Marine structures, such as ships, are vulnerable to fouling, leading to increased hull resistance (decreased propulsion efficiency). In order to reduce this phenomenon, ship owners tend to clean the hull and the propeller surface prior to dry docking. It is essential to understand which part of the ship is more beneficial to clean. Nowadays, various studies on the effect of the hull roughness to the resistance components have been published. However, a little information can be found about the propeller in the literature. The aim of this work is to experimentally study the effect of surface roughness on the hydrodynamic characteristics of a scaled propeller. To this respect, free flow tests as well as self-propulsion tests were performed at the towing tank of NTUA. A 4-blade wageningen propeller, with 0.16m diameter, p/d of 0.88 and 0.628 expanded blade area ratio was used for this purpose. Roughness has been generated by applying a sand strip on both surfaces of the propeller. Two conditions have been examined, i.e. clean surface and a rough surface at various speeds covering the operational area of the propeller. The Reynolds number is kept above 5×106. Results referring to the thrust, torque, thrust reduction, wake fraction and rotational efficiency will be presented in detailed. Finally, useful conclusions about the propulsion coefficients were drawn.

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