Efficiency of flexible power
The new approach to diesel-electric propulsion, (the Eprop concept), still involves the same vessel. There is a propeller in the stern and there is still the same rudder. The biggest difference is in the structure of the drive. There are no longer any "loose links' but a complete chain, where each link is optimally matched to the rest of the chain in order to achieve maximum propulsion efficiency. With the frequency-controlled diesel-electric process, the drive train consists of the propeller, gearbox, electric motor, control cabinet (frequency converter), 2 or more generators as well as diesel engines. It is a complex total concept in which all individual elements are aligned.When calculating the required power, special attention is paid to the vessel’s operating profile. Instead of a large main engine, there is a network of small generator sets. With the E-prop concept, substantially less fuel is used. It means that if you have 2 or more generator sets, you can switch one or more off.
Propeller Efficiency
Further efficiency advantages can be gained by the propeller. The efficiency of a fixed-pitch propeller depends on a large number of factors.The starting point for the design of the propeller is the maximum speed under given conditions. The propeller design is based on this. That principle is therefore decisive for some data, such as the diameter, pitch, pattern and leaf area of the propeller. Within that design, margins are maintained, so that the overall utilisation efficiency of the propeller can be drastically lowered.In addition, a number of flexible factors, such as speed, capacity, load factor, speed through the water and water supply to the propeller, are also taken into account. As soon as one item of the flexible data changes, the ideal equilibrium is disturbed, resulting in lower propeller efficiency. One of the reasons the loss of efficiency in the propeller occurs as soon as the balance is disrupted, is that in the design of a propeller, the power curve of a ship's diesel engine must to be taken into account. Certain adjustments to the propeller, such as the shallow-water characteristics designed to help the diesel engine under difficult circumstances, have a negative effect on the yield in other circumstances.
With diesel-electric propulsion, such design changes are not required, because external influences on propeller efficiency can be overcome by the electric drive. This gives more freedom in the design of the propeller, meaning that it can be more responsive to changing circumstances. The Eprop concept makes use of this additional design freedom and takes as its starting point a propeller that can achieve high efficiency under all circumstances. It is, in fact, a combination of the advantages of a fixed propeller and an adjustable propeller in a single concept. The propeller makes use of positive environmental factors such as the force of the water under the vessel as it proceeds downstream. As a result, the average propeller efficiency is the highest possible. This, in turn, results in significant fuel savings, the second major advantage of the system.
Resulting benefits
Besides a
very high thrust/power ratio, there are many 'smaller' benefits with the Eprop
concept:
- The thruster, cargo pumps, the electrical
system, and other items that use it, can be powered by the generators
- There are no more diesel engines in the
stern. So no exhaust pipes, no tanks and less soundproofing for the
accommodation
- More space in the stern, for example, a
larger accommodation area
- The maintenance intervals for a generator
are less expensive than those for a normal diesel
- The generators can be easily changed.
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