Page 25 - Industrial Plants

Hybrid propulsion for small medium

vessels assisted by energy storage

systems

The hybrid propulsion is a combination of a mechanical propulsion and
of an electric propulsion. The system can be assisted by an energy storage
battery in order to smooth the power peaks, to reduce emissions and to increase
the response time of the mechanical propulsion

Giordano Torri, CTO Fincantieri SI spa

he requirements for reducing the understand the reasons why the hybrid solution is
environmental pollution and emissions beneficial. The case of an harbor tug is quite
in port or in lakes or in protected representative due to its working cycle. An harbor tug
waters has become an important requires a high propulsion power, normally used for a
issue around the world. This need short period of time and a relative small power for
T implies new design approach for auxiliary onboard equipment. The propulsion power can
harbor tugs, ferries and in general for smaller be in a range of 3.500 – 5.000 kW while the auxiliary
vessels. These vessels have variable working engine is about 50 to 120 kW. Three main operational
cycles lasting for a short period of time that require modes can be identified: idle, transit and working. In
engines running in a wide speed range, “idle” mode the tug is waiting for an operation and its
changing frequently speed and power too. It turns out consumption is basically due to the auxiliary equipment,
that the efficiency is lowered and the fuel consumption since no propulsion is required. In
gets higher and higher. In order to mitigate this effect “transit” mode the tug is navigating
and improve efficiency, the hybrid solutions have been to the area of operation. Thetransit can In this paper a solution
provided for propulsion. be either at a speed lower than max is presented and the
Basically, an hybrid propulsion system is a combination (typically around50% of max key elements are
of a traditional internal combustion engines (ICE) and speed) or close to its max speed. In described, along with
of a propulsion electric motors (PEM). They can work “working” mode the full power is an example applied to
together, sharing the load or they can work separately, required because the tug must assist an harbor tug
according to certain rules of managing the vessels. An the ship. According
important equipment introduced in hybrid propulsions is to various experiences reported in
represented by the so-called electric energy storage many papers, the operational cycle of a tug (the
systems (EES). Typically it is based on electrochemical combination of the three states said above) spans for a
batteries, acting as a tank of energy to be used time about 3.000 to 4.000 h/year and it requires an
according to the power demand. This method helps in average power of about 30-40% of its rated full
increasing the overall efficiency of the propulsion power. The full power is then used for approx. 15%
system and it also provides a mean for getting a faster of the total time. As an example, a full cycle of about
response time in terms of torque. In this paper a solution 2:30 hours is taken into consideration (transit and
is presented and the key elements are described, along working) and the total time is divided in three zones as
with an example applied to an harbor tug. in fig.1: transit, working and transit again. Transit lasts
for 1 hour (T0-T1 and T2-T3) while working for 30
minutes(T2-T3). Of course this simplification is not
Required operational modes accurate, however it can be useful for explaining

Before entering in the technical details of the hybrid concept and how to conceive the size of the
the hybrid solution,some typical data of the operational various equipment and its usage. It must be noted that
modes of these vessels are shown in order to better each harbor tug has its own operational mode and this

IndustrIal Plants - May 2017
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