This study investigates the influence of a Ride Control System (RCS) with stern-mounted trim tabs and a bow-fitted T-Foil on slam kinematics and energy transfer during slamming, using a 2.5 m scale model of a 112 m Incat Tasmania high-speed catamaran in irregular waves. Towing tank tests were conducted at a forward speed of 2.89 m/s (37 knots at full-scale) in irregular head seas with significant wave heights of 60 mm and 90 mm, corresponding to 2.7 m and 4 m at full-scale, respectively. It was demonstrated that relative bow immersion is the kinematic parameter most strongly correlated with slam severity and is associated with a higher likelihood of severe slamming. In contrast, slam magnitude (quantified as peak integrated centre bow force derived from strain measurements) showed no strong correlation with either the relative bow velocity at the instant of slamming or the maximum pre-slam relative bow velocity. While these velocity factors showed weaker correlation with slam magnitude reduction compared to relative bow immersion, their importance increases when evaluating the effectiveness of control algorithms that similarly reduce relative bow immersion. The nonlinear pitch control algorithm was found to be the most effective in reducing relative bow immersion, reducing it by 17% and 21% in 60 mm and 90 mm wave heights, respectively, compared to the No RCS condition. Strain energy analysis revealed that this control algorithm reduced overall slam-induced strain energy of the model by 96% in 60 mm waves and 68% in 90 mm waves over a 54-second model test period compared to the No RCS mode. Furthermore, this algorithm mitigated the maximum peak strain energy in the centre bow by 70% in 60 mm waves and 47% in 90 mm waves, highlighting its potential to reduce slam-induced loads and improve the structural design of high-speed catamarans operating in challenging sea conditions.

Building on open-loop calm water investigations presented in Part 1, this study advances to closed-loop towing tank experiments to evaluate the effectiveness of a new RCS configuration, featuring dual demihull-mounted T-Foils and transom-mounted stern tabs, in reducing roll response. A roll control algorithm was developed to actively deflect the T-Foils and stern tabs based on real-time roll response feedback. Experiments were conducted at a model speed of 2.89 m/s (37 knots full scale) in Regular Waves with height of 60 mm and 90 mm (2.7 m and 4 m full scale), using a 2.5 m catamaran model towed at a 2° drift angle with bow to port to induce roll motion in encountered waves. The RCS was tested in three conditions: No RCS, passive RCS, and active RCS with linear and nonlinear roll control algorithms. The nonlinear roll control algorithm was most effective, reducing peak roll response by 58% in moderate waves and 43% in large waves. Overall, the new RCS mitigated roll, pitch, and heave motions in moderate waves by 58%, 34%, and 25%, respectively, demonstrating the potential of demihull-mounted T-Foils to enhance roll control while maintaining heave and pitch motion control effectiveness. Local vertical motion analysis showed the highest motion response at the bow-starboard and the lowest at the midship-port location, highlighting the influence of wave impact, drift-induced asymmetry, and combined motions. The results of this study offer valuable guidance for future RCS design in high-speed vessels.

Efficient roll motion mitigation is essential for ensuring the structural integrity and passenger comfort of high-speed catamarans in oblique seas. Ride Control Systems (RCSs) used by Incat Tasmania wave-piercing catamarans (WPCs) typically consist of a single centrally mounted bow T-Foil and two stern-mounted trim tabs, and roll control relies solely on the independent action of the stern tabs, limiting their effectiveness for heave and pitch while not providing optimal ability to mitigate roll in beam and oblique seas. This study experimentally evaluates a new RCS that integrates dual demihull-mounted bow T-Foils with stern trim tabs. The system was implemented on a 2.5 m scale model of a 112 m Incat Tasmania WPC and tested in calm water at 2.89 m/s (equivalent to 37 knots full-scale) using open-loop step and frequency response experiments. Step response tests assessed heel responses under various demihull T-Foils and stern tab deflection patterns. The most effective heel excitation was achieved when the port and starboard demihull T-Foils and stern tab control surfaces operated in antiphase, increasing the heel range by about 43% compared to the centre bow mounted T-Foil RCS configuration. Frequency response tests demonstrated that the integration of dual T-Foils enhanced the RCS roll excitation capability by 45%. A lumped parameter approach was employed to derive and solve the roll dynamic equation of the model, which accurately predicted the heel responses observed in step response tests, with an average deviation of just 4.7%. It also predicted roll response and phase lag trends across a range of excitation frequencies, closely aligning with experimental trends. These findings highlight the significant improvement in the system’s roll control capability by incorporating demihull-mounted T-Foils into the RCS configuration, providing strong support for the new RCS design and laying the foundation for the development of a roll control algorithm for future closed-loop control experiments.

To minimise motion sickness in high-speed catamarans and improve passenger comfort, ship designers require a thorough understanding of the Ride Control System (RCS). In this paper, the influence of various ride control algorithms on motion sickness on board a 112 m Incat Tasmania high-speed catamaran was investigated using frequency and time domain analyses of experimental data from towing tank tests conducted on a 2.5 m scaled model in irregular head sea waves. The RCS consisted of two stern-mounted transom tabs and a bow-fitted T-Foil. Frequency-domain analyses evaluated vertical acceleration spectra at three longitudinal locations to calculate Motion Sickness Dose Value (MSDV) based on the ISO 2631 standard. Time-domain analyses assessed the impact of the RCS and various algorithms on the probability and magnitude distribution of extremum accelerations and the duration of exposures to different acceleration levels. Cumulative MSDV trends, calculated across diverse conditions at three locations, were modelled using power functions and validated against frequency-domain MSDV values for 60-min exposures. The mathematical models demonstrated reliable predictive capability for extended-duration assessments, offering a powerful tool for optimising RCS activation to balance passenger comfort and energy efficiency. Results of this dual-domain analysis revealed the highest motion sickness at the bow and the lowest at the midship. A nonlinear pitch control algorithm reduced RMS vertical accelerations and MSDV at the bow by up to 41 % and 70 % in moderate waves, and 32 % and 54 % in large waves, respectively, which demonstrates significant improvement in passenger comfort. Alternatively, expressed in terms of the time domain analysis findings, deployment of the nonlinear pitch RCS enables passengers to travel 10 times longer before experiencing the equivalent level of motion sickness. Finally, specific operational needs of a ship are shown to affect which motions should be prioritised for reduction, affecting the choice of optimum algorithm.

This study aims to investigate the influence of a Ride Control System (RCS) on the load responses of a 2.5 m hydroelastic segmented catamaran model, which represents a 112 m high-speed catamaran. The efficacy of different control algorithms in mitigating slam rates and magnitudes was quantified by comparing results with those obtained for a bare hull with the No RCS control mode. Towing tank experiments were conducted in irregular head seas with a forward speed of 2.89 m/s (37 knots full-scale) at two significant wave heights. The results revealed that the nonlinear pitch control algorithm was the most efficient, achieving an impressive 96% reduction in slam occurrence, a 70% reduction in maximum slam magnitude, and a 66% reduction in maximum slam-induced sagging bending moments in moderate waves. Additionally, it was revealed that increases in wave height elevated the probability of slams, amplified variance in the distribution of slam loads and slam-induced bending moments and reduced the influence of the RCS in mitigating structural loads on the catamaran model. It was shown that irregular sea slam responses can be predicted from regular sea data, based on regular tests at a frequency corresponding to the modal period of the irregular sea case, with an accuracy of within 8 % for moderate waves and within 15 % at large waves.

To ensure high-quality passenger comfort and enhance the operability and performance of high-speed catamarans, reducing the severity of motions and structural loads using Ride Control Systems (RCS) is beneficial. To optimize ride control algorithms, it is essential to have a thorough understanding of the RCS in actual ship sailing conditions. In this paper, a set of towing tank tests was undertaken to study the effectiveness of different control algorithms, including linear and nonlinear versions of the heave control, pitch control, and local control, on motion responses of a 2.5 m scaled model of a 112 m INCAT Tasmania high-speed catamaran in irregular waves. The RCS included a centre bow-fitted T- Foil and two transom-mounted stern tabs. Obtained results were also compared with the scale model responses with passive RCS and with no RCS fitted. Heave and pitch motion responses as well as vertical accelerations of the catamaran were calculated in head seas at a model speed of 2.89 m/s (37 knot full scale), a modal period of 1.5 s (10 s full scale) and two significant wave heights of 60 mm and 90 mm, simulating full scale wave heights of 2.7 m and 4 m, respectively. It was demonstrated that deploying a passive RCS led to modest reductions in the peak motion responses. The most significant reductions in ship motions took place in the nonlinear modes of the heave and pitch control algorithms at a significant wave height of 60 mm (full-scale 2.7 m). In this condition, the nonlinear pitch control mode was demonstrated to be the most effective algorithm since this control mode mitigated the peak pitch RAO by 41% and vertical accelerations by 46%. This was a substantial reduction in ship motions with the RCS at an equivalent full-scale speed of 37 knot at 2.7 m wave height in the random sea condition.

Catamarans experience more types of global load than monohulls, these include pitch connecting moment, transverse bending moment, and split force. High-speed catamarans are widely used for passenger transportation but as the speed and size increase the severity of loads rises due to slam induced effects. In this study, full-scale CFD simulations are undertaken to investigate the loads acting on a 98m Incat wave-piercer catamaran (Hull 061) HSV2 Swift. Simulations are performed for conditions of a selected sea trial run in bow quartering seas at 20 knots forward speed undertaken by the Naval Surface Warfare Center, Carderock Division (NSWCCD), enabling comparisons and validation. In order to estimate internal global loads at different sections of the vessel, rigid body dynamics is applied based on the hydrodynamic and inertia forces. Those internal loads include longitudinal bending moment (LBM), pitch connecting moment (PCM), torsional moment (TorM), transverse bending moment (TBM), split force and prying moment. The estimated and measured global loads are also compared with design loads limits provided by DNV GL rules, and peak values of pitch and roll accelerations corresponding to each slam load are determined at the same wave height and wave period as the sea trial. The application of CFD to simulate sea trials runs in oblique seas is shown to provide a reliable estimation of slam induced loads for application in early design stages.

_ High-speed ferries of around 100mlength cruising at around 40 knots can cause significant passenger discomfort in head waves. This is due to the frequencies of encountering waves, of maximum hull response to encountered waves and of maximum passenger discomfort all falling within a similar range. In this paper, the benefit obtained by fitting active T-foils and stern tabs to control heave and pitch in head waves is considered. Ship motion responses are computed by numerical integration in the time domain including unsteady control actions using a time domain, high-speed strip theory. This obviates the need to identify transfer functions, the computed time responses including nonlinear hull immersion terms. The largest passenger vertical accelerations occur at forward locations and are best controlled by a forward located T-foil acting in combination with active stern tabs. Various feedback control algorithms have been considered and it is found that pitch damping control gives the greatest improvement in passenger comfort at forward positions. Operation in adaptive and nonlinear modes so that the control deflections are maximized under all conditions give the greatest benefit and can reduce passenger motion sickness incidence (MSI) by up to 25% in a 3-mhead sea on the basis of International Organization for Standardization (ISO) recommendations for calculation of MSI for a 90-minute seaway passage. Introduction When the first high-speed, lightweight catamaran car ferries were developed, it quickly became apparent that motion control systems were desirable to improve passenger comfort. This was a direct consequence of the high operating Froude numbers (based on waterline length) of up to 0.75, which gave rise to heave and pitch motions in excess of the wave height and wave slope. It was also a consequence of the period of encountered waves at high speed that becomes close to the period at which passengers would experience significant motion discomfort, approximately 5-6 seconds. As a consequence, active motion controls were introduced and have been fitted to most vessels operating on routes where significant wave heights might reach or exceed approximately 3m.

Global loads acting on high-speed wave-piercing catamarans are investigated using computational fluid dynamics (CFD). Catamaran vessels are subjected to load cases that are not present on mono-hull vessels, such as transverse bending moment, pitch connecting moment and splitting force. As the speed and size of a catamaran increases the severity of loads rises with slam induced effects. Full-scale CFD simulation is undertaken to investigate the pressure distributions and resultant global loads acting on the 98 m INCAT wave-piercer catamaran HSV2 Swift, validated against sea trial tests. Rigid body dynamics are then applied to estimate the internal loads at different sections of the vessel based on the relative hydrodynamic and inertial force distributions. The estimated global loads are then checked according to DNV GL rules by comparing "design load limits". Global loads are estimated for the 98 m INCAT HSV2 Swift catamaran in headseas at a forward speed of 20 knots. Splitting forces are found to have a longitudinal distribution along the catamaran hull, which causes prying moments. Peak values for LBM are examined relative to corresponding instantaneous wave height prior to the slam event. In addition, it is found that pitch acceleration has a linear correlation with LBM slam loads.

Wave slam produces dynamic loads on the centre bow of wave piercing catamarans that are related to the relative vertical motion of the bow to the encountered wave surface. Rapid slam forces arise when the arch sections between centre bow and main hulls fill with rising water. In this paper time domain solutions for high speed ship motion in waves, including the action of active motion controls, are used to compute the slam forces. Slamming occurs at specific immersions of the bow whilst the peak slam force is characterised by the maximum relative vertical velocity of the bow during bow entry. Vertical motions of bow and encountered wave are in antiphase at encounter frequencies where slamming is most severe. The range of encounter frequencies where slamming occurs increases with wave height. Wave slam loads reduce ship motions, the heave motion being most reduced. Deployment of a fixed, inactive T-foil can reduce slamming loads by up to 65 %. With active controls peak slamming loads on the bow can be reduced by up to 73% and 79% in 4 m and 3 m seas, local control feedback being marginally the most effective mode of control for reduction of slamming.

Active trim tabs are commonly used as part of the ride control systems of high-speed craft. This paper investigates the lift characteristics of rectangular stern tabs that are commonly fitted to INCAT wave-piercer catamarans. A test apparatus was developed to enable the testing of a model scale trim tab in a circulating water tunnel in the University of Tasmania hydraulics laboratory. The magnitude and location of the lift force produced by the tab were measured over a range of tab angles and flow velocities. From this the lift coefficient of the tab was calculated and the performance of the tab under varying conditions was analysed. The lift force produced by the tab was shown to increase with velocity and tab angle as expected, with the lift coefficient of the tab increasing linearly with tab angle and remaining relatively constant with increases in flow velocity. The magnitude of the measured lift coefficient was lower than had been previously estimated in shallow water tests and the force was found to act forward of the tab hinge, indicating that much of the lift force generated by the tab is due to the increased pressure on the underside of the hull forward of the tab.

This paper presents the impact of different geometrical parameters on the seakeeping of a trimaran in regular oblique waves. Experimental tests for eight different arrangements of outriggers were conducted for a range of wave frequencies where a constant wave heading, and wave height was maintained. It was found that the position of outriggers and the hull shape have significant impacts on dynamic performance of the model. Roll motions reduce with an increase in longitudinal spacing of main and demi hulls transoms, separation of outrigger centre lines and buoyancy fraction of outriggers, while heave motion and resistance are increased, and pitch motions are slightly influenced. It was concluded that positioning of outriggers can reduce the roll motions peak amplitude by 80%. This is due to the trimaran geometry and the effect of reflected waves between the hulls. In configurations with minimum roll motion, the added resistance peak is maximised when compared with other configurations.

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 closed- circuit water tunnel to measure model scale trim tab forces. The model scale system replicates the stern tabs on the full- scale 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.

Wave-piercing catamaran hull forms are widely used for high-speed ferry applications due to the hull slenderness, suitable for achieving high speeds. The global loads acting on these craft are of great interest as there is limited knowledge on determining the magnitude of the loads, in particular when operating in random sea conditions. Longitudinal and transverse bending moments as well as pitch connecting moments and hull torsion loads act on the hull simultaneously. This paper investigates the estimation of these global loads from full-scale catamaran sea trials strain gauge data using finite element methods. Det Norske Veritas (DNV) load cases are applied to a finite element model in order to determine the conversion between local strain values observed during sea trials and prevailing global loads. Comparisons are thus made of global loads determined from strain data collected from sea trials with DNV global load cases. The results show that this method is relatively reliable for the prediction of hull global loads in the absence of slamming. Comparisons have been made for different heading angles. The quasi-static design loads are important during the ship design stage, as they are good proxies in wavelengths comparable to the hull length for rationally determined loads obtained from a first-principles dynamic analysis. The broad aims here are to demonstrate the use of strain sensor data obtained during sea trials for determination of global sea loads, to reconcile the loads thus determined with DNV load cases and thereby to improve the accuracy of the predicted loads used in design to increase the structural efficiency of vessel design.

CFD has proved to be an effective method in solving unsteady Reynolds–Averaged Navier-Stokes (RANS) equations for analysing ships in free surface viscous flow. The research reported in this paper is intended to develop a better understanding of the parameters influencing high-speed trimaran motions responses. Variations of gridding system and time step have been investigated and reliability analysis was performed in solving the RANS equations. Different turbulence models were investigated, and the SST Menter K Omega turbulence model proved a more accurate model than Realizable K-epsilon model. In order to validate the CFD method, the results of the motions response of a high- speed trimaran are compared against a set of experimental and numerical results from a 1.6 m trimaran model tested in various head seas conditions. The results suggest that CFD offers a reliable method for predicting pitch and heave motions of trimarans in regular head waves when compared to traditional low speed strip theory methods. Unlike strip theory, the effect of breaking waves, hull shape above waterline and green seas are considered in CFD application. A wave resonance phenomenon was observed and wave deformation as a result of wave-current-wind interaction in CFD was identified as the main source of discrepancy. The results from this work form the basis for future analysis of trimaran motions in oblique seas for developing a better understanding of the parameters influencing the seakeeping response, as well as passenger comfort.

Twin hull high-speed catamarans encounter a wide range of sea wave loads. This paper studies the full-scale prediction of global loads on a high-speed catamaran using linear regression analysis based on finite element results. Load cases based on Det Norske Veritas rules are applied to a finite element model to derive load–strain transformation. Strain responses are evaluated at 16 different locations on the catamaran finite element model corresponding to the strain gauges positioned on the HSV-2 Swift 98m Incat catamaran during sea trials. A transformation matrix is generated using the concept of ordinary least squares, to convert from strain responses to the equivalent DNV global load cases. This is applied to determine global loads during several sea trial runs in different heading angles and speeds of 10, 20 and 35 knots. These loads then are compared to show each global load severity at specific speed or heading angle.

Slamming loads and pressures on high-speed catamarans with a centre bow (CB) differ from those on conventional catamarans with flat deck structures. The latter are well covered by class rules, which provide empirical formulae to calculate the design slamming pressure. An experimental study was therefore performed to quantify slamming pressures in the archways between bow and main hulls and the CB slamming force on a 112 m wave piercing catamaran. The CB length was systematically varied on a 2.5 m hydroelastic segmented catamaran model, which was tested in regular head sea waves at a speed of 2.89 m/s, full-scale equivalent of 38 knots. Slamming pressures were measured by 18 pressure transducers fitted into the CB, while data obtained from CB accelerometers and load cells enabled identification of the slamming force. The results indicate that slamming loads increase significantly with increasing CB length while the maximum peak slamming pressures varies to a lesser extent. It was also found that wave encounter frequency has a strong effect on the location of maximum pressure along the CB, considerably more so than any influence of CB configuration. The distribution of the peak pressures within the CB archway shows that the inboard peak pressures are larger than those at the top of the arch and the outboard locations.

ABSTRACT For wave piercing catamarans, the centre bow length and tunnel clearance are important design factors for slamming, passenger comfort and deck diving. This experimental study determined the influence of centre bow (CB) and wet-deck geometry on their motions and loads at reduced speed using five configurations. A 2.5 m hydroelastic segmented catamaran model was tested in regular head seas in wave heights equivalent to 2.7 m, 4.0 m and 5.4 m at full scale. Higher wet-decks had higher vertical accelerations but reduced slamming loads. The greatest peak vertical CB loads ranged between 18–105% of the total hull weight. Regression models were obtained for the vertical loads and bending moments. A reduction of speed from 38 knots to 20 knots reduces the maximum slam loads by approximately 30% in regular waves. Considering both low and high speeds, the Short CB was found to be a consistent design for slamming reduction.

The operation of high-speed craft in large waves can produce significant vessel motions that lead to passenger discomfort and extreme loadings sustained by the hull structure during full bow immersion and wave slam impact. These large motions and loads can be significantly reduced by a Ride Control System (RCS). The influence of ride control algorithms on the motion and load response of a 112 m high-speed wave-piercing catamaran was previously investigated by the authors using a 2.5 m hydroelastic segmented model fitted with a ride control system. The present study extends this to investigate the influence of the control algorithms on the slamming kinematics, water entry impulse and energy transfer. The model ride control system comprised two transom stern tabs and a central T-Foil beneath the bow. In order to activate the model scale ride control system and surfaces in a closed loop system six ideal motion control feedback algorithms were developed: local motion, heave and pitch control, each in a linear and nonlinear application. These results were compared with the results with inactive but present control surfaces and with no control surfaces fitted. From these analyses it was found that the pitch control mode was most effective where in 60 mm model scale waves it significantly reduced the water entry impulse by 40% and the total strain energy by 90% when compared to a bare hull with no control surfaces fitted.

BACKGROUND:Coagulation monitoring capabilities during transport are limited. Thromboelastography (TEG) is a whole-blood clotting test measuring clot formation, stabilization, and fibrinolysis and is traditionally performed in a laboratory. We evaluated a new point-of-care TEG analyzer, TEG 6s (Haemonetics, Braintree, MA), in a large animal model of combat-relevant trauma managed with extracorporeal life support during ground and high-altitude aeromedical evacuation. The objective was to compare TEG 6s used during transport versus the predicate device, TEG 5000, used in the laboratory. We hypothesized that TEG 6s would be comparable with TEG 5000 during dynamically changing transport conditions.METHODS:Thromboelastography parameters (R, K, angle, MA, LY30) derived by TEG 6s and TEG 5000 were compared during transport of 8 swine. TEG 6s was transported with animals during ground transport and flight. TEG 5000 was stationary in an adjacent building. TEG 6s activated clotting time (ACT) was compared with a Hemochron Junior ACT analyzer (Accriva Diagnostics, San Diego, CA). Statistics were performed using SAS 9.4 with Deming regressions, Spearman correlations, and average differences compared.RESULTS:Correlation between devices was stronger at sea-level (R, r = 0.7413; K, r = 0.7115; angle, r = 0.7192; MA, r = 0.8386; LY30, r = 0.9099) than during high-altitude transport (R, r = 0.4787; K, r = 0.4007; angle, r = 0.3706; MA, r = 0.6573; LY30, r = 0.8481). Method agreement was comparable during stationary operation (R, r = 0.7978; K, r = 0.7974; angle, r = 0.7574; MA, r = 0.7841; LY30, r = 0.9140) versus ground transport (R, r = 0.7927; K, r = 0.6246; angle, r = 0.6967; MA, r = 0.9163; LY30, r = 0.8603). TEG 6s ACT trended higher than Hemochron ACT when subjects were heparinized (average difference, 1,442 ± 1,703 seconds) without a methodological difference by Deming regression.CONCLUSION:Mobile TEG 6s during ground and altitude transport is feasible and provides unprecedented information to guide coagulation management. Future studies should assess the precision and accuracy of TEG 6s during transport of critically ill.