{{no references, date=September 2018 Stabilisation while not underway, stabilisation at rest, zero-speed stabilisation or on-anchor stabilisation refers to the process of augmenting

roll Roll or Rolls may refer to: Movement about the longitudinal axis * Roll angle (or roll rotation), one of the 3 angular degrees of freedom of any stiff body (for example a vehicle), describing motion about the longitudinal axis ** Roll (aviation), ...

reduction for a vessel that is not

underway Underway, or under way, is a nautical term describing the state of a vessel. "Way" arises when there is sufficient water flow past the rudder of a vessel that it can be steered. A vessel is said to be underway if it meets the following criteria: ...

. This process in some cases may be implemented through the use of equipment systems that are also used for roll stabilisation while underway. Vessels at

anchor An anchor is a device, normally made of metal , used to secure a vessel to the bed of a body of water to prevent the craft from drifting due to wind or current. The word derives from Latin ''ancora'', which itself comes from the Greek ἄγ ...

, at moorings, adrift, or keeping station are subjected to roll and pitch generating forces similar to those that affect vessels underway. Different strategies for mitigating the effects of these forces have been adopted. A variable system that uses " active fins" designed specifically for roll attenuation of a vessel while underway achieves lifting force through the flow of water over the fin's surface. By increasing the angle of attack of the fin to the water flow to some maximum working angle, a maximum lift force can be achieved for stabilising the hull. When these same systems are used for roll stabilisation of stationary vessels, the

lift force A fluid flowing around an object exerts a force on it. Lift is the Vector (geometric)#Vector components, component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag (physics), drag force, which is th ...

available from water flow over the fin while underway is not available. For a stationary vessel, the ability to generate a lifting force (i.e. roll-resisting force) is limited to that achieved by any powered fin movements, and by the water volume displaced while stroking the fins in one direction at a precise point in time. Active fin systems can provide incremental add-on stability for vessels at rest, but these systems will usually have larger actuators and fins, and will likely have special power source requirements in comparison to systems designed for stability underway. Various commercial suppliers produce a range of stabilization systems that can be used at rest, on-anchor, or at zero-speed.

See also