*5.1. Transit in Open Sea*

A combination of ship mission and sea condition profiles for three di fferent voyages sailing at open sea of the chemical tanker has been defined as shown in Table 4. Each voyage is divided into three parts, namely Transit A, Transit B and Transit C. In di fferent parts of the voyage the ship speed, transport distance and sea condition, which is represented by the sea margin (SM), are di fferent. Transit A is in a calm sea condition (low sea margin, 5%), Transit B is in heavy weather (high sea margin, 30%) and Transit C is in a normal sea condition (15% sea margin). The three voyages (I, II and III) have the same total distance (650 n miles) and the same average sea margin (15%), which is defined by Equation (8), but have di fferent average ship speeds from fast (13.5 kn) to slow steaming (10 kn).

$$\overline{\text{SM}} = \frac{\sum\_{i} \text{SM}\_{i} \cdot P\_{E,i} \cdot \Delta t\_{i}}{\sum\_{i} P\_{E,i} \cdot \Delta t\_{i}} \tag{8}$$

where *SM* is the average sea margin of each voyage obtained by averaging the power over the whole voyage; *SMi* is the sea margin of each part of the voyage; *PE*,*<sup>i</sup>* is the ship e ffective power at design draft with clean hull and calm weather; Δ*ti* is the time of duration in each part of the voyage.


**Table 4.** Ship mission profiles when sailing in open sea.

The average ship speeds for the three voyages are systematically going down from voyage I (13.5 kn) to voyage III (10 kn) and transit time is going up accordingly. However, to make it more realistic, for voyage I with average ship speeds of 13.5 kn, the ship speeds of Transit B (where the ship is in heavy weather and the sea margin is 30%) are reduced to 12 kn, because of the high sea state, while the speed loss is assumed to be recovered in part C of the transit. For the voyage II and voyage III in which the average speeds are 12kn and 10kn, respectively, the ship speed during the whole voyage remains the same. The detailed determination of the mission profiles when the ship transits in open sea can be found in Appendix A.

For each ship voyage, the influence of di fferent ship propulsion control modes and electric power generation modes on the fuel consumption and emissions of the ship over the whole voyage will be investigated. The ship propulsion control modes (Constant Revolution Mode and Constant Pitch Mode) and electric power generation modes (PTO Mode and Aux Mode) have been introduced in [41] in details and they are briefly summarised in Table 5. The combinator curves for the two di fferent propulsion control modes are shown in Figure A5 in Appendix C.


**Table 5.** Ship propulsion control modes and power generating modes.

> PTO, power take <sup>o</sup>ff.

Note that, if the commanded ship speed cannot be reached within the power limit of the main engine because of providing PTO power, the shaft generator will be shut down and the electric power needed by the ship will be supplied by auxiliary generators, such as Transit A and Transit C of voyage I during which the PTO switch is turned o ff and the main engine only provides power for propulsion due to the demanded high ship speeds under the corresponding sea margin shown in Table 4.

### *5.2. Manoeuvring in Coastal and Port Areas*

The ship mission profile during the close-to-port manoeuvre is shown in Table 6. The ship speed is 7 knots in coastal areas and 5 knots in port areas. The sailing time and sailing distance of the ship in the same area are combined together, respectively, in the ship mission profile in Table 6. In coastal areas, the total sailing distance when approaching and leaving the harbour is 40 nautical miles and the total sailing time is 5.71 h. In port areas, the total sailing distance is 10 nautical miles and the total sailing time is 2 h. The sea margin when the ship is sailing in coastal and port areas is assumed to be normal, i.e., 15% sea margin, and the added ship resistance is because of the smaller depth in coastal and port areas compared with the open sea, where the sea state is the main reason for the added ship resistance.

Five di fferent operation cases of the ship are studied to investigate the influence of the ship propulsion and the electric generation modes of a hybrid propulsion ship on the fuel consumption and emissions performance during the close-to-port manoeuvre.


**Table 6.** Ship mission profile sailing in coastal and port areas.


So, in case I, case II and case III, the ship propulsion system works in PTO mode but on different fuels; while in case IV and case V, the ship propulsion system works in PTI mode but on different fuels. Only the constant revolution mode, in which the ship speed is controlled by changing the propeller pitch and the propeller revolution is kept constant, will be studied during the close-to-port manoeuvre.
