Rudders

A great deal of effort goes into the design and manufacture of rudders because they are such an important part of a vessel. If a rudder is not given the proper protection against cavitation and the resulting erosion and corrosion damage, the financial consequences can be substantial for the owner.

Prevention of damage can start in the newbuild phase

In itself cavitation, if it is monitored correctly and kept under control, presents no serious danger. But in the long term, cavitation erosion appears. The effect is comparable to a steel tipped hammer that is repeatedly hit against a steel surface at exactly the same location; after a while damage will occur. If the surface of a rudder has been damaged by cavitation, the protective coating will have worn away, leaving bare steel. Large eroded areas can thus appear. . Besides the mechanical damage caused directly by the cavitation process, it also opens the door for corrosion damage. The cavities created will then grow deeper and deeper and in the end can eat right through the rudder. Ships losing large pieces steel or even entire rudders are unfortunately not uncommon.

Instead of the damaged rudders being repaired, they are often replaced every year or two. This recurring cost is unnecessary and can easily be avoided by choosing a coating that can offer permanent protection for rudders.

What needs to be done is either prevent the cavitation or make sure that it has no damaging effect. Ecospeed has been designed to give a very thorough and lasting defense against cavitation and corrosion for a vessel’s entire service life. The coating provides the rudder 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. If the cavitation cannot pierce the coating then no erosion or corrosion can occur.

Tests conducted in a flow channel have confirmed that Ecospeed performs extremely well under severe cavitation. These tests were divided into six stages during which the coating was exposed to an increasing pressure drop, creating a growing cavitation force. Even after the last stage no erosion was present on the test patch coated with Ecospeed. These tests were organized by the French Ministry of Defense and were carried out in Grenoble.

If a vessel with a damaged rudder comes into drydock, maintenance of the vessel’s stern area, especially cavitation damage repair, can be very time consuming. Because of the close proximity of the rudder, the propeller and the stern area, along with the strict procedures concerning blasting, painting, welding and propeller and stern tube seal work, most of the repairs that need to be done in these areas cannot be performed concurrently. Painting is then usually assigned to the end of the schedule and as a consequence may be brushed off or 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 problematic.

With an Ecospeed application one can avoid these problems from day one because no full repaint will be needed during drydocking. Ecospeed 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.

Ecospeed also the best solution for an existing vessel

The newbuild phase is the perfect time to apply Ecospeed, but the coating can also be used to protect vessels that are already facing cavitation and corrosion damage. After the required welding repairs are performed and surface treatment has been carried out, the cavitation pitting that is present on the rudders can be filled to regain a smooth surface. Once this is done the required two layers of Ecospeed can easily be applied, effectively providing the rudders with an impenetrable protective layer.

Ecospeed’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, propellers or bow thrusters the two coats required can usually be applied in one single day.

By removing the existing paint layers and applying Ecospeed on the rudder we can break the never ending cycle of painting, suffering damage, having to perform extensive repairs or full replacement in drydock followed by a full repainting, again and again.