Page 203 - Introduction to Marine Engineering

188 Deck machinery and hull equipment

motion. This is achieved by providing an opposite force to that
attempting to roll the ship.

Fin stabiliser
One or more pairs of fins are fitted on a ship, one on each side, see
Figure 10.7. The size or area of the fins is governed by ship factors such
as breadth, draught, displacement, and so on, but is very small
compared with the size of the ship. The fins may be retractable, i.e.
pivoting or sliding within the ship's form, or fixed. They act to apply a
lighting moment to the ship as it is inclined by a wave or force on one
side. The angle of tilt of the fin and the resulting moment on the ship is
determined by a sensing control system. The forward speed of the ship
enables the fins to generate the thrust which results in the righting
moment.

Finbox stiffeners are
aligned with ship's
framing

House/extend
cylinder

Hydraulic
rotary
actuator

Figure 10.7 Fin stabiliser