Question

(a) What is the effect on fuel consumption per unit time, if the ship's speed is outised its operating range?

(b) An oil tanker 160m long and 22m beam floats at a draught of 9m in seawater, Cw is 0.865. The mid ship section is in the form of a rectangle with 1.2m radius at the bilges. A midship tank 10.5m long has twin longitudinal bulkheads and contains oil of 1.3m3/t to a depth of 11.5m. The tank is holed to the sea for the whole of its transverse section. Find the new draught.

Answer 1

The fuel consumption is dependent on power developed. The efficiency of the engine is measured in terms of Specific Fuel Oil Consumption (SFOC), which is consumption/ unit of power per hour. The SFOC of ship for different speeds of ship is:

From the graph, it is seen that SFOC decreases upto a speed V2, which is most efficient for the ship. If the speed is increased beyond V2, then the power required is more and thus more fuel will be consumed to produce power to reach the increased fuel consumption.

Generally, the range V1 to V2 will be given for most efficient operation, as the operating range.

if this speed is exceeded, the fuel consumption per unit time will increase.

Fuel consumption / unit time ∝ power developed ∝ shaft power.

$$Shaft\:power\:\alpha\:\Delta^{\frac23}\times V^3^{};\:V=ship^{\prime}s\:speed$$

$$Fuel\:consumption\:per\:unit\:time\:\alpha\:V^3$$

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