Surface Piercing propeller
Surface-piercing propellers are specific type of super cavitating propellers that are commonly used as propeller systems with high performance for high-speed vessels. Among the most important advantages of these propellers comparing with fully-submerged propellers is that they can achieve high speeds, improve performance of propulsion system, and decrease noise and vibration. They are suitable for larger scale design since there is no limitation in terms of blade-body distance and maximum draft. Surface-piercing propellers are also featured with lower corrosion thanks to a decrease or lack of the destructive phenomenon of cavitation. Additionally, these propellers considerably decrease appendage drag so that they need a considerably less power to propel vessels comparing with the conventional propellers. However, since surface-piercing propellers function in two-phase condition, each blade enters water once in each rotation cycle so that the thrust and torque of each blade hit maximum level and then become zero. As a results surface-piercing propellers generate oscillating thrust and torque. Despite of being more than one century in operation as marine propellers, there is still a great need for conducting survey of the performance of these propellers. Nowadays and given the wide use of surface-piercing propellers in a wide range of vessels, many scientists are working on numerical and experimental studies on these propellers.
In the past and in absence of powerful software systems, studies on surface-piercing propellers were based on experimental tests and among these studies, Shiba [1], Hecker and Hadler [2], Hecker [3], Rains [4], Rose and Kruppa [5], Rose et al. [6], and Wang [7] are notable. These studies were aimed at extracting time-averaged thrust, torque, bending moments, and lateral forces and none managed to extract the accurate value of power and torque. Dobay [8], Olofsson [9], Szantyr and Miller [10], Dyson et al. [12], Nozawa and Takayama [13] are some the experimental studies that tried to calculate accurate force and torque on surface-piercing blades. In addition to dynamic performance, they tried to obtain induced forces on the blades, shafts, hub, and the like. Other experimental studies have focused on the effects of different parameters such as propeller pitch angle, blade profile, shaft inclination angle, propeller immersion depth, and cavitation number on hydrodynamic performance of surface-piercing propellers. Among these studies are Ferrando and Scamardella [14, 15], Ferrando [16], Ferrando et al. [17, 18], Nozawa and Takayam [19], Himei et al. [20] to name a few.