Abstract:
The stern hull portion of a sea craft through which main exit flow channels extend to projecting jet propulsion nozzles, is provided with facilities for controlled maneuvering of the sea craft, including steering, stopping, negative thrust backing and docking without substantial hydrodynamic loading and with facilitated installation. Such maneuvering control facilities include a secondary flow channel extending from each of the main exit flow channels having two angularly related subchannel branches for pressurized water outflow through gated openings in the hull from which propulsion jets emerge under maneuvering control. Either control of a subchannel diverting flapper, or by use of selective closure gates and a flow diverting flap within the main exit flow channel, maneuvering may be effected in response to inflow through inlet openings in the hull of water that is pressurized before supply to the main exit flow channels.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore. 

   The present invention relates to the maneuvering of sea craft having water jet propulsors. 
   BACKGROUND OF THE INVENTION 
   Water jet propulsion of marine vessel hulls as compared to screw propeller systems are more flexible in usage, involve less mechanical equipment for hull installation and provide for improved maneuverability of the ship being propelled. Conventional maneuvering systems for water jet propulsors include water intake motors and pumps for water inflow through hull inlets and accelerated nozzle outflow of the propulsion jets above the hull waterline. Heretofore commercial ships with such water jet propulsors utilized jet deflecting buckets, sleeves and vanes for effective steering and backing purposes, involving above water jet discharge. 
   According to U.S. Pat. No. 6,171,159 issued January 2001 to Shen et al., surface ships propelled by underwater jet discharge are provided with steering and backing types of maneuvering systems, not suitable however for a submerged sea craft. It is therefore an important object of the present invention to provide for simplified and efficient controlled maneuvering of a submerged sea craft with water jet propulsors, involving steering, backing and stopping operations. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, all maneuvering operations of an underwater jet propulsion system are performed by selectively controlled diversion of pressurized water through main water flow channels into secondary flow channels past flow smoothing vanes for controlled outflow discharge as the propulsion jets emerging from openings in the hull in one direction perpendicular to the hull centerline for steering purposes and in another direction at an acute negative thrust angle for backing and stopping purposes. Such directional outflow discharge jets are conducted to the hull openings from the secondary channels through subchannel branches under selective control of either closure gates at the hull openings or hinged juncture flow diverting flappers between the subchannels branches. 

   
     BRIEF DESCRIPTION OF THE 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 partial side elevation view of the underwater stern portion of a sea craft hull with jet propulsion and maneuvering facilities positioned thereon; 
       FIG. 2  is a section view taken substantially through a plane indicated by section line  2 — 2  in  FIG. 1 ; 
       FIG. 3  is a partial section view taken substantially through a plane indicated by section line  3 — 3  in  FIG. 2 , illustrating craft maneuvering control facilities enclosed within the sea craft hull; 
       FIGS. 3A ,  3 B and  3 C are partial section views similar to that of  FIG. 3 , showing different phased operational conditions of the maneuvering control facilities; 
       FIG. 4  is a partial section view taken substantially through a plane indicated by section line  4 — 4  in  FIG. 3 ; 
       FIG. 5  is a diagram illustrating a water jet propulsion and maneuvering control system associated with the sea craft shown in  FIGS. 1–4 , in accordance with the present invention; 
       FIG. 6  is a partial section view corresponding to that of  FIG. 3 , showing an alternative embodiment of the present invention; 
       FIG. 7  is a partial section view corresponding to that of  FIG. 3 , showing yet another alternative embodiment of the present invention; 
       FIGS. 7A and 7B  are partial section views similar to that of  FIG. 7 , showing different phased operational conditions of the maneuvering control facilities; and 
       FIG. 8  is a partial section view taken substantially through a plane indicated by section line  8 — 8  in  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawing in detail,  FIGS. 1–4  illustrate the stern portion of an underwater submerged ship or sea craft  10  having a generally conical-shaped hull  12  enclosing a ballast tank therein. The craft  10  is propelled in a forward direction by water jet propulsion on the stern portion of the hull  12  as generally known in the art, involving four (4) main tubular water outflow channels  14  extending from propulsors as disclosed for example in U.S. Pat. No. 6,171,159 to Shen et al. The channels  14  extend through the stern portion of the hull  12  in parallel spaced relation to the hull centerline  18 . Stern outflow nozzles  20  at the ends of the channels  14  project from the hull  12  for emergence of propelling water jets  22  as shown in  FIG. 1 . Conventional rudders  24  are mounted on and project from the hull  12  between the main channels  14 , spaced forwardly of the nozzles  20  along the hull centerline  18 . 
   The foregoing referred to jet propulsion system for the sea craft  10 , with which the four main water outflow channels  14  are associated, includes water inlets  26  on the hull  12  located adjacent to motor driven pump units  28  as shown in  FIG. 1  for pressurizing water received within the channels  14  so as to emerge from the stern nozzles  20  as the propulsion jets  22 . A pair of outflow gates  30  and  32  are formed in the hull  12  in alignment with each of the main channels  14 , pursuant to the present invention as hereinafter explained. 
   Referring now to  FIGS. 2–4 , positioned within the stern portion of the hull  12  between each of the four main flow channels  14  and an associated pair of the gates  30  and  32  aligned therewith is a secondary flow channel  42  which is connected to the main channel  14  at an opening  44  formed therein. Positioned within a streamlined convergent inlet section of the secondary flow channel  42  adjacent the opening  44  are guide vanes  46  for smoothing water inflow. An angularly related subchannel branch  48  extends from the secondary flow channel  42  into a sidewall outlet  50  projecting inwardly from the hull  12  at an acute angle to the centerline  18  as shown in  FIG. 3 . The gate  30  is hinged to the hull  12  within the outlet  50 , while the other gate  32  is hinged to the hull  12  at a sidewall outlet  52  into which a subchannel branch  49  extends from the secondary channel  42 . Also hinged to the main channel  14  at the opening  44  therein is a flap  54  pivotally connected to an actuator  56 . 
   As also shown in  FIG. 3 , pressurized water flow is confined to each of the main channels  14  when the openings  44  associated therewith are closed by the flaps  54  for emergence of the water propelling jets  22  from the nozzles  20 . With both of the gates  30  and  32  closed, straight course normal propulsion of the hull  12  is effected by the jets  22  in the direction of the centerline  18  without any hydrodynamic impact. 
   Under zero or low speed conditions the gate  32  is rotated about its hinge  55  into the hull  12  to open the outlet  52  as shown in  FIG. 3A , while the flap  54  is displaced about its hinge  57  to a position fully blocking exit outflow from the end nozzle  20 . Flow is then diverted by the flap  54  from the main channel  14  into the secondary flow channel  42  through the opening  44 . Exit jet flow from the hull  12  then occurs through the secondary channel  42  and the branch  49  past the opened gate  32  for emergence from the outlet  52  as a jet  58  in a direction perpendicular to the centerline  18  to produce side force and turning moment on the hull  12  for ship steering purposes. The guide vanes  46  smooth such flow from the main channel  14  into the secondary channel  42 . The differential pressure on the gate  32  is small, so that the force required to open and close the gate  32  is small. Since the exit jet vector  58  associated with outflow past the opened gate  32  is perpendicular to the ship centerline  18  as indicated in  FIG. 3A , a large steering moment arm is obtained for efficient ship steering and docking. 
   As shown in  FIG. 3B , the flap  54  is rotated into the main channel  14  to a position at an angle β between the channel side wall and the flap  54  so as to divert only a portion of the main channel flow into the secondary channel  42  during travel at forward speeds. A diverted flow portion Q s  in the secondary channel  42  then exits therefrom past the opened gate  32  for steering purposes. The flow portion Q m  continuing through the main channel  14  past the flap  54  will then exit the nozzle end  20  for forward motion propulsion of the hull  12 . The leading edge  55  of the flap  54  is rounded so as to improve hydrodynamic performance. There is a relationship between channel branch flows Q s  and total main channel flow Q t  denoted as Q s =Q t −Q m , where the flap angle β and the flow portion Q m  may be varied to provide the desired design speed and steering capability. 
   Referring now to  FIG. 3C , it denotes an acute angle γ between flow through the subchannel branch  48  and the hull centerline  18 , corresponding to that of a negative backing thrust (F) induced by an outflow jet  60  from the outlet  50  at a jet velocity (V j ) past the gate  30  opened by inward displacement into the hull  12  for backing and stopping purposes under low speed conditions. Negative thrust (F) for backing purposes, is reflected by the equations F=ρQV j Cosγ=ρQ 2 A j Cosγ. Maneuvering control is exercised in accordance with the foregoing relationships between flow, speed and thrust, as well as water density (ρ), flow rate (Q), jet velocity (V j ) and flow area (A j ) of the outlet  52  at the exit gate  32 . 
   As diagrammed in  FIG. 5 , the pump units  28  are driven by reversible motors  34  while the gates  30  and  32  as well as sidewall flaps as hereinafter described are displaced under control of a maneuvering control network  36 . Operation of the pump motors  34  and the control network  36  for maneuvering of the craft  10  as hereinbefore explained is effected by an electric power supply  38  through a switching control system  40  of the propulsion system. 
   Referring now to  FIG. 6 , a modification of the embodiment illustrated in  FIGS. 1–5  is shown, wherein the gate  30  is replaced by a gate  30 ′ hinged to the hull  12  radially outward of an inclined sidewall outlet  50 ′ opened by rotation of the gate  30 ′ outwardly from the hull  12 . The advantage of such location gate  30 ′ is that it may be angularly adjusted to directionally regulate the outflow of a jet  60 ′ for backing and stopping purposes. 
   According to the embodiments of the present invention as hereinbefore described, the pair of gates  30  and  32  or  30 ′ and  32  are provided on the surface of the hull  12  for use in association with each of the four main flow channels  14 . According to yet another embodiment as illustrated in  FIGS. 7 and 8  only one gate  62 , larger than the gates  30 ,  30 ′ and  32 , is provided on the stern portion surface of the hull  12  for use with each main flow channel  14 . The gate  62  is directly hinged to the hull  12  on top of an outlet  64  through which an exit jet  66  emerges in a direction perpendicular to the hull centerline  18  for steering maneuver purposes. The secondary channel  42  with the guide vanes  46  therein is provided at the opening  44  in the main flow channel  14 ; with the side wall flap  54  hinged for angular displacement between positions as hereinbefore described. However pursuant to the embodiment shown in  FIG. 7 , two outflow subchannels branches  68  and  70  are connected to the secondary channel  42 , with a flapper  72  hinged at a juncture between the subchannel branches  68  and  70  to directionally control flow into one of the subchannel branches  68  and  70  to the hull opening outlet  64 . The flap  54  is rotated to the fully closed position while the gate  64  is rotated to a fully closed position by an actuator  74  for normal operation. 
   When steering is needed under a zero or low speed condition, such as a docketing maneuver, the gate  62  is in the fully opened position for outflow of the exit jet  66  from both of the subchannel branches  68  and  70 , with the flapper  72  positioned between the subchannel branches  68  and  70 . With the flapper  72  closing the subchannel branch  70  as shown in  FIG. 7A , flow is then diverted only through the subchannel branch  68  in a direction perpendicular to the hull centerline  18  to thereby effect outflow of the steering control jet  66  from the hull opening outlet  64  during forward speed of travel, with the control flap  54  rotated to the acute angle (β) position shown to only direct a portion of flow through the main channel  14  into the secondary channel  42 . 
   For backing and stopping purposes the flapper  72  is rotated to the position shown in  FIG. 7B  totally diverting flow from the secondary channel  42  into the curved subchannel branch  70 . Outflow of the jet  66  is then directed from the branch  70  through the hull opening outlet  64  at an angle γ, while flow to the nozzle  20  is blocked by the flap  54 . 
   Obviously, 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.