As any shipowner knows, a ship’s rudder is particularly prone to damage caused by erosion and corrosion. The problem features more prominently in high speed container carriers and other fast ships, which are more seriously affected than slower vessels. However, it is a potential problem and hazard for all ships and boats. This problem results in frequent, costly repairs to or replacement of this vital part of the ship’s underwater equipment. So far, the bulk of efforts to relieve this problem have not been fully effective.
A ship’s rudder, placed directly behind the propeller to give the ship maximum maneuverability, is particularly prone to erosion followed by corrosion. The erosion in this case is caused by hydrodynamic cavitation. The forces involved are very large. It is as if the surface affected has been subjected to repeated, heavy blows from a hammer, as well as high temperatures. This causes what is known as cavitation erosion as the surface material, first paint and then steel, begins to flake away.
One need only examine a ship’s rudder that has been subjected to cavitation to see that very severe damage is caused by this phenomenon. Rudders become deeply pitted; paint coatings and hard steel simply disappear; whole plates can fall off and the rudder practically disintegrates altogether, all as a result of this cavitation damage.
Rudder design has mitigated the problem somewhat but far from solved it. Most coatings generally fail to provide adequate protection and usually erode. The use of cathodic protection systems has no effect on cavitation erosion.
The ideal approach to cavitation erosion would be a protection of the rudder which prevented any such damage from occurring. This solution does exist and is called Ecoshield.
Ecoshield is designed for use on rudders, bulbous bows, stabilizer fins, kort nozzles and other underwater gear which requires special protection. The coating has proven 100% effective in protecting all running gear from cavitation.
Aside from some minor touch-ups, none of the rudders that were properly prepared and coated have had to be recoated, even after more than ten years. None of them have suffered from cavitation damage since the coating was applied. For those shipowners and operators who have tried this coating for their rudders, the cavitation damage problem ceased to exist.
In terms of preparation and application requirements, the coating is not particularly demanding. The surface must be grit blasted to remove any previous coating and create a clean surface. Ecoshield is applied in two homogenous coats. The second coat can be applied approximately three hours after the first one, allowing very rapid completion of the coating job. No primer, no epoxy, no tie-coat, no AF. Once applied and cured the coating forms an extremely tough and durable surface which will continue to protect the rudder for the full service life of the ship without the need for replacement.
Since the original application, over 500 rudders have been coated on a wide variety of ships: cruise ships, cargo vessels, container carriers, ro-ro cargo ships, a cable layer, a dredger, crude oil tankers, research vessels, ice-going ships and icebreakers, tugboats, a reefer, passenger ferries, bulkers and others.
Shipowners and operators can consider the problem of cavitation damage to rudders to be solved. The solution simply remains to be implemented on all ships afloat to make this vexing problem a thing of the past.
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