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Stability in dynamism

New fin stabilizer covers reduce fuel consumption

1925 marked the maiden voyage for a ship with stabilizer fins, which would soon become an industry staple. However, the technology had one hitch—it raised fuel consumption. Today, in a world increasingly concerned with environmental and economic matters, this is a more pressing issue than ever. Over 90 years later, a solution is almost within reach.

Many vessels employ stabilizer fins, including ferries, yachts, and cruise liners. They ensure the safety of a ship’s crew members by preventing cargo from shifting, but also guarantee smooth sailing. After all, passengers expect comfort, not seasickness. Elsewhere, on research ships, stabilizers provide the stability needed for staff to carry out their work.

Background

A (very) brief history of stabilizers

In the early 1900s, the first technologies were developed to help balance ships—gyro stabilizers. Yet these hulking behemoths were soon replaced with practical, technically simpler fin stabilizers. And these instantly brought their own challenge with them.

The introduction of fins to the bilge radius area compromised its streamlined shape. More importantly, vessels with these fixed stabilizers were not able to land on quay bulkheads. This dilemma inspired the invention of retractable fins that folded away when they were no longer needed.

Stable or affordable

Modern fin stabilizers have a surface area of up to 20m2. Even when they are retracted, the fin boxes generate their own water resistance. This may have a significant influence on fuel consumption and emissions. The effect varies depending on vessel size. For a huge cruise ship, which accommodates enough passengers to populate a small town, it translates into significant extra costs when oil prices rise. Fuel consumption aside, shipowners today face ever stricter environmental and efficiency standards—factors that have driven them to seek a solution.

Back in the 1960s, the industry had already devised hatch covers to seal the hull while stabilizers were being retracted. But these covers were used only on research vessels—to reduce noise rather than water resistance.

Simple, yet effective

Up against tighter regulations than ever before, the shipping industry recently turned its attention back to hatch covers. SKF engineers set to work alongside shipowners to develop a permanent solution.

Two key requirements:

  • Simple structure for high reliability
  • Effective hatch covering for stabilizers in both retracted and extended state
Prototype of the Dynamic Stabilizer Cover

Prototype of the Dynamic Stabilizer Cover

After numerous tests with various materials and machinery, the engineers found their answer. The Dynamic Stabilizer Cover comprises two inflatable cushions on each side of the ship, made from a Kevlar mesh coated with neoprene rubber. The system is surprisingly straightforward. Once the stabilizer is housed, the cushions are filled with compressed air to seal the fin boxes. When the fin is extending, the cushions are deflated and subsequently reinflated. The operation is automatic and integrated within the standard stabilizer controls.

Mechanics of the Dynamic Stabilizer Cover

Mechanics of the Dynamic Stabilizer Cover

Operational reliability is the cover’s main advantage. Even in the event of a fault with the air cushion, the operability of the stabilizer is unaffected.

The first successful prototype trials began in early 2016. Since then, SKF has continued to optimize the solution. It is expected to launch the product next year.

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