Propelling, compelling

The mood for the conference was set by Ole Hoeg, executive vice president, technical organisation, AP M?ller, when pointing out in his opening remarks that the NOx levels of 4% set by IMO are still far too high. The industry, he claims, should aim for virtually sulphur-free bunker fuel with a NOx level of 0.5%.

He also put forward a wish list which included improved quality control systems by manufacturers to produce better made, longer lasting and more efficient equipment. This was particularly important in connection with propulsors such as pods, and equipment such as propeller shafts and rudders where the end users should expect a zero failure rate. These items are, after all, crucial to the safety of ships.

Pods in service

Podded propulsors featured strongly in a number of presentations and John Carlton, Lloyd?s Register?s senior principal surveyor, technical investigation department, highlighted a number of failures in the current second generation of pods. Problem areas centre around their transmission drives, particularly relating to the spiral bevel gears, bearings, seals and, to a lesser extent, with the motors.

These problems are to be expected in the light of the rapid increase in power absorption because design development in these situations can and does outstrip service experience, he said. There is always a danger in these cases of abandoning a basically good design or idea and it is important to keep the design concept in balance with operational expectations, he warned.

LR analysis of the faults shows that about 50 to 60% of the total number of failures is caused by human factors with the remainder attributable to mechanical or hydrodynamic origins. Since podded propulsors differ significantly from conventional propulsors and rudders, more information is required about design loads and specifications for podded propulsors in service, he said.

A Joint Industry Project (JIP) aimed at assessing and evaluating the safety and reliability of podded propulsors under operational conditions has been set up in Europe. Partners in the JIP are the Dutch research establishment MARIN, leading pod manufacturers ABB Azipod and Kamewa Mermaid, shipyards Chantiers de l?Atlantique and Meyer Werft, classification society Lloyd?s Register and the Technical Research Centre VTT.

Extensive monitoring campaigns onboard three vessels will be conducted within the JIP and will involve measurements of not only the pod system, but also the ship structure supporting the pod and steering gear. The findings will be analysed and compared with scale model test results and computational analysis. The five big classification societies are involved in this analysis in order to develop computational methods for determining pod and ship loads in the design stage. The project, which started at the end of 1999, will be completed by the end of this year.

Carlton emphasised it was important to recognise that podded propulsion is a good concept but requires a period of consolidation. Meanwhile, research work is being carried out in various organisations around the world into the feasibility of a third generation of podded propulsors. These initiatives are based on the ducted propulsion concept in which the duct embraces an electrical stator element while the propeller, perhaps with a ring element attached to the blades, forms the rotor.

CRP Azipod

Another development in the pod scenario is the podded CRP (contra rotating propeller) which was the subject of a paper delivered by Sakari Sorsimo, systems specialist at ABB Industry. Developed as a cost-effective solution to the ever-increasing demand for more power, the CRP is proposed as a viable propulsion system for 12,000 TEU ultra large container carriers and fast ropax designs.

The system is still undergoing detailed evaluation to overcome perceived problems of cavitation and vibration particularly where heavy loads are imposed on the pod during big course changes at high speeds. The results of the tests are hoped to be available later this year, said Sorsimo.

It was suggested by one of the delegates that problems with the podded propeller are more likely to be attributed to substandard manufacturing quality rather than design and installation. Sorsimo agreed except for tip cavitation which is a specific problem to CRP. There are many examples of poor prop castings around the world and unless quality can be improved then the design issues cannot be effectively tackled.

On a smaller scale, the compact azipod propulsion, also developed by ABB, was the subject of Jari Ylitalo?s talk. He emphasised the ease and speed with which these small pods can be fitted. He quoted a recent example where a 5MW unit was installed in a pilot vessel, which only took 11 hours to fit just before launching the vessel. The system has also been installed after the launch of a newbuilding without having to dock the vessel.

Alternative propulsion engines

Another topic which constantly exercises the minds of shipowners and engine manufacturers is the choice of prime propulsion movers and both Wärtsilä and MAN B&W expounded on this issue.

Oskar Levander, Wärtsilä?s R&D Engineer product development, proposed a number of options, one of which was the CODED (combined diesel-electric and diesel mechanical) machinery concept developed for the podded CRP fast ropax vessels. Two diesel engines would drive the mechanical propeller while three smaller diesels would supply the electrical power for the pod.

Alternatively, Wärtsilä is offering the DF-electric machinery system which is also based on the CRP concept. This machinery consists of the company?s dual fuel engines which run on natural gas and MDO instead of the typical HFO. In this instance however, the propulsion plant is totally electric and both propellers are powered by electric motors. The natural gas is stored in liquid form in special vacuum insulated tanks.

A question from a delegate raised the issue of insufficient bunkering facilities for LNG fuelled vessels. Levander agreed that this an aspect which will have to be addressed and that the cost to the industry in setting up gas bunkering terminals has not yet been established.

In contrast, MAN B&W put forward the CODAG (combined diesel engine and gas turbine) electric propulsion system as the real alternative to the diesel mechanical engines. CODAG as the prime mover has particular relevance to cruise ships and also LNG carriers according to Dirk Fabry of MAN B&W. This combines the advantages of the diesel engine as the most efficient combustion engine running on heavy fuel while the lighter and more compact design of gas turbines has low vibration levels.

Some of the advantages claimed for CODAG include space saving as a result of more compact engine rooms, although this was disputed. A question from the floor proposed that in the case of cruiseships, the extra cabin space created would be located in the less valuable area of the ship, i.e. deep down in the hull and below sea level. The extra passengers would also require additional crew, public spaces and this would effectively reduce the initial gain of 50 cabins down to 12.

Nevertheless, the gas turbine option is particularly attractive for certain ship types including cruise ships and fast ferries and both Rolls Royce and GE presented papers extolling the virtues of their systems. Geraint Lloyd from Rolls Royce expressed the hope that the newly developed 30MW MT30 turbine, a marine variant of the Trent 800 aero engine, will be launched onto the market in June this year.

GE on the other hand already has a track record of supplying commercial shipping with its LM aero derivative gas turbines with cruise ships featuring strongly in the order book. Janna Thames, GE?s marine account manager, highlighted the COGES arrangement (combined gas turbine electric and steam systems) as a very efficient use of energy whereby the gas turbine exhaust is captured by the boilers to produce steam turbine electric power generation and service steam use. Other configurations include plants where the diesel and gas turbines independently drive generators and waterjets, allowing simultaneous use of both prime mover types.

LNG carriers are perceived as a growth sector by the gas turbine manufacturers and an interesting scenario is likely to develop as owners of gas carriers begin to explore the advantages of electric propulsion using either diesel engines or gas turbines or a combination of both (CODAG) or even dual fuel engines.

LNG as a fuel taking off

Natural gas as a fuel was the subject of a lecture by Per Magne Einang from Marintek and was based on the Norwegian experience of operating a car ferry fuelled by gas. The ferry, Glutra, has been operating since February 2000 and has proven to be totally reliable while at the same time reducing potential pollution to water and harmful exhaust emissions, he said. It was pointed out that, although the level of sulphur will be reduced, the emission of hydrocarbons will be higher and the use of oxyburners was being looked into to reduce carbon levels.

With this positive service experience, Norway is building two offshore supply vessels and one small 1,100m3 LNG carrier for Knutsen OAS, all of which will be powered by gas. There is a proposal to build a larger ferry in Norway with LNG fuelled mechanical prime movers. Except for LNG carriers there are, as yet, no international rules or regulations governing gas fuelled ships and this issue needs to be addressed as a matter of urgency before entirely gas fuelled vessels can become a viable alternative to diesel. The other limiting factor is the current low number of gas bunkering facilities in certain parts of the world.

Another option involving natural gas is being offered by Wärtsilä in the shape of its dual fuel (DF) engine aimed at the LNG carrier market. With a capability of operating in either the diesel mode or gas mode, this electric propulsion system gives operators the best of both worlds using low pressure boil-off gas with marine diesel oil as backup fuel. In presenting his paper, Mika Laurilehto, the company?s director of product & application development, confirmed that designs have been drawn up for a 140,000m3 LNG carrier incorporating the DF diesel electric configuration and that approval was being sought from a number of class societies for the low pressure DF engines. In the meantime Wärtsilä has achieved a breakthrough for its DF engines with a contract to supply four units to power a 75,000m3 LNG carrier being built at Chantiers de l?Atlantique for the account of Gaz de France.

Propulsor talk

The search for the perfect propulsor continues unabated with various proposals being developed to increase ship speeds as well as reducing vibration and noise levels. Svein Olav Halstensen, hydrodynamic specialist at John Crane-Lips, put forward the findings on the efficiency rudder for high powered fast single screw containerships and ropax vessels.

These rudders have high-lift flaps fitted and can also be fitted with a torpedo shaped propeller hub to give improved output and efficiency while achieving a large reduction of pressure impulses against hull and propeller induced vibration levels. When comparing its performance against the pod, tank tests so far have shown that, for single screw vessels sailing on routes where one economical speed is required, the efficiency rudder offers significant advantages. These include lower power consumption, higher hull efficiency values and greater course stability particularly at higher wind speeds and waves.

The last lecture on the first day proved to generate a considerable amount of interest as Jens Kappel, of J.J.Kappel Marine Concept in Denmark, explained the concept of his own propeller design. Named, unsurprisingly, the Kappel propeller, this novel propulsor is based on the principle of non-planar lifting surfaces found in nature in the shape of certain birds of prey with upward curved wingtips. This idea has been successfully adopted in the aerospace industry by adding winglets to the wingtips of aircraft.

The blades of the Kappel propeller curve upwards towards the suction side in the tip region and model tests carried out since 1980 with 4-, 5- and 6-bladed Kappel propellers have consistently shown fuel savings of 4% to 5% compared to well designed conventional propellers. In addition to fuel savings, the reduced energy losses of Kappel is an important factor in designing propellers with lower levels of induced noise and vibration.

In July last year, the first full scale prototype for actual testing was built and was followed by delivery of the first fixed pitch Kappel propeller in April this year for fitting onto the 35,752 dwt tanker Nordamerika owned by Norden AS. Manufactured by Stone Manganese Marine, the propeller was installed at the Lisnave shipyard and the tanker is now in service with the expectation that fuel savings of about 5% will be achieved. Norden proposes to install Kappel propellers onto all its future newbuildings if the experience with Nordamerika confirms the potential savings, said Kappel.

Smokeless two-stroke operation

The second day opened with an account by Thomas Knudsen, vice president of research and development at MAN B&W, of Odfjell?s service experience with the electronically controlled camless engine onboard the 37,500 dwt chemical tanker Bow Cecil. The two-stroke engine has performed successfully for over 6,500 hours and experience has confirmed that the objectives of a smokeless engine ? enhanced reliability and operational flexibility with reduced operational costs ? have been achieved.

As a result, the Norwegian shipowner has ordered two 7-cylinder S50ME-C engines to be fitted in two sisterships to the Bow Cecil currently under construction in Norway.

The Sulzer RT-Flex electronically controlled common-rail fuel injection engine was the subject of a paper from Kasper Aeberli of Wärtsilä. The first RT-flex engine successfully completed its sea trials in September 2001 in the self-unloading bulk carrier Gypsum Centennial of Gypsum Transportation.

This 6RT-flex58T-B engine, of 11,275 kW output, was built under licence by Hyundai Heavy Industries. Most recently, Wärtsilä has received an order for two Sulzer RT-flex engines to be installed in two 30,000 dwt multipurpose carriers contracted at Shanghai Shipyard in China by Chinese-Polish Joint Stock Shipping Co (Chipolbrok). Each vessel will be propelled by a seven-cylinder Sulzer RT-flex60C engine with a maximum continuous output of 16,520kW.

The next set of papers covered the medium speed engines and started with Kai Rieck, responsible for the engineering design department at MAN B&W, introducing his company?s latest addition to the small engine family, the L21/31 which complements the L16/24 and L27/38. These three engines have taken six years to develop and are tailor-made for both genset and propulsion applications. Special attention was paid to a sufficiently large stroke, which allows the design for the combustion chamber to be optimised for the high compression ratios necessary for heavy fuel operation together with lowest possible emission levels.

The 21/31 is also the first MAN B&W engine which was fully designed within a 3-D CAD system which enabled closer cooperation between design and basic development on the one hand and design and production on the other. Ease of maintenance featured prominently in the design approach and, by using the cylinder unit concept, has facilitated the replacement of a cylinder unit in accordance with the maintenance schedule.

Prototype tests have been carried out for both the genset and propulsion applications and the first operational genset engines were installed onboard a ferry last month.

The other major development project by MAN B&W was the improved version of the four stroke 48/60 model, the 48/60B, which not only gives increased output but also has achieved low emission combustion with lower fuel consumption. In addition, the V model version had the structure of the engine changed resulting in a reduction of engine width. These new engines will be available early 2003 for the V line version and late 2003 for the in line version.

Another new series of four stroke engines was the subject of a paper from Caterpillar by Klaus Wirth, manager new product introduction. This was the development of the M43 in-line engine into a V-type to meet the market requirements to cover the range of 10 to 16MW to satisfy the containership, high speed ferry and cruise ship markets. The first prototype engine, a 12-cylinder version, started its tests in April and series production is scheduled to follow later this year.

Fuel issues

Don Gregory of BP marine fuels gave an interesting insight on the issues facing the oil industry in its attempts to reduce wastage and improve its environmental image. The paper concentrated on the 2 to 3% of bitumen residue which remains after crude oil has been processed into the various fuel grades. Options of dealing with this waste product include gasification for power station usage and coking which totally destroys the residue. However, there is a third option which enables the bitumen to be used as a component in marine fuels.

The drawback to this is the increase in soot emissions and to overcome this problem experiments have been carried out in Canada onboard the ro-pax ferry Leif Ericson using an exhaust scrubber. Marine Exhaust Solutions (MES), a division of DME Eco-Silencer in Canada, replaces the silencer in engine exhaust stacks (or incinerator or boiler exhaust stack) and through its innovative design, removes soot, reduces airborne noise, and greatly reduces harmful emissions which would otherwise be released into the atmosphere. The system also provides a net savings on operating costs.

The Eco-Silencer is a result of five years development work, including practical seagoing trials aboard a Canadian Coast Guard icebreaker and with MAN B&W, Copenhagen. The plant provides a compact, cost effective and reliable system for scrubbing exhaust gases and using seawater for this purpose has proven to be very effective.

The installation works by encouraging hot exhaust gas to mix in a turbulence cascade with seawater and the acid gasses and particulates in the exhaust are transferred to the seawater. To ensure that the surface area for contact between gas and water is high, and sufficient time for absorption of pollutants is provided, a patent-pending turbulence and mixing process was developed. The seawater is recirculated, and solid particles that were removed from the exhaust gas are trapped in a settling tank where they can be collected for disposal. Sulphur dioxide that was removed from the exhaust goes into solution in seawater as sulphate and sulphite, both harmless naturally occurring components in natural seawater. A modest amount of wastewater is filtered through a carbon/sand filter to be released to the ocean, thus disposing of the sulphur safely, and ecologically friendly.

The influence of common rail technology on today?s diesel engines is widely recognised and Rainer Jorach, senior manager development at L?Orange in Germany, spoke on the subject of diesel injection systems. Since L?Orange introduced the world?s first electronic common rail diesel injection system back in 1997, it has supplied all the leading engine manufacturers of medium and high speed diesel engines. Last month, the company launched its latest product in the shape of a HFO common rail injection unit with a system pressure of 1,600 bar with pilot as well as post-injection capabilities.

Lubrication issues

Next on the menu was the optimisation of cylinder condition by intelligent lubrication which involves the adjustment of the lube oil feed rate as well as the lube oil formula. In a paper given by Kjeld Aabo, manager of marine installations department at MAN B&W, the concept of utilising the latest electronic control technology for precise timing of the cylinder oil injection was explained. Excessive cylinder lube oil consumption is not only wasteful but is also detrimental to the engine leading to higher maintenance costs. MAN B&W has addressed this problem with the introduction of its Alpha high pressure electronically controlled lubricating system with very low feed rates.

The prototype was installed on a 7S35MC engine in 1998 and, following refinements, is now available for all the company?s two-stroke engines with some 100 systems on order. Large bore engines have two lubricators on each cylinder while only one is required on small bore cylinders and the amounts of oil can be adjusted automatically or manually.

Oil quality is a constant problem and a lot of effort has been expended in controlling this issue particularly in the field of fuel and lube oil condition monitoring. It was in this area that Martin Lucas, sales and marketing manager of Kittiwake in the UK, did a presentation focusing on methods of sampling using stand-alone instruments rather than laboratory-based tests. Few of the laboratory methods easily migrate to on-line techniques and the industry has to decide what aspects of bunker fuel it wants to target. Viscosity is regarded by many as the most important parameter with water, insolubles, base number and acid number all useful indicatives of quality.

Although much of the current technology does not lend itself to on-line applications, it is feasible to develop sensors but at a high cost and the marine industry has to decide what it is prepared to afford. Also, is the focus to be on oil life or engine condition and should sensor technology become part of the engine package?

Environmental issues

Nitrogen oxides (NOx) are deemed to be one of the most hazardous pollutants. Emissions from the world?s merchant fleet represent a significant source of air pollution at around 7% in 1995. However, this annual estimate is much smaller than for other methods of transportation. Horst Koehler, responsible for technical promotion with MAN B&W, described how the engine manufacturer has achieved notable success in not only reducing NOx to below the current IMO limit but has achieved further improvements which far exceed the IMO standard.

Another approach to calculating energy efficiency of shipping was expounded by Hans Otto Kristensen, professor in naval architecture in Denmark, using direct cost comparisons with road transport. These calculations include the cost of air pollution, noise, accidents and congestion to obtain a figure per transport unit, i.e. per ton cargo per km.

Kristensen?s analysis revealed that sea transport, in the majority of cases, is the most environmentally friendly form of transport and this is especially true for container ships, bulk carriers and tankers. For roro ships the specific energy consumption and exhaust emissions are higher than for corresponding road transport although this is compensated by the fact that it relieves a congested road network. It is this aspect of congestion and the associated costs to society that has prompted the Danish shipowner Scandlines to design the next generation of ropax ships under the project name Via Mare 5000. These proposed newbuildings will be 200m long and carry 500 trailers or 400 containers.

The final paper was submitted by Peter Skjoldager from the marine installation department of MAN B&W, on the subject of the installation of the selective catalytic reduction (SCR) system installed onboard the 7,500m3 LPG carrier Navion Dania. This SCR was introduced to the marine industry in 1989 and today still remains the superior NOx reduction method although the number of installations on two-stroke diesel engines is still small. The Navion Dania was built at Hyundai in 2000 and, when the 6S35MC engine was ordered, it was decided to prepare the ship for the later installation of an SCR and this was completed in June last year.

From the shipowner?s point of view, Lief Evan Tonnessen set out the reasons why Navion installed the SCR system. NOx reduction is not a mandatory requirement but it was nevertheless decided to fit the system in the light of future legislation when it could well become mandatory. This is particularly relevant for the Navion Dania which trades on the coastal route between the west coast of Norway and the west coast of Sweden where environmental issues are a high priority. In addition to this aspect, Navion wanted to gain operational experience for future installations.

Despite the reduction in fairway and port dues in Sweden and the environmental rating for Norwegian taxes, this is not sufficient to offset the operating costs of the plant. However, at present the SCR system is individually designed for each engine but, for the future, the cost, functionality and ease of installation will be improved as the system is standardised for the different type of engines

Expectations from SCR have been fulfilled by not only reducing NOx but also in terms of the engine operation in general. Minor problems occurred when corrections to the SCR control system had to be made while modifications to other minor parts were implemented after the first few months in service. The engine performance with the SCR system is acceptable and visual inspection of cylinder condition from the scavenge air port shows no signs of irregularities. The plant is being operated by regular crew members.