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Of course, cruise vessels are part of the worldwide ecological system but also part of the economical system. This means if there is a lack of international rules, economy decides. By

When the German environmental protection organization Nabu (Naturschutzbund Deutschland) awarded at the end of last year both German cruise lines[ds_preview] Aida and TUI Cruises – as pars pro toto – the negative prize »Dinosaur«, this »honoring« had been published unreflectedly by most of the daily papers. Thus it is a welcome opportunity to ask what is the state of the art?

The questions arising refer not only to the technical solutions but also to the quality of the fuel used aboard cruise vessels. And to comment the Nabu award for the cruise lines: the organization had chosen the wrong addressees with the wrong arguments because there is no approved technical solution available on the world market for running diesel engines on board ships with as low emissions as automotive power units. It is absolutely impossible to apply the technical solutions of any transport system to shipping. Many engineers had already to make this experience about hundred years ago when trying to use the diesel engine for marine propulsion.

However, no cruise line will order today a new vessel with only one or two main engines and some auxiliary engines for electric power generation on board. Most of the new-buildings will be equipped with diesel-electric drives. Thus, there is already a certain power splitting which can avoid in general unnecessary emissions. The question how far the splitting may go can only be answered taking into account the power demands for ship propulsion, for the general electric power systems on board and for the hotel load. But the power splitting is not only a question of electric power generation. It starts with the layout of the propulsion power plant with one, two or even more propellers, or with a combination of a conventional propeller with rudder propellers or with pod drives. This all depends on the size of the ship, its destinations and the philosophy of the owner. But with this thinking we have the first step to minimize emissions.

A concrete example for optimal power splitting

A good example for an optimized diesel-electric propulsion plant is that which the new ferries of Scandlines »Berlin« and »Copenhagen« will receive. They are of course no cruise liners but the approach to save fuel and emissions is very interesting in this context. Before any decision was made about the propulsion system a systematic CFD analysis and simulation study was carried out to find the best way to minimize fuel consumption. Besides others, three different propulsion concepts were examined: two conventional propellers and bow rudder, double ender solution with thruster and propeller and center propeller with two wing thrusters. The best results offered a solution consisting of a center controllable pitch propeller with rudder combined with two wing thrusters and a bulbous bow: high propulsion efficiency over the whole speed range and high maneuverability. At low speed only the wing thrusters are used for propulsion and at high speed all three propellers.

There are three main engines with an output of 4,500 kW each at a speed of 750 min-1. All three can drive the center CP propeller via a gearbox to which they are connected with multiple disc clutches. To the free end of one of these engines a generator is connected with an electrical output of 4,342 kW. In addition there are two main generating sets with an output of 4,300 kW each and one auxiliary genset with 1,450 kW output. Thus these vessels have many different ways to optimize fuel consumption. The diesel power needed for propulsion varies, for instance, between 1,000 and 15,399 kW in at least four steps.

Forthcoming changes at the fuel front

The next matter of concern is the quality of the fuel used. Looking at sulfur emissions, since the beginning of this year the sulfur content of the fuel is limited to 3.5 % globally and shall go down to 0.5 % in 2020. But this step is linked to the question of availability of fuel with such a low sulfur content and may thus be postponed to 2025. Within the SECAs (SOx Emission Controlled Areas) the sulfur limit of today is 1.0 % and will go down to 0.1 % at the beginning of 2015. And where are the SECAs? The first was the Baltic Sea in 2006, followed by the North Sea and the English Channel in 2007. Alternative methods to reduce the sulfur emissions to the required levels are explicitly allowed, but at the time being, there is only one approved product on the market and only available for the same make of engines!

Looking at the strong competition between the ports in the European Community, the ports in Northern Europe – especially in Germany – are confronted to an economical disadvantage. Thus they tried to intervene with support of the German Government the legislation of the EU to avoid different rules for ships approaching ports at the Mediterranean respectively the North and the Baltic Sea, as far as the sulfur content of the fuel burnt is concerned. The Southern countries having no SECAs are against any change supported by France and Great Britain as these countries have both, ports inside and outside the SECAs. The European Parliament is just preparing a decision, which might influence the later decision of the European Commission.

Particle emission of seagoing vessels

Up to now there is no regulation to limit the soot emission of the power plant of large vessels. Thus also the owners of cruise vessels are not obliged to install filter equipment to reduce this emission. At the time being particle filters for use on board ships are only offered up 3,000 kW engine output. If such filters shall be installed one has to take into account that not only the filter elements but also the piping generates an exhaust gas back pressure which may not be tolerated by the engines. There are no technical solutions suitable for large cruise ships.

Regarding the total engine power of a cruise vessel put into service last year, the »Celebrity Silhouette«, one may imagine the job to install particle filters on board of such a vessel. She is equipped with four MAN four-stroke engines of the 48/60 common rail series. The 14-cylinder engines have a power output of 16.8 MW each. Even if only two of them will be equipped with particle filters for clean operation during lay time in a port, eleven to twelve of the largest filter units would be needed. According to current emission rules the loss of space combined with such a measure cannot be compensated. Additional power splitting possibly can simplify solutions like that with filter equipment, but not only the investment but also maintenance of this equipment is very costly as long-term testing of small units on board of inland waterway vessels in Germany have proved. After conclusion of the test phase all filters except one had been removed because the maintenance of the units alone led to unequal business conditions without any chance for compensation. Thus here again economy decided.

Special measures at the ports

Electricity supply from the pier has been under discussion for years. Now we have an internationally agreed standard for takeover of electric power from the shore, but for several reasons the discussion has not come to an end. For instance, there is no solution for a possible blackout on board which could restrict the power supply of a whole city. And how shall the electric power needed by one or more cruise vessels be generated – with conventional coal power plants? Than the emissions just appears at another site with no advantage at all. So-called »Power Barges« with generating sets burning LNG will probably be a less costly and flexible solution with the lowest exhaust gas emissions.

In Hamburg the question of electric power supply from the pier has been discussed for many years and studies ordered to find out the best way to achieve this. Probably the senate of the city is now – after the prize for Aida and TUI – under higher pressure to present concrete solutions and time schedules for their realization. Although the main electric power supply company of Hamburg is building a new coal power plant this does not offer any advantage for the power supply of ships.

As a temporary solution the authorities are thinking about electric power supply of the cruise vessels visiting Hamburg by mobile generating sets burning liquid natural gas. Containerized power units might, for instance be, rented from the specialist Aggreko International Power Projects. This company has 20-foot container units available equipped with Cummins 16-cylinder gas engines and a generator with an output of 1,100 kW at 50 Hz and 1,300 kW at 60 Hz. The engines will be supplied with a gas pressure between 0.2 and 6.0 bar. It goes without saying that the emissions of such engines must not be discussed but the NOx which is, according to Aggreko, below 500 mg/m³. These container units have a weight of 21.5 t including exhaust gas silencer and cooling system.

Cruise lines like Aida state that all their vessels are prepared to install the necessary equipment to takeover electricity from the pier and that the company will support the city of Hamburg – free of charge – to find out the best solution for external ship power supply until availability. Michael Thamm, President of Aida Cruises in Germany, said that Hamburg might serve as a model developing the best concept for electric power supply from the piers in Europe. As the port of Hamburg has now two terminals for cruise liners and while on special occasions five and more liners are lying at the same time at the pier it is very urgent to find a generally accepted solution for the city. The next date for the senate to present an expert report and a comprehensive feasibility study is the end of April this year. And officials are expecting again more than 100 cruise vessels during the coming season.

At this point one may ask why a temporary solution on the pier instead of a principle one on the water? And why not putting standard container generating sets operating with LNG as fuel with a cryogenic tank and the gas system just on a simple pontoon, which may be flexibly used at several places in the port moved by a tug? Such container generating sets can supply, as the example of Aggreko shows, at least 1.1 MW electric power. That means, to serve the needs of an average cruise liner at the pier about eight units plus one in reserve are necessary. Looking at the overall demand of a port like Hamburg a lot of power pontoons with different power ranges offering environment-friendly external electricity could be put in service. With such pontoons there is no space required at the pier, no safety area obligatory. Bunkering is much easier than ashore. And this could be a permanent solution until the seagoing vessels are equipped with dual-fuel engines or Otto engines and bunker LNG. In this case bunker barges or vessels for LNG would be needed.

A more comfortable solution was presented by the German Eckelmann Group of Hamburg last year. By the beginning of the cruise season 2013 the company will have in service a so-called »E-Power Barge« to supply electricity to the cruise liners and of course other vessels in the port of Hamburg. The first barge is said to be an 80 m long unit carrying three generating sets with an electrical output of 2.5 MW each. Up to now, there is nothing said about make and technology of the engines – dual-fuel or Otto engines. This alternative is not understandable as it does not make sense to choose the more expensive dual-fuel engines if emissions shall be reduced by burning LNG instead of MDO. The fuel tank of the barge will be a type C LNG tank according to the latest standard with a volume of about 300 m3. This is enough to supply full-load electricity with the above mentioned engines for about 100 hours without bunkering. The investment for the barge will be in the order of 15 mill. €, says Eckelmann.

If after January 2016 more and more vessels will be built with dual-fuel engines running on gas in the ECAs and outside with any kind of diesel fuel it is no longer the question of external power supply in the ports because the on-board generating sets could than run also during lay time in the port. The question is then whether gas supply from the pier is necessary or only bunker barges for LNG. Engines of any power range for main and auxiliary power supply running on natural gas are available already today. Thus it only depends on a general agreement at IMO and the international legislation to accept gas as fuel for seagoing vessels and which way electric power generation for ships will go in the future.

For the next generation of cruise vessels Aida Cruises is planning the use of gas as fuel with dual-fuel engines. Already, the company could reduce the amount of energy used on board per person and day by 18.2 % within the past five years – a remarkable contribution to the protection of the environment.