**5. Application Case: Reference Vessel Description**

The methodology described in paragraph 4 is now applied on a reference vessel to evaluate propulsion system alternatives. The application platform is a research vessel designed and equipped to navigate the far reaches of the globe. These types of vessels support researches on the sea analyzing temperature gradients, sea chemical composition, carrying out biological or geophysics investigations, or bottom topography. The overall characteristics of a research vessel are identified by the scientific equipment, the specialized personnel on board, the required speed and range. The propulsion system has to be designed to ensure flexibility and a wide range of activities at different speeds. The original propulsion system of a model vessel and proposals of alternative configurations described in the following paragraph would be our starting points for investigations and analysis.

The main vessel dimensions and features are described in Table 1. The ship is equipped, in the original version, with two independent shaft lines, each provided with the main diesel engine, a small electric motor, a gearbox, and a controllable pitch propeller. Mechanical and electrical systems work together in the propulsion train, optimizing the ship propulsion efficiency and providing the right amount of power delivery to a propeller in any scenario.


**Table 1.** Main ship dimensions and performances.

This hybrid propulsion system works as a CODELOD (COmbined Diesel and ELectric Or Diesel) where the only electric motors are used for low speeds (up 8 kts), and the diesel engines are instead used

for high speeds (from 9 to 17 kts). The electric power generation at 400 V and 50 Hz, in all operating conditions, is ensured by three independent diesel generators connected to the main distribution grid. The emergency power generation is carried out by a dedicated diesel generator, located in a different small engine room. A simple functional scheme of the propulsion and electrical generation layout is shown in Figure 4.

**Figure 4.** Original propulsion system layout.

The two propulsion engines are typical four strokes engines based on a supercharged diesel cycle with direct fuel injection. The supercharge is ensured by a turbo-compressor group driven by engine exhaust gases. The two diesel engines installed onboard can supply power output of 2289 kW, irreversible rotation, and opposite turns. A pneumatic system with compressed air is provided for the engines start, while the cooling system is made by a closed high-temperature freshwater circuit and a low temperature opened one.

The electric generation onboard is ensured by three gen-sets located in the main engine room. The electric power produced onboard is mainly used for the "payload" services (that include accommodation services but also scientific equipment power demand) and for the electric propulsion at low speed as well. The gen-sets can produce 650 kWe each at 1500 rpm with an electric output at 400 V and 60 Hz. A single gen-set is made up by a four strokes diesel engine with a direct fuel injection connected to an electric alternator. Table 2 provides a direct comparison between the propulsion types of diesel and the diesel gen-sets (MDO is the acronym of Marine Diesel Oil; MGO stands for Marine Gas Oil).



It is important to define one or more profiles before starting the comparative analysis because they can strongly influence the results. As a research vessel, the ship will be optimized to work at two different speed range: low speeds during the maneuvering and oceanographic operations (typically from 0 to 8 knots) and high speeds during shift operation at design or maximum speed (from 12 to 17 knots).


Figure 5 shows the operational profiles of the reference ship: the percentages refer to 165 days/year when the ship is operating at sea. In the remaining 150 days/year, the ship is considered in harbor, and in the remaining 50 days/year, in dry dock. In this scenario, 10% of working life (16 days) is spent at 0–5 kn; 35% (58 days) is spent at 6–8 kn in research operations; 5% (8 days in total) at 9–11 kn during speed transient phases; 35% (58 days) at 12–14 kn at design speed; 15% (25 days) at maximum speed.

**Figure 5.** Reference ship operational profile.

All future considerations in this work would be based on this particular operating scenario.

To compare different design alternatives, the first step is to define how the vessel propulsion system works at a different speed and then to identify possible design alternatives to satisfy the operational profile most efficiently. These alternatives will be identified, during this first working phase, as composed by the elements listed below:


The flexibility of the tool structure ensures a further implementation of new WBS systems.

The operational profile has been related to a ship resistance prediction, to connect each speed to a propulsion power demand, and an electric balance, to better understand the total power demand during ship operations. The propulsion resistance prediction has been coupled to a controllable pitch propeller and the two propulsion diesel engines described above. A general overview of the ship propulsion system and ship power demand has been provided and used as a starting point.
