3.2 Economic Analysis
A comparison of each plant considered above is shown in Table 2. Capital index is described as the percentage of capital cost of plant with steam turbine plant as 100. The operational cost consists of the fuel cost, the maintenance cost and the lubricating oil cost.
In this paper, the fuel cost is based on the dual fuel mode i.e. to use natural BOG as fuel and fuel oil as make up fuel. Because the RLQ plant is not able to utilize BOG as fuel, fuel cost of a round trip is not practical to estimate RLQ. Therefore the operational economy index is considered.
Assumed operation conditions and unit prices are shown in Table 3. And maintenance costs are assumed as per Table 4.
It shows that the GIDE1 has an advantage over other plants, and that ST is the least efficient based on the operational economy index. Regarding the feature of RLQ, there is no loss of BOG even if the ship is in slow steaming condition. On the other hand, ST has a great advantage based on maintenance cost clue to less consumable parts.
The diesel engine consumes more lubricating oil than the steam turbine. In addition to system oil, low speed diesel needs much cylinder oil.
Although the above show a disadvantage of the low speed diesel, overall GIDE1 is most economical plant per Table 2.
3.3 Propulsion Redundancy
The propulsion redundancy is defined as the capacity to restore propulsion power and steering capacity to move the ship to a safe area after any single failure in the propulsion system. The results of its evaluation are shown in Table 5. This table shows that all plants have a good redundancy. Especially, GIDE2 and DE are able to maintain 50% of propulsion power after any single failure.
