Over the last two months the rudders of several types of vessels were given an Ecoshield protective coating at yards in China, the US and Turkey. These ships include an oil tanker, a tug boat, a general cargo vessel and several newbuild container ships. The owner of the container vessels decided to give the rudders of his new ships the best possible protection from the very start. This decision was made after he saw the excellent result achieved with Ecoshield on his other vessels.
Before Ecoshield was launched, the problem of cavitation damage to rudders remained unsolved. Cavitation caused erosion, pitting and sometimes complete failure, necessitating very expensive repairs or replacement. 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.
Ecoshield puts an end to these problems. The coating is a specially 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 have seen no further cavitation damage erosion once the glassflake coating was applied. Some of them have been sailing for as long as 10 years after application with no sign that the coating will need replacement during the life of the ship.
Protection from day one
Protection of he running gear of your vessel is best begun at the newbuild phase. When a vessel comes into drydock, maintenance of its stern area, especially cavitation damage repair, can take a long time. There are strict procedures concerning blasting, painting, welding and propeller and stern tube seal work. Painting is then assigned to the end of the schedule. As a consequence it may be rushed or not done at all or else prolong the stay in drydock.
With an Ecoshield application one can avoid these problems from day one because the underwater gear will not need to be repainted during future drydockings. Ecoshield will remain intact for the lifetime of the vessel. It is guaranteed for ten years. At the most, quick and easy 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.
The newbuild phase is the perfect time to apply Ecoshield, as the owner of the container vessels understood. The coating can however also be used to protect vessels that have been in service for some time and are already facing cavitation and corrosion damage, like the other rudders coated over the last months.
Ecoshield’s flexibility makes it easy to adapt the application schedule to the rest of the activities scheduled at the shipyard or drydock in a way which does not interfere with them. Overcoating time can be as short as three hours, which means that for smaller surfaces such as rudders or bow thrusters the two coats required can usually be applied in one single day.
Lasting protection, lasting savings
With an Ecoshield application no repaint will be needed during drydocking. It is the only coating known to fully protect a rudder from all cavitation damage.
The smoothness attained by the coating also provides optimum hydrodynamic conditions. This allows rudders to operate at maximum efficiency. The ship's performance therefore remains stable. This brings tremendous savings for the owner.
Ecoshield is also ideally suited for other areas prone to cavitation erosion or other damage, such as propeller nozzles, thruster tunnels, the bulbous bow or stabilizer fins. For this reason both the tugboat and the oil tanker had their nozzles coated.
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 very easily won back. For this reason more and more owners have Ecoshield applied on the rudders and other running gear of a large part of their fleet or have it included in the rudder specs of their newbuild vessels. These owners invest in the right coating system for protection because they know the savings that will result.
A White Paper with full details about protecting rudders and running gear from cavitation damage is available in the Publications/Papers section ofwww.shiphullperformance.org for free download.