A great deal of effort goes into the design and manufacture of rudders and other running gear because it is such an important part of a vessel. Without the proper protection against cavitation and the resulting erosion and corrosion damage, the financial consequences can be substantial for the owner.
Over the last months the rudders, bow thruster tunnels and Kort nozzles of several types of vessels were given an Ecoshield protective coating at yards in China, Canada and Germany. A number of container vessels, tankers, general cargo ships, navy vessels and a research ship were treated. The applications will protect their running against cavitation and corrosion damage for the remainder of their service lives.
Ecoshield has been developed especially for the protection of areas that are most often subject to cavitation. It has the same advantages as the regular Ecospeed coating but it is even more resistant to cavitation due to its increased strength. It is ideally used over smaller areas that need extra protection. Ecoshield provides the running gear with an impenetrable protective layer while its flexibility enables absorption of the forces that are produced by cavitation, thereby preventing the damage normally caused by this phenomenon.
Prevention of damage can start in the newbuild phase
As a consequence of cavitation and corrosion damage on their rudders many ships are given a condition of class. Such a condition of class can have a great impact on the vessel’s sailing schedule if for instance it is not allowed to enter certain ports or needs to go to drydock before a certain period of time has passed.
Understandably the owner then wants to try to hold off going to drydock as long as possible and ideally until the five-year interval has passed. Temporary repairs are carried out after which the class requires that a new inspection is performed every three months.
When such a vessel eventually comes into drydock, maintenance work on the vessel’s stern area, especially cavitation damage repair, can take a long time. Most of these repairs cannot be performed concurrently. This is the result of the close proximity of the rudder, the propeller and the stern area, along with the strict procedures concerning blasting, painting and welding work. Painting is therefore usually assigned to the end of the schedule and as a consequence may not get done at all or else prolongs the stay in drydock. Taking into account the tight drydock schedule of most vessels this is often very problematic.
With an Ecoshield application one can avoid these problems because no repaint of the running gear will be needed during drydocking. Ecoshield will remain intact for the lifetime of the vessel and is guaranteed for ten years. At the most, touch-ups amounting to less than 1% of the surface area will be required. Planning the maintenance of the vessel’s stern area therefore becomes much easier.
An existing ship can also be protected with Ecoshield. If for instance a rudder has already suffered corrosion damage, the coating can prevent any further damage from occurring. In such case Ecoshield can be used in combination with another product in the Subsea Industries family: Ecofix.
Ecofix is a superior, tested and proven filler that restores the steel to its original shape with a smooth surface prior to recoating. Because it uses the same basic resin, Ecoshield can be applied just one hour after the filler.
Ecoshield’s flexibility makes it easy to adapt the application schedule to the shipyard or drydock instead of the other way round. The minimum overcoating time is three hours, which means that for smaller surfaces such as rudders or bow thrusters the two required coats can usually be applied in one single day. By removing the existing paint layers and applying Ecoshield on the rudder we can break the never-ending cycle of painting, suffering damage, having to perform extensive repairs in drydock followed by a full repainting, again and again.
If one takes into account the costs of the temporary underwater repairs and the regular inspections required by a condition of class until the next drydocking, it becomes clear that the investment in a coating system that offers extra protection from day one is easily won back. For this reason more and more owners have Ecoshield applied on a large part of their fleet or have it put in the specs of their newbuild vessels.
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