US2979010A - Ship stabilization system - Google Patents

Description

April 11, 1961 F. D. BRADDON ET AL SHIP STABILIZATION SYSTEM 6 Sheets-Sheet 1 Filed June 20, 1955 INVENTORS ED. BRADDON, LEBL'AC/l, LMc//ArwcA/,m EL@ lATTORNEY April 1l, 1951 F. D. BRADDON ET A1. 2,979,010

SHIP STABILIZATION SYSTEM Filed June 20, 1955 6 Sheets-Sheet 2 ATTORNEY April 11, 1961 F. D. BRADDON ET AL 2,979,010

SHIP STABILIZATION SYSTEM Filed June 20, 1955 6 Sheets-Sheet 5 A'ToRNEY April 11, 1961 F. D. BRADDON ET AL 2,979,010

SHIP STABILIZATION SYSTEM foo 5 g5 0MM HaR/Z 36 na/M c l IRNEY April 11, 1961 F. D. BRADDON ET AL 2,979,010

SHIP STABILIZATION SYSTEM 6 Sheets-Sheet 5 Filed June 20. 1955 ATTORNEY April 11, 1961 F. D. BRADDON ET AL 2,979,010

SHIP STABILIZATION SYSTEM Filed June 20, 1955 6 Sheets-Sheet 6 ATTORNEY SHE? SEABLIZATION SYSTEM Frederick D. Braddon, Babyion, Lennox F. Beach, Sea

Ciif, and lioseph E. lhadwck, Jr., Levittown, NY.,

iiiied .inne 2.0, i955, Ser. No. 6,662 es autres. (ci. ini-ias) The present invention relates generally tothe stabilization of marine vessels and more particularly to improvements in the roll stabilization thereof by means of activated fins projecting substantially horizontally from each side of the ship hull preferably at the turn of the bilge. These tins are operated-automatically and independently about normally horizontal axes in response to orders oriffinating in sensing instruments which detect and meat'- ure several functions of the ships rolling motion. These fins are operated in such a manner as the counteract the disturbing moments applied to the ship by the action of the waves on the hull. The stabilizer is designed to cope with all kinds and types of sea motions that are encountered in service. The ns are angularly fully retractable or stowed in the hull when not in service.

The activated fin roll stabilization of ships has been known for a great number of years hut these fins have found only limited use by the marine industry. The success of prior systems has been impaired by two principal drawbacks, viz. controlling the angle of tilt of the iin with respect to the craft, and the large hold space required for stowing the fins when not in use. For maximum lift eifect, the lift exerted on each side of the vessel by each fin should be equal in magnitude and opposite in sign thereby producing a pure couple about the craft metacenter or longitudinal axis. However, in the past, the desired lift of each iin was approximated by controlling simultaneously the angle of tilt of the ns with respect to a fixed reference in the ship. Such flu angle control in most applications is not desirable since a pure couple is not produced. This is caused by several factors. Firstly, the lift produced at any angle of attack of the hns is roughly proportional to the square of the speed and a n angle control system therefore requires a very accurate and complex control of system gain with speed. Secondly, the relation between lift and angle of attack is by no means linear. Finally, and most important, the actual angle of attack of the tins with respect to the local sea flow direction differs radically from the angle of tilt of the blade or tins with respect to the ship. This will inevitably be the case under heavy sea conditions when maximum stabilization elfect is most desired. In fact, the false angles of attack created by ship and wave motion may be as much as l to 20 degrees, and hence may equal or even exceed the iin angles ordered for stabilization if angle control is employed. These false angles of attack have an obviously undesirable effect on the performance of the system and even a more serious effect on the safety and reliability of the system since they cause the fins to be subjected to heavy and repeated overload.

it is therefore the principal object of the present invention to position the tins in such a manner as to produce the correct stabilizing lift or moment at any instant rather than a particular iin angle with respect to the ship.

It is a further object of the present invention to position the fins in accordance with a commanded lift, rather 2,979,010 'Patented Apr. il, i961 than in accordance with a commanded angle of tilt, by means of a signal generator or lift transducer which measures the actual lift exerted by each iin and repeat this measure back agalnst an ordered lift command.

Each lin is operated by means of a servomotor which is actuated by the difference between ordered lift and actual lift and therefore the lift produced by each` tin is held substantially equal to the ordered lift in spite of any and all false angles of attack produced by sea ilow relative to the ship hull.

Another object of the present invention is to provide limiting means on the ordered lift command and hence on the actual lift produced by each iin in accordance with ships speed.

Another object of the present invention is to provide an activated iin roll stabilization system for ships wherein the tins stabilize the vessel at the apparent vertical'rather than to the actual vertical such as provided by a vertical gyroscope. In other words, the roll angle signals for the system are derived from a linear accelerometer or inclinometer rather than from the gyror vertical. The use of a linear accelerometer eliminates the vertical gyro and hence the problem of long term gyro drift. Furthermore, by stabilizing to the apparent vertical, the system operates to place the apparent gravity vector straight down through the deck which is the most comfortable condition for the passengers and also the best condition for the ship in regard to structural stresses and cargo stability. A linear accelerometer also senses centrifugal accelerations and hence anticipates rolling due to yaW-heel coupling effects whereby improved ship performance in following and quartering sea conditions is obtained under which conditions the Wave frequency becomes very low with respect to the ship due to shipsspeed and approaches resonance with the ships natural frequency.

Another object of the present invention'is to provide a roll stabilization system of the above character wherein roll rate, as measured by a rate gyroscope, is the primary control term, the basic roll rate signal being supplemented by signals proportional to roll angle and roll acceleration, the former being useful in improving ship performance in following and quartering seas, i.e.,'seas coming from abaft the beam and the latter being useful in meeting the impact effect of bow and head seas, i.e., seascoming from forward of the beam.

All of the above objects of the present invention contribute to a more efficient roll stabilization system employing activated tins than has heretofore been available in prior systems of this general character.

A further disadvantage of prior activated roll iin stabilization systems for marine Vessels is the excessiveamount of space required for the iin operating gear; also the excessive space required for the stowage of the iinY when not in use. Heretofore, the tins have been stowed by retracting them axially on the axis about which the iin pivots, i.e., the fins are retracted alongV a substantially athwartship axis. A further disadvantage resulting from axial stowing is that the iin actuating torques must be applied through long shafts and are therefore subject to shaft torsion errors.y Furthermore, such prior stowing systems and methods in many cases required a free accessible hold space which extended completely through the beam of the ship thereby requiring excessive modification of the internal hull structure.

Therefore, another principal object of the present invention is to provide a method and apparatus for stowing the tins which requires a minimum storage space for the iin and a minimum space for the iin control gear.

it is a further object of the present invention to provide stowing apparatus for the tins which is more contpact and lightweight and therefore saves valuable space in the hull. These latter objects are achieved by angularly retracting the tins into hull boxes which extend fore and aft along the ships side rather than athwartship. This design not only allows a considerable saving 1n space and weight but provides a tighter positioning system in that linkages and shaft lengths between the tilting ram and the fin are held to a minimum.

It is a further object of the present invention to mount the iin on a substantially horizontal shaft mounted in a housing for rotation about a substantially horizontal, ie., athwartship axis, the housing in turn being mounted on stub shafts for rotation about a substantially vertical axis. The first shaft tilts the iin for stabilization purposes and the second shaft rotates the housing and iin into the side of the hull for stowing purposes. Generally, the activated fin roll stabilization system of the present invention consists of fins mounted on each side of the vessel. Each iin may be of conventional hydrofoll design and may employ a full iiap for increasing hydrodynamic efiiciency similar to the brake iiaps used on aircraft to effect increased lift. The stabilizing moment is obtained by controlling the angle of attack by use of a fast response hydraulic servo system for each iin. The fins are retracted into the ships hull by foldling longitudinally when not in service. Ship motions are measured by means of a rate gyro, an inclinometer or lateral accelerometer, and an angular accelerometer. These instruments -and the associated circuits continuously compute the required stabilizing moment or iin lift and the hydraulic servo simultaneously maintains the iin angle such that the actual lift as measured by the iin stress is balanced to the ordered value. The objects of the present invention set forth above may be summarized as follows:

" (a) To provide roll stabilization by controlling iin lift rather than iin angle;

(b) To provide stabilization of the craft to the apparent vertical rather than the actual vertical;

V(c) To provide n actuating gear which is more cornpalct and therefore requires a minimum of hull space; an

(d) To provide an improved system of iin retraction and stowage.

Other objects and advantages of the present invention not at this time particularly enumerated will become apparent as a detailed description of a preferred embodiment thereof proceeds, reference being made to the attached drawings, wherein:

Y Fig. is a schematic diagram of the system of the present mvention;

` Fig. 2 is a schematic cross-sectional view of a ship showing the -relative position of the fins in the hull and the ship motion sensing devices employed for controlling the same;

Fig. 3 is a top plan view of the n actuating gear showing the iin in its extended or rigged out position;

Fig. 4 is a vertical sectional view of the fin tilting gear showing the iin in its stowed position;

Fig. 5 is a horizontal sectional view of the iin in its stowed position in the lin box, the view being taken along lines 5-5 of Fig. 4;

Fig. 6 is a vertical sectional view of the fin shaft housing taken along the lines 6 6 of Fig. 3;

Figs. 7 and 8 are elevational views of the side of the ships hull showing the tins in their rigged out and stowed positions respectively;

Fig. 9 is a sectional view of a suitable signal pick-off or signal generator for providing a signal proportional to the lift of the fin;

Figs. 10, 11 and 12 are views illustrating a modification of the lift transducer.

Referring now particularly to Figs. 1 and 2, the activated roll n stabilization system of the present invention consists generally of two fins and 21, one projecting horizontally from each side of the ship. It will be understood, however, that a plurality of tins on each 4 side of the vessel may be employed depending upon the size and speed of the ship upon which the n installation is to be made. Furthermore, the tins may have a slight downward inclination relative to the beam of the ship and the term horizontally as used in this specification is intended to include. this slight downward tilt which may be on the order of 0 to 2O degrees relative to the horizontal. Each tin is provided with a full-span flap 22 and 23 respectively (23 not shown) which will increase the maximum lift of each fm and thereby minimize the space and weight of the installation. Such flap will also tend to reduce the average drag of the iin by reducing the wetted area. Each n has an aspect ratio of approximately 2.0 thereby providing a 'reasonable compromise between induced drag and bending stress in the iin mounting shaft. The iin may be of any of a number of known constructions and is shown as being of a conventional spar and rib construction with an al1-welded steel skin (see Fig. 6). The iins are operated automatically and independently about normally substantially horizontal axes 24 (Fig. l) in response to orders originating at sensing instruments mounted in a suitable control panel or console in the wheel house or bridge'forming a part of the ships superstructure schematically Indicated at 25 in Fig. 2. These sensing elements detect and measure displacement, rate and acceleration of the ships rolling motion and produce signals proportional to ships motions produced by all types of sea motions encountered in service. The fins are operated through electro-hydraulic servo systems in such a manner as to counteract the disturbing moments applied to the ship by wave action.

Each iin 2G, 21 is operated in tilt by a hydraulic ram 26 about horizontal axis 24, which cylinder in turn is controlled by a variable delivery hydraulic pump 27., the operation of which is controlled in accordance with a computed lift command through command servo system 28. The stowing or rigging out of each iin is accomplished by two hydraulic cylinders 29, 30 operated by solenoid valve 31 using oil supplied from an auxiliary pump 32 (Fig. 3). Stowing rams 29 and 30 operate to rotate the tins about a substantially vertical axis so that. the fins are stowed by angularly folding them longitudinally into suitable iin boxes in the hull. A manual hydraulic pump control for either axis may be provided in the event of complete electrical power failure. lt should be noted that the two fin assemblies operate completely independently of each other with no mechanical or hydraulic connection between the assemblies. The iin tilt servo system consists generally of the variable delivery pump 27 driven by an electric motor 33, an electric motor stroke servomotor 34 which is driven from the output of a magnetic servo ampliiier 35 receiving a lift command signal from the sensing elements land lift signal servo loop 36. The lift command servo loop 36 is preferably mounted at the ships bridge in a suitable console containing sensing elements which measure roll angle and its time derivative. It will be noted that the lift command servo operates two separate signal generators, one of which .is shown at 37, which supply separate lift order signals to each of the fin actuating servo systems. In Fig. l only the port stabilizing iin and actuating means therefor is illustrtaed, it being understood that the starboard iin actuating means is exactly the same, except that the tin structure and operating apparatus are mirror images. Furthermore, the output of servo loop 36 drives two signal generators, i.e., synchro generator 3'7 for supplying the lift command signal to the port iin mechanism and another similar synchro (not shown) which supplies a separate signal degrees out-of-phase to the signal from synchro 37 to the starboard iin actuating mechanism. Hence there are two independent iin positioning servos having the same ordered lift in common.

The lift Vcommand signal for controlling the motion of the stabilizing tin is a composite or summation of three signals separately generated through the effects of ship motion on the signal generating devices. These three signals include a signal proportional to the roll angle of the craft, a signal proportional to the roll rate of the craft, and one proportional to roll acceleration of the craft. The roll angle component of the lift command signal is provided by means of a linear accelerometer 39 of conventional form mounted with its sensitive axis disposed athwartship having any suitable signal generating means adapted to provide an alternating current output having a phase depending upon the direction of roll of the ship and an amplitude depending on the magnitude of such motion. The effect of this linear accelerometer or inclinometer signal is to provide static and low-frequency stabilization of the craft to the apparent vertical rather than the true vertical. The linear accelerometer also senses centrifugal acceleration and hence anticipates craft rolling due to yaw-heel coupling, i.e., the tendency of the craft to heel as the craft turns. The physical significance of this signal component of the ordered lift signal proportional to roll angle is to increase the effective GM of the ship without at the same time increasing the moment acting on the ship produced by a given wave slope, as an actual or physical increase in .the GM of the ship would do. The GM of the ship may be defined as the distance between the center of gravity of the ship and the metacenter thereof (see Fig. 2).

The lift command signal component proportional to roll rate is provided by means of a conventional rate gyro 4t) which is mounted in the craft such that precession thereof occurs upon rolling of the craft about its longitudinal axis, i.e., about its metacenter. A signal-proportional to the angle through which the gyro processes may be supp-lied by means of any suitable type signal gene-rator 41 which produces an alternating current output of phase depending upon the direction of rolling motion of the ship and of an amplitude depending upon the magnitude of such motion. The physical significance of the roll rate signal in the composite lift command signal is that it increases the effective damping of the ship in response to rolling motion thereof produced by wave action. This signal proportional .to ships roll rate is the primary control signal because a ship in its natural state is highly under-damped in roll and hence the principal need is for roll damping.

The third signal, i.e., roll acceleration signal, is provided by means of lan angular accelerometer 42 of conventional form which is provided with a suitable pick-off device .3 which generates a signal having a phase in amplitude proportional respectively to the direction an amount of angular acceleration of the craft about its longitudinal axis. The physical significance of the ro-ll acceleration signal component of the ordered lift signal on craft operation is to effectively increase the moment of inertia of the craft about its longitudinal axis.

Hence, the roll angle signal and the roll acceleration signal are subsidiary signals that improve performance under extreme conditions of high or low Wave frequencies. As above stated, because the roll angle detecto-r is actually an apparent vertical detector, it also senses centrifugal accelerations due to yaW rate and thereby provides improved performance of the ship in following seas.

The roll angle, roll rate, and roll acceleration signals are applied respectively to the windings of potentiometers 44, 45 and 46, the outputs of which are combined in magnetic amplifier 47 which forms a part of the command signal servo loop 36. The sum of the above three signals drives an electric servomotor 4S, the output of which positons command signal generator 37 through a limit stop apparatus 51 and slip clutch 49. In order that the output shaft S of servo loop 36 correspond exactly to the sum of the acceleration, rate, and displace.- ment signal, a position feedback signal is generated in feedback synchro 55, the output of which is applied to the input of amplifier 47. A meter 56 may be connected to sense the feedback signal for providing an .operator with an indication of the magnitude'Y of .the ordered lift commanded by the lift command servo loop 36.

As illustrated in Fig. l, several external adjustments are provided for increasing the -versatility of the stabilization system of the present invention. A list correction control is provided to buck out any constant roll angle that might be present. This is accomplished by means of a knob or control handle 57 which actuates through an eccentric 5S to vary the neutral axis of linear acceler ometer 39. For this purpose accelerometer 39 is mounted on a platform 59 pivotally secured to the craft by means of hinge 60 for rotation about an axis parallel to the craft longitudinal axis. This list correction control is provided because it is not economical to use the stabilizing tins as a means for trimming out any permanent 11st of the vessel. it will be understood, of course, that under emergency conditions the system may be so used.

In order that the control sensitivity of the system may be adjusted for the purpose of conforming with the requirments of various sea conditions that are encountered, a sea state selector or weather adjustment is provided. In the presen-t embodiment, a knob 61 adjusts the magnitude of the input signals to amplifier 47 by adjusting the wipers of potentiometers 44, 45, 46 simultaneously.

The limiter device 51 on the output shaft of servomotor 48 is for the purpose of limiting the ordered lift signal as a function of craft speed since the effectiveness of the fin in producing roll moments about the craft longitudinal axis varies as a function of craft speed. Thus at high speeds smaller command lift signals must be supplied to the fins and viceversa. The speed adjustment is provided by means of a knob 62 which adjusts the limits stops `63 and hence the magnitude of movement of shaft 5ft. A slip clutch 49 is provided for preventing overload of the servomotor 48 after the limits have been reached. Speed selector knob 62 also controls certain of the sensitivities in the iin positioning servo systems so that these servos operate at an optimum manner at all times, as will be hereinafter described. It will be noted that all of the sensing devices for the lift command computer or servo loop 36 are spring centered and are hence free from mechanical drift which might otherwise be a problem as would be the case if a position or displacement type gyro were employed. Furthermore, it will be noted that electrical drift is eliminated by the use of A.C. signals throughout.

ln the illustrated embodiment of the present invention all of the apparatus shown at the left of amplifier 35 may be included in a console mounted on a bridge bulkhead or mounted if desired, on a pedestal at the bridge station. The portion of Fig. l to the right of and including amplifier 35 is located at the n sites in the ships hull and thus it will be seen that the two fins operate completely independently of each other but are controlled in accordance with the same lift order. The output of ampiifier 35 which is proportional to the difference between the ordered lift and the actual lift of the fin is applied to stroke servomotor 34 which actuates through gearing 7G, slip clutch 71, and lever 72, to stroke control lever 73 of variable delivery pump 27. A stroke feedback synchro 74 is provided for insuring that the position of stroke rod 73 of variable delivery pump 27 corresponds to the error signal applied to the amplifier 35. A speed feedback signal may be further employed for insuring smooth and rapid operation of the stroke control servo loop. A tachometer 75 gearedto the output shaft of stroke servo 34 is provided for this purpose.

The output of variable delivery pump 27 is applied to iin tilting ram 26 which ram rotates tin 2i) about axis 24 through crank 76 and n stub shaft 77. Ram 26 continues to rotate fin 20 until water pressure on the latter produces a lift which is equal and opposite to that commanded. A signal proportional to ythis lift force is generated by means of a lift signal transducer 78 which is fed back through lead 79 to the input of amplifier 7 3S. The mechanical structure of lift transducer 7S and its actuating means will be hereinafter more fully described.

The operation of the iin Itilt servo loop is as follows:

the ordered lift signal from the bridge control station 25 -A and the actual fin lift signal from the lift transducer 78 are applied to servo amplifier 35 which supplies an output proportional to the difference between these signals, i.e., lift error. Servomotor 34 is energized by this output and positions stroke lever '73 until the stroke position feedback synchro 74 supplies a signal which is equal and opposite 4to the lift error signal. As n position is applied through ram 26, the increase or decrease in actual fin lift will result in a signal from lift transducer 73 which gradually replaces the stroke position feedback signal and cancels the ordered lift signal. As the actual lift approaches the ordered lift, the pump stroke arm 73 returns to its neutral or zero position. When the actual 'and ordered lift signals are equal and opposite, the pump stroke remains stationary. Thus, the pump stroke feedback synchro signal stabilizes the servo system by preventing any over-shooting of the ordered lift. Further assistance in assuring smooth, non-oscillatory iin operation is obtained from the stroke velocity tach generator 75 'as described. While the ordered lift is limited on an absolute basis in accordance with craft speed by means of limit stops 51, 63, local conditions at each iin require lfurther limit stops to prevent greater iin angles than are physically possible. As illustrated in Fig. 1, completely mechanical means are provided for limiting the mechanical operation of the iin. If the ordered lift command tends to produce a fin deflection of greater magnitude than is mechanically possible, a projection 8b on the end of ram piston shaft S1 contacts one or the other of two projections 32 associated with bell-crank 83 which through the link S4 positions stops 85 cooperable with stroke arm 73 to thereby limit the motion of the latter. Thus, the latter limit stop arrangement overpowers all other orders to the pump stroke arm 73 of variable delivery pump 27.

In order that the stroke positioning servo system operation be optimum for all craft speeds, the speed selector knob 62 aiso controls the sensitivity of the iin positioning servo loop by controlling, throughshaft 86 and pov tentiometer S7, the energization voltage applied to stroke yfeedback synchro 74. in this manner the sensitivity of the stroke positioning servo system is also controlled as a function of craft speed.

The structural details and design of the fin actuating and stowing mechanisms and the stowing compartments are illustrated in detail in Figs. 3 to S, inclusive. As shown in Figs. and 6, the iin 20 is bolted or otherwise rigidly secured to a short, hollow shaft or trunnion 77 which is journaled in spaced bearings 89, 90 in a substantially cylindrical housing 91 for rotation about tilt axis 24. Housing 91 in turn is provided with upper and lower stub shafts 92, 93, respectively, for rotation about a substantially vertical axis 3S, preferably at right angles to the axis of rotation of iin 20 in suitable bearings 94, 9S (Fig. 4) in the upper and lower surfaces of a water-tight n actuating mechanism box defined by walls 96, 97, 98 and 99. Since this iin box is filled with sea water, suitable hydraulic seals 100 and 161 are provided for preventing sea water from entering the ships hull. in this connection, housing 91 is provided with suitable hydraulic seals 102 for preventing sea water from entering this housing. To further insure that no sea water enters the housing 91, it may be completely filled with oil from a sump (not shown) which is maintained under a pressure just greater than the pressure of the sea water at iin depth.

Lift forces or loads produced by the iin 20 are transmitted to the housing 91 through horizontally spaced. bearings 89 and 90 and thence to ships hull through stub shafts 92 and 93 and vertically spaced bearings 94 and 95. The boxes may beY suitably reinforced in any coni ventional manner by means of plates and stieners.

Mounted on the upper stub shaft of housing 91 is a plate having formedthereon a cross-head 106 to which stowing ram pistons are attached. This plate further carries a verticalcylinder 107 to the top of which is secured the n tilting ram 26. Connected with the piston 10S of ram 26 is a 'cylindrical cross-head 109 which slides within cylinder 107 and pivotally mounted there-in is a connecting rod 110 which extends downwardly therefrom and is pivotally connected as at 111 to crank 76 which forms a part of iin actuating shaft 77.

Thus, with the fin rigged out, motion of piston 108 in ram 26 is transmitted through cross-head 109 and connecting rod 110 to pivot iin 20 about axis 24 (Fig. 1) through crank 76. Controlled oil pressure from variable delivery pump 27 is applied to ram 26 through suitable hydraulic connections 113 and hydraulic slip rings 114, thereby permitting the entire ram 26 to rotate about vertical axis 38 without the requirement of yany flexible tubing, etc.

The mechanical linkage limit stop mechanism described with respect to Fig. 1 is illustrated in more detail in Figs. 3 and 4. As shown, this limit stop mechanism is enclosed in a housing 115 which is mounted in fixed relation with respect to top plate 105 and ram 26 by means of a suitable mounting bracket (not shown) which may be secured to the deck or fixed upper ange 122 of bearing 94. Ram motion is imparted to limit stop mechanism v11S by me-ans of yoke 116 and shaft 117. The operation and structure of the limit stop mechanism has been described above, reference being made to Fig. l, and corresponding numbers therein have been applied to corresponding parts of Figs. 3 and 4. Furthermore, the stroke servomotor 34, tachometer 75, stroke feedback synchro 7d, gearing 70, clutch '71 and link 72 are all conveniently packaged in ya common housing 118 of Fig. 3.

In Figs. 6 and 9, there is shown a means for providing a signal proportional to the amount of lift being produced on the ship by the fins. As illustrated, the fins 20 being rigidly bolted to horizontal shaft 77, this shaft is subjected to the entire stress produced by water action on the iin. In the illustrated embodiment of the present invention, means have been provided for measuring this stress. `A disc is rigidly secured, as by welding, to the inner surface of shaft 88 and is positioned as near as convenient to the outboard end thereof. Rigidly secured to this plate, as by bolting, is a cantilever beam 121 which extends substantially axially of the shaft toward the opposite or inboard end thereof. Rigidly and preferably vertically adjustably secured to the end of the shaft 77 adjacent the free end of beam 121 and cooperable therewith is pick-off device or lift transducer 78. It will be noted, partlcularly with reference to Figs. 4 and 6 that this lift transducer' 73 is mounted in shaft 77 so that it is aligned with a normally vertical axis. Withl this arrangement, the signal generated thereby includes only the normal component of the strain or stress imposed upon shaft 77 thereby eliminating in the actual life signal any component produced by tangential forces imposed on the fin, i.e., drag. Cantilever 121 will be deected only upon stresses imparted to n support shaft 77, which stresses will be measured by means of pick-olf 7S to provide a signal proportional to the lift being imparted to the ship by the iin.

Any suitable type of pick-off may be employed and one form thereof is illustrated in Fig. 9. As shown, this pickoff is an inductive pick-off device which comprises a threaded casing adjustably threaded in shaft 77 which has fixed thereto a pick-off core and windings 124 of the E transformer type. Two such cores are provided for failsafe purposes. A spring loaded plunger 125 having al1 armature 1261s operated by movement of cantilever 121:`

which generates in the output winding of the pick-off a signal proportional to the stresses in shaft 77, and since stress is produced by the lift of the 1in, the signal is, therefore, proportional to the lift being imparted to the ship by the fin. This signal, as described above, is compared with the ordered lift command and the iin tilting servo system reduces the difference therebetween to zero, thereby positioning the iin until the actual lift is equal to the commanded lift.

At this time it should be pointed out that another important function of the iin tilting servo system is its regulator action, i.e., it eliminates the elect of extraneous lift forces due to extraneous disturbances in the angle of attack of the tin. For example, if the iin servos are in operation but for some reason no lift is ordered, the fins would go through continuous motions depending on seaway conditions, thereby eliminating the effect of local false angles of attack. As stated above, these false angles of attack, due to local currents about the ships hull, can be :as large as l to 15 degrees under severe sea conditions. Obviously, if these disturbances are not eliminated, there will not be a very close correspondence between the ordered lift and actual lift,

In accordance with one of the important objects of the present invention, means are provided for angularly stowing the fins when not in use. For this purpose, an aft extension 13 of the tin actuating mechanism box is provided in the ships hull for accommodating the iin when in a stowed position, as shown more particularly in Fig. 5. When the iin is in a stowed position, a failing plate 104 is provided for preventing turbulence around the lin box. The stowing of the n is controlled by solenoid operated fin stowing control valve 31 (Fig. l) which controls hydraulic pressure supplied by pump 32 to stowing cylinders or rams 29 and 30 through hydraulic lines 29', 30. These rams act in opposition as by means of crossed flexible hydraulic lines 13S, 139 (see Fig. 3). The output rods 140 and 141 of rams 138 and 139 are connected to cross-head 106 which rotate housing 91 about vertical axis 3S to thereby stow or rig out the ins. However, before `such stowing can take place, the iin must be locked in a predetermined or neutral position with respect to the ships hull. For this purpose a synchro device 130 or other suitable signal generator (see Fig. 1) is provided for measuring the yactual angle of the ns with respect to the hull, the zero position of synchro 130 corresponding to a level or zero-detiection position of the tins. This synchro is positioned by means of feedback shaft 81 in the schematic of Fig. l. As shown in more detail in Fig. 4, feedback shaft 117 is provided with a rack portion 131 which engages pinion 132 for positioning synchro 130 in accordance with n position. When a stowing operation is to be initiated, the ordered n lift signal is severed from the input to amplifier 35 as by means of a suitable stowing switch 133. At the same time this switch substitutes the output of synchro 130 for the lift command signal. Thus, if the iin is not centralized, the lin tilting servo will drive the fin towards its zero position.

The finis locked in its zero-deflection position by means of link-coupled, spring-loaded latches 134 and 135 (Fig. 4) which, during normal operation of the system, are held in the position shown by means of hydraulic pressure supplied by source 32. Upon initiation of a stowing operation this hydraulic pressure is cut ofi, allowing spring 136 to force latches 134 and 135 into the cylinder 107. As the iin positioning servo drives the n toward its zero position, a shoulder 137 on cross-head 109 is engaged by one or the other of the extended latches, arresting movement of cross-head 109 and thereby securing the fin in its zero position. Since there is no position feedback, i.e., the synchro 130 provides the only control of ram position, the ram 26 will tend to drive cross-head 109 through the zero position. The stowing of the fin may be continued after locking the fins.

As shown in Fig. 3, means are provided for locking the lin in its stowed or rigged out position. For locking the tin in its rigged out position, spring-loaded, hydraulically actuated latches 142, 143 engage cross-head 106 when in its full clockwise, as seen in Fig. 3, position as determined by means of mechanical stops 144 and 145. A switch 146 is provided for actuating an indicator in the control console in the bridge and/or at the n site for indicating to the operator that the iin has reached its fully extended position and is locked therein by latches 142 and 143. Similarly, latch 148 is provided for locking cross-head 106 and hence iin 20 in its fully stowed position, as indicated by the dotted lines in Fig. 3. A similar switch 149 is provided for indicating that the finis stowed.

After the iin tilting servo system has positioned iin 20 in its horizontal position and locks 134 and 135 have been engaged with cross-head 109 to maintain the tin in this position, latches 142 and 143 are disengaged as by means of small hydraulic rams 151, 152 which operate through suitable linkages 153 to withdraw the latches lfrom contact with the cross-head 106. A slight rig-out pressure from rams 29 and 30 may be provided to insure release of the latches. Hydraulic pressure is then applied through lin stowing control valve 31 to stowing cylinders 2,9 and 30 to cause rotation of cross-head 196 and hence fin 20 in a counterclockwise direction, as seen in Fig. 3, to stow the iin 20 into the iin box 103 in the hull. When iin 20 has reached its fully stowed position, crosshead 106 abuts stop 154 and the spring-loaded latch 148 engages the cross-head to maintain it in this locked position. This latch 148 may be the same as latches 142 and 143 and may be similarly released upon a rig-out operation.

The entire rigging-out and stowing operations may be controlled remotely from the bridge control console. However, it may be more practical and more convenient, equipment-wise, 'to rig out and stow each iin separately at the fin sites in the hull by suitable manually controlled switches, such as by switches 133 and 133. Furthermore, in order to prevent premature or inadvertent operation of any event in the iin rigging out or stowing cycles, suitable interlocking controls may be provided. For example, switches associated with the centering latches 134, for fin tilting ram 26 may be provided for preventing operation of the lin stowing control valve 31 prior to centering the switches may complete circuits allowing solenoid controlled iin stowing control valve 31 to be operated. Further interlocking switches may be associated with latches 142 and 143 which may be in series with the switches associated latches 134 and 135 whereby to prevent operation of iin stowing control valve 31 until the latches 142, 143 are released. It will be noted that the source of hydraulic power for the stowing rams 29 and 30 and for the hydraulic latch releases is supplied by the same motor which drives the variable delivery pump 27. Therefore, in order to prevent any pressure build up on either side of the locked tilting ram piston 108 during rigging out or stowing of the ns, solenoid controlled by-pass valve 160 electrically interlocked with latches 134 and 135 is provided. The upper surfaces of the 1in actuating mechanism box and the fin box 103 provide a convenient space for all of the fin-operating gear, hydraulic equipment, control instruments, stowing consoles, etc.. thereby keeping to a minimum the space required for the entire iin and fin actuating mechanism.

As described above, iin 20 is provided with a full flap 22 which is so connected to the iin actuating mechanism that it moves in the same direction but through a `greater angle than movement of the main iin 20, for the purpose of increasing the hydrodynamic efficiency of the iin. For this purpose an extension 155 (see Fig. 7) is preferably integrally formed with housing 91 which carries a pin or stud 156 thereon. Since the housing 91 is fixed with respect to the n 20, the stud 156 is also xed with respect thereto. Projecting forwardly from the hinge pivot Y157- E 1l orthe Hap 22 is a fork 158 whichengages stud 156. Thus, upon rotation of iin 20 about axis 24, flap 22 is caused to rotate in the same direction but through a greater angle than iin 20 throughV the restraint on fork member 158 imposed by xed stud 156. This action is clearly indicated in Fig. 7.

ln Figs. l0, 1l and l2 there isillustrated a modification of the means for providing a measure of the actual lift being exerted on the ships hull by the ns. It will be noted that the general arrangement of the iin mounting structure remains essentially the same as that shown in Figs. 4, 5, and 6. As shown schematically in Fig. the fin is pivotally mounted in housing 91 for moving about horizontal axis 24, the vertically extending stub shaft 92 and 93 thereon supporting the housing for rotation about vertical axis 38 in lower and upper bearings 93 and 94. As in the apparatus of Fig. 4l, the upper bearing 94 is designed to support substantially the entire Vertical load of the housing 91, the lower bearing 93 being subjected substantially only to the lateral loads produced by water forces on the iin 2G, i.e., lift forces and drag forces.

In the present modification, it is the horizontal and athwartship component of these lateral loads which is weighed or measured to obtain a signal proportional to the vertical lift exerted on the hull by the n 20. For this purpose, the outer race 162 and its support ring 165 of lower bearing 95 are not rigidly secured to the ships structure as in Fig. 4, but are flexibly fastened thereto as by means of radially extending webs or anges 163, 164. These ilanges form a preferably integral part of outer race support ring 165 and extend radially therefrom in a direction parallel to the longitudinal axis of the ships hull. These flanges are in effect extremely stift springs 'which are capable of transferring the lifting moment of the fins Ztl to the hull but on the other hand in doing so will be deflected by the lift force. Since the anges are rigid along their support axis, i.e., with respect to the ships fore and aft or longitudinal axis, the deflection of stub shafts 92 and 93 is in a direction substantially athwartship or at right angles to the ships longitudinal axis. Thus, the lift transducer 167 is positioned with its sensitive axis along this athwartship axis and between the ring 165 and lower bearing housing 166. As clearly shown in Fig. ll, two such transducers are employed for fail-safe purposes. The signal generator or lift transducer 167 is preferably of the induction type and may be similar to the one illustrated in detail in Fig. 9.

It will be understood, or" course, that the actual movement of the lower stub shaft 93 with respect to the bear- -ing housing 166 is very, very small, i.e., on the order of a few thousandths of an inch, and hence the upper and lower uid seals 100 will be completely unaifected by such movement.

One of the advantages of the modification illustrated in Figs. l0, ll and l2, is that the litt transducer is readily accessible Within the ships hull and is, therefore, easily repaired or replaced if for some reason it become defective. Another advantage of this modiiication resides in the fact that the lift transducer is sensitive to only the truly vertical loads on the ship produced by n 20 and is independent of the angle of tilt of the tins. Thus, the lift transducer signal, i.e., the lift repeatback signal, is exactly proportional to the vertical lift exerted `by the ns.

In regard to the iin tilt servo loop 28 which actuates the iin 2t), it may be desirable to add to the lift feedback signal, a predetermined small amount of fin angle signal whereby to provide additional stability to this loop. For this purpose, a potentiometer 170 is energized by the output of signal generator or angular synchro 13% which, as described above, is positioned in accordance with iin angle. The variable tap of potentiometer 170 is combined, through a suitable mixing circuit 171, with the'lift s ignal from 'lift transducer 78, the output thereofY being awa-01o supplied as a combined repeatback signal proportional to iin lift and iin angle to the input of ampliiier 35.

, It will be understood that the lift repeatback signal may be generated in a number of different ways and by a number of different types of lift transducers. lt may be generated by means of strain gauges which may be iixed to the fm itself or to any other element of the liu support assembly which transmits the lift produced by the iin to the ships structure and is therefore subjected to stress; for example, one or more strain gauges may be bonded or otherwise secured to the external or internal surface of the iin Vsupport shaft 77. Alternatively, the iin surface mayA be provided with a exible diaphragm extending along substantially the entire length thereof such that flexure of the diaphragm by water pressure produces a signal output proportional to the average lift being produced by the n. Other means for providing a signal proportional to the magnitude of the lift being exerted on the craft bythe iin may be envisioned by those skilled in the art.

Furthermore, although in the foregoing description of a preferred embodiment of the present invention, the fins are shown and described as extending substantially horizontally from the side or bilge of the ship, it will be understood that it is within the scope of the invention in its broader aspects, that the ns may extend substantially vertically downward from lthe ships bottom, the deflection thereof producing a similar righting couple thereon.

Also, it should be understood that the ships motion sensing devices, instead of being located at the bridge console, may be mounted below decks, preferably at the n location thereby placing the signal sources and the apparatus responsive thereto close together. Also at such a location, ships vibrations are at a minimum, lateral accelerations due to roll are very small, weather conditions are no problem, and space limitations are not critical.

From the foregoing description and from an inspection of the attached drawings, it will be noted that the iin assembly box consists of a fabricated box with the upper and lower bearing walls 96 and 98, the side walls 97 and 99, and the fore and aft side walls 99 and 103' forming an integral unitary structure. Assembled within the box are the iin 20 and fin linkage 112, connecting rod 110, cross-head 109, and cross-head guide or cylinder la7. The machinery deck, i.e., the upper surface of top wall 96 has assembled thereon the stowing cylinder yoke or cross-head `106, with its latches and stops, all located and assembled, and the stowing cylinders 29 and 30 completely assembled and mounted. The top plate 96 also supports, completely assembled, the iin actuating controls, Le., the variable pump 27, with its stroke servo 1118 and controls, power motor 33, and auxiliary pump 32., This lntegral assembly may be completely tested prior to transportation and installation. The assembly is designed for convenient mounting, as 'a unit, on a standard railroad ilat car for convenient transportation. More importantly, ythe completed assembly may be conveniently slid through a suitable rectangular opening in the shipsv hull and welded in place, after which the shell plating and doub ling plate may be secured. Such complete prefabrication not only facilitates installation but greatly cuts installation time, an important factor especially when the installation is on a dry-docked vessel. 1

Since many changes could be made in the above cou struction and many apparently Widely different embodiments of this invention could be made Without departing from the scope thereof, it is intended that all matter contamed in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a` limiting sense.

What is claimed is:

l. In a ship stabilization system, a n, mounting means for supporting said n on a ship to rotate about an axis extending generally longitudinally of said iin and nora mally in a generally athwartship direction, drive means having an output coupled with said iin for rotating the same about said axis, means for producing a signal in accordance with rolling motions of said ship, means coupled with said iin for obtaining a repeat-back signal proportional to the lift exerted by said iin, control means coupled with said drive`means and responsive to both said signals for controlling said drive means in accordance with the algebraic sum thereof whereby to produce a displacement of said tin in accordance with the lift exerted thereby, means for limiting the maximum value of the signal controlling said drive means, and further means coupled with said drive means for limiting the maximum displacement output of said drive means independently of the lift exerted by said nn.

2. In a ship stabilization system, a iin, a tirst mounting means for supporting said tin on a ship to rotate about a first axis extending generally longitudinally of said iin and normally in a generally athwartship direction, a second mounting means for supporting said iin to pivot about a secondaxis normally extending in a generally vertical direction, a first drive means coupled with said first mounting means for rotating said Viin about said first axis and a second drive means coupled with said second mounting means for pivoting said iin about said second axis, means for respectively controlling the operation of said first and second drive means, means for producing a signal in accordance with rolling motions of said ship, means for providing a signal proportional to the position of said iin about said rst axis, means for obtaining a repeat-back signal proportional to the lift exerted by said iin, control means for controlling said first lin-driving means in accordance with said roll-motion, position, and lift signals, means for selectively controlling said iirst iindriving means in accordance with said n position signal only, and means responsive to the operation of said tirst iin-driving means under the latter condition for controlling the operation of said second tin-driving means.

3. in a ship stabilization system, a nn, a first mounting means for supporting said iin on a ship to rotate about a first axis extending generally longitudinally of said fin and normally in a generally horizontal direction, a second mounting means for supporting said iin to pivot about a second axis normally extending in a generally vertical direction, a rst drive means coupled with said lirst mounting means for rotating said lin about said rst axis and a second drive means coupled with said second mounting means for pivoting said iin about said second axis, means for producing a signal in accordance with rolling motions of said ship, means coupled with said iin for obtaining a repeat-back signal proportional to the lift exerted on said ship by said iin, control means coupled with said first drive means for controlling the same in accordance with said roll signal, means coupled with said iin for producing a signal in accordance with the position of said tin about said rst axis and manually operable means coupled with said first iin drive means, said first and second drive means for controlling said first drive means in accordance with said position signalonly and for controlling said second drive means in dependence upon a predetermined position of said iin about said iirst axis.

4. In a ship stabilization system, a pair of stabilizing :tins mounted one on each side of the ship, means for supporting said tins for rotation about axes thereof extending generally outwardly from the ship whereby rotation of said tins about said axes serves to produce a litt on each side of 4said ship as the ship moves through the water, separate means coupled with each lin for respectively driving the same about said axes, means for obtaining signals dependent on roll motions of the ship, means coupled with each iin for obtaining independent repeatback signals proportional to the lift exerted on each side of said ship by each iin, and means coupled with each drive means for independently controlling each drive 14 means in accordance with said roll signals and its respective repeat-back signal.

5. In a roll stabilization system for ships, a pair of stabilizing ns mounted one on each side of the ship, means for supporting said lins for rotation aboutV axes thereof extending generally outwardly from the ship whereby rotation of said ns about said axes serves to produce a lift on each side of said ship as the-ship moves through the water, separate drive means coupled with each iin for respectively driving said tins about Vsaid axes, means for obtaining signals dependent on roll motions of the ship, means coupled with each drive means for independently supplying said roll signals to each of said driving means, means responsive to the separate operations of said ns for obtaining independent repeat-back signals proportional to the magnitude and direction of the lift exerted on each side of said ship by each of said fins, and control meansrcoupled with each drive means for independently controlling each drive means in ,accordance with its respective roll signals and its respective repeat-back signal.

6. In a ship stabilization system, a iin, mounting means for supporting said iin on a ship to rotate about an axis extending generally longitudinally of said fin and normally in a generally horizontal direction, drive means coupled with said iin for rotating said iin about said axis, means for supplying a signal proportional to roll rate of the ship, means for supplying a signal proportional to roll accelerations of the ship, means for supplying a signal proportional to the angle of roll of the ship with respect to the apparent vertical, means responsive to iin operation for obtaining a repeat-back signal proportional to the lift exerted by said iin, and control means responsive to all of said signals for controlling said drive means in accordance with the algebraic sum thereof.

7.*In a ship stabilization system, a iin, mounting means for supporting said fin on a ship for rotation about an axis extending generally longitudinally of said iin and normally in a direction substantially at right angles to the longitudinal axis of said ship, drive means connected to said tin for rotating the same about said iin axis, means for supplying signals proportional respectively to the roll angle, roll rate, and roll acceleration of Said ship, first servo means responsive to said signals for supplying a lift command signal proportional to the algebraic sum thereof, a second servo loop responsive to said lift command signal for controlling said iin drive means in accordance therewith, means coupled with said iin for supplying a repeat-back signal in accordance with the lift exerted on said ship by said tin, and means for additionally controlling said second servo loop in accordance with said lift repeat-back signal.

8. Apparatus as set forth in claim 7, wherein said feedback signal further includes a signal which varies in accordance with the displacement of said iin with respect to said ship. l

9. In a ship stabilization system, a lin, mounting means for supporting said tin on a ship to rotate about an axis extending generally longitudinally of said iin and normally in a generally athwartship direction, means for producing a signal in accordance with rolling motions of said ship, a lirst servo loop responsive to said signal for producing a lift command signal, means for limiting the output of said Viirst servo loop whereby to limit the magnitude of said commanded lift signal, drive means having an output coupled with said tin for rotating the same about said axis,fmeans responsive to the operation of said tin for producing a repeat-back signal proportional to the lift exerted on said ship by said iin, a second servo loop responsive to the sum of said lift command signal and repeat-back signal for controlling said drive means in accordance with the algebraic sum thereof whereby to limit the actual lift of said fin to the limited value of said lift command signal.

l0. Apparatus as set forth in claim 9 further including means responsive to the displacementV of said tins with respect to said ship for limiting theY operation of said second servo loop independentlyof said commanded lift signal.

11. In a ship stabilization system, a iin, mounting means for supporting said n on a ship to rotate about an axis extending generally longitudinally of said iin and normally in a generally horizontal direction, means for producing a signal in accordance with rolling motions of said ship, a iirst servo loop responsive to said signal for supplying a lift command signal proportional thereto, means for limiting the maximum value of the output of said iirst servo loop whereby to limit the maximum value of said lift command signal,` drive means having an output coupled with said lin for rotating the same about said axis, means for supplying a repeat-back signal proportional to the lift exerted on said ship by said lin, a second servo loop responsive to said limited command signal and said lift repeat-back signal for controlling said drive means in accordance with the difference therebetween, and means controlled byy said limiting means for varying the ratio of the output of said fin driving means to the value of said lift command signal. l

12. In a stabilization system for ships of the activated iin type, in combination, a hollow housing, having arms arranged generally in the form of a T bearing means for supporting one arm of said' housing in a ship to rotate about a substantially vertical axis, a iin having a trunnion thereon, spaced bearings in the other arm of saidhousing for supporting said. trunnion for rotation about a substantially horizontally axis, drive means coupled with said trunnion for rotating the iin about said horizontal axis whereby to produce lifting couples on said ship through said one arm, and force measuring means within said trunnion for measuring the llexure of said trunnion produced between said support` bearings by the iin lift transmitted thereto.

13. Apparatus as set forth in claim 13 wherein said last-mentioned means comprises a cantilever beam secured at one end thereof to said trunnion adjacent the bearing at one end of said trunnionand the other end thereof terminating adjacent the bearings supporting the other end of said trunnion, and signal generating means coupled .between said trunnion and said other end of said beam for measuring the flexure of said trunnion between said bearings produced by said lifting couples whereby to produce a signal proportional to the lift exerted on said ship by said iin.

14. The combination with a marine vessel of an antiroll fin rotatably supported on said vessel and adapted to extend generally laterally of said vessel and beneath the surface of the water, and fin control means for controlling the rotational position of said iin whereby to control the lift exerted by the fin on said vessel, said control means including motive means connected with said fin for rotating the same, inertial roll-rate responsive means for supplying a primary control signal proportional to the rate of roll of said vessel, servomotor means connected to be controlled by said roll rate signal for rotatably positioning said iin, forceresponsive means coupled with said fin for supplying a force signal proportional to the lift exerted .by said iin on said vessel, and means for feeding said force signal back in controlling relation to said servomotor means in a sense to oppose said primary control signal whereby said iin is positioned such that the detected roll rate is opposed by a substantially equal and opposite induced roll rate thereby to maintain the resultant roll rate of said vessel substantially zero.

15. The combination set forth in claim 14 further comprising pendulous means for providing a secondary control signal in accordance with the magnitude of the deviations of the vertical axis of said vessel from the apparent vertical, and means for additionally supplying said sec- 16 ondary control signal in controlling relation to said servomotor means.

16. The combination set forth in claim 14 further comprising inertial means responsive to roll accelerations of said vessel for providing a further secondary control signal proportional to said roll accelerations, and means for supplying said further secondary control signal to said servomotor means.

17. The combination set forth in claim 14 further comprising signal limiting means responsive to said primary control signal for limiting the maximum value thereof whereby to limit the operation of said servomotor means, and means coupled with said limiting means for varying said maximum limit in accordance with ships speed.

18. The combination set forth in claim 17 further comprising additional limiting means coupled with said iin and responsive to the magnitude of the rotational position thereof with respect to said vessel, and means coupled with said servomotor means and responsive to said additional limiting means for limiting the maximum value of said rotational position of said tinA independently y of said control signal.

19. Apparatus for arresting rolling motions of a marine vessel of the type having an underwater lin adapted upon tilt thereof to exert a roll moment on said vessel when the vessel is under way, said-moment being produced by the force exerted on said iin as a result of the angle of attack thereof relative to the direction of the resultant water velocity adjacent said iin, the direction of said resultant water velocity being dependent on the relative magnitudes of not only horizontal components but alsovertical components of water velocity with respect to said vessel, and drive means for angularly positioning said fin with respect to said vessel, said apparatus comprising, inertia responsive means carried by said vessel for providing a primary control signal proportional to rate of roll of said vessel, control means coupled with said drive means and responsive to said primary control signal for rotationally positioning said iin with respect to said vessel, force responsive means coupled with said iin for producing a force signal proportional to the lift eX- erted on said iin by said resultant water velocity whereby to provide a measure of the angle of attack of said fin with respect to said resultant water velocity, and means for supplying said force signal to said control means in a sense to oppose said primary controlsignal whereby to position said iin with respect to said ship in accordance with the angle of attack of said n with respect to said resultant water velocity and thereby independently of the angular position of said n with respect to said ship.

V2l). In a stabilization system for marine vessels of the activated tin type, the combination comprising a hollow housing having arms arranged generally in the form of a T, a first pair of spaced bearing means for supporting one arm of said housing in the vessel to rotate about a substantially vertical axis, a iin having a trunnion thereon, a second pair of spaced bearings in the other arm of said housing for supporting said trunnion for rotation about a substantially horizontal athwartship axis, drive means coupled with said iin trunnion for rotating the iin'about said horizontal axis whereby to produce lifting couples on said vessel through both of said spaced bearing means, and force measuring means associated with one pair of said spaced bearing means for measuring the magnitude of the couple therebetween produced by the iin lift transmitted therethrough. l

Y 21. Apparatus as set forth in claim 20 wherein said force measuring means includes strain gauge means responsive to flexure of said trunnion between Said second pair of spaced bearing means.

22. Apparatus as set forth in claim 20 wherein said force measuring means includes strain gauge means coupled with one of said first pair of bearings and responsive to the lift force produced therebetween.

23. In a ship stabilization system, the combination com-l prising a iin adapted to be rotated from a stowed position to a rigged-out position and when so rigged-out to be tilted to produce righting couples on said ship when under weigh, a hollow housing having arms arranged generally in the form of a T, one arm thereof supported in a ship for rotation about a substantially vertical axis and having said tin supported in the other arm thereof for tilt about a substantially horizontal axis, tirst motive means coupled between said ship and said housing for rotating said housing about said vertical axis whereby to rotate said iin from a stowed to a rigged-out position and vice versa, and second motive means carried by said housing for rotation therewith and including a fin actuating coupling extending within said housing and engageable with said iin for tilting the same about said horizontal axis, said second motive means including an hydraulic ram secured to and rotatable with said iirst mounting means and having its drive axis coincident with said vertical axis.

24. In a ship stabilization system, the combination comprising a iin adapted to be rotated from a stowed position to a rigged-out position and when so rigged-out to be tilted to produce righting couples on said ship when under weigh, a hollow housing having arms arranged generally in the form of a T, one arm thereof supported in a ship for rotation about a substantially vertical axis and having said tin supported in the other arm thereof for tilt about a substantially horizontal axis, the longitudinal axis of said iin being laterally spaced from said vertical axis, iirst motive means coupled between said ship and said housing for rotating said housing about said vertical axis whereby to rotate said iin from a stowed to a rigged-out position and vice versa, and second motive means carried by said housing for rotation therewith and including a n actuating coupling extending within said housing and engageable with said iin for tilting the same about said horizontal axis, said second motive means including an hydraulic ram secured to and rotatable with said first mounting means and having its drive axis coincident with said vertical axis, said coupling means comprising a connecting rod and crank between said ram and said iin for converting the linear motion of said ram along said drive axis to rotary motion of said tin about said longitudinal axis.

25. In stabilization system for marine vessels of the activated rin type, in combination, a prefabricated box-like structure having top, bottom, and side walls, one of said side Walls having a n receiving opening therein-and adapted to be installed as a unit within the hull of said vessel with said opening on the exterior thereof, a iinsupporting housing having arms arranged generally in the form of a T, bearing means in said upper and lower walls for supporting one arm of said housing to rotate within said box about a substantially vertical axis, a iin, bearing means in the other arm of said housing for supporting said 1in to rotate about a substantially horizontal axis, a first hydraulic ram secured to and rotatable with said housing and having its drive axis substantially coincident with said vertical axis and a crank arm coupled between said ram and said iin for rotating said n about said horizontal axis, a second hydraulic ram means supported on the top w-all of said box-like structure and crank arms secured to said housing and coupled with said second ram means for rotating said housing about said vertical axis whereby to rotate said iin through said opening.

2.6. In a ship stabilization system, a iin, mounting means for supporting said tin on a ship for rotation about an axis extending generally longitudinally of said iin and normally in a direction substantially at right angles to the longitudinal axis of said ship, drive means connected to said iin for rotating the same about said iin axis, means for supplying signals proportional respectively to the roll angle, roll rate, and roll acceleration of said ship, iirst servo means responsive to said signals for supplying a lift command signal proportional to the algebraic sum thereof, a second servo loop responsive to said lift command signal for controlling said iin drive means in accordance therewith, means coupled with said iin for supplying `a rst repeat-back signal variable in accordance with the lift exerted on said ship by said iin, means also coupled with said tin for supplying ya second repeat-back signal variable in accordance with the angular displacement of said iin with respect to said ship, and means for additionally controlling said second servo loop in accordance with said tirst and second repeat-back signals.

References Cited in the tile of this patent UNITED STATES PATENTS 967,565 Rohan Aug. 16, 1910 1,800,408 `Schein Apr. 14, 1931 2,188,834 Fischel et al. Jan. 30, 1940 2,626,114 Alderson Ian. 20, 1953 2,638,288 Hanna May 12, 1953 2,723,089 Schuck et al. Nov. 8, 1955 2,770,429 Schuck et al Nov. 13, 1956 2,809,603 Bell Oct. 15, 1957 2,832,305 Bell Apr. 29, 1958 FOREIGN PATENTS 515,665 France Nov. 27, 1920 581,776 Great Britain Oct. 24, 1946 671,699 Germany Feb. 11, 1939 UNITED STATES PATENT UEEICE eeiirieii eoeemlv Patent No 2,9799010 April llv 1961 Frederick Du Braddon et elil It is hereby certified that error appears in the above numbered patent requiring correction and that the, said Letters Patent should read as A corrected below,

' Column l line 25u for "tloef'U first oeourrehoewread to column ii, line 52 for 'illuetrtaed" read illustrated column 8u line 66g or 'life" read m lift Column 9v line 75, after "looking" insert me of -mg column l0(J line 45V after "centering" insert H- the fin 2O.a Howevery es soon as the iin is so CenteredU en; column l3yI line 57I strike out "said first iin drive means"; Column 15XI line 39Y for the Claim reference numeral "13" read -nl2 wel,

Signed and sealed this 7th day of November 1961.,

(SEAL) Attest:

ERNEST W. SWTDER DAVTD E. LADD Attesting Officer Commissioner of Patens USCGMM-DC

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