On A Natural Ballast Water Exchange Method

Abstract

Ballast water and sediment discharge are currently pointed out the principal cause for the international introduction of non-indigenous aquatic species that exert an influence on environmental pollution to human and marine life beyond its historic range. A new method to exchange ballast water is proposed, in which clean water is guided from ship’s bow front and discharged out of bellmouth on the bottom of tank utilizing pressure difference around the hull surface of ship in forward motion. The idea does not require any pumping operation except for topping up water to initial water level. The test using model ship of 1/120 scale confirmed the exchange of water in a tank. The water exchanging rate is investigated using model ballast tanks of 1/50 scale for single and double hulled ships. The power loss and power consumption of pumping and total system are estimated on Aframax type of tanker and compared with those of the flow-through method. The power consumption of pumping of new system is about one tenth and the power consumption of total system is one fifth to those of the flow-through method.