Novel application of large area propeller to optimize Energy Efficiency Design Index (EEDI) of ships

Abstract

Environmental pollution and rising cost of fossil fuels are posing a major threat to the shipping industry. After globalization its contribution is significant and time has come to curb the emissions from ships. The reduction of CO2 emissions has been the key target since IMO's Marine Environment Protection Committee (MEPC) published its findings in 2009. A number of measures resulting in technical and operational reductions were made mandatory in 2011. Among these and nearly all new build ships (20) have to conform is Energy Efficiency Design Index (EEDI). This provides a method of establishing the minimum efficiency of new ships depending on the type and size. With increasing competition the key to survival will be to design and operate the ships efficiently. In the current phase designers relied to retrofit methods and achieved slight gains of hull efficiency. In later phases tougher restrictions will be imposed which needs more changes in ship design. The EEDI has become an important design parameter that has to be complied. This master thesis is a holistic approach to analyze possible methods and implement one in the form of large area propeller as demonstrated in the R&D project Streamline initiated by the seventh frame work of European commission. Increasing the propeller diameter together with low rotational speed reduces axial and rotational losses (41) there by propulsive efficiency can be improved. But the constraints in the form of hull and ship baseline restrict this. Much research have been done so far by increasing the propeller diameter in the original position and in this work the large area propeller is moved axially aftwards to two positions between the initial location and transom where there was ample space to install it. This resulted in a partial success which will be explained at the end of this thesis. However apart from improved propulsive efficiency, improvement of other factors such as hull efficiency, suction on the hull and wake profile have been gained. The increased clearance reduces the pressure pulses transferred to the hull. An extensive analysis is made by means of a sliding grid approach in the RANSE CFD code Star-CCM+, with a series of self propulsion tests, for the chosen locations and propellers by moving it systematically aft. Results were validated with the experimental data from Ship Design and Research Centre (Centrum Techniki Okrętowej S.A., Gdańsk, Poland - CTO S.A.). These tests are a starting point of the experiments targeted to achieve the desired efficiency by choosing the optimum Pitch-Diameter ratio (P/D ratio) of the propeller.