This paper presents experimental and numerical investigation of stability and rooster tail of a mono-hull high-speed planing craft with a constant deadrise angle. Initially, a one-fifth scale model was tested in a towing tank, which showed porpoising phenomenon at 8 m/s (equal to the speed of sailing). Subsequently, two wedges of 5 and 10 mm heights, based on the boundary layer calculations, were mounted on the aft section of the planing hull. These wedges were shown to increase the lift at the aft section. These experiments were carried out at different speeds up to 10 m/s in calm water. The experimental results indicated that the installed wedges reduced the trim, drag, and the elapsed time for reaching the hump peak, and also eliminated the porpoising condition. All these test cases were also numerically simulated using Star CCM+ software. The free surface was modeled using the volume of fluid scheme in three-dimensional space. The examined planing craft had two degrees of freedom, and overset mesh technique was used for space discretization. The obtained numerical results were compared with experimental data and good agreement was displayed in the presented comparisons. Ultimately, the effect of the wedge on the rooster tail behind the planing craft was studied. The results of this investigation showed that by decreasing the trim at a constant speed, the height of the generated wake profile (rooster tail) behind the craft decreases, albeit its length increases.

One of the most well-known strategies to eliminate or reduce the longitudinal instabilities in planing hull, is to reduce the trim of the craft. In the current study, porpoising is controlled through creating a transverse step, and the combination of adding a wedge to the stern and transverse step in the vessel. Usually, performance of stepped boats is not suitable in preplaning regime. However, through the proposed method, stepped model performance can be improved prior to the planing regime. The investigated craft is a 2.56 m long monohull high speed model with speed range of 1,3,5,7 and 9 m/s. The obtained results indicate that best performance is acquired by the step and wedge model at the beginning of the planing regime. From 3 to 7 m/s, drag of stepped and wedged models has the lowest value and above 7 m/s and at 9 m/s, the stepped model has the lowest resistance. Among the investigated methods, using combined step and wedge indicates largest reduction in trim angle (At speeds of 3 to 9 m/s). It can therefore be concluded that model equipped by combination of wedge and step improves the poor performance of the stepped models prior to the planing regime.

In the present study, the effect of the duct angle and propeller location on the hydrodynamic characteristics of the ducted propeller using Reynolds-Averaged Navier Stokes (RANS) method is reported. A Kaplan type propeller is selected with a 19A duct. The ducted propeller is analyzed by three turbulence models including the k-ε standard, k-ω SST and Reynolds stress model (RSM). The numerical results are compared with experimental data. The effects of the duct angle and the location of the propeller inside the propeller are presented and discussed.En el presente estudio se reporta el efecto del ángulo de ducto y la ubicación de la hélice sobre las características hidrodinámicas de la hélice con ducto, usando el método RANS (Reynolds-Average Navier Stokes). Una hélice de tipo Kaplan es seleccionada con un ducto tipo 19A. La hélice con ducto es analizada por tres modelos de turbulencia, incluyendo k-ε standard, k-ω SST y el modelo de esfuerzo de Reynolds (RSM -Reynolds Stress Model). Los resultados numéricos son comparados con datos experimentales. El efecto del ángulo de ducto y la ubicación de la hélice son presentados y discutidos. 42In recent year, considerable eff orts have been made to improve the propulsive effi ciency of the propeller on the ships. One of these propulsors is called a ducted propeller found as widespread application. Th e duct is generally used to obtain augment thrust, but it is also used to minimize cavitation and underwater noise or to protect the propeller from damage. Th ere are two types of duct, the fi rst type is called an acceleration duct or Kort nozzle and the second type is a deceleration duct. Fig. 1 shows both types of the ducted propeller. Th e Acceleration duct has a fl at surface on the outside of the curve in the inner area. Th e outer surface is high-pressure surface and the inner surface is low-pressure surface (or suction). Th e suction allows more current to be directed into the duct and thus increase the fl ow rate. Th e increased infl ow velocity causes a decrease in the thrust and torque of the propeller. At the same time, a circulation develops around the duct section resulting in an inward directed force which has a forward component, the duct thrust. Th e duct also has a drag directed aft. Th e effi ciency of the ducted propeller is therefore greater than of the open propeller (Ghose, Kogarn, 2004).In recent years, computational fl uid dynamics (CFD) have been extensively used for the analysis of marine propellers. Due to the complex shape, fl ow turbulence, fl ow separation and the possibility of cavitation, the analysis of marine propellers is a diffi cult task; however, some works have been done in the fi eld of ducted propellers. For example, (Taketani et al., 2009) presented the advanced design method of a ducted propeller which has high bollard pull performance. A nozzle section shape and a propeller have been designed according to a parametric study of the numerical simulation in order to have higher performance than a conventional ducted propeller. Th e o...

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