Underwater hull cleaning by using cavitation method and its effect

The result of scarce resources on the petroleum has been led the fuel prices to rise. Hence, these consequences has been the main problem of the companies which have been dealing with sea way transportation. Researchers have beeen working to find systems that save fuel energy for many years. It is very difficult to reduce fuel consumption by keeping the same efficiency of a ship. The only way is to reduce the ship resistance. Resistance is of great importance to ships since it affects ship performance and fuel consumption. The more resistance a ship has, the more fuel it consumes for the same range. This decreases the efficiency thus increases emissions. Therefore reducing the ship resistance is an aim to reach for both naval architects and ship owners. Especially in the last decades it becomes more important to reduce the fuel consumptions because of the restrictions and regulations entered into force by the international organisations about environmental issues. Negative effect of roughness on ship performance has been known since the first seafaring activities. Increasing roughness on the hull surface, affects wake characteristics, so the propeller operating on this wake needs more thrust power to overcome increasing resistance. Ship resistance can be broken into two parts; frictional resistance and residuary resistance. Especially for merchant ships which sail with normal or low velocity, frictional resistance can be 60-90% of the total resistance. Therefore reducing the ship frictional resistance is very important considering the volume of world trade by sea. The best way of reducing the frictional resistance is the treatment of hull surface in terms of improving surface condition due to physical and biological roughness. Physical roughness can be avoided or minimised by taking measures during the shipbuilding procedure easily. On the other hand, it is not easy to avoid fouling (biological roughness) since it occurs immediately as soon as a ship immerses, continues on her seaway and it depends on various parameters such as time spent in sea, surface condition, the salinity of the sea, etc... With ascending immersion time, the amount of fouling raises; ultimately, the frictional resistance increases dramatically. The most effective method against the fouling can be considered as the application of "anti-fouling" paints. The coating-system mentioned above acts as a barrier against corrosion on hull briefly and has a fundamental function which is to prevent or decrease the rate of attachment of marine organisms on the hull of the ship and growth there by releasing biocides can be found in various types.In order to obtain benefits from "anti-fouling" system, a ship must be active. Otherwise, the performance of this system can not be observed. Briefly, marine organisms start to attach and grow on the hull if a ship is inactive (etc. out of service, on dock) for long time. As a result, it can be seen that the increase on the rate of fouling on inactive ships is much more than the active ships. Every ship is docked for a specific period which is determined in design process. During this period, the maintenance is provided and the hull is cleaned briefly. The docking of a ship is a laborious and expensive procedure. Up to docking period, the drag force on ship due to fouling increase and this formation cause decrease on the maximum speed of a ship and increase on fuel consumption and emission rate. For this reason, scientists have been working on the methods for the cleaning of a hull without docking of a ship. In Chapter 2, the information about the total drag and the frictional-drag force which is related to topic is discussed. In addition, some studies on frictional-drag force are given. In Chapter 3, the information about roughness on hull and propeller and the formation for roughness are given. Following, the process for biofilm and biofouling, the effects and the rates of fouling are presented. In Chapter 4, the information about the hull cleaning methods that are cavitation-cleaning and conventional-cleaning is given and the difference of these two methods are indicated. In addition, the working principle of the system used for cavitation-cleaning is expressed and the effects of hull-cleaning applications to drag force are demonstrated graphically. In application part, the information about the pre/post-cleaning situations in technical literature is given. Moreover, test results obtained from high-speed craft are presented. Regarding the test results, the evaluation on cost analysis and financial gain for the economy are discussed. In final part, overall results in the scope of the dissertation are discussed. Following that, the evaluation on this work is performed and some points are addressed for the future work.