Abstract:
Depressors mounted on the stern of a marine vessel are deployed by displacement from positions retracted from the seawater to positions immersed therein so as to divert exit flow of the seawater along retarded flow paths from the stern during vessel travel. Such deployment of the depressors is regulated under motion stabilizing control to produce corrective roll and pitch inducing forces on the vessel in response to diversions of the exit flow by the depressors.

Description:
The present invention relates generally to stabilizing motions such as roll and pitch imparted to marine vessels during seawater travel. 
     BACKGROUND OF THE INVENTION 
     Marine vessels such as naval ships often slow down during travel in rough seas so as to reduce seawater wave induced motions such as roll and pitch, because excessive amounts of such motions may seriously degrade combat readiness, adversely affect performance of on-board systems such as weapons and have other deleterious affects. Various methods have therefore been developed to reduce roll and pitch including use of active devices. Such active devices applied for example to fins, gyros, tanks and rudders often introduce cavitation, vibration and tip vortex problems at high travel speeds. It is therefore an important object of the present invention to provide active devices for inducing corrective roll and pitch motions on marine vessels during seawater travel under rough wave conditions for motion stabilization purposes without introducing the problems heretofore experienced. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a motion stabilizer system includes a pair of depressors in sliding contact with each other disposed on the stem of a marine vessel between the port and starboard sides thereof, for displacement between positions retracted from the seawater and deployed positions immersed therein. Lower end portions of such depressors immersed in the seawater in the deployed positions divert and smooth exit flow of the seawater from the stem between side plates along curved flow path surfaces during vessel travel. Such diversion of the exit flow increases dynamic forces heretofore induced by such exit flow. One of such depressors, on either the port or starboard side, is deployed by an appropriate distance into the seawater under motion stabilization control to produce increased hydrodynamic forces in response to correspondingly diverted exit flow of the seawater from the stem for imparting corrective roll on the vessel in one angular direction to cancel roll otherwise imparted by the seawater under rough wave conditions. Both of the depressors are simultaneously deployed on the other hand under stabilization control for immersion into the seawater by some other appropriate distance to produce hydrodynamic forces in response to exit flow which impart corrective pitch on the vessel for cancellation of pitch otherwise resulting from seawater flow under rough conditions. 
    
    
     BRIEF DESCRIPTION OF DRAWING 
     A more complete appreciation of the invention and many of its attendant advantages will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein: 
     FIG. 1 is a side elevation view of a portion of a marine vessel during seawater travel having a stern mounted depressor type motion stabilization system in accordance with one embodiment of the present invention; 
     FIG. 2 is an end view of the vessel shown in FIG. 1, illustrating a pair of depressors associated with the motion stabilizer system in retracted positions; 
     FIG. 3 is an enlarged partial side elevation view, similar to that of FIG. 1 showing the depressors of the motion stabilizer system in a deployed position immersed in the seawater; 
     FIG. 4 is an end view corresponding to that of FIG. 3, showing both of the depressors in the deployed position immersed in the seawater; 
     FIG. 5 is an end view showing one of the depressors in the deployed position immersed in the water an appropriate distance for achieving roll stabilization; 
     FIG. 6 is an end view showing both of the depressors in deployed positions immersed in the seawater by an appropriate distance for achieving pitch stabilization; 
     FIG. 7 is a partial side elevation view similar to that of FIG. 3, illustrating another embodiment of the motion stabilizer system featuring a modified form of depressor; and 
     FIG. 8 is a partial side elevation view similar to that of FIG. 3, illustrating yet another embodiment of a motion stabilizer system. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawing in detail, FIG. 1 illustrates a transom portion of a marine vessel  10 , having an end stern  12  to which is attached a motion stabilizer system generally referred to by reference numeral  14 . Such stabilizer system  14  as shown in FIG. 1 is retracted relative to a surface  16  of a body of seawater  18  on which the vessel  10  is floatingly supported during normal operational travel. In such retracted condition of the stabilizer system  14 , flow of water from the stem  12  occurs without disturbance from a lowermost exit end  20  of the system  14  at a level  22  of the water surface  16 , closely spaced rearwardly from the intersection  24  between the stern  12  and the slope of a surface  26  of the vessel buttock  28 . 
     As shown in FIG. 2, the system  14  includes a pair of depressors  30  and  32  having lower end portions  31  in sliding contact with each other to accommodate relative vertical displacement during deployment from their retracted portions as hereinafter explained. Plates  33  attached to the lower end portions  31  of the depressors project into the seawater. Displacement is imparted to the depressors  30  and  32  through actuators  34  extending into the vessel  10  to a hydraulic or electrical control  36  as diagrammed in FIG.  1 . 
     Referring now to FIG. 3, the starboard sided one of the depressors  32  is shown deployed into a position relative to the water  18  to thereby retard and divert exit flow from the water surface level  22  around the stem  12  between side plates  33  from intersection  24  with the slope of the buttock surface  26  to the lowermost exit flow end  20  of the deployed depressor  32 . The depressors  30  and  32  are fitted with such side plates  33  to enhance generation of hydrodynamic force induced by water exit flow. The rearwardly facing surface  38  of the depressor  32  or  30  between the intersection  24  and the exit flow end  20  is curved to insure smoothing of the retarded exit flow along a stern wave path extending from the intersection  24  below the water surface level  22 , as depicted in FIG. 3, to increase hydrodynamic pressure distributed over the surface  26  of the buttock  28  and thereby provide a resultant force (F) as a function of several variables including the slope angle of the buttock surface  26 , vertical depressor deployment distance (h) between the water surface level  22  and the exit flow line  20 ; and the thickness (t) of the depressor  32  or  30 . One or both of the depressors  30  and  32 , as shown in FIGS. 4 and 5, may be downwardly deployed into the water  18  during vessel travel by vertical displacement below the water surface  16  corresponding to the deployment distance (h). 
     FIG. 5 shows deployment of one of the depressors  32  a distance (hr) into the water  18  for roll-stabilization purposes. Thus, a force (F) as a function of (hr) is hydrodynamically produced in an upward direction on the starboard side of the vessel  10  during travel as a result of the exit flow diversion, as hereinbefore pointed out with respect to FIG.  3 . At the same time, a downward hydrodynamic force is produced by exit flow on the port side of the vessel  10  as shown in FIG. 5, where the depressor  30  is retracted. Such upward and downward forces in 180° directional phase relation to each other on the port and starboard sides of the vessel  10  adjacent its stem  12 , is induced under controlled deployment of the depressors  30  and  32  by means of the control  36  to impart a desirable roll moment to the vessel  10  used to cancel roll moment induced by incoming waves, and thereby effect roll stabilization. 
     FIG. 6 shows synchronized deployment of both of the depressors  30  and  32  a distance (hp) by means of the control  36  for pitch stabilization purposes. The increase in dynamic forces thereby created under diverted exit flow at locations on both the starboard and the port sides of the buttock  28  results in a pitch moment as a product of the increase in forces and the distances from the buttock locations thereof to the center of gravity of the vessel  10 . Operation of the control  36  to provide such simultaneous in phase deployment of both of the depressors  30  and  32  by the appropriate distance (hp), will accordingly generate and impart a maximized pitch moment to the vessel  10 , canceling pitch movement otherwise imposed by the seawater during vessel travel, to effect pitch stabilization. 
     The cross-sectional profiles of the depressors  30  and  32  through which the desired hydrodynamic performance is achieved under regulation of the control  36  as hereinbefore described may be varied as illustrated for example in FIG.  7 . Exit flow as shown in FIG. 7 is diverted by a depressor  30 ′ modified along an extended smoothing flow path formed by a rearwardly facing curved surface  38 ′. 
     According to yet another embodiment as illustrated in FIG. 8, the depressors  30  and  32  as hereinbefore described with respect to FIGS. 1-6 are respectively replaced by depressor plates  40  pivotally connected to the vessel  10  at stern intersection  24  by hinges  42 . The depressor plates  40  accordingly undergo arcuate displacement from positions aligned with the water line level  16  to deployed positions as shown in FIG. 8 causing diverted exit flow of the seawater similar to that described with respect to FIG.  7 . Displacement of the depressors plates  40  is effected by a suitably controlled actuator device  44  attached to and projecting rearwardly from the stern  12 . Curved actuator rods  46  attached to the depressor plates  40  therefore extend through the actuator device  44  for imparting displacement to such depressor plates  40 . 
     Obviously, still other modifications and variations of the present invention may be possible in light of the foregoing teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.