Multi-hull vessels have been considered for high-speed, military and commercial applications for decades. More recently the trimaran vessel, with three hulls, has captured interest among naval ship designers and stakeholders. A definition of multi-hulls is introduced as a continuum with monohulls on one end, catamarans on the other, and trimarans in-between. A review of methods to assess intact and damaged stability follows in addition to an overview of current research in the area of dynamic stability for monohulls and trimarans. An investigation of intact stability characteristics for multi-hulls along the continuum is presented and their trends are examined. Next, a series of trimaran configurations are modeled in CAD with subdivision to determine their allowable KG according to USN deterministic criteria and using quasi-static methods. A response surface model was determined for allowable KG as a function of center hull length to beam, side hull beam to draft, transverse position, and displacement for use as a rule of thumb measure and potential optimization constraint. / Master of Science / Ships which have more than one hull are called multi-hulls. In contrast to a monohull, which comprises of a single hull form, catamarans, trimarans, quadramarans, and pentamarans consist of two, three, four, and five hulls respectively and make up the multi-hull group of ships. Multi-hulls have been considered for high-speed, military and commercial applications for decades. More recently trimaran ships, with three hull forms, have captured interest among naval ship designers and stakeholders. This thesis provides a definition of multi-hulls as a continuum with monohulls on one end, catamarans on the other, and trimarans in-between. An assessment of ship stability quantifies a ship’s risk of capsize in a particular loading condition and environment. The intact ship condition is assessed as well as damaged ship conditions where the certain compartments are subject to flooding from the sea. Initially, a quasi-static method is first undertaken where the ship characteristics are computed at discrete motion points of interest and integrated. This thesis includes a review of quasi-static methods employed by United States and British navies to assess intact and damaged stability. Additionally, an overview of current research in the area of dynamic stability for monohull and trimaran. Assessing stability using dynamic methods involves a more detailed assessment of extreme events a ship may encounter in its lifecycle. These assessments were beyond the scope of this thesis. The first investigation of this thesis assessed the intact stability characteristics for multi-hulls along the continuum, including a monohull, five trimarans, and a catamaran. Trends were examined and the effect of displacement distribution between hulls on stability characteristics was analyzed. The results of the first investigation set the bounds for a more detailed investigation of trimaran geometric parameters affecting intact and damaged stability. The second investigation established a design of experiments to formulate a series of trimaran configurations consisting of a center hull, two side hulls and cross deck structure joining the hulls from above. This series of trimaran hull forms varied particular parameters that were determined to be influential to intact and damaged stability. Each hull form configuration was modeled using three-dimensional CAD software with subdivision defining compartments to be flooded. The maximum center of gravity was determined which would satisfy all stability criteria published by the United States Navy for each intact and damaged condition. After tabulating the data, a response surface model was determined for maximum vertical center of gravity as a function of center hull ratios, side hull ratios, and the transverse distance between the center and side hulls. The response surface model is intended for use as a rule of thumb measure and potential constraint for optimization.

The purpose of this thesis is to advance research in the development of trimaran hullforms and analyze the feasibility of the hullform for a possible naval surface combatant using current hullform design tools. The “Generalized” Trimaran Methodology is a new process that focuses on the manipulation of the three hulled system’s total sectional area curve. The methodology is intended for rapid hull form development during the conceptual design phase, and can analyze an infinite number of trimaran hullforms. The thesis first proposes a new methodology for the design of trimaran hullforms, describes how the process was applied to an existing hullform, presents results of the analysis, and provides validation data from a tow tank resistance experiment.

O presente trabalho aborda o desenvolvimento de um modelo de síntese para o projeto conceitual de uma embarcação rápida do tipo trimarã, destinada ao transporte de passageiros. Tal modelo visa possibilitar o entendimento dos mecanismos que governam o projeto deste tipo de navio, através de analises comparativas (atributos de desempenho) entre diferentes soluções de projeto, em função dos parâmetros escolhidos para sua representação (variáveis de projeto). Foram desenvolvidos dois modelos de síntese, em programas comerciais distintos. Cada modelo gera a superfície do casco, a partir de series sistemáticas, e calcula a resistência ao avanço dividindo-a nas parcelas viscosa e de ondas. A parcela viscosa e calculada pela aproximação de placa plana e a parcela de ondas calculada pela teoria de navio no. São feitas, ainda, estimativas preliminares do fator de forma e da resistência adicional em ondas. O arranjo geral dos principais espaços e subsistemas foi parametrizado com base no arranjo de embarcações semelhantes e o conforto dos passageiros a bordo e calculado segundo padrões estabelecidos por sociedades classificadoras internacionais. As variáveis de projeto escolhidas foram o comprimento do casco central e razões entre as demais dimensões, de modo a permitir o calculo das dimensões principais de cada casco e o posicionamento relativo entre eles. Com isso, tem-se que, ao mudar o valor do comprimento, escala-se o casco mantendo-se todas as proporções. A vantagem buscada ao se utilizar esta abordagem e a extinção das restrições geométricas implícitas, pois estarão embutidas diretamente nas restrições explícitas que definem os limites de exploração de cada variável de projeto. Estes modelos foram integrados a procedimentos de otimização mono e multiobjetivo, com base em diferentes versões do algoritmo genético, e aplicados a um problema de projeto exemplo. As funções de mérito, ou funções objetivo, escolhidas para este problema foram a potencia requerida pela embarcação para navegar na velocidade de projeto e a disponibilidade operacional da embarcação, calculada a partir dos índices de conforto dos passageiros. Com isso, descobriu-se que os parâmetros com maior influencia na resistência ao avanço e no conforto dos passageiros são o comprimento do casco central e sua razão de comprimento por boca. O posicionamento relativo entre os cascos e extremamente importante para a resistência de ondas geradas pela embarcação, mas não e possível observar nenhuma grande tendência em relação a posições que privilegiam seja a resistência seja o comportamento, pois o posicionamento ótimo para cada objetivo depende tanto do número de Froude quanto das demais dimensões da embarcação. / The present work studies the development of a synthesis model for the conceptual design of a fast trimaran passenger vessel, in order to understand the mechanisms that govern the design of such a vessel through a comparative analysis (performance parameters) between different design solutions, as a function of the variables chosen to uniquely represent them (design variables). Two separate models were developed, using different commercial softwares. Each model generates the hull surface based on systematic hull series and calculates the ship\'s forward resistance as the sum of the viscous and wave components. The viscous component is estimated by at plate approximation, corrected by a form factor, and the wave component is calculated according to thin ship theory. A preliminary estimate of the ship\'s added resistance in waves is also made. The general layout of the main volumes and systems was parametrized following design trends of similar ships and passenger comfort on board was calculated using international classification societies standards. The design variables chosen were the length of the center hull, the ratios between the main dimensions of each hull as to allow for their calculation and two coeficients regarding the relative positioning of the center and side hulls. The advantage sought by adopting this approach is the elimination of implicit geometrical constraints, once they will be automatically included in the explicit constraints defining the exploration range of each design variable. These models were then coupled to mono and multi objective optimization procedures, based on different versions of the genetic algorithm, and applied to a case study.The objective functions taken for this problem were the required power to achieve the design speed and the operational availability, measured from passengers comfort thresholds. It was found that the parameters with the most influence on the forward resistance, and thus on required power, and on passengers comfort level are the center hull length and its length to breadth ratio. The relative positioning of the side hulls play an important role on the total wave resistance of the ship, although it was not possible to observe any clear trend concerning positions that would favor nor the ship forward resistance neither its seakeeping performance. This is due the fact that the optimum positions of the side hulls are also a function of the Froude number and the remaining design variables.

O presente trabalho aborda o desenvolvimento de um modelo de síntese para o projeto conceitual de uma embarcação rápida do tipo trimarã, destinada ao transporte de passageiros. Tal modelo visa possibilitar o entendimento dos mecanismos que governam o projeto deste tipo de navio, através de analises comparativas (atributos de desempenho) entre diferentes soluções de projeto, em função dos parâmetros escolhidos para sua representação (variáveis de projeto). Foram desenvolvidos dois modelos de síntese, em programas comerciais distintos. Cada modelo gera a superfície do casco, a partir de series sistemáticas, e calcula a resistência ao avanço dividindo-a nas parcelas viscosa e de ondas. A parcela viscosa e calculada pela aproximação de placa plana e a parcela de ondas calculada pela teoria de navio no. São feitas, ainda, estimativas preliminares do fator de forma e da resistência adicional em ondas. O arranjo geral dos principais espaços e subsistemas foi parametrizado com base no arranjo de embarcações semelhantes e o conforto dos passageiros a bordo e calculado segundo padrões estabelecidos por sociedades classificadoras internacionais. As variáveis de projeto escolhidas foram o comprimento do casco central e razões entre as demais dimensões, de modo a permitir o calculo das dimensões principais de cada casco e o posicionamento relativo entre eles. Com isso, tem-se que, ao mudar o valor do comprimento, escala-se o casco mantendo-se todas as proporções. A vantagem buscada ao se utilizar esta abordagem e a extinção das restrições geométricas implícitas, pois estarão embutidas diretamente nas restrições explícitas que definem os limites de exploração de cada variável de projeto. Estes modelos foram integrados a procedimentos de otimização mono e multiobjetivo, com base em diferentes versões do algoritmo genético, e aplicados a um problema de projeto exemplo. As funções de mérito, ou funções objetivo, escolhidas para este problema foram a potencia requerida pela embarcação para navegar na velocidade de projeto e a disponibilidade operacional da embarcação, calculada a partir dos índices de conforto dos passageiros. Com isso, descobriu-se que os parâmetros com maior influencia na resistência ao avanço e no conforto dos passageiros são o comprimento do casco central e sua razão de comprimento por boca. O posicionamento relativo entre os cascos e extremamente importante para a resistência de ondas geradas pela embarcação, mas não e possível observar nenhuma grande tendência em relação a posições que privilegiam seja a resistência seja o comportamento, pois o posicionamento ótimo para cada objetivo depende tanto do número de Froude quanto das demais dimensões da embarcação. / The present work studies the development of a synthesis model for the conceptual design of a fast trimaran passenger vessel, in order to understand the mechanisms that govern the design of such a vessel through a comparative analysis (performance parameters) between different design solutions, as a function of the variables chosen to uniquely represent them (design variables). Two separate models were developed, using different commercial softwares. Each model generates the hull surface based on systematic hull series and calculates the ship\'s forward resistance as the sum of the viscous and wave components. The viscous component is estimated by at plate approximation, corrected by a form factor, and the wave component is calculated according to thin ship theory. A preliminary estimate of the ship\'s added resistance in waves is also made. The general layout of the main volumes and systems was parametrized following design trends of similar ships and passenger comfort on board was calculated using international classification societies standards. The design variables chosen were the length of the center hull, the ratios between the main dimensions of each hull as to allow for their calculation and two coeficients regarding the relative positioning of the center and side hulls. The advantage sought by adopting this approach is the elimination of implicit geometrical constraints, once they will be automatically included in the explicit constraints defining the exploration range of each design variable. These models were then coupled to mono and multi objective optimization procedures, based on different versions of the genetic algorithm, and applied to a case study.The objective functions taken for this problem were the required power to achieve the design speed and the operational availability, measured from passengers comfort thresholds. It was found that the parameters with the most influence on the forward resistance, and thus on required power, and on passengers comfort level are the center hull length and its length to breadth ratio. The relative positioning of the side hulls play an important role on the total wave resistance of the ship, although it was not possible to observe any clear trend concerning positions that would favor nor the ship forward resistance neither its seakeeping performance. This is due the fact that the optimum positions of the side hulls are also a function of the Froude number and the remaining design variables.