Many can relate to the concept of sizing fins, a hull unit, or even adjusting the control parameters to run the system, but few understand the complexities of specifying a proper hydraulic power unit (HPU) that enables the stabilizers to move and the system to run optimally. There’s been an evolution of features in the design, engineering, and performance of HPUs that power a stabilizer:
- Full automated touchscreen controller with many sensors providing diagnostics and feedback
- Sophisticated sound and vibration technology integrated in various locations
- Many configurations and sizes depending on available space and performance requirements
- Accumulators to manage electrical load surges
- Variable pressure or flow pumps to minimize environmental impact
- Pressure filters to ensure clean oil runs through the cylinders
- Type of cooling medium provided to optimize oil temperature
- Manifolds to precisely control the cylinder movement on the stabilizer or other consumers
- Expertise offered in shipyard connections to ensure minimal noise and vibration transfer throughout the vessel
The Vessel’s Natural Roll Period:
The roll period — the time for a ship to roll from port to starboard and back to port again — is critical to the stabilizer’s power requirements.
When comparing a five-second roll period to a 10-second roll period, the fin force required is more than five times greater. Imagine the force required to move the vessel back and forth within five seconds versus 10 seconds. Likewise, the system itself carries a corresponding burden with the faster roll period, as it has to produce five times the force.
Another element that affects the power requirements is the clipping factor, which denotes the required fin velocity. For example, take a fin that has an operational range of 30°, but in order to maximize the stabilization, the fin speed must increase. To achieve this, the theoretical range is then increased to 40° — which is referred to as the clipping factor.
Other important factors include what stabilizer system is specified; the size of the fins, foils, or rotors; how many fins, foils, or rotors (two or four); where are they positioned fore and aft; and a study of the flow of power and pressure through the system and the related pressure drops expected.
Space is another major consideration, whether it’s a refit or new build, especially for a stabilizer refit. Often, some existing equipment can be retained (e.g., the fins), but the controls and the actuator may require updating and upgrading.
Many factors play into choosing the right system for optimal performance. When the power requirement is adequately sized to meet the stabilizer capacity, the result is a quiet, more efficient, smooth cruise.
This article originally ran in the November 2021 issue of Dockwalk.