The present paper contains the test results of a planing Catamaran model. The aim of the tests was to study the effect of hydrofoil in these types of crafts. First, experiments were carried out on the bare body (i.e. without hydrofoils) to obtain non-dimensional hydrodynamic resistance coefficient versus speed. Then, the model with hydrofoils, by various locations and attack angles were subjected to tests and the results were compared with those from the tests with the bare body. Results show that great reduction in hydrodynamic resistance of hydrofoil-supported Catamaran is accessible especially at high speeds. In addition, hydrofoils positioning is important and un-suitable designs may result in instability in motion and increased in hydrodynamic resistance.

High speed craft have longitudinal instabilities in waves and calm water, so, it is very important to know the dynamics and behavior of these vessels. In recent years, there has been more attention paid to the study of hull form optimization, movement improvement and instability control for planing marine vessels. The problem of increasing movement and acceleration of marine structures, especially in high speed craft, has a negative effect on the performance of the structure, its crew, passengers and equipment. So, estimation of vessel movement is an important part of its design. In this regard, wide studies have been carried out, experimentally and numerically, on the motion of these vessels in regular waters.But, in high speed craft, due to the complex and nonlinear behavior of the motion equation, the numerical solution of the equations of motion in the time domain is highly complex and time-consuming in calculating irregular waves. Therefore, researchers prefer to use experimental testing. Due to a limitation of equipment in marine laboratories, the use of irregular wave makers and expensive tests for real vessels in open seas, it is necessary to obtain an analytical solution for estimation of motion in irregular waves. The purpose of this study is to illustrate how we can achieve an analytical method, based on initial conditions, for planing vessels in irregular waters. In this study, an analytical model, with low computational cost, will be provided for the longitudinal movement of a Catamaran. This model is based in consideration of analytical and numerical studies, and during this research, other published findings will beproduced. The proposed method uses the principle of a superposition of forces, which has no antonym with the nonlinear motion of high speed craft. In this method, the hydrodynamic coefficients must be constant, relative to movement frequency, so, numerical evaluation of the hydrodynamic coefficients has been discussed in every motion frequency. Various experiments have shown the hydrodynamic coefficient tendency to be constant at high collision frequency. By examining the various hydrodynamic coefficients in collision frequencies, an increase in the frequency of collisions, as well as fixed coefficients, were observed. The method used in this research has acceptable answers for high wave lengths, with respect to vessel length.

The wake wash from passing ships can cause environmental damage. The wake wash is an important issue for naval architects and shipbuilders in concentrating on more environmentally friendly designs. This paper presents results of a parametric study of Catamaran hull form to obtain low wake wash hull form configurations or low speed inland waterway boats. The study uses a Computational Fluid Dynamics (CFD) simulation, and model experiments were carried out for validation of the CFD software set-up. The study concentrates on the asymmetric Catamaran hull form. The investigation is conducted on two configurations of hull form, Flat Side Inward (FSI) and Flat Side Outward (FSO) configurations. The investigation is conducted on a hull form with a Length to Beam (L/B) ratio of 12.2, 15.2 and 18.3 and a Separation to Length (S/L) ratio of 0.2, 0.3 and 0.4. The results based on wave height criteria at various longitudinal cuts have shown that the FSO configuration has a lower wake wash compared with the FSI configuration. Considering L/B and S/L ratios, hull forms with a larger separation or higher L/B ratios produce lower wave heights.

Conventional ships have been used for many years with usual body forms. But recent developments in high speed crafts have created many different alternatives. Therefore the selection of hull type becomes an important issue in the preliminary design stage. This selection should be based on performance comparisons and also other parameters such as building costs. Since planing monohulls and Catamarans are very popular types of high speed crafts, in this paper their behaviors from resistance at high speeds are compared. The results may prove useful for designers at conceptual or preliminary design stages.

Extensive experimental investigations of hydrofoil-assisted Catamarans have identified the main hydrodynamic parameters affecting the performance of these vessels. Design principles of existing vessels are discussed in the light of these hydrodynamic findings. The experience gained from experimental testing has provided the basis for the development of a non-linear vortex lattice method for design purposes. The method is validated by comparison with experimental results and applied to the problem of optimizing a 40- knot, 40m hydrofoil-assisted Catamaran with a hydrofoil system developed for modem high speed Catamarans. It is -shown that the method can be successfully applied to optimization problems of these vessels as it successfully captures the complex hull-foil interactions. Results of the numerical investigation performed, indicate that optimizing the mutual distance between the hydrofoils can significantly improve the lift to drag ratio of such a vessel.

Catamaran added V-like center bow (INCAT) is investigated as a wave-piercing vessel to decrease vertical acceleration and diminish slam events during sea-keeping operation. The Catamaran and the vessel bow were modeled and the vertical acceleration of model was validated with experimenal test. The geometry of V-like center-bow such as slope of center bow and elevation from demi-hulls was optimized numerically in the case of 3 different slops of bow model. Considering different center bow elevation of 9.5 and 49.5 mm, the pressure contour of the INCAT vessels was compared numerically. The optimized INCAT vessel as well as the Catamaran vessel was fabricated and exposed experimentally in a wavy environment with two significant wave height of 11 and 17 cm using a towing tank test. Thus hydrodynamic parameters such as vertical acceleration, heave, pitch, and resistance force were measured and compared. The results show no slam event in the environment with a wave height of 11 cm but the slam event occurr at the experiment with the wave height of 17 cm.

Today, researchers exploit hybrid craft more than they used to be. The main reason is that they need to high speed as well as extra portability. For instance, a famous hybrid craft is named Hysucat, was designed through the combination of Catamaran and hydrofoil. Catamarans, a type of multihull boats, have always considered by designers because of their simultaneous supply of high speed and stability. These boats hold high drag despite more wetted surface as well. By using hydrofoil the wetted surface reduces, and then the drag of boat will decline. Meanwhile, sketches in the layout of hydrofoil processes notice to weight and center of gravity. This paper investigated application of hydrofoil in the high speed Catamaran with considering different conditions in terms of center of gravity and load conditions. The model has exploited in the three states of loading (partial, ballast and over) and two centers of gravity for each diverse weight. Hence, nine series tests in towing tank have been carried out on the model boat in scale 1 ratio to 11. 43. Eventually, results were computed to full scale boat by Froude number and ITTC model. According to the test results, usage of the hydrofoil brings about 50% drag reduction.

In common Catamaran vessels, demihulls are parallel to each other. In this paper, the total resistance of a Catamaran vessel with non-parallel demihulls is investigated experimentally and numerically. Experiments are carried out at different Separation Ratios (S.R.), that is the ratio of fore to aft separation of the Catamaran demihulls; and also in two ratios of length to separation in amidships (L/Sm). The FLUENT solver, based on the Finite Volume Method (FVM), was used for numerical solution. Applying the VOF model, the free surface around the Catamaran vessel and total resistance are calculated and compared with experimental results. Finally, the frictional resistance of the Catamaran from the ITTC 1957 correlation line is calculated and compared with CFD frictional resistance. The results show that non-parallel demihulls cause total resistance to increase at Froude numbers below 0.8, and decrease at Froude Numbers over 0.8. In the numerical part, at low Froude numbers, numerical results have an error up to 10% relative to model test results, but error increases at high Froude numbers up to 25%.