25 Maggio 2022
Hybrid propulsion is increasingly in demand in the marine sector and particularly in recent years there has been a considerable increase in the request for installations on board various types of vessel.
Around the word “hybrid” there is a large and still immature sector where progress can be seen day by day. And it is the newness of the topic, but also its complexity, that creates a certain confusion. Hybrid propulsion is an alternative or auxiliary form of propulsion compared with the normal system with internal combustion engines. The combination of diesel engines and electric motors gives several advantages in navigation: comfort thanks to the silence and lack of vibration when navigating HYBRID PROPULSION in electric mode; slow speeds to access protected marine areas and for manoeuvres in port (with a consequent reduction of emissions); reduction of fuel consumption and emissions in these ranges of operations; use of the electric motor to generate electricity during diesel propulsion; greater safety during navigation thanks to the redundancy of the propulsion system and finally the possibility of maintenance and servicing of the diesel engine during navigation. Vessels with hybrid propulsion can attain the performance demanded even with very low electric power. Speaking of propulsion, usually it is possible to obtain a good electric cruising speed, even with 6-8% of the power produced by internal combustion engines. This is because, in hydrodynamic terms, the propeller needs only low power for low speeds.
Different types
It should be noted that hybrid is not a macro group but a subset of the family of electric propulsion. Speaking of electric propulsion there is a difference between:
• Diesel-electric propulsion, also known as serial hybrid;
• Hybrid propulsion, also called parallel hybrid.
Diesel-electric propulsion is a kind of principle propulsion in which the electric motors are the main source, replacing the usual diesel engines, while the power needed to make the electric motors work comes from diesel generators. Electric motors are installed directly on the propeller shaft, be it traditional with fixed pitch propellers, with controllable pitch propellers all with azimuth systems. The benefits are very similar to those of hybrid propulsion, but what can really make the difference is the flexibility of installation: the “engine room” for the generators can be sited anywhere in the vessel, with cables leading to the electric motors, with benefits for comfort and space on board. Obviously this all affects the cost: the diesel-electric solution is more costly than the hybrid solution. Diesel-electric propulsion is also called “serial hybrid”, since all the components of the propulsion chain are in series. There are the generators, with internal combustion engines and the alternator, that supply the power for the electric propulsion motors and finally the propellers. As mentioned above, hybrid propulsion is also called “parallel hybrid”, since the electric motor is used as an alternative to the principal diesel engine. There are very few applications were the two power sources are used together, since the power of the electric motors will have very little effect compared with the power of the diesel engines. It would mean an increase in top speed of just a few tenths of a knot...