Paint product ends cavitation damage
‘Elisabeth Russ’, first of five ro-ros to make good use of Ecospeed coatings
Ecospeed vinylester glassflake coatings are said to have successfully ended a rudder cavitation damage problem on a class of five ro-ro vessels operated in Finland and managed by Hamburg-based Ernst Russ.
The 1999-built ships had been recorded as suffering particularly from cavitation damage, thought to be because of their relatively high propeller rotational speed.
Grzegorz Girjat, superintendent at Ernst Russ, responsible for the ships, says that the rudders were originally coated with a standard epoxy coating. He explains: “During the first intermediate docking, between two and three years from launch, we observed that we already had extensive cavitation damage on the rudders.”
In an attempt to remedy the situation, a doubler plate was installed on the most affected parts of the rudders. “Then it was 2004 when we went to the drydock in Antwerp,” says Girjat. “All the vessels were in drydock. The doublers hadn’t helped. I would say the situation worsened a bit because the gap between the hub and the rudder was reduced by the doubler plates. Cavitation is a well-known phenomenon. It’s known there has to be a certain distance between the hub and the rudder. If that distance is not sufficient then the cavitation will be worse.”
During that 2004 docking, Ecospeed was applied experimentally on the Elisabeth Russ. The application was close to the end of the docking. There was only time to grit blast the rudder and apply two coats. The pitting and damage from the cavitation was not repaired but the paint simply applied over it.
The trial was successful; when the ship next came out of the water in 2007 it could be seen that, despite the last minute application, no further cavitation damage had occurred. As a result, the rudders of the remaining four ro-ro ships were coated with Ecospeed, all with similar results.
Subsequently Ecospeed was applied to the bulbous bows of the ships for protection against ice, and to the stabiliser fins. Since then, none of the rudders have displayed any further evidence of cavitation damage. They have been touched up where the paint was chipped or scraped.
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