![]() Thus, in situations such as closed tanks where hydrogen can collect, an explosion hazard can arise. In impressed current systems, and sometimes with magnesium anodes, excessive polarization can cause evolution of hydrogen on the protected structure. ![]() Very little transverse and longitudinal interplay occurs.Īlireza Bahadori Ph.D., in Cathodic Corrosion Protection Systems, 2014 1.4.3 Hydrogen Evolution Parametric rolling problems are least on box-shaped vessels or full-form barges where the aft and forward contours are not too dissimilar. The IMO suggests that parametric rolling is particularly dangerous when the wavelength is 1.0–1.5 times the ship’s length. Such condition can cause containers to be lost overboard due to broken deck lashings. ![]() Parametric rolling is worse when a ship is operating at reduced speed in heavy sea conditions. A more dangerous situation develops because of the interplay between the pitching and rolling motions. If T P = T R or T P = ½ × T R, then interaction exists and the rolling of the ship is increased. This causes a twisting or torsioning along the ship, leading to extra rolling motions. In effect, the rolling characteristics are different at the stern to those at the bow. It is worst when T P = T R or when T P = ½ × T R. This remains unchecked as the bow next dips into the waves due to pitching forces. It is most marked when the pitching period T P is either equal to or half that of the vessel’s rolling period T R.Īs the stern dips into the waves it produces a rolling action. The cause depends very much on the parameters of the vessel, hence the name ‘parametric rolling’. Pitch Induced or Parametric Rolling on a Container Vessel. It is likely that no one solution will fit all ships.įigure 46.2. More research is needed and a variety of systems are being developed. Ultrasonic, specific frequencies killing different organisms. UV radiation which is used ashore to prevent the spread of disease and is being considered for water treatment plants as a replacement for chlorine. Magnetic forces which can kill certain invertebrates. The chemicals must not themselves pollute the water. Ĭhemicals such as chlorination or ozone.Filters should be back washed after ballast water is taken on board so that any organisms are restricted to their original environment. Pre-filtration, using a series of filters of reducing mesh size, is likely to be needed before other treatments are applied. Ī combination of filtration and other treatments.No one ballast water management technique can remove all organisms from ballast tanks and a combination of different methods is needed. The effects in some areas have been devastating and the rate of bio-invasions is increasing at an alarming rate with new areas being invaded. ![]() The transferred species may initiate a reproductive population in the new environment, possibly growing into pest proportions. Tankers and bulk carriers tend to have capacities greater than 5000 m 3.īallast water is needed for safe ship operations, but it may pose serious ecological, economic and health problems due to the multitude of marine species in the ballast water. The typical ballast water capacity of passenger and general cargo ships is in the range 1500–5000 m 3. It will require ballast water treatment to be used in place of ballast water exchange. The BWM, expected to come into force in 2012/13, will require all ships to implement a Ballast Water and Sediments Management Plan and carry a Ballast Water Record Book. The IMO has developed the International Convention for the Control and Management of Ships’ Ballast Water and Sediments (BWM) to regulate discharges of ballast water and reduce the risk of introducing non-native species. Tupper BSc, CEng, RCNC, FRINA, WhSch, in Introduction to Naval Architecture (Fifth Edition), 2013 Ballast Water
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