Propeller Diameter Difference and Its Impact on Propulsion Performance on Actual Sea Conditions 

When considering the propulsion performance of a ship, one of the most important factors is the propeller design. Generally, it has been known that propulsion efficiency is greater if a propeller has a larger diameter and low propeller shaft speed. However, it is equally important to maintain sufficient distance between the hull and the propeller, known as ‘propeller clearance’, to mitigate fluctuation pressure and the potential for inducing severe hull vibrations. Therefore, propeller designers must consider the propeller clearance while sizing a propeller. KITANIHON SHIPBUILDING CO., LTD is producing 27 chemical tankers of 19,950DWT, using three kinds of propellers with different propeller diameters. Each kind of propeller is similar in geometry except for the diameter. The sea trial results will demonstrate how the propeller diameter affects the ship’s performance. The wave conditions were not ideal during the sea trials, hence the investigation on the performance of propellers requires highly accurate hydrographic data. The authors have analyzed the sea trial data using values from ‘wave hindcast database’ which is reanalyzed historical database from the Japan Weather Association (referred to as JWA) and the authors examined the influence of propeller diameters on performance.