Both for new buildings and also for retro-fits, Energy Saving Devices (ESDs) are widely accepted as one of the important measures to tackle these problems. An energy saving device for a ship is often installed to the stern of the vessel close to the propeller and working together with the propeller forming a total propulsion system. An ESD can be a pre-duct, a pre-swirl stator and fins in the upstream of the propeller, or a post stator, a rudder bulb, rudder fins, a PBCF® or a twisted rudder in the downstream. Many new ideas and patents have been proposed in the last decades, and some of the ideas were tested in the towing tanks around the world. Several of the ideas were installed to real ships and tried in full scale. However very limited trial data are available to the public. According to publications, the best achievement on improving efficiency by adding an ESD to an existing vessel with existing propeller was more than 10%, according to the model tests. The feedback of full-scale sea trials show typically more than 5% improvement on total propulsive efficiency. These achievements are very promising, which attract a lot of attentions of the ship owners, the ship builders and the regulators.
Until now, there is very limited information on why and how an ESD can improve the total propulsive efficiency of a vessel. There are very limited studies carried out trying to understand the working principles of an ESD. Therefore, many ESDs were designed by try-and-error method and the designers had to hope that their designs would be proven by model tests. On the other hand, as widely known already, an ESD suffers a lot on scale effects so that the achievement on full scale is almost always different than that in model scale. This makes the implementation of an ESD to full scale sometimes questionable for ship owners and builders.
Objective and deliverables
The objective of this JIP is to understand the working principles of the ESDs in general by investigating the flows around the hull and the ESDs by using advanced PIV system to the aftbody of a ship, fitted with or without the ESDs, by measuring the forces and moments on all the components of the propulsor including the ESDs, by investigating the flow details with Particle Image Velocimetry (PIV), and by studying the scale effects using smart dummy model tests (see below) and CFD calculations. Based on the results of the tests and calculations, a novel extrapolation method will be developed to predict the performance of the vessel fitted with ESDs.
- Understand the working principles of ESDs
- Technical report with guidelines on ESD designs
- Extrapolation method for ESDs