ShipInsight Critical information on marine technology and regulation
Energy Saving Devices
AN IN DEPTH TECHNICAL GUIDE
The latest in research, technological advances and regulation
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Introduction TO ANYONE who has been directly involved with the shipping industry for even a short time, the idea that those who run ships need to be beaten with a regulatory stick to make them adopt more efficient means of doing so is laughable. Old hands will remember the oil crises of the 1970s when fuel prices began rising in 1973 and went on doing so for around 7 years before falling back over a similar period to levels adjusted for inflation that were similar to those in 1973. Over the next fifteen years the adjusted price of fuel did fall slightly and rise again back to the base line before taking off once more on what has since been an inexorable rise. Effectively that means that fuel prices have been on an upward trend since the mid-1990s and show no signs of an early reversal. In another time fuel prices might just be affordable but owners now have had other calls on their pocket to contend with: ballast water treatment systems, emission controls to limit supposed pollutants, additional administration costs in the way of ISM, ISPS and numerous other codes and even a potential levy on fuel use by way of a CO2 tax. More to the point, since 2008 all those costs have come on top of falling revenues caused by global depression. Efficiency has therefore become a key driver for all operators so any measure that helps is welcome. Looking back, it can be seen that some of the energy saving devices now being used were conceived decades ago and others more recent were still developed long before the now mandatory EEDI was even considered by regulators. The fact that the effect of these devices can be included in the calculation of a ship’s EEDI means they will become an even more useful tool in meeting both owners and the regulators’ ambitions.
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Energy Saving Devices
Contents Editor: Malcolm Latarche email@example.com
Chapter 1 – Regulation...........................................4 EEDI still a work in progress
Head of Design: Chris Caldwell Layout & Production: John Amy Advertising Sales: firstname.lastname@example.org ShipInsight Ltd 145-157 St John Street London EC1V 4PW United Kingdom www.shipinsight.com The Energy Saving Devices Guide is produced by ShipInsight Ltd. Care is taken to ensure the information it contains is accurate and up to date. However ShipInsight Ltd accepts no responsibility for inaccuracies in, or changes to, such information. No part of this publication may be produced in any form or by means including photocopying or recording, without the permission of ShipInsight Ltd. Register at shipinsight.com to receive the next free guide.
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Chapter 2 ESDs - An Overview.............................10 Fighting to keep costs down Chapter 3 – Bow Forms.........................................14 New shapes show the way to saving Chapter 4 – Hull Appendages.............................20 Directing the flow Chapter 5 – Rudders and Propellers....................25 Combinations and changes aid efficiency Chapter 6 - Engine Related Systems...................29 Getting more for less Chapter 7 – Innovative Technology.....................34 Future fuel saving ideas Chapter 8 – Case Studies......................................38 Success stories for pioneers
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Energy Saving Devices
Regulations Image: Det Norske Veritas
AS THINGS stand there is no regulatory requirement for any ship to be built with, or to employ at any stage in its life, any means of energy saving whatsoever. However, as from January 2013 there has been a requirement for some new ships to meet an Energy Efficiency Design Index (EEDI) rating otherwise the vessel may not be permitted to trade. EEDI will apply to ship orders placed on or after 1 January 1 2013 and to ships delivered after 1 January 2015 but ordered before 1 Jan 2013. Initially ships will need to meet or better the average efficiency (as decided by the IMO) of the current fleet of that particular ship type. Ships being built to designs that are currently above the line will have to be modified in some way which could involve employing one or more energy saving devices.There is also a requirement for all ships of 400gt and above to have an individual Ship Energy Efficiency Management Plan (SEEMP). The SEEMP is not required to be on board before the first renewal/ intermediate survey of the IAPP certificate after 1 January 2013. These regulations have come about as a result of the adoption of amendments to MARPOL Annex VI by parties to that particular annex at MEPC 62 in July 2011. 4 Â | Â shipinsight.com
Regulations Not every state is a party to MARPOL Annex VI but most major maritime nations are, and since those that are can require all ships entering their waters and ports to comply with the Annex, there is no chance for ships to avoid complying except by trading domestically or only with a neighbouring state that is also not a party. It has to be said that the adoption of the amendments was not without controversy and several countries voted against the adoption and concessions have been granted to some developing countries with regards to the timetable associated with the EEDI. Even before its adoption, the EEDI was heavily criticised from several quarters both within the shipping industry and from those in academia because it appeared to be promoting a future standard of ship that was either likely to be underpowered or less robust than would be considered desirable. Other opposition to the whole concept of energy efficiency indexes and management plans spring from the widely held view that operational strategies are not the province of the IMO or even local regulators but purely a matter for the shipowner or operator to decide. It is also no secret that the decision to include carbon dioxide emissions in Annex VI which was originally intended to deal with genuine pollutant gases such as SOx and NOx is in no small way connected to the UNFCCC’s attempts to build a large fund for dispersal to developing countries. Regardless of individual viewpoints, it is a fact that the regulation has been adopted by the IMO and is in place and must therefore be complied with. Soft Option SEEMPs are now mandatory on all vessels above 400gt and without a doubt a lot of owners are employing consultants or opting for offthe-shelf instant plans when many – including BIMCO – believe that preparing a plan is a relatively easy undertaking that could be done in-house. The organisation even publishes a Step-by-Step Ship Energy Efficiency Plan which it claims ‘allows owners and operators to create ship-specific SEEMPs with ease’. The publication costs the princely sum of £100 for members and £130 for everyone else. Classification societies are another good source or advice on preparing SEEMPs with most of the major societies having produced templates which are freely available and which could be used by an owner to produce a compliant plan without too much difficulty. The IMO document detailing the essentials requirements of a SEEMP is Resolution MEPC.213(63) adopted on 2 March 2012. It replaces shipinsight.com | June 2013 | 5
Energy Saving Devices MEPC.1/Circ.683 which contained the earlier guidelines used for preparing most of the voluntary SEEMPs now in use. Even though it is now mandatory for each ship to have its own SEEMP, there is no compulsion or force to adopt any particular energy saving measure. In its own words, Resolution MEPC.213(63) says it provides guidance for the development of a SEEMP that should be adjusted to the characteristics and needs of individual companies and ships. The SEEMP is intended to be a management tool to assist a company in managing the ongoing environmental performance of its vessels and as such, it is recommended that a company develops procedures for implementing the plan in a manner which limits any onboard administrative burden to the minimum necessary. The SEEMP should be developed as a ship-specific plan by the company and seeks to improve a ship’s energy efficiency through four steps: planning, implementation, monitoring, and self-evaluation and improvement. These components play a critical role in the continuous cycle to improve ship energy management. With each iteration of the cycle, some elements of the SEEMP will necessarily change while others may remain as before. At all times safety considerations should be paramount. The trade a ship is engaged in may determine the feasibility of the efficiency measures under consideration. For example, ships that perform services at sea (pipe laying, seismic survey, OSVs, dredgers, etc.) may choose different methods of improving energy efficiency when compared to conventional cargo carriers. The length of voyage may also be an important parameter as may trade specific safety considerations. The guidance given by the IMO sets out the various tasks to be undertaken in each of the four stages mentioned earlier and identifies areas which an owner could usefully focus on to improve fuel saving. There is very little in the guidance that will come as being a startling revelation to owners who have been looking at every fuel saving opportunity available for some time but having it codified may help to focus minds over the longer term. The fact that there need be no genuine outcome from the SEEMP as regards definitive efficiencies would seem to dilute their usefulness and it is almost certain that for many operators it will be nothing more than a paper exercise. Because the key to improved efficiencies can be something as simple as getting the office and ships’ crews to work together, 6 | shipinsight.com
Regulations operators who fail to involve all parties will lose out, especially as the SEEMP must be available in a language that the crew can understand. Owners that have been pioneers in making use of voluntary SEEMPS have reported significant savings from simple things such as improving trim, better cargo stowage, use of weather routeing and speed optimising. These are things that the crew are best involved in while hull and propeller cleaning are areas that need to be arranged by shore staff. EEDI - COMPLEX AND CRITICISED Πfj (ΣPME*CFME*SFCME) + PAE*CFAE*SFCAE + (Πfj*ΣPPTI – Σfeff*PAEeff)*CFAE*SFCAE - Σfeff*Peff*CFME*SFCME fi * Capacity * Vref * fw A ship’s EEDI rating is devised from the latest version of the original formula shown above which, until broken down into its constituent parts, looks far more complicated than it is. The formula has been amended more than once since it first appeared and the latest version is contained in MEPC.212(63). That document is a 20-page manuscript which as well as the latest version of the formula also contains other information related to dispensations given for certain ship types such as shuttle tankers with redundant propulsion systems. It is likely that the formula will be amended again because there is still debate over certain aspects of it. Even at the time of its adoption the final formula applicable for the first vessels had not been fully agreed. There are also some ship types to which the formula will not apply. Essentially the formula adds the CO2 emissions of the main engine(s) less any power take out device, to the CO2 emissions of the auxiliary engine(s) and the CO2 emissions due to power supplied by any power take in system. It then deducts any CO2 emissions saving allowed by ESDs and systems. The result is then divided by the product of the deadweight and the speed of the ship to give a figure that represents grams of CO2 per tonne/nautical mile. Allowance for reserve power for use in heavy seas is made by calculating main engine power at 75% and a similar allowance against deadweight is made for container ships which rarely carry a full deadweight cargo. The EEDI regulations will lay down a target rating that a ship will not be permitted to exceed so simple mathematical logic dictates that the lower the final figure above the line and the higher the figure below, the shipinsight.com | June 2013 | 7
Energy Saving Devices greater will be the chance of meeting the required EEDI. That can be achieved in one of several ways. The first is reducing the power of the main and auxiliary engines which is easily achieved but has led to accusation that the result could be dangerously underpowered ships. Alternatively the deadweight and/or speed could be increased but doing the first would give the same underpowered vessel result and increasing speed could probably only be done by increasing power which would be counter-productive as an increase in power would be needed. All of which leaves reducing the above the line figure by making use of ESDs and power take in such as could be provided by waste heat recovery as the best option. The reference line from which the rating of measured ships will be read has been formulated using data of the existing fleet. As the reference line has been placed in the mid-range of the fleet, meeting the first reduction will likely not present too many problems for shipyards and designers. Reference lines have been drawn up for several ship types beyond the seven categories that will be included from the outset. The ship types first affected are; bulker, tanker, containership, gas carrier, general cargo, reefer and combination carrier. As things stand, agreement has not been reached on an acceptable formula for diesel electric cargo ships or for non-cargo vessels. EEDI will apply to ship orders placed on or after 1 January 1 2013 and to ships delivered after 1 January 2015 but ordered before 1 Jan 2013. This first tranche of ships will only need to meet the reference ratings set by the IMO. It is said that this represent a 0% efficiency improvement but that is true only for current ship designs that are at or below the IMO base line. Ships being built to designs that are currently above the line will have to be modified in some way. Greater efficiencies are demanded for the future. The current programme will require 10% greater efficiency for ships delivered between 2015 and 2019, 15-20% depending upon ship type and size between 2020 and 2024, and 30% from 2025 onwards. The idea of drawing a line at certain dates may suit regulators but it poses a big problem for yards and owners ordering series of vessels. At present the world orderbook does not extend far into the future so only a relative few ships will be affected but further forward that may not be the case. A series of ships that straddle one or more of the EEDI deadlines will either have to be designed to meet the most stringent rating or else 8 Â | Â shipinsight.com
Regulations will have to be modified between dates meaning that the advantages of building series ships will be lost. A ship will not be given an EEDI certificate until it is confirmed that it has met the required criteria. Effectively this can only be down when the ship is completed and undergone sea trials. Model testing and computer software can help predict actual performance but these methods are not 100% accurate and it may be possible for a new design of vessel to fail at the last hurdle which would require it to return to the yard for modification.
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Energy Saving Devices
ESDs - An Overview Image: Maersk Line
ENERGY SAVING DEVICES (ESDs) come in many guises from hull modifications, through to propeller/rudder combinations and appendages and adaptations to engines and machinery. Taking things a little further, the term can include means of exploiting energy from the wind, sun and waves or storing excess power by way of batteries for use later. It is even possible to consider coatings systems and some software as ESDs as both of these very different products can reduce a ship’s fuel costs by as much as 10% when chosen wisely. Their effect can be though be transient as coatings will gradually deteriorate and software is only as good as it can be when its recommendations are followed by the crew. Today, ESDs have become linked in the minds of many to the slow steaming strategies adopted by some operators – particularly in the container trades. While it is true that some devices such as turbocharger cut-outs and concepts such as variable turbine geometry have come about simultaneously with slow steaming, their use can be extended to vessels for other reasons as well. Slow steaming as a strategy to absorb surplus tonnage has proven invaluable to many operators in the poor economic circumstances exist10 | shipinsight.com
ESDs - An Overview ing since 2008 but whether it is viable in the long term remains to be seen. To meet the demands of world trade, the various sectors of the shipping industry must have sufficient capacity available. Meeting demand historically has been a combination of more ships, faster ships, bigger ships and improved cargo handling techniques reducing port stays to the minimum. There are limits to all of these strategies that will vary with demand. More ships means more crews are needed which would make the existing problem of a lack of trained seafarers even worse. Faster ships tend to require more fuel but ESDs can reduce the negative effect that has in this time of high fuel prices. Bigger ships do indeed give economies of scale but only when running fully loaded, otherwise the additional port costs and reduced choice of ports can become diseconomies of scale. Improved handling techniques have been promised but since the advent of the container these have come only in tiny increments as regards ship efficiency as opposed to cost. Many of the ESDs available today have their genesis in earlier financial crises when fuel costs rose but slow steaming was not seen as the universal answer it is presently. The object then was not to save fuel by going slower but to travel faster or further using the same amount of fuel. In the 1980s and 1990s, Japanese yards were very much to the fore in developing ESDs especially for the bulk carriers and tankers that the country – then the world’s leading shipbuilder – was most renowned for. These improvements came mostly in the way of improved bow shapes and hull appendages such as ducts and pre-swirl stators. One Japanese shipbuilder – Tsuneshei could even lay claim to have invented today’s buzzword Eco-ship when in 1984 it revealed the first in its long running series of TESS bulk carrier designs. At the time Tsuneshei said that TESS was an abbreviation for Tsuneshei Economical Standard Ship. Since the first vessel in 1984, the builder has delivered several hundred ships to variants of the original design with some more recent versions adopting other ESDs as well. Despite their claimed improvements in efficiency, these ESDs are still not standard on all current bulker and tanker designs. However, the fact that many of them have been incorporated into series ships has allowed their efficiency to be reasonably well defined and confirmed by comparing performance with similar ships without the devices. It is much harder to calculate the cumulative effect of various ESDs as this will never be the shipinsight.com | June 2013 | 11
Energy Saving Devices
EDSs - An Overview
sum of all of the claimed efficiency savings. As previously mentioned the EEDI recognises the benefit of higher speeds but perversely will inevitably restrict average speeds because of its demand for lower power. Adding ESDs could be one way around this conundrum and could increase the flexibility of ships in a way that designing them solely for restricted speed will not. A ship that can increase speed when necessary or slow down as appropriate is – so long as its fuel consumption is within reasonable bounds – always going to be a more attractive proposition than a vessel that struggles to reach a service speed considered normal for its type.
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Energy Saving Devices
Bow Forms Image: Ulstein Group
Rethinking the bulb Until the 1980s, the sight of the now ubiquitous bulbous bow on a cargo ship was an uncommon occurrence. Although bulbous bows were nothing new and had been around for at least 50 years in naval and high speed passenger vessels were they were designed to increase speed, their adoption on slower cargo ships was always more connected with economy. The bulbous bow works by producing a bow wave of its own that equalizes that produced by the ship. The result is less resistance which can either translate as higher speed or less fuel consumption. However, the beneficial effect of any particular bulbous bow is only available across a narrow band of speed and depth. Outside of these parameters, the effect is at best neutral and more often than not negative. Because ships frequently have varying operating conditions – especially bulk carriers and tankers which can both spend much of their time sailing in ballast – the shape and size of the bulbous bow will be such as to give optimum performance at the most prevalent operating condition and minimal performance loss at other times. Often the bulb is a comshipinsight.com | June 2013 | 13
Energy Saving Devices
promise that takes into account the effect of slamming, potential damage by the anchor and chain and other factors such as not being extended beyond the bow proper for safety reasons. Again, if the operating strategy changes, it may well become noticeable that the ship’s performance drops because the bulbous bow it has been fitted with is no longer suited to the changed operating conditions. This phenomenon has been particularly noticeable in container ships adopting slow-steaming strategy as most have been doing since 2008. In cases where an operator decides that a new operating strategy is called for, a replacement bulb may well be a better option than continuing with the original. Germanischer Lloyd’s FutureShip research section was one of the first organisations to promote the idea of a bulb change and presented a technical paper on the subject at NorShipping in 2009. Using the case of an 8,000teu container ship designed to operate at a service speed of 25.5kt but then slow steaming at 18kt, FutureShip was able to devise a new bulb that model tests showed would give a 2.5% reduction in resistance and fuel consumption when slow steaming and a 1% reduction at the design speed. An even better performance at 18kt would have been possible but the operator of the ship that had requested the trials did not then plan to operate a slow steaming strategy indefinitely. At the time fuel costs were approximately half of what they are today so the payback time then quoted of 18 months might be just nine months now assuming the replacement work cost was about the same. Since then several major operators including Maersk line have begun a retrofit programme for some ships in their fleet. Improved bow forms A noticeable trend in recent years has been the development of new bow forms some of which dispense with bulbous bows altogether while others retain the bulb or integrate it into the main body of the bow. Many of the most recent new bow forms have originated in the offshore sector where all the leading ship designers have produced new designs. Offshore ships do have a different operational profile from most cargo ships and spend a lot of time in dynamic positioning mode where fuel is consumed purely to stay stationary. However, offshore ships also spend a considerable amount of time in transit between jobs and often in some of the harshest seas. Designers such as Ulstein group, Rolls Royce and STX Offshore (now 14 | shipinsight.com
Bow Forms trading as VARD since Fincantieri took a controlling stake) have all developed bow forms that are claimed to improve efficiency in transit mode for offshore vessels. Ulstein has developed cargo ship versions of its X-Bow design but as of yet none have been built. VARD has kept its attention purely on offshore but Rolls-Royce can claim cargo ship references for its Wavepiercing bow which retains the bulb but in an integrated rather than protruding position. The Rolls Royce bow form is an essential part on the company’s Environship design portfolio. So far cargo versions include a fish food carrier and a multipurpose cargo ship for coastal and short sea work. Japanese innovation In the cargo ship sector, the development of new bow forms has been at a slower pace but has been going on for considerably longer, particularly in Japan where most major shipbuilders have developed bow forms that depart from the conventional shape for their type. In 2000 NKK (now part of Universal Shipbuilding) developed the AxBow and first applied it to Mitsui OSK Line’s Capesize bulker Kohyohsan. The Ax-Bow introduced a much sharper bow shape above the bulb compared to the rounded bows of more conventional vessels. The effect of the was to deflect the incident wave to the side rather than forwards reducing resistance. It was claimed that this modification offered fuel savings of 3%-4% or the option of a similar reduction in horsepower of the main engine. Soon after, Universal Shipbuilding developed the Ax-Bow further by extending the leading edge of the bow down to meet what remained of the bulb. This new shape was dubbed Leadge-Bow from combining “Leading” and “Edge.” Model tests confirmed the Leadge bow has the same wave making resistance in still water as the conventional hull with bulbous bow but in waves it outperforms the Ax-Bow allowing a further efficiency saving of 1-2%. Several ships have been built with the Leadge bow but Universal was unable to patent it because it was considered to be too similar to bow forms of earlier generations of ships. A similar bow form to the Leadge Bow is the Oshima Seaworthy Bow which has been incorporated into a number of bulk carriers and tankers including the Tsuneshei TESS58 HandyMax type. The bow form was also an integral part of the Oshima ECO-Ship 2020. The Open Hatch Bulk Carrier concept features a number of interesting design solutions to be researched and developed for reduced fuel consumption and efficient operations. The project has been executed as a joint project between shipinsight.com | June 2013 | 15
Energy Saving Devices Oshima and DNV. Rolls-Royce Marine has contributed ideas for LNG engines and propulsion and Kockums of Sweden and FiReCo from Norway has contributed to the development of GRP solutions for areas of the ship’s structure to reduce weight. Other Japanese builders that have their own bow forms include Onomichi, whose Straight Bow has a shape somewhere between the Ax- and Leadge bows and Shin-Kurushima Dockyard which with Hiroshima University has jointly developed the SKBow (Shin-kurushima Knuckledshape Bow). Dutch designs Novel bow forms are not restricted to Japanese shipbuilders as Dutch and Korean builders have also had some success in introducing new designs. Damen Shipyards has its Axe Bow and Groot ship Design has the Cross Bow. The Damen Axe Bow was developed in conjunction with Delft University of Technology it incorporates an almost perpendicular bow of very fine knife edge proportions. Based on the Axe Bow Concept, Damen has developed the Sea Axe Patrol Vessels and Fast Crew Suppliers. Damen claims the Sea Axe concept can give a dramatic reduction in wave resistance allowing fuel use to be cut by 20% because of the optimisation of the hull form in actual operating conditions although the primary intention had been to increase seaworthiness and comfort. Cargo ships are most definitely the target of the second Netherlandsbased designer Groot ship Design which has developed the Groot Cross-Bow. The shape of the bow, which was tested in the ice-tank in Hamburg, together with an optimised hull shape allows for a significantly smaller main engine, resulting in lower fuel consumption and a smooth ride in heavy weather with more comfort for crew and cargo. The bow design can be found on the Super Green 8500 series of 8,000dwt single-hold general cargo ships built at Jiangsu Yangzijiang Shipbuilding for Carisbrooke Shipping and the later and larger Super Green 10000 series for the same owner.
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Energy Saving Devices
Hull Appendages A SHIP’S hull lines are optimised to both house the intended cargo and to enable the ship to move through the water with the least resistance at its intended service speed. Sometimes meeting the two requirements results in something of a compromise and this is especially so if the ship’s design has also required its dimensions to be restricted so as to allow entry to particular ports. Often it is possible to reduce the element of compromise that is required by making use of hull appendages that in some way improve the efficiency of the vessel. The bulbous bow is one such appendage and was considered in the previous chapter. Most appendages are to be found at the aft end of the vessel and are more common on ships with a high block coefficient such as bulk carriers and tankers than on container ships. This is because on wider vessels, the water flow to the propeller can benefit from being modified so as to allow the propeller to impart greater thrust to the vessel. There is one appendage that has been developed by Japanese builder Naikai Zosen Corporation that is placed forward on the hull. The device is known as STEP (Spray TEaring Plate) and comprises of a pair of plates shipinsight.com | June 2013 | 17
Energy Saving Devices
around 5m in length, one attached to either side of the bow above the waterline. At first sight in calm water conditions the device would seem to offer little in the way of energy saving but it is designed to operate by reducing the resistance caused by the bow wave that builds in heavy seas above the waterline in medium and high speed ships including car carriers and container vessels. In tank tests, the device was estimated to decrease the wave resistance by about 18% under heavy wave conditions and to reduce the energy consumption by about 2% under head waves at Beaufort scale 6. The energy consumption of the first vessel fitted with the device – the PCTC Jupiter Spirit – was compared with ship operation data obtained from a similar car carrier without the STEP, built in the same period. The comparison was carried out by Class NK using sample data referring to design conditions of The STEP, which include full load condition in summer, head wave angle range within +/- 90 degrees, and significant wave height of 3 m. As a result, about 3% decrease in energy consumption was proved under the conditions of 2m or more high waves. Channelling the flow Concentrating the flow of water to the propeller on slow, widebodied vessels is widely recognised as having a beneficial effect on a ship’s efficiency although the majority of ships of this type built have no modifications aimed at improving their performance. The possible modifications available fall into three categories of appendages fitted upstream of the propeller. The categories are; fins or spoilers, ducts and pre-swirl stators. The devices can be employed alone or in combination and may even be complemented by more devices downstream of the propeller and optimised rudder/propeller systems. Different builders have developed proprietary versions of one or more of the devices and in Japanese and some South Korean yards they will be offered as part of the package when selling standard designs. Fins or spoilers are superficially similar to a bilge keel but much smaller and located strategically to concentrate and direct the wake flow to the propeller. As well as improving efficiency, these devices can also contribute to a reduction in propeller cavitation which produces other benefits including more comfort and less noise. Several shipbuilders have developed designs that feature fins of this type and have given them proprietary names such as Sanoyas Tandem 18 | shipinsight.com
Hull Appendages Fin, Onomichi Parallel Fin, Namura Flow Control Fin and Oshima Flipper Fin to name but a few. Although all those mentioned are Japanese, South Korean builders also employ similar devices. Some builders have adopted very similar systems while others have unique patented devices. Regardless of type, energy savings between 1% and 4% are claimed. For EEDI purposes, the fuel saving effect can be measured either by comparing identical hulls with and without the devices during sea trial or by model testing of CFD. Ducts that equalise the wake and concentrate it more than fins can deliver significant savings alone and can further enhance the small benefits that fins can confer. As with fins, ducts come in many forms from simple LJ bracket types to more complex versions such as Becker’s Mewis Duct. In some cases, the duct will be formed by structures either side of the skeg but some are fully circular structures placed just forward of the propeller. In the latter case they should not be confused with a nozzle propeller in which the propeller is located inside the nozzle. Ducts are said to be more effective on wide bodied slow moving vessels and savings have been claimed in some instances to be in double figures. Many builders of bulk carriers and tankers have standard designs that feature some form of duct. In recent years, Becker Marine has promoted its Mewis Duct as a retrofit ESD and has managed a considerable number of sales. The device is also suitable for newbuildings and these make up around 40% of sales. Since so many have now been retrofitted to vessels, the company claims that statistics of ‘before and after’ consumption figures can now prove an average fuel saving of 6% rising to 8% when combined with an appropriate design of Becker Rudder. The basic concept has been further into the Becker Twisted Fin designed for use on vessels with finer lines than the bulkers and tankers the Mewis Duct was developed for. In the Twisted Fin, the nozzle ring is considerably smaller than the Becker Mewis Duct and has a slimmer profile. The fins on the inside of the nozzle ring extend outwards beyond the nozzle. To prevent the formation of a swirl with cavitation at the ends of the fins, Becker has developed special end caps for the fins similar to the winglets familiar from modern aircraft wings. The final type of ESD fitted forward of the propeller is a pre-swirl stator. These generate a swirling flow opposite to the rotation of the propeller that the propeller blades as an additional blade loading, through shipinsight.com | June 2013 | 19
Hull Appendages which the delivered thrust per unit of power is raised. A pre-swirl stator can result in fuel savings of around 4%-6%. The device has the appearance of a small fixed multi-bladed propeller mounted directly forward of the propeller itself. The number and size of blades varies between designers and shipyards and may be described using a proprietary name. The fins inside the Mewis Duct act as a variety of pre-swirl stator. It is usually possible for a pre-swirl stator to be fitted as a retrofit on most vessels.
Rudders and Propellers
Rudders and Propellers Image: Wärtsilä
POSSIBLY the highest efficiency gains possible can be made by optimising the propeller and rudder combination. A propeller change on a Northern European ferry has produced a claimed 17% improvement in efficiency although figures in the region of 9%-11% are more commonly quoted. Azimuthing and podded propulsors are found on many cruise and offshore vessels and are said to give a fuel saving advantage. However, very few cargo ships make use of such an arrangement and since the ships they are usually employed on are generally diesel-electric and thus outside of EEDI as things stand, their potential is not covered here. An incredible amount of time and money has been spent upon research aimed at improving propeller performance over recent years. As well as looking at the propeller itself in terms of size, blade shape and number of blades and the speed at which the propeller turns, some research has gone in other directions and resulted in more complex propeller configurations such as contra-rotating propellers and attachments such as boss cap fins. A contra rotating propeller has two powered shafts with one inside shipinsight.com | June 2013 | 21
Energy Saving Devices the other and rotating in the opposite direction. The outer shaft carries the main propeller and a secondary propeller is mounted on the inner shaft behind. The principal behind the contra-rotating propeller is that the rotational energy losses behind the first propeller are recovered by aft propeller which has a different direction of rotation. A propeller with a boss cap fin works on similar principals but here the propeller boss has integrated vanes that break up the hub vortex generated behind the rotating propeller. Originally developed in the mid-1980s by Japanese operator MOL in co-operation with West Japan Fluid Engineering Laboratory and Mikado Japan, the device has now been fitted to over 2,000 vessels some as retrofits. Test on the device attached to an Aframax tanker conducted by BMT Defence Services demonstrated a reported 4% fuel saving. Because retrofitting a propeller boss cap fin is a relatively simple and inexpensive modification it is becoming increasingly popular among operators of many different ship types. Improving efficiency by way of a propeller change is an undertaking that is not without risks considering the time and expenses involved in manufacturing and fitting a new propeller. As with modifying the bulbous bow, a change of propeller will require professional advice on the shape and size of the replacement. Modern computer aided design and CFD can remove some of the risk of the replacement being no better or worse than the original. Assuming a propeller change does produce beneficial results – and in most cases it is likely that it will – it is a relatively simple task to repeat the operation on sister vessels. The propeller change that reportedly produced 16% fuel savings on the Stena Germanica was in fact a change of blades on a controllable pitch propeller as opposed to a complete propeller change. On a newbuilding, an appropriate propeller choice can allow for a de-rated engine to be fitted without a detrimental effect on the ship’s speed in comparison to existing ship types. The relationship between engines and propellers is a very good reason why some of the main engine manufacturers have their own propeller making divisions. Last year, MAN Diesel & Turbo increased its Alpha range with its take-over of Kappel propeller. Compared to conventional designs, the Kappel propeller blade designs offer fuel savings by up to 6% due to the tip vortices formed due to the difference in pressure between the pressure and suction side of the propeller.
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Rudders and Propellers Working together Further efficiencies are available from propeller/rudder combinations which are recent arrivals on the propulsion scene. Possibly the two most well-known are the Rolls-Royce Marine Promas system and Wärtsilä’s Energopac but other companies working alone or in tandem with others have similar systems on the market, one example of this co-operation is that between German propeller maker MMG and Dutch rudder maker Van der Velden. Typical efficiency savings of between 2% and 9% are claimed with the wide range due to different vessel types. The Rolls-Royce Promas consist of a twisted full-spade rudder with bulb that is smoothly connected to the propeller hub by a hubcap, and is adapted and optimised to the propeller design. A well-designed twist adapts the rudder to the rotation of the propeller slipstream and reduces the local angle of attack on the rudders leading edge. This gives a more efficient rudder with lower drag and better recovery of rotational energy from the propeller slipstream. The best results are achieved on blunt single screw vessels with a block coefficient of 0.75-0.85 and a design speed in the 14 to 16kt range. Here the efficiency gain can be as much as 6-9% compared with conventional solutions. For faster and slenderer single or twin screw vessels such as car carriers, efficiency improvements of 2-5% can be expected. Wärtsilä’s Energopac is a very similar design and is claimed to create less drag than conventional rudder systems. Most notably, when using small – corrective – steering forces to maintain course, the difference in rudder resistance is significant. The high-lift performance of Energopac requires smaller steering angles, which consequently reduces rudder resistance. The reduction in fuel consumption depends very much on the type of vessel, its operational profile, and on the reference propeller and rudder. Proven savings in required power for a vessel’s trial speed vary between 2–9%. The potential savings are large for vessels with highly loaded controllable pitch propeller systems, such as RoRo-vessels, ferries, container / multipurpose vessels, and vessels with an ice class notation. The two systems described above are designed from the outset with matched rudder and propeller but modifications to existing vessels are also possible. Promas Lite, a simplified version of Promas is intended for retrofit upgrading. The vessel’s existing rudder is retained, but is fitted with a prefabricated bulb, while the propeller is equipped with a special hubcap and new blades. shipinsight.com | June 2013 | 23
Energy Saving Devices The propeller is designed to utilise the fitted bulb and is matched to the vessels current operational profile, which may have changed since the vessel was built. Installation of a complete Promas Lite upgrade kit can normally be undertaken within a normal 7-10 day docking period. Recent Promas Lite installations on twin screw cruise vessels demonstrate efficiency improvements up to 20% can be achieved, giving a payback period of well under two years. For these vessels the propeller designs were not only adapted to the Promas Lite system but also for the vessels current operational profile. Rudder manufacturers have also been developing new rudder forms that both improve manoeuvrability and fuel efficiency. Typical developments included new rudder leading edge profiles, bulbs and fins.
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Engine Related Systems
Engine Related Systems Image: MAN Diesel & Turbo
THERE ARE two main ways in which additional energy can be taken from an engine in ways that affect the EEDI calculation. Both shaft generators and waste heat recovery involve complex systems rather than simple devices but are worth careful consideration by operators looking to improve energy efficiency. Shaft generators have been around for many years and are quite common on ships. They draw power from the shaft between the engine and propeller or gearbox reducing the need to run auxiliary generator sets. But there have been limitations. The ship’s electrical system normally requires a fixed frequency and this means that engine speed has to be kept constant, which often leads to inefficient engine operation. Rolls-Royce has recently developed a hybrid shaft generator that as well as taking power off of the main engine can also be run in reverse and used a power take in device. Under EEDI regulations the fuel consumption of power take in devices has to be added to that from other main and auxiliary engines, which leaves the hybrid shaft generator in an odd position of potentially being included in both sides of the equation. Discussions are ongoing on the matter of how it should be treated for shipinsight.com | June 2013 | 25
Energy Saving Devices EEDI purposes. Although considered the most efficient type of internal combustion engine, marine diesels are only around 50% efficient at best and half of the energy in the fuel is lost as waste heat. Some of that heat is recovered using a heat exchanger to provide hot water for domestic services onboard but most is carried away in the exhaust. In a waste heat recovery system, the heat energy is generally converted to steam which then runs a turbine producing electricity but there are other options. Waste heat recovery systems have come to the fore in recent years mostly as a means of eliminating an auxiliary engine particularly on container vessels where the electrical requirements of reefer boxes means that demand for electricity is always high. The electricity produced can also be fed to a power take in device to supplement the main engine if required. Both main engine manufacturers – Wärtsilä and MAN Diesel & Turbo – promote WHR for use with their large two-strokes and see them as an effective tool to meet EEDI requirements. The energy that can be recovered by means of a WHR system is significant and into double figures but the system can be demanding of space and is therefore best suited to a newbuild situation. A factor that has to be considered if opting for a WHR is that the system must be matched to the engine and operating strategy. A number of systems installed on container ships in the years up to 2008 have likely never been used to their best potential as the slow steaming practised by the operator has meant that the exhaust temperature is lower and also that there is insufficient pressure to run the turbocharger and the power turbine simultaneously. The simplest and cheapest system consists of an exhaust gas turbine (also called a power turbine) installed in the exhaust gas bypass, and a generator that converts power from the power turbine to electricity onboard the ship. The power turbine and the generator are placed on a common bedplate. In MAN Diesel & Turbo’s TCS-PTG (Turbo Compound System – Power Turbine Generator) the power turbine is driven by part of the exhaust gas flow which bypasses the turbochargers. The power turbine produces extra output power for electric power production, the amount of which depends on the bypassed exhaust gas flow amount. The TCSPTG WHRS solution offers both standalone and parallel running electric power sourcing for the ship. In the TCS-PTG the exhaust gas bypass valve will be closed at an engine power lower than about 50% SMCR, where the engine will run 26 | shipinsight.com
Engine Related Systems with the same high efficiency as for a normal MAN B&W low speed twostroke engine. Using a TCS-PTG WHRS solution will provide a 3-5% recovery ratio, depending on the main engine size. The first order for the system was by German shipowner Reederei Horst Zeppenfeld which decided to install the system in a pair of 4,700teu container vessels being built by Samjin Shipbuilding in Weihai, China. The second system is the Steam Turbine Generator (STG). When designed as a stand-alone solution, the exhaust gas bypass stream is mixed with the exhaust outlet from the turbocharger(s), increasing the exhaust gas temperature before the boiler inlet. By installing a steam turbine (often called a turbo generator), the obtainable steam production from the exhaust boiler system can be used for electric power production. The steam turbine is installed on a common bedplate with the generator in the same manner as the power turbine and the generator. The system is more efficient that the TCS-PTG having a 5-8% recovery depending on engine size, rating and ambient conditions. Combining the two systems provides the most effective waste heat recovery system and is the best option if the electric power demand on the ship is very high. In such a system, the power turbine and the steam turbine are built onto a common bedplate and, via reduction gearboxes, connected to a common generator. The power output from the power turbine can be added to the generator via a reduction gear with a special clutch. However, first the steam turbine will start at 30 – 35% SMCR main engine power followed by the power turbine which starts power production at 40 to 50% SMCR. A shaft motor / generator (PTI/PTO) connected to the main engine shaft is an option with this system. Some 8-11% power can be recovered, depending on the main engine size, engine rating and ambient conditions. All of the systems could be negatively affected if a wet scrubber is installed as the scrubbing action has a cooling effect upon the exhaust gasses. To be effective a WHR needs a constant source of heat which is why they are usually run from the main engine, but the concept has also been extended to auxiliary engines, where it is claimed potentially significant reductions in fuel bills can be achieved. Alfa Laval Aalborg introduced its XS-TC7A auxiliary engine exhaust waste heat economiser at the end of 2012 and said at the time of its launch shipinsight.com | June 2013 | 27
Energy Saving Devices that if can be fitted to newbuildings or retrofitted to existing ships. The company says the in-line device is designed to have a low weight to output ratio and small size. Based on load factors, the economiser is capable of completely supplying or supporting ship steam requirements during manoeuvring and port stays. Two years of testing at sea has allowed Maersk to capitalise on the potential for waste heat recovery in both the main engine and the auxiliaries. As a result, the company has signed contracts for further installations of the economiser. Alfa Laval Aalborg suggests a quick return on investment – typically between 12 and 18 months. However, in some cases, it claims, payback could take only six to eight months. Actual returns depend on various factors, including the number of days when the steam produced can be used and a ship’s redundancy requirements. It is highly likely that in the not too distant future a new technology now being trialled on tugs, ferries and offshore vessels will become mainstream technology on cargo ships also. Lithium ion batteries – there are in fact several very different types of materials and technologies that go under that generic term – are currently at an early stage of development but show promise for storing surplus electrical energy for use later. Diesel engines do tend to have a quite narrow range of loading at which power output is most efficient but the fluctuating demands of many ships means that auxiliary engines are often running outside of their most efficient range. Often it is necessary to bring a second engine online to cover periods when one is not sufficient which usually results in both engines being run inefficiently. This can be overcome by replacing one auxiliary engine with a battery pack and running the other at the most optimum speed continuously. When not all of the power produced is needed, it can be diverted to charging the battery and when demand increases above the optimum output, the extra energy needed is drawn from the battery instead of bringing another engine online. A battery might also be topped up using other forms of electrical production such as WHRs and renewable sources such as solar panels. In some of the ferries now being built and incorporating battery systems the recharging is done using shore power supply. A joint computer modelling project between DNV and Norwegian shipowner Grieg Star has shown that installation of a battery pack in place of a diesel generator could cut fuel use by 30% and have a payback time of less than a year when used for powering ships’ cranes during 28 | shipinsight.com
Engine Related Systems cargo handling operations. Data obtained from Grieg Star’s latest Handymax Star Laguna’s four 75-tonne SWL cranes during operations over an extended period allowed DNV’s simulation tool to model a conventional and a battery hybrid power production system on board the vessel. The simulation included the cranes using a conventional system of diesel gensets to produce electric power while the hybrid system had a lithium-ion battery installed and fewer gensets. The cost and payback calculation on the vessel was on the basis of a 312kWh battery pack measuring approx. 3m3 and weighing three tonnes and costing approximately 10% more than the 995kWh generator it would replace. The generator operating parameters used in the model were based upon those used by the ship under operational conditions.
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Energy Saving Devices
Innovative Technology Image: Eco Marine Power
A NUMBER of innovative energy saving technologies are being considered or incorporated as prototypes into a small number of vessels. Some of these such as making use of wave energy have not yet made it off of the drawing board but projects involving wind and solar energy have and so also has air lubrication as a means of reducing the hydrodynamic resistance all ships experience. There have been many projects to re-introduce sail on ships over the years but none have achieved mainstream acceptance. Even so new concept ships making use of wind power are announced on a regular basis. The sails of these ships are planned to make use of new materials and technologies and are quite different from the canvas and rigging of the true sailing ships of old. Some concepts envisage sails made using solar panels that would also produce energy as well as making use of the wind. Despite the enthusiasm with which new types of sail are promoted, there are many practical hurdles to clear. As one example, modern day line of sight rules for ships would mean that sails are not viable as add-ons to existing ship designs where the bridge and engine rooms are normally placed at the stern. Other problems include the fact that very little genu30 Â | Â shipinsight.com
Innovative Technology ine testing has been carried out on how sails might affect the attitude of a vessel under sail. It could well be that maintaining an optimum trim for a vessel also running on its engine may be more difficult and the benefit of any savings would be lost. Kite assistance is another method of harnessing wind power that has been much talked about over the last ten years or so. Only one company, SkySails based in Germany has been consistently active in this arena but since the demise of its principal proponent, Beluga Shipping, very little activity has been reported. The latest news mentioned on the SkySails website would indicated that the company has branched out into trim optimisation software in 2013. Harnessing wind power by way of onboard wind turbines is another area that is being explored. In April 2013, Lloyd’s Register announced that wind monitoring project carried out in conjunction with Totempower Energy Systems on a bulk carrier managed by Zodiac Maritime Agencies had just been concluded. A year earlier, a fully autonomous wind-monitoring system, designed and assembled by Totempower, was installed on the Cape Flamingo. Sensors were installed in locations where the best wind conditions and the most relevant environmental data (wind speed, direction and turbulence) could be expected, with consideration given to the potentially most effective locations for onboard wind generation. The project has successfully identified and measured the potential generating capacity from wind power for the ship’s trading patterns. This data will be used to support the development of computational fluid dynamics-based simulation models, suitable for predicting the potential energy yields on other Zodiac ships. The results illustrate the potential of placing wind energy generators in way of the bridge wind stations where the vessels receives the best quality of unobstructed air flow. Designing a wind turbine for the prevalent conditions and the environment it is used in are important factors to consider at implementation level. Wind turbines of the conventional type may be able to contribute to the on-board auxiliary power supply, but are highly unlikely to replace it completely for practical as well as for operational safety considerations. A novel technology that has been long discussed but difficult to be proven in tank testing is the use of air to reduce the resistance of a ship. The difficulty with proving the technology lies in the fact that, while many thinks are possible to scale, the size of bubbles and their effect on an actual ship rather than a model is not one of them. shipinsight.com | June 2013 | 31
Energy Saving Devices Different proposals have been made as to the best place to generate bubbles. One method favoured by DK Group involves designing ships with a shallow cavity under the forward part of the hull which is filled with air from compressors on board the ship. The air then passes out of the cavity leaving a thin film of air bubbles between the hull and surrounding water. The company has said that retrofitting the technology is a possibility on most vessels. The first system is planned to be fitted to a Danish vessel which was said to have been scheduled for delivery in late 2012. No further details have since been released on the installation or on any sea trials. A very similar system was chosen by Japanese builder Mitsubishi. This has already been commercialised as the Mitsubishi Air Lubrication System (MALS) on at least three vessel including two NYK-operated chip carriers and a ferry. The system has been shown to reduce fuel consumption by around 10% on the two cargo ships. Results for the ferry have not yet been announced.
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Case Studies No. 1 – Bow form Theoretical knowledge is all very well but practical experience is a much better yardstick by which to judge the performance of new technologies. The following case studies have been selected to illustrate some of the devices and ideas in earlier chapters of this guide. Germanischer Lloyd was asked by Carisbrooke Shipping to assist with EEDI certificates for four low emission dry cargo vessels. Built by Chinese shipyard Jiangsu Yangzijiang Shipbuilding, the four 8500 DWT sister vessels, the Vectis Eagle, Falcon, Harrier and Osprey incorporate a number of innovative features, including the distinctive Groot CrossBow. The four vessels, which have been built to Finnish Swedish Iceclass 1A, have been designed and constructed to optimize energy efficiency in almost every facet of operation. The Groot Cross-Bow was incorporated to minimise vessel pitching and reduce the load fluctuations on machinery and speed loss in heavy weather – resulting in less wasted energy and fuel consumption.
No.2 – Ducts and fins Damen Shiprepair Rotterdam recently completed the installation of the propulsion-boosting Becker Twisted Fin on seven container vessels belonging to German operator Hamburg Süd. The Becker Twisted Fin devices have been installed on seven Santa class container vessels, each with a capacity for 7,100teu and design speed of 22 knots. Becker Marine Systems said the system offers a fuel saving of up to 4%, reduces NOx and CO2 emissions, and requires no moving parts or maintenance. Becker Marine Systems developed the energy saving device for container ships and other types of fast vessels with bulbous sterns after shipinsight.com | June 2013 | 33
Energy Saving Devices
two years of research. The Becker Twisted Fin generates a pre-swirl to counter the effect of propeller swirl, which reduces the efficiency of ships. Becker has developed special end caps for the fins, which help prevent swirl formation, while the small nozzle ring generates thrust and provides stability to the fins and reduces vibration. The installation follows after a model test of the Becker Twisted Fin prototype on a Hamburg Ship Model Basin HSVA in early 2012 and June 2012, which demonstrated fuel savings of close to 4%. Tank tests were conducted in October 2012 and first installation took place in December 2012 at Damen Shipyard in Rotterdam.
No.3 – Propeller swaps Several years ago, ferry operator Stena successfully refitted new blades on several of its vessels. Although initial analysis by Stena and RollsRoyce indicated fuel savings of around 8% would be achieved, the overall result has been around 10% on the Stena Germanica, operating on the Gothenburg-Kiel route. In practice the ship can now maintain its schedule using only one engine per side instead of two. The additional advantages are that the level of redundancy is increased and maintenance costs cut. Sister ship Stena Scandinavica was subsequently given the same treatment. New blades were then fitted to two more ferries which resulted in Trelleborg recording a fuel consumption reduction of 10-12%, while on Stenna Nordica the cut in fuel burn has been approximately 17%. Another operator, Royal Caribbean International replaced the blades on the 48,500gt cruise vessel Empress of the Seas. Careful records were then kept allowing performance before and after to be accurately compared. Speed before and after the blade change is unchanged. In low pitch manoeuvring slightly more throttle is need for the same thrust, but this was as predicted. The reduction in fuel consumption is around 13% on a like-for-like basis when on cruises that range from 3-11 days. A side benefit is reduced engine running hours as the new blades enable the ship to run at the same speed with less power. The number of engines on line can be cut, with a saving in running hours of around 10%. Vibration was also reduced with no increase in noise levels.
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In August 2010, Miami based Norwegian Cruise Line placed an order with Rolls-Royce Marine for a Promas Lite upgrade on their cruise vessel Norwegian Sun. The upgrade, which involved the ship’s twin main propellers, was conducted during a regular dry docking in January 2011. The existing 5.8 meter Rolls-Royce Kamewa controllable pitch propellers were upgraded with new fuel optimized propeller blades, specially designed hub caps and custom fit rudder bulbs. Sea trials were carried out before and after the dry docking and sophisticated onboard shaft torque measurements were used for verification of the efficiency gain. The official findings were presented by DNV at the end of February 2011 and showed an efficiency gain of greater than 10% at the sailing speed range of 17-21kt. The success of the upgrade on Norwegian Sun led Norwegian Cruise Line to place a follow-on order for their vessel Norwegian Spirit. Norwegian Spirit was equipped with a pair of four bladed Kamewa mono-block propellers which were replaced with twin Rolls-Royce fixed bolted propellers as part of the Promas Lite upgrade. The 5.8m fixed bolted propellers had bronze propeller blades bolted to stainless steel propeller hubs. Installation took place during Norwegian Spirit’s scheduled dry docking at the end of September 2011. Again the final calculation of efficiency improvement was conducted by DNV and the results this time showed an efficiency gain of 11%.
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Energy Saving Devices
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