Feature 2 | CAD/CAM
The efficacy of air-bubble lubrication for decreasing friction resistance
Reducing the frictional resistance by air injection is an active area of research; alleged performance gains are large. Te paper gives an overview of model and full scale measurement results of ships with air bubble lubrication by Evert-Jan Foeth, Maritime Research Institute Netherlands, Wageningen.
SMOOTH. Te experiments focused on an inland shipping vessel that was tested both on model and on full scale, with and without air lubrication. No appreciable effects of air bubble lubrication were found during the resistance and propulsion tests at either model or full scale. At the Maritime Research Institute
T
Netherlands (MARIN), for a number of years air lubrication as a means of reducing the frictional resistance of ships has been investigated and three approaches are recognised:
• Injection of air bubbles along the hull • Air films underneath the hull
• Air cavities in recesses in the hull. Till et al. (2005) studied the capabilities
on theoretical and numerical grounds and by extensive model tests. Te reductions in resistance found encouraged two follow-up projects: PELS 2, focusing on air cavity ships and the EU-funded SMOOTH project, focusing on air-bubble and air-film lubrication. Tis paper presents the results of model and full scale tests within the SMOOTH project. Te effect is discussed of air lubrication by bubble injection on resistance and propulsion, using both model and full scale experiments.
Background Friction is
the dominant resistance component for low-Froude number ships.
Figure 4: View of the model of the Till Deymann showing the typical bow shape and the fore thruster recess. The right image shows the opening for air injection on the inner wall, prior to the fitting of the porous material.
44 The Naval Architect April 2011
Figure 3: Drawing of the bow and stern of the vessel, showing the location of the air injectors.
Figure 1: Measured resistance of the model. A 1% increase is measured (except for one outlier).
Figure 2: Measured shaft power onboard the Till Deymann with and without air lubrication both for salt water and fresh water conditions.
he experiments were performed performed within the European Union (EU)-funded project
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