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Cavitation of a Propeller and Influence of an Wake Equalizing Duct

Martinas G.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

2015

Vol. 9, no. 2

235--241

The wake equalizing duct (WED) is one of the most commonly used energy saving devices for improving the propulsion performance of a ship; and reducing the propeller-excited vibrations and viscous resistance forces. During the last three decades considerable research and development activities have taken into place within this context. Most of these devices are used to improve propulsive efficiency, but some of them aims to improve other performance characteristics, such as cavitations, vibration, noise, maneuverability, etc. Marine propellers are the most common propulsion systems; nevertheless, it is possible to improve its propulsive performance using additional auxiliary propulsor devices (unconventional propulsors). Two versions of an existing ship in normal version and fitted with WED device were analyzed in order to demonstrate the influence on the WED device on the propeller cavitations . It was determined that the values for the pressure coefficient is 1.98 for without WED situation and 2.029 for WED situation. The difference is not so significant that, the conclusion is that WED device did not have influence over the cavitations of the propeller. Either optimization of dimension and form of WED did not help in reducing negative effects of cavitations. Not being a study in this paperwork, to decrease the cavitations we have other choices including a sound design of the propeller biased to improve the propeller behavior in cavitations. WED is clearly not a choice.

A Study on the Propulsion Performance in the Actual Sea by means of Full-scale Experiments

Kayano J., Yabuki N., Sasaki N., Hiwatashi R.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

2013

Vol. 7, no. 4

521--526

The IMO has adopted Energy Efficiency Design Index (EEDI), Ship Energy Efficiency Management Plan (SEEMP) and Energy Efficiency Operational Indicator (EEOI) in order to reduce GHG emissions from international shipping. And, the shipping industry is required to develop and improve the energy saving ship operation technologies to meet the above IMO guideline. The weather routing is one of the energy saving navigation technologies and widely adopted by oceangoing merchant ships. The effectiveness of the weather routing mainly depends on the accuracy of weather forecast data and the ship’s propulsion performance prediction. The propulsion performance in the actual sea is usually predicted using the Self Propulsion Factors obtained by model tests. It is necessary to understand the propulsion performance characteristics in the actual sea conditions for the improvement of propulsion performance prediction. From the above points of view, the authors performed full‐scale experiments using a training ship in order to investigate the propulsion performance characteristics in the actual sea. This paper describes the analysis results on the characteristics of Power Curves and Self Propulsion Factors under various weather and sea conditions.