{{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 Vessel(s) or The Vessel may refer to: Biology *Blood vessel, a part of the circulatory system and function to transport blood throughout the body *Lymphatic vessel, a thin walled, valved structure that carries lymph *Vessel element, a narrow wat ...

that is not underway. 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 ...

, at

moorings A mooring is any permanent structure to which a vessel may be secured. Examples include quays, wharfs, jetties, piers, anchor buoys, and mooring buoys. A ship is secured to a mooring to forestall free movement of the ship on the water. An ''a ...

, 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 component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the force parallel to the flow directi ...

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