144   ANTI-ROLL DEVICES FOR SHIPS

The Schlick ship stabilizer shortens the period of the ship's roll by increasing the metacentric height by the amount (Art. 86):

mg

h S2 K, [ mK, (    2 9 a)J

The quantity within the parentheses represents the rotational energy of the gyro, K, represents the moment of inertia of the gyro with respect to the spin-axis, and m and K, refer to the entire ship.

A ship gyro-stabilizer of the inactive type is effective only when the rolling of the ship is periodic. As a matter of fact, the rolling

of a ship in a seaway remains periodic but for brief intervals of time. The Schlick device has not been built since the invention of ship stabilizers of the active type (Art. 93).

91. The Fieux Ship Stabilizer. - This consists of two electrically driven gyro-wheels of great moment of inertia spinning in opposite directions about axes that are horizontal and athwartship, Figs. 117, 118. The two gyroframes are capable of precessing about vertical axes. The two gyro-casings are geared together

so that at any instant the velocities of precession of the two gyros are equal and in the opposite direction. This arrangement avoids any effect of the gyros on the steering of the ship. As shown in Art. 89, the stabilizing torques developed by the two gyros are in the same sense about the fore-and-aft axis of the ship.

The outstanding feature of the Fieux* stabilizer is the hydraulic brake mechanism employed to absorb the energy of the ship's roll. This device has the following important properties:

(a) It permits the maximum angle of precession.

(b) It produces zero brake effect when the precession is changing in direction.

(c) It produces maximum opposition to precession when the velocity of precession is maximum and diminishes the brake effect progressively as the precessional velocity decreases.

* Ravue Maritime. 1924. n. 351: 1925. T). 180.

THE INACTIVE TYPE OF GYRO SHIP STABILIZTIR, 145

Figure 119 represents a vertical section through the stabilizer in a fore-and-aft plane, and also a horizontal section through ab. The brake mechanism is in a tank forming the base of the appa

ratus. This base is filled with a mixture of glycerine and water. Keyed to the lower end of the vertical precession axle x of each gyro art twn vartiral vnnac V. 17- _4,;nh -- 1-1, n-A t..,.+1,