CHAPTER ONE
INTRODUCTION
1.0 GENERAL OVERVIEW
Though the maritime industry is setting a broad exposure in ship designing through advanced technologies and varying simulation software, the research seems to be never ending in producing finer and optimized design of the vessels. When most of the vessels in the maritime industry are dominated by the conventional mono hull design with distinguishing shapes for desired commercial purposes there is always space available for multihull vessels when stability and hydrodynamic performance are considered as the main criteria for rapid express dent of the high-speed ship market in the past decade, multi-hulls are considered as the best option to be used in naval and recreational purposes where performance of the vessel could have a profound effect. Hydrodynamic performance is an important aspect to be taken into consideration as it has direct impact on the operational costs. So, at an early stage a designer need to be aware of finding the best possible method which determines or sets a compromise between vessel shape and operational costs to get the desired performance. Though the theoretical approach of hull resistance is complex in nature, it seems economically feasible when compared to model test evaluation.
This justifies the effort involved in studying many different theoretical methods in order to evaluate hull resistance properly. (Moraes, Vasconcellos and Latorre, 2004). In general, catamaran hull forms had already proved to be good enough in providing double the deck space even after meeting all the requirements such as stability and performance. Although there is an increase in frictional resistance due to increased wetted surface (demi hulls) area, the effect can be negotiated once the design hull reaches sufficient speed. Though interference between the waves hardly affects the resistance of the hull it can be reduced by the optimized design of hull shape, (Schneekluth and Bertram, 2002), (Larsson and Baba, 1996), (White, 1991). However, finding the resistance and the interactive forces between demi hulls still remained a significant design challenges. The size and shape of the demi hull have an impact on resistance as well as on interference of the vessel. One of the most important considerations for a naval architect is the powering requirement for a ship. Once the hull form has been decided upon, it is necessary to determine the amount of engine power that will enable the ship to meet its operational requirements. Knowing the power required to propel a ship enables the naval architect to select a propulsion plant, determine the amount of fuel storage required, and refine the ships center of gravity estimate. Throughout history, naval architects have endeavored to increase the speed of ships. Increased speed would enable a warship to close with its opponent, or conversely, to escape from an attack. Increased speed enables merchant vessels to reach port sooner and maximize profit for its owner. Until the early 1800’s, wind was the force used to propel ships through the water and ships could only go as fast as the wind would propel them. Additionally, because ships were constructed of wood, the structural limitations of wooden hull configurations drove hull designs to primarily meet the structural needs while hydrodynamics was only a secondary concern. With the advent of steam propulsion in the early 1800’s, naval architects realized that ship speeds were no longer constrained by the wind and research began into the power required to propel a hull through the water using this new propulsion medium. Testing of full-scale ships and models determined that the power required to propel a ship through the water was directly related to the amount of resistance a hull experiences when moving through the water. The development of iron hull construction produced radical changes in hull strength and hull design. Gone were the blunt bows and full hull forms of early sailing vessels. Capitalizing on the added strength of iron hulls, naval architects could design ships with finer bows and as a result, ship speeds increased. About the time of the Civil War, the modern screw propeller was developed, replacing the paddle wheel as the prime mode of ship propulsion. The screw propeller, with many modifications to its original design, remains the principle method of ship propulsion to this day.
1.1 BACKGROUND OF RESEARCH
The concept of multi-hull is known to the mankind since ages of sailing. But it took quite a long time to have a scientific look over the pros and cons of catamaran hull design. Speed is the main parameter which resulted in the evolution of multi-hull from the conventional monohulls as the mechanical propulsion came into big picture. In case of monohulls the high speed is achieved by a finer hull which exhibits minimum drag characteristics. A slender hull with high L/B ratio would serve the purpose. This initiated the need of second hull as a supporting structure which led the innovation of catamaran hulls without a compromise between speed and stability of the vessel. As the twin hulls are finer and exhibits stability efficiency as well as desired speed more than the conventional mono hull design, the researchers have always been interested in the optimized design of the hull to get the desired hydrodynamic performance. When good performance is the output needed from a hull design one should have a great insight in the reduction of resistance characteristics of the hull. Since the catamaran has twin hulls which represents more wetted surface area would also experience more drag characteristics. Also the resistance experienced at slow speeds is much greater when compared to any other conventional mono hulls.
1.2 AIM
The aim of this project is to make a comparative analysis of the hull resistance and effective power of a given monohull vessel converted into catamaran.
1.3 OBJECTIVES
The objectives of this research work were as follows;
To source and obtain the principal parameters of a given monohull (i.e conventional vessel)
From the parameters obtained, use Delftship software to model the conventional vessel hull and run resistance analysis of the modelled hull.
To use the results obtained from software analysis, determine the Resistance and Power of the Monohull vessel.
To Use the results of the parameters of the monohull vessel and determine the corresponding parameters of a catamaran. Then calculate the Resistance and Power of the catamaran.
Make comparison of the resistances and powers of both monohull vessel and catamaran vessel.
1.4 DEFINITION OF THE PROBLEM
Most conventional fishing vessel are monohull. Monohull vessel offer some advantages such as reduced resistance hence less power requirement. However, such vessels also have their setbacks such as reduced Tonnage. Hence for core fishing areas, catamaran vessel could be considering advantages due to the added tonnage due to the advantage of double hulls. Catamaran has her own challenge of increased resistance and hence added power requirement. This research work seeks to investigate and compare the resistance and power requirements of both monohull and Catamarans such as to help inform the decision of ship owners.
1.5 RESEARCH GOALS
Upon completion, the following goals are achievable;
It will serve as total for informed decision making as regards choice of vessel to be built or procured based by prospective shipowners.
It will serve as a reference material and a reliable guide for further research to students who may be interested in this area or related areas of research.
1.6 SCOPE OF THE RESEARCH
This project focused on hull resistance and effective power of a specific monohull fishing vessel and a corresponding catamaran vessel. The total resistances and powers of both types of vessel hulls were investigated and compared. From the results of the comparison, the conclusions were drawn.
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