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%.

Calculation of hydrodynamic resistance is one of the most important steps in design of vessels. Nowadays, using numerical methods and specially Computational Fluid Dynamics (CFD) for calculation of ship resistance is one of marine engineering fields. In this research, flow around the hull of a catamaran vessel is investigated numerically and resistance is calculated. Numerical modeling is done with FLUENT CFD code. This software solves governing equations by Finite Volume Method (FVM). Modeling is carried out for two ratios of separation to length of vessel (S/L) and finally numerical results are compared to experimental results from model tests. At low speeds, numerical results have a good agreement with experimental results but in higher speeds, the difference between numerical and experimental results increases about 10-20%. Also, by the increase of hull separation, the total resistance of catamaran decreases due to reduction of demi-hulls interferences.

Increase in speed and range of hydrodynamic systems, which ultimately lead to enhancement in its performance, is one of the most important goals in design of marine systems. To achieving this goal, it is required to reduce hydrodynamic drag. Micro-bubble injection technique is one of the active methods to reduce hydrodynamic drag. This approach has high efficiency for drag reduction and in comparison to the other active methods, it has less environmental pollution and it is easy to install on the hydrodynamic vehicles. The main aim of this research is experimental investigation of the hydrodynamic drag reduction of a catamaran vessel using micro-bubbles injection method and to find the effective parameters on the performance of this technique. For this purpose, at first, a catamaran vessel model is made with length of 70cm. Then the micro-bubble injectors are designed and installed with necessary equipment, for measurement of air flow rate, on three locations at fore, middle and aft sections of the model. Experimental tests are carried out in towing tank laboratory for catamaran vessel with and without injection system for Froude numbers in the range of 0. 44 to 1. 48. And finally, the ability of micro-bubbles injection method to reduce hydrodynamic drag of catamaran vessel model was evaluated at different velocities. The experimental results revealed that the average hydrodynamic drag reduction is attained about 17%. Additionally, by increasing Froude number, the capability of micro-bubble injection method to reduce drag decreased from 21. 15% to 11. 8% for Fr=0. 54 and Fr=1. 25, respectively.

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.

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.

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.