This year’s edition of SMM, the leading international maritime trade fair, had many talking points. One particular highlight was the unveiling of the Dynamic Stabilizer Cover (DSC) at the SKF booth. The audience was captivated. For decades the industry had been looking for ways to seal stabilizer hatches to decrease water resistance on vessels. However, the only solutions had been rather impractical. That was until the presentation of the DSC—a simple solution that has seemingly come from nowhere. It also doesn’t require a huge investment compared to the millions of dollars shipping companies usually pay to reduce fuel consumption.
Using inflatable cushions made from a Kevlar mesh coated with neoprene rubber, the system seals the fin box opening when the fin is retracted and housed. Thanks to its simple construction, the stabilizer itself will never be harmed—even if the DSC gets damaged by e.g. a contact with ice. (Learn more about the system here.)
Optimizing before launch
However, after several weeks of prototype testing, a challenge emerged. While the covers worked in normal operation, retracting the fin while sailing at full speed (tested up to 22 knots) could harm the DSC. The shipowner therefore had to reduce the vessel’s speed to a safe speed. So although the prototype worked, it didn’t quite live up to the high standards SKF engineers aim for. Further development began immediately. The goal was to raise the safe speed of operation—or better yet, to eliminate any such limitation entirely.
Soon after, the engineers altered the cover’s basic design. They changed it from a single-chamber system to one with multiple chambers, all of which can be filled with air. The result is greater stability, allowing higher vessel speeds while retracting the fin. The first simulated underwater tests have been successful. Real-world tests will follow in early 2017.
Installation without docking
SKF made one thing very clear: every fin stabilizer the company builds from now on will come with built-in compatibility for DSCs. However, this does not mean a shipowner has to use the covers. Should he decide to retrofit DSCs—to reduce costs because of rising oil prices, for example—he can do so without docking the vessel. Divers install the cushions, then the controls are integrated with those of the existing fin stabilizer. Stabilizers already in use can be retrofitted, too.
“A user of our prototype measured the effect and said he was able to reduce his fuel consumption with the DSC,” Christopher Schnäckel, technical director stabilizers and steering gear, at SKF, explains. The goal is to reduce resistance on the fin stabilizers by as much as 90 percent. This in turn cuts resistance on the whole ship by up to two percent.
The DSC was originally developed for cruise liners. Variants for ferries and expedition cruisers are now in the pipeline and will also be available in 2017.