Page 25: of Maritime Reporter Magazine (May 2005)
Marine Enviroment Edition
While much effort and attention is being paid to solutions to the problems inherent in a ship's ballast water - specifically the transportation and relo- cation of non-indigenous species and the resultant environmental harm - researchers at the University of
Michigan are studying a novel concept: the Ballast-Free Ship Concept.
Rather than eliminating non-indige- nous species carried in ballast water, a
University of Michigan project takes a different approach - eliminating the bal- last tanks that harbor foreign species.
Project investigators examined the cost and technical feasibility of building a ship that eliminates ballast tanks, replac- ing them with a series of slow flow bal- last tubes, or trunks.
The ballast-free ship concept uses a varying flow of water through the tubes to change a ship's buoyancy and main- tain optimum stability. When no cargo is on board, the structural tubes are opened to the sea, and the flooding lowers a ship to its required ballast drafts.
The pressure difference between the entrance to the tubes near the bow of the ship and the exit openings near the stern produces a slow flow of water.
This flow ensures that the ballast trunks are always filled with "local" sea water-eliminating the transfer of foreign ballast water and non-indigenous species.
Results of Computational Fluid
Dynamics studies and model tests have shown the following: • Trunk operation will result in a modest increase in required ship power; The need to lower the ballast tubes below the ballast draft for flooding to occur raises the cargo hold and requires that the hull become deeper to accom- modate the same cargo volume; A new hull configuration can be accomplished by adding a few hundred tons of hull weight and extra costs of this new configuration would be offset by the elimination of a ballast water treatment system and the ballast piping within a ship's cargo region.
Evaluating Ballast Exchange
All ships entering the Great Lakes are currently required to exchange ballast water at sea using one of two methods: One method involves emptying and refilling each ballast tank in succession; Ships that cannot use the method above, due to structural design or heavy seas, are allowed to use the flow- through method in which new ballast is pumped into a tank, forcing existing bal- last to overflow through tank vents.
According to researchers at the
University of Michigan, the removal of old ballast water can be improved by proper placement of the tank filling con- nections, design of manholes in the internal structure and placement of vents.
Using Computational Fluid Dynamics researchers have been investigating the effectiveness of the flow-through ballast exchange method. Project investigators studied typical tank configurations and variations found on containerships and bulk carriers. Results show that certain areas of the ballast tanks studied experi- ence a low flow of new ballast water during the exchange process.
May 2005 25 ) L Q D Q F L D O 0 D Q D J H P H Q W ( Y H Q W K H E H V W F D Q E H E H W W H U 7 K H 8 O W L P D W H &