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

2 2015

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Numeric Wake Equalizing Duct Geometry Optimization for a Given Ship

Martinas G., Cupsa O.S.

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

2015

Vol. 9, no. 2

243--248

The reduction of fuel cost has always been one of the key strategic business goals for ship owners and operators. In the current climate of high oil prices, the reduction of fuel costs becomes essential; and furthermore a variety of recent legislations require owners and operators to move towards the reduction of emissions from ships of SOx, NOx and CO. Hence the pressure on designers to achieve both reduced fuel costs and reduced emissions by optimising the hull and propeller has never been higher. In parallel to the performance improvement of new built vessels, there has been great interest in the potential to enhance the performance of existing vessels through retrofit of devices to the hull. In any case for instance the WED device must be customized to fit to the afterbody of the ship in terms of performing its supposed function. The Designer is therefore placed in the front of multiple geometric solutions from between he has to make a choice. This paper is intended to help the Designers to have a rational choosing approach by involving the numeric optimization of the geometry of the WED in order to select the best fitted WED to perform the best in order to achieve some predefined parameters. In this paperwork a given geometry of a WED device is taken and via Design Optimization the geometry of the duct was refined so that better results are achieved with a smaller and more compact WED. In doing so, the Designer is assisted by numeric optimization methods to choose from only three final candidates instead of several thousands in order to provide the best fitted WED geometry for a given ship afterbody.

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.