Class 1 (Chief Engineer) Engineering Management 📅 Feb 2025

Exam Question

Recent stress on the control of emission from ships has led to the development of a series of devices aimed at the improvement of propeller propulsion effectiveness. Discuss various such devices with special focus on the following: -

(a) Wake Equalizing Devices. (4)

(b) Pre-swirl Devices (4)

(d) High-efficiency Propellers. (4)

Reference Answer

Recent international regulations, such as the Energy Efficiency Existing Ship Index (EEXI) and Carbon Intensity Indicator (CII), have intensified the focus on improving ship propulsion effectiveness to reduce greenhouse gas emissions. A suite of Energy Saving Devices (ESDs) has been developed to optimize the hydrodynamic performance of the propeller and rudder system. This discussion details four principal categories of such devices.
### (a) Wake Equalizing Devices (WEDs)
**Concept:**
The flow of water (wake) into the propeller of a ship, particularly a full-form vessel like a tanker or bulk carrier, is non-uniform. The water velocity is slower at the top of the propeller disc (due to the hull boundary layer) and faster at the bottom. This non-uniform wake field causes the angle of attack on each propeller blade to fluctuate significantly during every revolution. This fluctuation leads to:

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