High-speed Catamaran Research Articles

Pressure Distribution due to Stern Tab Deflection at Model Scale

"Trim tabs form an important part of motion control systems on high-speed watercraft. By altering the pitch angle, significant improvements in propulsion efficiency can be achieved by reducing overall resistance. For a ship in heavy seas, trim tabs can also be used to reduce structural loads by changing the vessel orientation in response to encountered waves. In this study, trials have been conducted in the University of Tasmania hydraulics laboratory using a closedcircuit water tunnel to measure model scale trim tab forces. The model scale system replicates the stern tabs on the fullscale INCAT Tasmania 112 m high-speed wave-piercer catamaran. The model was designed for total lift force measurement and pressure tappings allowed for pressures to be measured at fixed locations on the underside of the hull and tab. This investigation examines the pressures at various flow velocities and tab deflection angles for the case of horizontal vessel trim. A simplified two-dimensional CFD model of the hull and tab has also been analysed using ANSYS CFX software. The results of model tests and CFD indicate that the maximum pressure occurs in the vicinity of the tab hinge and that the pressure distribution is long-tailed in the direction forward of the hinge. This accounts for the location of the resultant lift force, which is found to act forward of the tab hinge."

Low Reynolds Number Performance of a Model Scale T-Foil

"Submerged T-foils are an essential forward component of the ride control systems of high speed ferries. A model scale T-Foil for a 2.5m towing tank model of a 112m INCAT Tasmania high-speed wave-piercer catamaran has been tested for both static and dynamic lift performance. The tests were carried out using a closed-circuit water tunnel to investigate the lift and drag characteristics as well as frequency response of the T-Foil. The model T-Foil operates at a Reynolds number of approximately 105, has an aspect ratio of 3.6 and a planform which is strongly tapered from the inboard to outboard end. All of these factors, as well as strut and pivot interference, influence the steady lift curve slope of the model T-foil which was found to be 61% of the value for an ideal aerofoil with elliptic loading. The T-foil dynamic performance was limited primarily by the stepper motor drive system and connection linkage. At the frequency of maximum motion of the 2.5 m catamaran model (about 1.5Hz) the model T-foil has approximately 5% reduction of amplitude and 15 degrees of phase shift relative to the low frequency response. Only very small limitations arose due to the unsteady lift as predicted by the analysis of Theodorsen. It was concluded that the model scale T-foil performed adequately for application to simulation of a ride control system at model scale."

Improving the Efficiency of a High Speed Catamaran Through the Replacement of the Propulsion System

The high speed vessels are primarily designed for short distances services as public transport of passengers and vehicles. The range of high speed, according to the Code of high-speed vessels begins at 20 knots, which depends on the cruise speed you desire for your vessel; you will have to use the most appropriate type of propellant. In general, in the past 20 years, they have been building high-speed vessels with speeds above 33 knots, which meant installing water jet propellants coupled to powerful engines and therefore of high consumption of fuel, increasing operating costs and causing increased air pollution. Although the prices of fuel have been reduced to half, due to the sharp fall in oil prices, the consumption of fuel and the air pollution remains high at these speeds and powers used, in addition to that the reduction of the time spent on each trip is not excessive, mainly in short routes that are less than an hour . This article is about adapting a ship of high-speed service, with a maximum speed in tests of 34 knots and to reduce its operating costs (fuel, maintenance, etc.) and make it economically viable; before the transformation, this vessel was operating with a service speed of 22 knots, and with a consumption per mile of 135 litters of MGO. The transformation process has consisted by: – Replacement of the two original water jet with four shaft lines with fix pitch propeller. – Replacement of the two original main engines (2 x 6500 kW = 13000 kW) by four engines (4 x 1380kW = 5.520 kW). – Changing the underwater hull shape to fit the new propellers and maximize its efficiency. – Relocation of auxiliary engines, to achieve the most efficient trim. – Installation of two lateral propellers to improve maneuverability and shorten the total time of journey. After the reform and the return to service of the vessel with a service speed of over 22 knots, it has been verified that the consumption per mile is of 45 litters MGO, representing a reduction of 65% of consumption and even more reduction of emissions as the new engines comply with the latest regulations.

Numerical computations of resistance of high speed catamaran in calm water

In this paper, the in-house multifunction solver naoe-FOAM-SJTU is applied to study the resistance and wave-making performance of a high-speed catamaran sailing at different velocity in calm water. The volume of fluid (VOF) method is used to capture the free interface and the finite volume method (FVM) is adopted as the discretization scheme. The hull model is fixed with initial trim and sinkage. The numerical results of the presented paper agree very well with the measurement data of model test. Wave making and vortex field are well simulated to analyze the hydrodynamic performance of a catamaran.

Design-space dimensionality reduction in shape optimization by Karhunen–Loève expansion

The paper presents a methodology to reduce the dimension of design spaces in shape optimization problems, while retaining a desired level of geometric variance. The method is based on a generalized Karhunen–Loève expansion (KLE). Arbitrary shape modification spaces are assessed in terms of Karhunen–Loève modes (eigenvectors) and associated geometric variance (eigenvalues). The former are used as a basis in order to build a reduced-dimensionality representation of the shape modification. The method is demonstrated for the shape optimization of a high-speed catamaran, based on CFD simulations and aimed at the reduction of the wave component of calm-water resistance. KLE is applied to three design spaces with large dimensionality (≥20), based on a free form deformation technique. The space with the largest geometric variance is selected for dimensionality reduction and design optimization. N-dimensional design spaces are used, with N=1, 2, 3, and 4, retaining up to the 95% of the geometric variance associated to the original space. The correlation between the objective reduction achieved, the dimension N and the geometric variance of the reduced-dimensionality space is shown and found significant.

Operability assessment of high speed passenger ships based on human comfort criteria

The growing popularity of passenger cruise lines means continual challenges are faced concerning both a vessel׳s design and its operational ability. Vessel dimensions, service speeds and performance rates are rapidly increasing to keep pace with this expanding interest. It is essential that vessels demonstrate high performances, even in adverse sea and weather conditions, and ensure the comfort of passengers and the safety of cargo. A vessel׳s operability can be defined as the percentage of time in which the vessel is capable of performing her tasks securely. In order to calculate a vessel׳s operability index, many key parameters are required. These include the dynamic responses of the ship to regular waves, the wave climate of the sea around the ship׳s route, and the assigned missions of the vessel. This paper presents a procedure to calculate the operability index of a ship using seakeeping analyses. A discussion of the sensitivity of the results relative to three different employed seakeeping methods is then given. The effect of seasonality on a ship׳s estimated operability is also investigated using wave scatter diagrams. Finally, a high speed catamaran ferry is explored as a case study and its operability is assessed with regards to human comfort criteria.

Risk assessment of cross structure slamming of high speed ro-pax catamaran at initial design stage

One of the urgent issues of the modern theory of the ship design, in other words the appliance of the risk theory at the initial design stage has been considered. It is shown that accidents occur due to the following main reasons: collision, contact, fire or explosion, grounding or stranding, loss of hull integrity, machinery or electrical failures. For the high speed catamarans, the slamming is the main reason which leads to the loss of vessel hull integrity. Based on the research, the author presents a general method to determine the risk value from the accidents. Also, the scientific publications on the given problem are analyzed. The article also describes the algorithm of the damage probability calculation of the cross structure of the high speed ro-pax catamarans, which is based on the probability of the cross structure slamming and on the probability that the slamming dynamic load is more than the bearing capacity of the cross structure shell plate.

Ship Hull Structural Multiobjective Optimization by Evolutionary Algorithm

An evolutionary algorithm for multiobjective optimization of the structural elements of the large spatial sections of ships is presented. The evolutionary algorithm where selection takes place based on the aggregated objective function combined with domination attributes as well as distance to the asymptotic solution is proposed and applied to solve the problem of optimizing structural elements with respect to their weight and surface area on a high-speed vehicle-passenger catamaran structure with several design variables such as plate thickness, scantlings of longitudinal stiffeners and transverse frames, and spacing between longitudinal and transversal structural members. Details of the computational models were at the level typical for conceptual design. Scantlings were analyzed using the selected rules of a classification society. The results of numerical experiments with the use of the developed algorithm are presented. They show that the proposed genetic algorithm can be a foundation of the effective multiobjective optimization tool for ship structure optimization. Further development of the tool should include more advanced methods for ship structural analysis.

A parametric study on water-entry of a twin wedge by boundary element method

High speed catamarans are used for pleasure, racing as well as passenger transportations. Optimal design of these crafts requires knowledge of sea loads exerted on their structures. The total load may be estimated by integration of loads exerted on a series of two-dimensional sections along the hull. In order to access the cross-sectional loads, the problem may be simplified to solve the water-entry problem of a twin hull. In this paper, water-entry problem of a twin wedge at constant vertical water-entry speed is studied. The problem is solved in the framework of potential theory using boundary element method where gravity effect on the flow is neglected. A simplified model based on Wagner theory is employed. Free surface elevation and pressure distribution on the body in different deadrise angles have been evaluated. A parametric study has been done to investigate effects of deadrise angle, distance between demi-hulls and free surface elevation on maximum pressure coefficient. Finally, a regression formula for maximum pressure coefficient has been proposed. Results of parametric study reveal that as time advances the interaction between two demi-hull gets more severe, besides the interaction effect on pressure coefficient is nonlinear.

Experimental investigation of interference effects for high-speed catamarans

We have performed an experimental investigation aimed at assessing the relevance of hull interference effects on the total resistance of a catamaran model advancing in calm water. To this purpose, drag and attitude measurements have been carried out for several values of the hull separation, as well as for the monohull, at changing the Froude number in the range 0.1–0.8. Data concerning the two-dimensional wave field around the models have also been collected. Our results indicate that, except for a narrow range of conditions where favorable interference is observed, the interaction between the catamaran hulls usually results in a marked increase of the total resistance as compared to the monohull case. This penalization can be as large as 30% for the narrowest hull spacing at Fr≈0.5. At larger hull spacings, the effect is attenuated and occurs at smaller Froude numbers. Interference effects are less evident both in the small and large Froude number range, namely when Fr<0.3 and Fr>0.7 respectively. Insight into the mechanisms underlying this behavior is obtained by examining the relational dependence between the resistance variation and the data concerning attitude of the vessel and wave-field elevation.

Slam occurrences and loads of a high-speed wave piercer catamaran in irregular seas

In order to optimise the structural design of large lightweight high-speed catamarans, a thorough understanding of the structural loads is required. Not only is slam severity an important factor in the structural design, but also the occurrence rates of such events in realistic sea conditions is vital for long-term load estimations. The slamming behaviour of a 2.5-m hydroelastic segmented model representative of an Incat wave piercer catamaran was investigated over a range of realistic irregular sea conditions. The model was instrumented with strain gauges to record centrebow slam loads, pressure transducers, wave probes and linear variable displacement transducers. More than 2000 slam events were identified over 22 test conditions, providing an extensive database of slam events. Slam events were identified from the pressure transducer measurements and two important slam parameters investigated: occurrence rates and slam severity. The slam magnitudes were found to be scattered; numerous outliers were detected with magnitudes up to 4 times the median observed in every tested condition. Slam occurrence rates and severity are generally greater in conditions where motions are large. A slam occurrence threshold was identified by extrapolating the experimentally measured occurrence rates. For a 112-m vessel with speeds between 20 and 38 knots and with a modal wave period of 8.5 s, slams are shown not to occur at significant wave heights less than 1.5 m. The slam loads and occurrence data obtained through scale model testing can be used by high-speed catamaran ferry designers to assist the development of structural load cases and operation limits for future designs.

Experimental investigation of a fast catamaran in head waves

The present work is about the seakeeping behavior of a fast catamaran advancing in head sea. To this aim seakeeping tests with transient, regular and irregular waves are performed in the rectilinear water tank of CNR-INSEAN. Seakeeping transient tests are used to provide the response amplitude operator for a wide range of wave lengths and several speeds of advancement. These tests allow identifying the Froude number at which the maximum vertical response occurs and an analysis of natural heave and pitch frequencies. A comparison with theoretical predictions is provided. Regular wave tests are used to assess nonlinear effects on the hull motions, as well as the added resistance generated by the increasing steepness and dependency on both the Froude number and wave lengths: therefore several ship speeds, several steepness and wave lengths of the incident wave system are considered. For a similar Froude number range, irregular wave tests are also pursued to investigate the seakeeping properties of the vessel in real scenarios. The estimation of added resistance in wave, its dependency on the Froude number, the investigation of nonlinear effects and the analysis of increased resistance in a real scenario are addressed as well. To make sure the present experimental campaign is valid, it is checked with repeatability analysis and matched with ad hoc experimental data collected at TU Delft. The whole set of measurements is a valuable database for both hydrodynamic studies of high speed catamarans and CFD validation.

An insight into the slamming behaviour of large high-speed catamarans through full-scale measurements

The slamming behaviour of a large high-speed catamaran has been investigated through the analysis of full-scale trials data. The US Navy conducted the trials in the North Sea and North Atlantic region on a 98 m wave piercer catamaran, HSV-2 Swift, designed by Revolution Design Pty Ltd and built by Incat Tasmania. For varying wave headings, vessel speeds and sea states the data records were interrogated to identify slam events. An automatic slam identification algorithm was developed, considering the measured rate of change of stress in the ship’s structure coupled with the vessel’s pitch motion. This has allowed the slam occurrence rates to be found for a range of conditions and the influence of vessel speed, wave environment and heading to be determined. The slam events have been further characterised by assessing the relative vertical velocity at impact between the vessel and the wave. Since the ship was equipped with a ride control system, its influence on the slam occurrence rates has also been assessed.

Historical perspective on the structural design of special ships and the evolution of structural design methods

Recent decades of ship design and construction have produced numerous examples of innovative and special-purpose hull forms, structures, speeds, size and complexity. These include progressively larger container ships, ultra-large crude carriers and cruise vessels, liquefied natural gas (LNG) carriers, high-speed catamarans, small-waterplane-area twin-hull (SWATH) vessels, trimarans and others. The geometries, structural topologies and materials required for these vessels did not fit well with traditional design methods and procedures, rooted in empirical approaches. Instead, these ships and their structures required some form of direct analysis or first-principles approach, which by its nature is computer based. The ship design and design approval community responded to this new set of requirements by developing and implementing new procedures, new methods and new technologies to adequately address the need for first principles in the design. This design methodology innovation in turn placed new and significant demands on the state of the design software environment under which the new methods and procedures were being developed. This paper traces some of the innovative ship types that have evolved over recent decades and the associated computer-based structural design technology evolution during this time. In particular, the innovations of Professor Owen Hughes in establishing a first-principles approach to ship structural design, documenting the theoretical basis for this approach in the textbook Ship Structural Design: A Rationally-Based, Computer-Aided, Optimization Approach, and developing the MAESTRO computer-based implementation of the methodology are presented

Simulation of dynamic behaviour of high-speed catamaran craft subjected to underwater explosion

In recent years, shock trials for surface ships have been conducted in many countries for qualification of ship integrity, systems and subsystems in response to shock. A ship trial identifies design and construction deficiencies that negatively impact ship and crew survivability. Such a trial also validates shock hardening and performance of shipboard equipments. However, live-fire ship shock trials and underwater explosion testing are both complex and expensive. As a possible alternative, numerical modelling and simulation may provide viable information on the details of dynamic characteristics of ships, including at the component and sub-component levels. Ship shock analyses were conducted using a finite-element-based coupled catamaran-type ship with a fluid model. This model is also applicable to underwater explosion (UNDEX) simulation for movements of a high-speed catamaran-type ship. Catamaran-type ship shock modelling and simulation were performed and the simulation results were compared with the empirical data. The high-speed catamaran-type ship shock analysis approach is presented and the important parameters are discussed.

Hull-form Design and Wave-resistance Performance Analysis of a High Speed Catamaran Hull

Hull-form Design and Wave-resistance Performance Analysis of a High Speed Catamaran Hull

高速双胴船のファジィローリング制御

高速双胴船のファジィローリング制御

A Practical Design Approach including Resistance Predictions for Medium-speed Catamarans

Medium-speed catamarans are under development as a new class of vessels to meet requirements for highly efficient sea transportation with low environmental impact. Reduced service speed and increased deadweight will increase transport efficiency. Compared to current high-speed catamarans, these new vessels will operate in a transitional speed range between high-speed craft and conventional displacement ships. In this paper, design guidelines to choose appropriate main dimensions for medium speed catamarans with minimum resistance were derived and a preliminary design was made. These vessels will operate at Froude numbers of about 0.35 and have a relatively low prismatic coefficient of about 0.5 in conjunction with a small transom immersion. Different methods are discussed to correctly predict the calm water resistance, with RANSE (Reynolds-averaged Navier-Stokes equations)-based flow simulations being the most promising. It is shown that they are capable of predicting the hydrodynamic characteristics of medium-speed catamarans, such as drag force, trim and sinkage with acceptable accuracy.

Full-Scale Motions Of A Large High-Speed Catamaran: The Influence Of Wave Environment, Speed And Ride Control System

To assess the behaviour of large high-speed catamarans in severe seas, extensive full-scale trials were conducted by the U.S. Navy on an INCAT Tasmania built vessel in the North Sea and North Atlantic region. Systematic testing was done for different speeds, sea states and ride control settings at different headings. Collected data has been used to characterise the ship’s motions and seakeeping performance with respect to wave environment, vessel speed and ride control system. Motion response amplitude operators were derived and compared with results from a two-dimensional Green function time-domain strip theory seakeeping prediction method. An increase of motion response with increasing vessel speed and a decrease with the vessel moving from head to beam seas was found. In higher sea states and headings ahead of beam seas an increasing influence of the centre bow on pitch motion damping was found. Significant motion RAO reduction was also found when the ride control system was active. Its effectiveness increased at higher speeds and contributed to heave and pitch motion RAO reduction. Predicted motion magnitudes with the time domain seakeeping code were consistent with the measured motion responses, but maximum heave was predicted at a rather higher frequency than was evident in the trials.

On The Macro Hydrodynamic Design Of Highly Efficient Medium-speed Catamarans With Minimum Resistance

A new class of fuel-efficient and environmentally friendly twin-hull vessels is currently under development. Compared to high-speed catamarans, a significant reduction in speed combined with an increase in deadweight tonnes will lead to a highly efficient medium-speed catamaran design. Recently-built conventional and high-speed ferries are compared to each other in terms of length, speed, deadweight and transport efficiency to classify the new design. The goal of this study is to find a preliminary macro design point for minimum total resistance by considering the main particulars of the catamaran vessel: block coefficient, prismatic coefficient and slenderness and separation ratios of the demihulls. Publications containing recommendations towards the optimum hull form parameters for moderate Froude numbers are reviewed and existing experimental data analysed to identify parameters for this new class of vessel. Designs with varied L/BOA-ratios and constant deck area are compared to find configurations of low total resistance for carrying a nominated deadweight at a particular speed, the associated change of the light ship weight has been taken into account. Two different model test series of catamaran models have been considered and their resistance curves agreed to each other. Recommendations are made; with the most important being the vessel should not exceed a speed of Fr = 0.35, with optimal prismatic coefficients around CP ≈ 0.5 and low transom immersion. This study presents the preliminary design of medium-speed single and twin-hull vessels for operations close to hump speed.