The turbulence of the ship passing through water together with pressure changes due to the propeller, creates hydrodynamic cavitation which produces forces large enough to erode steel.
The unprotected, eroded surface is further degraded by corrosion causing rapid damage to the rudder: a dry dock repair or replacement is the consequence. The Belgium based company Ecospeed recently treated the rudders of four container vessels owned by three different owners claiming to give lasting protection against cavitation damage. According to the manufacturer, the rudders will not require repainting as the surface coating is guaranteed for ten years and will remain intact for the lifetime of the vessels, thereby preventing similar damage from recurring. The Ecospeed solution is to apply a cavitation damage proof coating to the rudder surface using a Surface Treated Composite (STC) of specially formulated glass-flake vinyl ester resin. Ecospeed’s first candidate for treatment was the RoRo MV Elisabeth Russ in 2004. Since then their treatment has been applied to 110 rudders. Not one has suffered from further cavitation damage and none has needed to be recoated. [More]