ballastfreebulkerw 
Shipping

Ballast-free ship design saves on fuel

Baird Maritime

Proof of concept for a bulk carrier that does not require traditional ballast tanks is advancing past concerns about its damage stability and may offer fuel savings as well as a way of preventing the spread of invasive species found in ballast water.

Professor Michael Parsons of the University of Michigan, USA, is model testing his Variable Buoyancy Ship concept.

Instead of adding weight for ballast, the seaway-sized bulk carrier design has trunks running the length of the hull that are open to the sea when no cargo is carried.

As ballast water is not stored, there is no need to perform ballast water exchange or install onboard ballast water treatment equipment.

Three longitudinal trunks per side, in a deepened hull, provide safe operating draughts. The pressure difference between bow and stern induces a flow of seawater that is exchanged about once an hour. Computational fluid dynamics (CFD) has been used to demonstrate the pressure differential is great enough and that flow will occur when the vessel is underway.  

Following concerns that the design would lead to damage stability problems if the trunks were damaged while empty, Professor Parsons altered the design to include some isolation valves to the two outward-most trunks on each side.

The design now meets SOLAS and Society of Naval Architects and Marine Engineers (SNAME) guidelines for safety and, despite the extra steel required by the design, is expected to result in a 1.7 percent fuel saving in the light load condition compared with a standard design.

Work underway this year will confirm propulsion requirements and refine the ability of the Variable Buoyancy Ship to handle all the required draft and trim variations of a working vessel.

Wendy Laursen