrust generated by the hull vane.
Another consideration in the positioning of the hull vane is the angle of water flow near the stern of the vessel. The largest angle of attack can be achieved by placing it in the steepest part of the transom wave. But at high speeds, this location is found to be too far aft of the hull. An Additional complication is that this optimal location is very dependent on the wavelength and thus on the ship speed. In the vertical direction, a higher angle of attack can be achieved by placing the hull vane closer to the hull which is restricted by the free surface effect on the lift generated by hull vane, slamming by waves and pitching motions if it is placed too close to the water surface.
Hull Vane fitted behind the transom
Image courtesy- Google Images

INFLUENCE OF SHIP SPEED AND SHAPE OF THE HULL


According to Moerke, the hull vane is more effective at higher speeds. This statement was also supported by MARIN as they observed a power reduction of 3.3% at 17 knots (Fn 0.21) and up to 10.2% at 21 knots (Fn 0.27) for a 169m container vessel during its model tests. For high Froude numbers, the results in saving are much better. Also from tests and trials, it has been found out that hull vane is most favourable for Froude numbers in the non-planing region, between 0.2 to 0.7. 
Comparison of Resistance for a 42m, 47m and 55m motor yacht and 300m container vessel fitted with and without hull vane.
Image courtesy- Google Images

The addition of hull vane adds to the wetted surface area, the friction resistance thus increases in comparison to a vessel without hull vane. Above Fn 0.2, pressure resistance becomes more dominant. Therefore, best results are obtained for a range of 0.2 to 0.7 Fn. At higher Fn, the force generates by the hull vane creates an unbeneficial bow-down trim.
According to Moerke and Zaaijer, if the buttock angle is increased, the angle of attack of the flow to the hull vane increases and the lift vector is directed more forward increasing the resulting decomposed force in the x-direction. Also, the effect of pressure is minimized if the water column near the transom is maintained as much as possible. The leading edge of the hull vane experiences a lower hydrostatic pressure than the trailing edge when it is positioned below the front of the transom wave. The shape of the stern of the ship also a major role. Flat buttocks are considered ideal as they ensure a uniform flow.                                             

HULL VANE AND SHIP TYPES


The effectiveness of the hull vane is also dependent on the ship type as stated earlier. It is not very effective for bulk and crude oil carriers. For vessels less than 30m LOA, the investment costs are high as compared to savings using a hull vane.
Ideally, hull vane is best suited for medium and large-sized vessels operating at moderate or high non-planing speeds like the ferries, supply vessels, cruise ships, patrol and naval vessels, motor yachts, reefer ships, Ro-Ro vessels, car carriers and container vessels.
Hull Vane
Image courtesy- Google Images

The hull vane is a fuel saving device aimed to lower the pressure resistance which is the dominant component at higher speeds. CFD computations, model tests and sea trials have shown potential resistance reductions of more than 20% depending on the ship speed and hull shape, especially on merchant ships with resistance reduction between 5% and 10%.


This is a hull vane documentary video. It will give better insight about the concept of hull vane.


                    Video courtesy- Hull Vane Bv (YouTube channel)



Acknowledgements:
Hull Vane (Van Oossanen Naval Architects, The Netherlands)

Article by: Kushagra Gupta

Sunday, 4 February 2018

Parametric Roll

Introduction


As it is known to us that a surface ship has 6 degrees of freedom, viz. surge, sway, heave, roll, pitch and yaw. Surge, sway and heave represent the translational motion of a ship along the x-axis, y-axis and z-axis respectively. Roll, pitch and yaw are associated with the rotational motion of a ship about the x-axis, y-axis and z-axis respectively. The picture shown below depicts the 6 degrees of freedom of a surface ship.

6 degrees of freedom of a ship (Courtesy- Google images)

Ship rotational motions just seem normal. Almost each and every vessel experiences motion in the seaway and the magnitude of the motion depends on the efficiency of the designer behind it.
Just have a look at this picture.
 Image courtesy- https://www.ilwu19.com/photos/china/apl28.jpg

Guess what would have caused such a macabre to the containers?
Well, obviously, one would say it's due to extreme rolling motion the ship has encountered, probably due to the resonance of the ship’s natural frequency with the encountered wave frequency in the seaway.
Generally, beam waves (waves perpendicular to the ship’s centerline axis or the x-axis) are the reason behind roll motion of the ship.
But what if this is rolling is not caused due to beam waves? It seems illogical, but here is what we will be discussing in this article, rolling due to head waves (along the ship’s centerline axis or the x-axis). This phenomenon is also called as Parametric Rolling resulting due to resonance and certain special processes as discussed below.

Parametric Rolling – The phenomenon 


Now, assume a ship is moving in a straight line with zero drift angle and a wave is encountered opposite to the direction of its motion. Now if the wavelength of the waves is same as the length of the ship then major transient changes will occur in the water-plane of the ship, which would consequently change the transverse stability of the ship. Generally for a typical ship design, looking at the plan view, the midship is made fuller and the aft and forward ends are fine-form to balance with the cargo carrying capacity (or space requirement) and streamlined shape of the vessel. Also, the local breadth of the ship at any station decreases as one goes down the waterline to the keel.
When the wave crest is at amidship, due to the shape of the ship, the aft and forward ends of the ship contribute less to waterplane area. So stability decreases as we know the transverse stability of a ship is directly proportional to the waterplane area. And when the trough is amidship, stability increases as crests prevail at the forward and aft end of the ship. This transition in transverse stability takes place with a certain frequency which gives rise to parametric rolling. The picture below illustrates the change in waterplane area with respect to wave position.

Image courtesy – Team LSD

For a particular location and loading condition, natural roll period of the ship is a function of waterplane area, mass and added moment of inertia and hence remains constant. Assuming the frequency of the head wave remains constant; hence we know that there are particular bands of frequencies which cause parametric rolling. But the fact that we have ignored here is that there is a relative motion between ship and waves, which consequently changes the frequency with which a wave hits the ship. The actual frequency with which the waves hit the ship in a seaway is known as Encounter frequency.

Ο‰e =Ο‰- (Ο‰2*U*cos ΞΌ)/g

Ο‰e is Encounter frequency
ΞΌ is wave heading angle of the ship
U is velocity of ship
Ο‰ is angular frequency of the wave


One of the fundamental conditions for the parametric roll to set up is that the encounter frequency of waves should be twice that of natural roll frequency of the ship. So, there will be a certain set of ship speeds, heading angle and wave frequencies which will cause parametric rolling. Under this frequency condition, when the crest is amidships, the stability decreases, so the ship would roll, but after half the natural frequency of roll of the ship, stability increases abruptly due to increase in waterplane area, so the restoring force contributes to further rolling. This small roll angle slowly turns to a large parametric roll.
The image below shows parametric rolling of a ship (damping neglected). The changing GM values pertain to changing waterplane which we have already discussed. More water plane area means more GM. As the transverse stability and natural roll come near in phase, the roll angle increases. If the two are in-phase then resonance occurs. The image depicts the above-mentioned concept.
Image courtesy- of Thesis paper; Parametric roll instability of ships by Irfan Ahmad Sheikh, University of Oslo 

Hull Form Impact on Parametric Roll


Also, there are certain types of hull forms, which are susceptible to parametric rolling and same can be inferred by analyzing previous voyage data. Due to improvement in hull designs for better cargo capacity and flow efficiency, the bow flare, stern overhangs and fuller amidship are introduced in ship design. Due to this when waves travel along the length of the ship, gradients in waterplane area are very significant. This results in parametric rolling.

Parametric Roll- Havoc and Prevention


The picture of the container ship we saw at the beginning is of container vessel APL China. Due to parametric roll, 60% of her cargo was lost to waters.
To tackle this serious issue, most of the ships are now being engaged with sensor systems which alarm the crew about the possibility of parametric roll and paves a way to take immediate actions. Although, this phenomenon can never be eliminated, so other measures are adopted to reduce rolling amplitude of the ship such as bilge keel, stabilizing fins, anti-roll systems, etc. Since the phenomenon depends upon the encounter frequency, a ship can simply change its speed or heading angle to counter parametric roll especially to avoid resonance.
Although this phenomenon takes place very rarely, it’s consequences force the naval architects to incorporate preventive measures. With the help of simulation software, the response characteristics of the ship in different wave conditions can be easily predetermined, which helps in techno-economical motion based designing of ships.

The following video shows an experimental demonstration of parametric roll for a ship model in a wave flume. Hope it helps you to visualize the havoc it creates in large vessels.

(Video courtesy- YouTube channel tupsumato) 

Article by: Kartik Garg

Sunday, 28 January 2018

Shallow Water Effects

Any shipbuilding process starts with the owner signing the contract with a shipyard after giving the details of his requirements. Of these, the displacement and speed of the vessel are of utmost importance to the owner. If these requirements do not match with the owner’s specifications, then fine is levied on the shipyard. The shipyard builds the ship. Before the yard delivers the ship to the owner, it performs a lot of tests. One such test is the speed test. The objective of the test is to substantiate that the vessel has met the speed requirements of the owner. However, during the speed trial, the vessel speed is found to be less than the specified speed.
                So, is the shipyard at fault?
   Is there fault in the design?
   What could have gone wrong?
                Well, the answer to this lies in a phenomenon called shallow water effects. Actually, a ship is basically built to operate in deep waters but its speed trials are mainly confined to the shallow water areas which affect its speed.
Image Courtesy- www.google.com

                The reason for the drop in speed in shallow waters is that the water which is flowing just below the ship reaches very high speeds fast due to less water depth. We all know that when the velocity is high at any point in a liquid, there is a corresponding drop in pressure at that point which is explained by Bernoulli theorem. This is the same pressure which provides the upthrust and keeps the ship in floating condition, hence the ships will experience a bodily sinkage and its draft will increase. As a greater surface area is under water the frictional resistance will increase which will cause a drop in the speed of the ship.

                 Also, this drop in pressure is not the same everywhere. It is more in the fore part and less in the aft causing the ship to trim by fore which is an undesirable condition. This is known as ship squat.
Image Courtesy- www.google.com

EFFECT ON WAVE PATTERN


This drop in speed is not the only effect in shallow water, another prominent effect is the change in the wave pattern of the ship and hence the wave making resistance of the ship. Actually, the total resistance of a ship can be divided into frictional and residuary resistance. Wave making resistance forms a major part of the later. 
Image Courtesy- www.google.com

This is the general wave pattern developed when a ship moves through the water. As we can see two sets of waves are generated, transverse waves and diverging waves. The diverging waves are contained in an angle of 19O 28’ called angle of envelope. Let’s see what happens in shallow waters.
The general relation between speed of a wave (v) and wavelength (LW) in deep water is
                     V= (g*LW/2Ο€)1/2
Now for a wave in shallow water,
        V= (g*h)1/2
We can see that the wave has a limiting value in shallow waters, varying with depth, known as critical velocity. When the velocity of ship increases, the angle of envelope increases, till the velocity of ship equals critical velocity, where the angle of envelope becomes 90O. At 90O, the transverse waves disappear.
                Now if the speed is further increased, the wave pattern changes completely. The angle of attack increases and the divergent waves become convergent in nature but no transverse waves are formed. So, there is a major change in the wave pattern. We know that the wave making resistance is dependent on the wave pattern. So, there is a difference between wave making resistance in deep and shallow water.

INTERMEDIATE SPEED


It’s pretty much clear that wave making resistance differs for deep and shallow waters. Let’s say a ship is going in deep waters at a speed V.
It will have some wave-making resistance.  When in shallow water the same wave making resistance will occur at a low speed which we call intermediate speed (VI).
This drop in speed is denoted by Ξ”C= V-VI, which is due to the wave making resistance component.
Now the total resistance of the ship in deep waters will be equal to the total resistance of the ship in shallow waters at a further lower speed. We denote this speed as Vh. This drop in speed in shallow water is denoted by Ξ”VP. This drop in speed occurs due to the augment in the frictional resistance component in shallow water.
Image Courtesy- Principles of Naval Architecture Volume-2

EFFECT ON TURNING CIRCLE


The diameter of a ship's turn varies with several factors in addition to rudder angle, and water depth is one of them.  For maneuvering, deep water can be assumed when a water depth of more than five times the ship's draught is available. At three times the draught, the shallow-water effects come into action. When depth decreases from twice the draft the effects become more prominent. So, water depth plays a key role in the maneuvering of a ship and if it is neglected it can give wrong interpretations.  The rate of turn depends on the ship's directional stability, and though the rate increases at first on leaving the deep water, it decreases as shallower water is reached. These changes in the rate of turn are comparatively small to be perceived by the ship handler, but in combination with a smaller speed-loss in the turn, as under keel clearance decreases, it results in an increase in the ship's turning-circle diameter.
Image Courtesy- www.google.com

INTERESTING FACTS


• A fishing boat normally can run at 10 knots in deep water. If the water depth is 14 feet, then we can expect a speed loss of about 4%. That means that its speed is reduced by about one-half knot.
• A supply boat is expected to run 15 knots in deep water. However, during sea trials in 20 feet deep water, it did not make this speed. The 14 % typical speed loss means that we would expect a bit less than 13 knots on trial.
• A river workboat is trying to run at 10 knots in 9 ft. of water. It will lose almost a knot and half.

SUMMARY OF WHAT HAPPENS IN SHALLOW WATERS


1.       Ship maneuvering becomes sluggish.
2.       A decrease in ship speed.
3.       Change in the wave pattern.
4.       A decrease in propeller rpm.
5.       Increase in turning circle diameter.
6.       Increase in stopping distance and stopping time.


Article by: Anil Kumar Singh

Saturday, 2 December 2017

Green Ships

Introduction

The plea to have pollution-free vehicles running on the road have been ringing in our ears for quite a long time, without realising that the same applies to the marine environment. Thus the concept of green ships plays a significant role in the life of a naval architect. As much as ships are considered as the most efficient way of cargo transportation, they are also the sources of great pollution in oceanic and marine areas. Indian Maritime Organisation(IMO) has estimated that the Carbon dioxide emissions from the ships are about 2.2% of the global man-made emissions in 2012. The rules that the IMO prescribes for greener ships have been intensifying over the years. Green shipping can incorporate aspects like greener fuel, reducing carbon output and energy wastage, and to reduce the impact on marine life. The efficiency of a ship can be calculated by its EEDI value. Energy Efficiency Design Index (EEDI), formulated for new ships, is an index that estimates grams of CO2 per transport work (g of CO2 per tonne‐mile).   It can be expressed as the ratio of “environmental cost” divided by “Benefit for Society”.

Image Courtesy: Google Images

The lower the EEDI of a ship the more efficient the ship is considered to be. Green shipping technology focuses on reducing the impact of ships on the environment while maintaining a very less EEDI value.

History

 
The history of green shipping goes back to ancient times to the days when men found that floating wood can be used to cross water bodies. From the days when the sailors were on the mercy of the wind to the emergence of an engine coupled with the advances made in power delivery which began with a simple paddle wheel evolving to a single screw propeller and then to a twin screw made the overall efficiency of the power delivered better. From the process of creation of a small explosion inside the cylinder of an engine to the thrust generation required for propulsion of mammoth ships at a speed necessary to run the modern world at a pace never seen before. All this came at a cost. The cost of melting of the polar ice caps, the global increase in average temperature etc. It is only after the Industrial Revolution took place when internal combustion was first used to drive the propellers used on today’s ships. It is a common understanding that the conventional sources of renewable energy like wind, sun and bio-fuels cannot completely replace an internal combustion diesel engine of a ship. So we can actually depend on the more unconventional renewable energy sources like hydrogen or nuclear energy to power the modern day ships and that just might be the way for the shipping industry to pave in the future.

Technology and Steps to be Involved

In lieu of the ever increasing environmental aspects related to pollution, no environmentalist leaves any stone unturned to scrutinize the massive global maritime industry to check their pollution standards and the steps being adapted to minimise it. A ship affects its environment and the pollution of the world’s oceans and atmosphere has become a cause for increasing international concern.


  •           In 1972 the United Nations held a conference on the Human Environment in Stockholm. It was recommended that ocean dumping anywhere should be controlled.
  •           No Ballast Water: Ballast water is needed for safe ship operations but it poses serious ecological, economic and health problems due to the multitude of marine species in Ballast Water. Although IMO developed the International Convention for the Control and Management of Ship’s Ballast water and sediments (BWM), still No ballast water management technique can remove all organisms from ballast tanks while maintaining transverse stability, bow and propeller submergence and reduce windage for adequate manoeuvrability.



    To read more about ballast free ships click the link below

     
 
 
  •         LNG Fuel: Ships used to run on unrefined crude oil full with sulphur and environmentally-harmful impurities. Gas carriers around the world have been using liquefied natural gas (LNG) as part of their fuel source for decades. 

    Norway has been at the forefront of marine LNG applications, dating back to 2000.
    In Stockholm, bunkering of Viking Line cruise ships with passengers on board was approved in 2013.
     
    These developments highlight the changing environment of safety regulations and public acceptance of LNG as a viable fuel option. 

    While different technologies can be used to comply with air emission limits, LNG technology is a smart way to meet existing and upcoming requirements for the main types of emissions (SOx, NOx, PM, CO2). LNG can be competitive price-wise with distillate fuels and, unlike other solutions, in many cases does not require the installation of additional process technology.It has been shown that a high-speed ferry by moving from diesel to LNG can cut CO2 emissions by 25%, NOx by 35 % and eliminate SOx emissions completely. When moving from heavy fuel oil to LNG the reduction of NOx emissions can naturally be significantly higher, possibly 85-90%.
  • Flue Gas Desuphurisation :Also known as the SO2 scrubber system, this system can reduce SOx emissions by up to 98%. It consists of 3 basic components –

    •               A vessel which enables the exhaust stream from an engine or boiler to be intimately mixed with water – either seawater or freshwater (or both). For reasons of available space and access the exhaust gas cleaning units tend to be high up in the ship in or around the funnel area.
    •  
    •               A treatment plant to remove pollutants from the “wash” water after the scrubbing process.

    •               Sludge handling facilities – sludge removed by the wash water treatment plant must be retained on board for disposal ashore and cannot be burned in the ship’s incinerators.

  • Advance Propulsion System : Maersk Line's Triple-E is not only the world's largest container vessel but also boasts world record energy efficiency. Triple-E incorporates a 'twin skeg' or two-engine, two-propeller propulsion system with two 'ultra-long stroke' engines contributing to efficiency by operating at slower revolutions, thereby consuming about four percent less energy than the single engine / single propeller system used on the company's Emma MΓ¦rsk class vessels.

Auto­tuned engines and optimized low-speed marine engines replace infrequent, manual adjustments with ongoing electronic ones. They potentially reduce fuel consumption by up to 3 % by constantly adjusting to factors like engine load and operating condition.

  •  Waste Heat Recovery: The waste heat recovery system effectively prevents the loss of 25% of the energy contained in the vessel's fuel by harnessing the hot exhaust gas before it escapes into the atmosphere.


  •  Hull Paint: The International Convention on the Control of Harmful Anti-Fouling Systems on Ships prohibits the use of harmful organotin compounds. 3-8% of the fuel can be saved by using correct paint at specific areas of the hull.
    Advanced Techniques like EP-2000 utilizes sunlight in the water column to generate hydrogen peroxide around the hull, deterring biofouling.
     

  • Exhaust Gas Recirculation: The new IMO regulations on NOx emissions for 2016, Tier III, will require that ships reduce emissions by 80%.

         Having mentioned the prospective ideas above, Clear, consistent, and efficient regulatory frameworks are an essential requirement  for the deployment of any new technology.
 

Impact

Comparison of stats before and after the introduction of Green ships.



Here are some basic comparisons and stats which can give how an efficient green ship can be proved to be cost-effective as well as safe to our nature

  • Sail system is a huge part of green ship technology as it brings in the use of a renewable source that is wind. Sail systems like kite sail, rig sail and solar sail can reduce fuel consumptions by 20-40%, 30% and 20% when used as a hybrid sail mechanism.
  • An optimised cooling system can save up to 25% electricity and 1.5% of fuel cost.
  • An efficient exhaust scrubber can reduce 98% of the release of harmful oxides of sulphur.
  • A speed nozzle can increase efficiency at higher speeds and can reduce 5% of fuel needs.
  • Improved hull paints can reduce friction and can save up to 8% of fuel.
  • Air bubble hull lubrication can also save up to 8% of fuel costs.




Conclusion


Shipping is vital to the world economy. It is a critical part of international  import and export markets and supports the global distribution of goods.  As for all industries, concerns about climate change require keen insight on pollution from the shipping sector.This way the international trade will be on a smooth track and the maritime industry will be blooming without any hardship .The industry must prepare  for the new future and investigate alternative, more green ships for a greener and better world that we dwell upon.



Image Courtesy: Marine Insight
Article by: Shivansh Singh and Sunand Krishna.