refit2save

In the present shipping, sustainability requires optimum fuel economy of ships. Not only is the cost of fuel a large share of the operational costs, it also has a direct impact on the bottom line figures. Slow steaming has been widely accepted as a direct way to reduce fuel consumption. At the same time regulations are underway to reduce emissions of ships in operation. One of the measures to improve existing ships is to fit highly efficient propellers and rudders or to equip them with energy saving devices (ESDs) such as nozzles and fins aiming to improve the flow around the aftbody. Such replacements or additions, referred to as “Refit”, are normally combined with a docking. Suppliers of such appendages claim fuel efficiency gains of 2 up to 8%. However, such figures are normally weakly supported. As these appendages all work in the boundary layer of the vessel, computational analysis require advanced viscous flow CFD which are often not validated for this type of application. Model tests are also hampered by the viscous effects which lead to unquantified scale effects. Finally, proper full-scale trials are rare since they require an extra docking to distinguish the effects of hull cleaning and refit. Yet, for ship owners and operators a reliable quantification of the potential fuel reduction is essential for a proper business case. At the same time insight into the physical working of the device is also required to optimise the working and effect.