Stabilization & tranquilization

A safer and more confortable ship

SIREHNA can provide complete ship motion stabilisation control system solutions based on classical stabilisation concepts (Passive anti-roll tanks, fin anti-roll stabilisation) or more advanced dynamic control functions (yaw/roll coupled stabilisation, dynamic anti-pitch, rudder roll stabilisation, moving mass)

SIREHNA designs control algorithms for the stabilisation of the vessel based on the rudders pairs. The Rudder Roll Stability Control System (RRSCS) system fulfils two main functions:

  • Autopilot in Manual, Hand wheel, Heading Keeping and Track Keeping modes,
  • Stabilization mode (Roll Reduction, Yaw reduction, Silent and Comfort).

During the operation of the ship, the RRSCS is responsible to define permanently and in real time the rudder position commands necessary to perform Heading Keeping, Track Keeping (follow a defined geographical track or a route defined as set of geographical locations (waypoints)) together with roll motion reduction through the anti-roll forces produced by the rudders. The motion stabilization function requires large motions of the rudders at wave encounter frequency and fast rudder angular rate (21°/s).

The RRSCS includes two dedicated user interfaces independent from the INS (Conning stations) network based on LCD screen graphical information display and command inputs with trackball and joystick input device.

The RRSCS is now installed successfully on various vessels for the French, Moroccan, Egyptian and Italian navies.

Aircraft carrier tranquillization – SATRAP

SIREHNA designed and optimized the performances of the French Aircraft Carrier « Charles de Gaulle ». This unique and totally custom design permits the vessel to have gyration in any conditions keeping strictly horizontal the track, in order to allow the aircrafts to be ready to take off at any time.

This critical Control system takes full control of all stabilization actuators on board (2 pairs of antiroll fins, 1 pair of rudders, 12 wagons that weight 250t) and manages throughout the vessels the orders for the stability of the vessel.
The SATRAP system is fully redundant and allow full performance, even in case of failure.

Moving mass

For different reasons, some vessels are not fit to receive the most common stabilization actuators. Therefore, SIREHNA has developed a new solution by the control of a moving mass. This moving mass is constantly moved on rails from portside to starboard in order to counter the roll movement of the vessel by changing quickly the center of gravity of the vessel.

Anti-roll tanks

The motions undergone by a ship result in the motion of any fluid contained within a partially filled tank. By adjusting the dimensions of this tank and its filling, it is possible to reduce the motions of the ship, in particular in roll. The roll reduction can be active or passive. SIREHNA proposes two main types of passive tanks: free surface tanks and U-tube tanks.

SIREHNA’s free surface tank is a parallelepipedic tank extending across the ship breadth and partially filled, in which internal liquid can slosh from one side to the other. SIREHNA’s U-tube tank consists of two reservoirs (each one on a side of the ship) linked by a duct at the bottom of the ship and the internal liquid can flow from one reservoir to the other.

SIREHNA has developed a methodology to study passive tanks (both free surface and U-tube tanks). The work is made up of 3 steps:

  • preliminary dimensioning of the anti-roll tank;
  • numerical simulations (CFD) to validate the anti-roll tank characteristics and fine tune its dimensions and internal configuration;
  • sea trials to check and adjust the anti-roll tank settings.
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