| The evolving requirements for ballast water treatment to reduce the probability of the introduction of additional nonindigenous aquatic species into U.S. coastal waters and the Great Lakes will result in increased capital and operating costs for trans-oceanic vessels. As an alternative to ballast treatment systems, a new ship concept that will essentially eliminate the trans-oceanic transport of ballast water is investigated in this dissertation. The Ballast-Free Ship concept involves a new paradigm that approaches ballast operation as the reduction of buoyancy rather than the addition of weight to get the vessel to its required ballast drafts. The traditional ship ballast tanks are replaced by longitudinal structural ballast trunks that surround the cargo hold below the ballast draft. These trunks, which are connected to an intake plenum near the bow and a discharge plenum near the stern, are flooded in the ballast condition to decrease the ship's buoyancy. The pressure differential between the bow and the stern is utilized to drive a slow flow through the ballast trunks to ensure that the trunks always contain "local seawater." At the end of the ballast voyage, the trunks are isolated and pumped dry using conventional ballast pumps. This dissertation describes the development and investigation related to this new ship concept. The available pressure differential as well as the development of the ballast water flow in the trunks is established through a number of simulations utilizing Computational Fluid Dynamics (CFD). The impact on ship resistance and propulsion is investigated through towing tank experiments as well as CFD simulations. The required structural re-arrangements to incorporate the Ballast-Free Ship concept are thoroughly examined. The effect of the structural re-design on damage survivability, intact stability and seakeeping performance of the vessel is evaluated. The economic impact of the proposed concept is compared with alternative ballast water treatment methods. The results show that the Ballast-Free Ship concept could provide a viable, more cost effective alternative to ballast treatment systems. Furthermore, it could provide superior protection from the introduction of nonindigenous aquatic species through ballast water. |
