Textos de Apoio (pdf)

Case 3: Post-Panamax container ship
In this case, a typical Post-Panamax container
ship with a container capacity of around 7000
TEU might be specified with an eleven-cylinder
Wärtsilä RT-flex96C main engine. However, if a
12-cylinder engine is employed instead, the daily fuel
consumption can be reduced by some 2.4 per cent.
In the engine/propeller layout for this ship as
shown in figure 10, the CMCR points for the two
alternative engines are on the same rating line
(α = 0.2) through a common design point for the
same ship service speed (knots).
The calculation of annual fuel costs given in table
6 is based on 6000 hours running with heavy fuel oil
costing US$ 500 per tonne.
The resulting payback time for the extra cost
associated with the additional engine cylinder is
estimated to be between two-and-a-half and four
years depending on the bunker price of US$ 600–
400 per tonne respectively (Fig. 11). The calculations
of the payback are based on an interest rate of eight
per cent.
Table 5: Typical ship parameters for a Post-Panamax
container ship
Length overall: about 325 m
Beam: 42.8 m
Design draught: 13 m
Scantling draught: 14.5 m
Sea margin: 15 %
Engine service load: 90 %
Table 6: Main engine options
Alternative engines: 11RT-flex96C 12RT-flex96C
Cylinder bore, mm: 960 960
Piston stroke, mm: 2500 2500
Stroke/bore ratio: 2.6:1 2.6:1
MCR, kW / rpm: 66,330/102 72,360/102
CMCR, kW / rpm: 66,330/102 65,919/98.9
BMEP at CMCR, bar: 19.6 18.4
CSR at 90% CMCR, kW / rpm: 59,697/98.5 59,327/95.5
BSFC at CMCR, g/kWh:
– 100% load: 171.0 168.0
– 90% load: 166.8 163.8
Daily fuel consumption, tonnes/day:
– ISO fuel, LCV 42.7 MJ/kg: 239 233.2
– LCV 40.5 MJ/kg: 252 245.9
– As percentage, %: 100 97.6 – 2.4%
Annual fuel costs, US$: 31,500,000 30,738,000
Fuel saving, US$: 0 – 762,000
Engine length, mm: 21,550 23,230
Engine mass, tonnes: 1910 2050
— 8 — © Wärtsilä Corporation, June 2008