This paper investigates the effect of the immersion ratio parameter on the hydrodynamic performance of three Surface-piercing propellers with diameters of 0.125, 0.132 and 0.140m at different advancing speeds. Experimental tests have been carried out in the free Surface water tunnel of the Babol Noshirvani University of Technology. The results showed that the maximum thrust coefficient of three propellers occurs in the velocity range of 3-3.5 m/s. This interval represents the transition area of the three propellers. Also, the effect of the blockage ratio on the hydrodynamic coefficients of three propellers relative to the advance coefficient has been studied. By increasing the immersion depth raises the propeller's wet Surface and increases the thrust and torque hydrodynamic coefficients. However, growing the propeller's diameter to 0.140m causes the effect of the blockage ratio parameter by increasing the immersion and the propeller's torque experiences a decreasing trend. Therefore, maximum propeller efficiency value with diameter 0.140m in immersion ratio 0.60 and 0.70, incresing 38% and 44%, respectively; relative to other proepllers. Also, the curve of the efficiency gradient of three propellers in the optimum immersion ratio of 0.40 compared to the advancing coefficient shows that the maximum efficiency gradient occurs in the range of 0.7 to 0.9.

In this work, considering a propulsion system of a planing boat, the effects of the air ducts with a square cross-section on the thrust, torque, performance, and ventilation of the Surface piercing propeller (SPP) are investigated. The fluid flow is simulated using solving of the Reynolds-averaged Navier–Stokes equations (RANS) by the multi-physics computational fluid dynamics software STAR-CCM+. The simulations are validated by studying its grid independency and comparing the numerical results with the extracted results from the sea trial. Then, by considering the actual arrangement of the duct and SPP, the SPP is examined in the open water test in five cases for both condition of the lack and existence of the aeration. Also, the effects of aeration, the advance coefficient and the immersion ratio on the hydrodynamic characteristics of the SPP are studied. In a constant distance between the air duct and propeller, the results show that by increasing the hydraulic diameter of the air duct, the torque and thrust decrease, and the efficiency remains almost constant. Also, it is numerically demonstrated that the effects of the advance coefficient on the torque and thrust coefficients are different for the models with and without aeration.

The Surface-piercing propeller blades move in and out of the water with each rotation to reduce the immersion depth from the free Surface to the shaft axis . The main challenge facing Surface piercing propellers, however, is their lower efficiency at lower advance velocity, compared to other propulsion systems. To improve the performance of the propeller, an aeration mechanism was used at low advance velocities so that air was blown to the Surface behind the propeller. Experimental studies were carried out on a propeller model in the Hydrotech laboratory of the Iran University of Science and Technology, and the effect of the injected air velocity ratio was evaluated at different immersion ratios. Based on the results obtained, it was concluded that an increase in the injected air velocity ratio could only promote thrust enhancement under specific conditions. For immersion ratios of 0.85 and more, as well as advance coefficients of 0.6 and more, a change in the velocity ratio of the injected air could not lead to an improvement in thrust. The best performance was identified with an immersion ratio of 0.4 and an advance coefficient of 0.4, while thrust performance at below or above of this condition declined .

Surface piercing propellers are special supercavitation propellers operating at free Surface. These propellers are designed to have the best performance at the highest speed. The geometric parameters of the number of blades and the pitch ratio will significantly impact the critical advance coefficient range, ventilation and consequently the hydrodynamic performance of the propeller. Therefore, in this paper, the effect of two crucial parameters of pitch ratio and number of blades were experimentally studied in free Surface water tunnel. After calibration and evaluation of uncertainty, two 5-bladed propellers with same section profile and pitch ratio of 1.5 and 1.4 used to investigate effect of pitch ratio. The results of two 5-blade and 6-blade propellers with same section profile and pitch ratio of 1.4 were compared. The immersion ratio was 40%, and the shaft inclination angle was zero. Results showed that increasing the pitch ratio increased the thrust and torque coefficients by 30%; while increasing the critical advance coefficient. Consequently that has led to the development of a full ventilation range and improved hydrodynamic performance of the propeller. In addition, by increasing the number of blades, at values greater than the critical advance coefficient, the thrust and torque coefficients were increased by 10%. However, the critical advanced coefficient changes were negligible. Comparing the results in the three-dimensional contours showed that with the change in the number of blades, by increasing the pitch ratio, the critical advance coefficient increased; which led to a further increase in efficiency.

Surface-piercing propellers have been widely used in light and high-speed vessels because of their superior performance. One of the major steps in propeller selection algorithm is the determination of thrust as well as torque hydrodynamic coefficients. For the purpose of simplifying design and selection procedure, some relations are presented for determining hydrodynamic coefficients in some studies, precision, and accuracy of which must be validated due to the importance of the issue as well as having high development and operational costs. Therefore, these issues are evaluated in this study by field study and recognizing the presented relation set as well as acquiring experimental test data. The acquired results show lack of full agreement between semi-experimental relations and experimental data. In the following, due to the limitations of the regression relations presented in the determination of hydrodynamic coefficients, the database was developed from experimental data, the number of series is determined by extracting the regression relations for each series, these relations are used to determine the hydrodynamic coefficient of thrust and torque in the propeller selection algorithm. Finally, a suitable algorithm for selecting the Surface-piercing propeller was presented and discussed.

In the current paper, numerical simulations of Fluid Structure Interaction (FSI) of a SP (Surface piercing) hydrofoil are conducted in order to study the in uence of elasticity on the initial water entry ventilation. Using ANSYS multi physics solvers, twoway FSI analyses are conducted by the implicit coupling of URANS (Unsteady Reynolds Averaged Navier-Stokes) equations with a  nite-element method. Numerical results are validated by the well-known rigid and elastic wedge water entry problems. Subsequently, computational results are presented for ranges of di erent velocity ratios (0. 38, 0. 64) and elasticity factor [0, 4]. Similar to the Surface piercing propeller (SPP), performance curves of a wedge water entry are de ned. The obtained similar trend of propeller and wedge performance curves in fully ventilated, transition, and partially cavitated operation modes shows that the adopted approach (2D-study) can be appropriate for future related studies. FSI simulation results indicate that structural deformation can highly a ect the location of transition point and shift it toward the fully ventilated part at high Froude number and elasticity factor. The overall e ciency loss due to the increase of foil elasticity is observed, and overshoot time of the foil deformation related to the variation of Froude number and elasticity factor is evaluated.