D&A Electric from Ridderkerk developed this E-prop system. To understand this system well, we first have to explain how the conventional power train of an inland ship is developed. The head diesel engine on board of a conventional inland ship is basically just used for the propulsion, so only to drive the propeller. The thruster, for example a loading pump uses separate diesel engines. Thus, the conventional power train only has a few switches, which determine the efficiency of the propulsion together.
By calculating the required power of this traditional power train and by determining the optimal propeller/diesel engine combination, we mostly assume an overall freight, a certain speed - mostly full engine power - and deep waters. The result: an engine which converts available engine power as a result of fuel efficiency and a thereafter tuned propeller into a propulsive set. A cast-iron combination, provided that the power demand lays in the optimal speed range, so on longer extends, well loaded and without plural use of the available power.
If the power demand comes outside this optimal speed range, the efficiency of the propeller/diesel engine combination descends quickly and steadily. The turbo is not entirely functional and the turbo is not on at all if at half the power.
With the propeller/diesel engine combination, it can be said that circa 22% of the energy in the fuel is converted into propulsion in an optimal situation. If the ship is not fully loaded or does not reach the optimal speed range for whatever reason, this efficiency will drop to about 11 to 13%.
Unfortunately, there are considerable defects with the optimal speed range and with this the attached efficiency loss happens all too often in reality. The power demand is influenced by changing circumstances, such as water supply, knots, arriving and departure, the hull type, unevenness on the hull, load factor, depth of the water, etc.
The only possibility the shipper has is the speed range. If the circumstances give any reason to throttle back for a while, the efficiency of the propeller/diesel engine combination decreases from an average of 22% to 17% or even lower.
The E-prop concept
With the new approach of diesel-electric propulsion (the E-prop concept from D&A Electric BV) you have the same ship; in the stern is a propeller and the same helm. This does not just count for the Amulet, which is driven by L-drives from Veth Propulsion. There is nothing new about this. The biggest difference is the construction of the driving. There are no ëloose linksí, but a complete chain in which every link is optimally adjusted to the rest of the chain, reaching an as high as possible efficiency of the propulsion. The frequently controlled diesel-electric power train consists of the propeller, gearbox, electric engine, switch box (frequency converter), 2 or more generators and ditto diesel engines. It is a complex overall concept, in which every separate element are adjusted to each other.
Efficiency flexible power.
The power is not just used for the propulsion. The thruster and any other parts are connected. It is not necessary to install extra power for this. When calculating the needed power, you mostly look at the user profile of the ship. How many times does she sail with a full load? How much counter current? How much power do they want to use under all the different circumstances? Etc. By replacing the head engine through installing a system of smaller generators, the shipper is able to choose a different generator combination. The control of the power management system ensures the interaction, the dynamics with the outside world.
The shipper himself chooses based on the covered route, the water level, load factor (so the expected load) and the number of used generators. Every shipper knows how much power and how much fuel he uses with a particular load. Roughly translated: the shipper easily switches from the large motor power to a smaller motor capacity, with as a result: drive, which delivers the wished capacity in the desired speed range and therefore gives optimal fuel efficiency. This result is possible, because a generator set always runs on the same rpm (revolutions per minute) and is all set on this. The load factor just plays a small part.
With a loading of over 55%, the efficiency will practically stay at 40%. This is largely explained because the blower is always taking a part. After all, a generator motor always runs at full rpm. The efficiency of the generator diesel will get lower if it comes under the 55% loading. This is why the E-prop concept uses multiple generator sets, so that the used generators always get a fuel efficiency of at least 40%.
Furthermore, there are all sorts of advantages with the E-prop concept:
- The generators can drive the thruster, loading pumps and the electrical system.
- In the stern are no diesel engines, so no exhausts and no tanks, less sound isolation for the accommodation.
- More space on the stern for a possible bigger accommodation.
- The maintenance intervals of a generator are twice as long as on a normal diesel engine.
- The generators are easily switched.
- If a traditional ship with a double propeller (ships with a length of over 110 meters, have to have at least 2 driving propellers, if they want to sail the Rhine) takes a turn, the outermost propeller takes more power, while the innermost provides hardly any propulsion. The result is that the turning circle increases. In the E-prop concept you keep as much thrust on both propellers, which makes the turning circle decrease.
- Better manoeuvrability, the power is at all times, because the generator is already running on maximum rpm. On top of this, an electro engine accelerates faster than a diesel engine.
In the future, we would definitely choose for the E-prop system again.