After more than 10 years of testing, Subsea Industries, a Hydrex company, has launched the rudder protection coating, Ecoshield, for permanent protection against cavitation damage for rudders. The glassflake reinforced coating protects the rudder for the service life of the ship without need for recoating or major repair and comes with a ten-year guarantee. Ecoshield is also suitable for bulbous bow, stabilizer fins, thruster nozzles and other underwater ship gear which needs special protection from corrosion.
Until now, the problem of cavitation damage to rudders, causing erosion, pitting and sometimes complete failure, Hydrex said, necessitating very expensive repairs or replacement has remained unsolved. The need for repair to rudders, involving welding and resurfacing in drydock has been almost universal. The cost of rudder maintenance and the safety hazards connected with worn and failing rudders are out of proportion to the relatively small surface area involved. Efforts to solve this problem have taken the form of redesigning the rudder, changing its position relative to the propeller, trying various materials including stainless steel, metal facing the surface, cathodic protection and a variety of coatings. But the problem has persisted.
Now a very durable, tough, long-lasting glassflake resin coating is putting an end to these problems. Ecoshield is a specifically reinforced version of the well-known Ecospeed non-toxic underwater ship hull coating which is designed for the entire underwater hull of any ship or boat. Small but significant variations of the Ecospeed formula have been tested on rudders since 2002 with extraordinary results. Ships that were experiencing heavy cavitation damage to their rudders, once the glassflake coating was applied, have seen no further cavitation damage erosion for as long as 10 years after application, with no sign that the coating will need replacement during the life of the ship.
Ecoshield is designed to be applied at newbuild (best) or in drydock for ships already in service. Application is simple. It requires blasting to create a 75µm profile and a surface preparation of SA 2.5 or SP 10 and then the glassflake paint is applied in two coats to a thickness of at least 1,000 µm DFT, with an overspray time of about three hours minimum and no maximum. A pitted rudder can be repaired using a thick resin paste (a new, soon-to-be-announced product) which is capable of building up the pitted surface to its original form and which is as tough or tougher than the steel it is used to fill. The heavy glass content of Ecoshield insulates the rudder or other part, making cathodic protection systems including sacrificial anodes virtually unnecessary, as evidenced by the very little wear on the anodes when a ship’s rudder, coated in this way, is inspected in dry-dock and by the fact that an impressed current can be turned right down with no ill effect.
Evidence of the success of the new product is the number of companies who began by coating one rudder experimentally and who, after seeing the results in service, have ordered this coating for the rudders on other ships with plans to convert their entire fleet. Shipowners who have previously applied Ecospeed to rudders on ships in service are specifying the coating for the rudders and other underwater gear on their newbuilds.
Ecoshield comes with a 10-year guarantee. According to the manufacturer, it is the only coating known to fully protect a rudder from all cavitation damage.