Patent GB-408796-A (GB)
Title: Improvements in anti-rolling tank systems for ships and other craft
IPC: B63B39/03
Filed: 1933-03-20
Abstract: 408,796. Stabilizing ships. MINORSKY, N., 611, Ehn Avenue, Swarthmore, Pennsylvania, U.S.A. March 20, 1933, No. 8388. Convention date, April 11, 1932. [Class 113 (i).] In anti-rolling devices for ships comprising tanks on either side of the ship and means for varying the weight of liquid ballast in the tanks on one side relatively to that in those on the other side the magnitude of the time-rate of change of the stabilising-moment is continually controlled proportional to the angular acceleration of moment. The time phase of the time rate of change of the stabilising- moment is also continuously adjusted to remain substantially in phase with the angular acceleration of rolling by means of a device responsive to the time rate of angular acceleration to reduce time lags in the stabilizing - system. The tanks 2, 3, Fig. 1 are connected at the bottom by the passage 4, the movement of the stabilizing-fluid from one tank to the other is activated by airpressure applied alternately to the surface of the liquid in the tanks by a blower 6 through connections which are reversed every half period of the roll. Pairs of valves 11, 12, Fig. 2, and 13, 14 placed in pipes 7, 9 connecting the tanks 2, 3 are simultaneously operated in opposite directions through rods 35, 36 and wormgearing from a follow-up motor whereby the tanks are alternately connected to the suction and pressure sides of the blower. In order to produce a rate of flow in the connecting pipes which is proportional to the instantaneous angular acceleration of the ship, an accelerometer 56, Fig. 1, is employed comprising a beam 51 carrying two weights 52, 53 mounted about an axis parallel to the longitudinal axis of the ship and supported in the ball-bearing 54 by the spring 57. This inertia-element is connected by the flexible link 64 to the flat spring 65 controlled by a dash-pot 67 and by the flexible link 70 through the counter-weighted amplifying- levers 71, 72 with a plate 69, Fig. 6, carrying wire-coils 77, 78, in the air-gap of alternating current electromagnets 79, 80 energized by coils 81, 82. These electromagnets are slidably mounted in guides. Angular acceleration of rolling causes proportional angular adjustment of the coils 77,78 thus affecting the flux linkages of the magnets 79, 80. A rod 90, Fig. 4, secured to the sliding-block 85 carries at its lower end a roller 41, associated with a cam 110 operated by a stream-line shaped body 92 located in the lower channel connecting the tanks 2, 3. This body is supported on levers 93, 94, pivotted on axes 95, 96 the lever 93 being centred or controlled by a dash-pot and the oppositely-disposed springs 102, 103. When in response to angular acceleration to port, water flows in the connecting-pipe 4, Fig. 1, in the direction shown by the arrow, the body 4 is dragged to the right, the rod 90 is lowered through the operation of gears 106, 109 on the cam 110. This arrangement constitutes a follow-up system between the angular acceleration of the ship initiated by the accelermeter 56 and the velocity of flow in the tank system. The electrical arrangements controlling the pilot-motor 50, Fig. 7 comprise a direct current generator 117, driven by the motor 116 and connected Ward Leonard fashion with the pilot motor 50. Control of the speed of the motor 50 with the associated valve control of the blower is achieved by varying the field of the generator 117. A series brake 120 on the shaft 48 of the motor 50 with the coil 121 is in series with the circuit of armatures armatures 117, 118. The generator 115 has three differentially-wound split fields 122, 123, 124 of which the two first have a large number of turns of thin wire whilst the latter is made of a smaller number of turns of heavier wire. The fields 122, 123 are connected up to the coils 77, 78 of the angular acceleration instrument through a thermionic system controlled by the modulation of the electromotive forces induced in those coils. The coils 77, 78 are connected to the cathodes of valves 132, 134 which are transformer coupled to power valves 130, 131 working as rectifiers and connected to the split field 122. High ratio transformers 136, 137 are inserted between filter circuits 145, 146 inserted between the plates of the valves 130, 131 and the field 122, these transformers being inter alia connected to the grids of power valves 138, 139 the plates of which are connected to the split field 123. A second follow-up system for the follow-up motor 50 is provided by connecting the split field 124 to a resistor 125 arranged parallel to the shaft 48 of the motor 50. A sliding-contact 126 carried by the travelling-nut 127 contacts with the resistor 125. The central tap of the field 124 is connected to a source of direct current and movements of the contact 126 causes variations in the respective halves of the coil. In a modification a block 150, Fig. 8, of heavy metal employed as the inertia element and working vertically between anti-friction rollers 153, 154, 155, is suspended from a spring 151, the vertical motions of the block, which are damped by the dash-pot 160, control the fluid contents of a chamber 165, these variations being hydraulically conveyed to the surface of mercury in a U-tube 167. A highresistance rod 169 dips beneath the level of the mercury on the second limb of the U-tube and the variations in the levels of the mercury thus causes variations in the electrical resistance between the terminals 171, 172, and further proportional to the instantaneous angular acceleration of the ship. A similar U-tube 713 is controlled by a bellows arrangement controlled by the stream line drag body 92 and a third tube 190 is controlled through the bellows 180 from a nut 127 working on the screwed shaft 48 of the pilot motor 50. The terminal 171 is connected in series with a condenser 192 across the primary of a transformer 175 and the circuit comprising the U-tubes is closed on the source of alternating current supply across the terminals 176, 177, and constitutes a phase shifting network operating two hot cathode grid-controlled rectifiers 186, 187. This arrangement is operatively connected up with a controlling-system of the character indicated in the right-hand side of Fig. 7. In order to eliminate the cumulative error to which apparatus employing integration processes is liable and which would result in liquid ballast accumulating in one of the tanks advantage is taken of a quiescent period in the rolling to remove any accumulated excess. To this end relief valves 208, 209, Fig. 1, on the tanks are controlled by solenoids connected with the differential fields 122, 123 of the generator 115 when a period of quiescence develops both valves are opened. In another modification a propeller 300 placed in the connecting channel 4 is employed to promote the displacements of the liquids in the side tanks. The propeller is driven by the oil-motor 314 connected by the oil-lines 312, 313 to the variable delivery oilpump 314. The control member 309 of the pump is adapted for longitudinal displacement through the screw drive of the pilot motor 50. The velocity of the flow in the conduit 4 controls the flow body 92 which in turn determines the position of contacts 324, 325 of a potentiometer. The contacts are connected across the field 329 of the generator 115 which introduces the required follow up action. In a form in which the tanks are provided with openings open to the sea, the operation of the tanks is improved by fitting over the openings a pivoted casing 401 this casing being tilted from side to side by screw gear operated by a pilot motor 50. An automatic arrangement simultaneously responsive to the amount of water in the tanks and to angular acceleration of rolling is provided to diminish the intensity of the resultant controlling action when the disturbing moment of the waves exceeds a certain predetermined limit. Specification 368,281 is referred to.