Abstract:
The launch and recovery system provides a dive wing and drogue assembly that is towed behind a ship by cables. The dive wing imparts a downward thrust to the drogue, so that the drogue is towed underwater, placing tension on the cables. The cables become stiff due to the speed of the ship and the weight and depth of the dive wing and drogue assembly, so that the cables take on the character of rails. The boat or watercraft to be launched is placed on a sling carriage that is slidably mounted on the cables, so that the sling slides down the cables, launching the watercraft in the stable wake of the ship. The watercraft is recovered by tying a winch cable or line to the watercraft, winching the watercraft back onto the sling, and winching the sling back onto the fantail of the ship.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/680,312, filed May 13, 2005. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for launching and recovering watercraft, and particularly to a launch and recovery system for launching watercraft from, and recovering the watercraft to, a boat or ship while the boat or ship is underway. 
   2. Description of the Related Art 
   For many years, it has been a requirement to stop a ship dead in the water (DIW) to launch watercraft at sea. However, stopping the ship dead in the water causes increased motion as a ship begins to roll in the wave trough while losing underway status. Typically, ships use davits or cranes to deploy watercraft over the ship sides using cable lines, blocks and tackles. When the watercraft are being raised or lowered in the aforementioned manner, motion of the ship is amplified and correspondingly increases the swing of the watercraft as it is suspended from the davits. 
   In rough seas, launching and recovery operations using the aforementioned method becomes more difficult and dangerous. Efforts have been made to develop motion compensation systems for DIW launch and recovery operations, but such compensation systems have not been able to compensate for decreased ship stability during a DIW launch or recovery attempt. 
   When a ship remains underway it is much more stable than in the aforementioned DIW status. Stern wave action is substantially reduced by the ship as it displaces the sea. For example, water skiers and the like are known to move into the flat area of calm sea to the rear of a pulling craft to take advantage of this effect. Similarly, it would be desirable to have a launch system capable of deploying a watercraft into the flat area “sweet spot” behind the ship. 
   During combat, interdiction and coastal patrol ships can easily lose their enemy by having to stop or even slow in order to launch boarding craft, and vessels launching scouting or raiding parties can become exposed to defensive fire by losing headway while making a launch or recovery. Having the ability to launch such craft safely while underway and still at speed could prove extremely valuable in many such operations at sea. 
   Moreover, at sea, rescue operations for seamen or passengers who have fallen overboard are very difficult. A ship is generally required to go DIW to launch a rescue craft with current techniques, which can take considerable time and distance in many instances. Thus, using related art techniques for launch and recovery, a ship&#39;s captain executes a special turn known as a “Williamson Turn” in order to return to the overboard personnel. With aids such as global positioning systems, the location can be accurately determined, but the maneuver can take so much time that a single person lost overboard can still be difficult to locate and especially in strong currents, high waves, etc. Cruise ships may be particularly susceptible to losing passengers who have fallen overboard due to the time required to turn around, get back on course, slow down, and launch a recovery boat. The ability to launch a recovery craft immediately while still underway may therefore prove to be a great benefit to rescue operations. 
   Traditionally, most small boat launches are done over the lee side of the ship. While combat craft have been experimenting with stern launching from ramps in recent years, nevertheless, the ship must still slow down to launch from a ramp. It remains true that the ship is most stable while underway, and the smoothest place near a ship is aft of the ship where the ship has smoothed out the surface wave action by its shear size moving through the ocean. 
   Thus, a launch and recovery system for launching a watercraft from a ship while still underway solving the aforementioned problems is desired. 
   SUMMARY OF THE INVENTION 
   The launch and recovery system provides a dive wing and drogue assembly that is towed behind a ship by cables. The dive wing imparts a downward thrust to the drogue, so that the drogue is towed at a consistent depth underwater, placing tension on the cables. The cables become stiff due to the speed of the ship and the weight and depth of the dive wing and drogue assembly, so that the cables take on the character of rails. The boat, watercraft, or other payload to be launched is placed on a sling carriage that is slidably mounted on the cables, so that the sling slides down the cables, launching the watercraft in the stable wake of the ship. The watercraft is recovered by tying a winch cable or line to the watercraft, winching the watercraft back onto the sling, and winching the sling back onto the fantail of the ship. 
   The system may be modified to use a single tow cable, which tows a pair of drogues. The drogues are towed by separate lines attached to a yoke at the end of the single cable at a point calculated to be just before entry into the water during launch, so that the vessel being launched is clear of the single cable upon entry into the water. 
   The launch and recovery system may be used to launch manned craft of various sizes, unmanned undersea vessels, mine hunting vehicles, emergency rescue craft, and other types of payload. The system may be deployed for military purposes, for commercial enterprises, and for emergency rescue work for cruise ships, fishing trawlers, merchant ships, and the like. 
   In some instances where the cable angle is insufficient for a gravity launch, a secondary drogue device can be used to assist the deployment process. 
   These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is an environmental perspective view of a boat launch and recovery system according to the present invention. 
       FIG. 1B  is an exploded top plan view of a drogue chute in the boat launch and recovery system according to the present invention. 
       FIG. 2  is an environmental perspective view of the dive wing and drogue assembly of the boat launch and recovery system of the present invention. 
       FIG. 3A  is a detailed perspective view of the dive wing of a boat launch and recovery system according to the present invention. 
       FIG. 3B  is a side view of the dive wing of  FIG. 3A , depicting drogue and cable attachment points. 
       FIG. 4  is a perspective view of the sling carriage of a boat launch and recovery system according to the present invention. 
       FIG. 5  is an environmental perspective view of a watercraft after being launched by a boat launch and recovery system according to the present invention. 
   

   Similar reference characters denote corresponding features consistently throughout the attached drawings. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   As shown in  FIG. 1A , the present invention is a launch and recovery system, designated generally as  105  in the drawings. The system includes a dive wing and drogue assembly, including dive wing  125  and drogue  130 , which may be deployed from the stern or other region of a ship  103  or boat by cables  110  (a dual cable system is shown in  FIG. 1A , a single cable system being described below). A sling carriage  115  is slidably mounted on the cables  110 . A boat  120 , craft, or other payload to be launched is supported above, between, or below the cables  110  on the sling carriage  115 . Cables  110  are played out from split or dual drum winches on the fantail until the dive wing  125  and drogue  130  reach the desired depth and angle to tension cables  110  and provide a safe angle of entry of the boat  120  into the water. A sling recovery line  111  is attached to the sling carriage  115 , and is used to haul the sling carriage  115  back onboard after launch of the boat  120  using winch  102 . The split drum winches retrieve the cables  110 , dive wing  125 , and drogue  130  after launch. 
   The system may be modified to a single cable system for launching smaller watercraft or other payload. In a single cable system, a single tow cable  110  tows a pair of small drogues. The drogues are towed by separate lines attached to a yoke at the end of the single cable  110  at a point calculated to be just before entry into the water during launch, so that the vessel being launched is clear of the single cable  110  upon entry into the water. Floats may be used to maintain constant drogue depth. 
   The drogue  130  is a modified trawl-type net composed of a robust, resilient material that can be easily repaired aboard ship. A wide variety of polymeric, elastomeric, or thermoplastic materials, e.g., nylon or Dacron, may be used as material for construction of the drogue  130 . Accordingly, the drogue  130  may be repaired, i.e., by suturing and the like. This may cause some distortion in its shape, but the drogue  130  will still remain hydrodynamically effective as a stable drogue. 
   As shown in  FIGS. 1A ,  1 B, and  2 , the drogue  130  has a front opening  134  and a rear opening  136 , the openings being provided by joining a bottom net  138 , which may be trapezoidal in shape, to preferably two lateral or side nets, each lateral net  140  comprising a bottom net attachment edge  142 , a leading edge  144 , a top edge  146 , and a trailing edge  148 . Preferably, the leading edge  144  of lateral side  140  is swept back towards the rear of the drogue  130 . 
   Additionally, the lateral nets  140  are preferably of the same shape and dimension. The symmetrical design of the lateral nets  140  provides a symmetrical hydrodynamic drag force that advantageously limits oscillations of the drogue  130  during high-speed towing. For ease of use, a netted, mesh design of the drogue  130  is provided so that the drogue  130  may readily dump water and collapse when being hauled out of the water. 
   Preferably the front opening or mouth of the drogue is approximately three square meters or less to produce the required drag force. 
   Thus, according to the present invention, the limited mouth opening is too small to catch most marine creatures. Additionally, the opening at the aft end of drogue  130  is approximately one square meter to further limit any retention of marine life within the drogue  130 . The drogue  130  preferably has an upward sloping side to deter marine animals from entering the drogue  130 . 
   Drogue dimensions may be scaled to fit a particular launch application. However, a ratio of the length  150  of leading edge  144  to the over all length  132  of the drogue  130  is preferably approximately 0.3828. 
   As shown in  FIGS. 3A and 3B , the dive wing  125  is a concave foil including an intermediate component having an intermediate length  306  that laterally spans the bottom corners of the drogue  130  when attached to the drogue  130 . Lateral ends of the concave foil are folded back to form keels  312 . Preferably the fold back angle is approximately 20°. 
   Keels  312  are preferably identical in shape and dimension. Each keel  312  may have a tapered trailing edge. Overall span  304  of the dive wing  125  may be scaled to suit a particular application; however a ratio of overall span  304  to intermediate length  306  is preferably approximately 1.336 to 1. The dive wing  125  may be made of iron, steel, or any other durable, non-buoyant material without regard for minimizing the weight of dive wing  125  because increased weight enhances stability of the system. 
   Hydrodynamic features of the dive wing  125  include as design parameters, for example, angle of attack, degree of wing concavity, foldback angle of keels  312 , and overall surface area of the dive wing  125 . Utilizing well established fluid dynamic principles the dive wing  125  can be parametrically designed to provide a shape that optimizes lift and drag for a given application so that when deployed, the attached cables  110  meet the water behind the ship  103  in a flat, non-turbulent zone behind the wake of ship  103 , and at a useful angle for safe deployment of the watercraft. Exemplary specifications are summarized below: 
   Exemplary Case: 
   Ship 
   Top speed . . . 20 m/sec 
   Bollard pull of 22300 kg at . . . 7.5 m/sec 
   To generate 11000 kg of dive force, 
   Surface area of dive wing at 7.5 m/sec . . . 1.5 to 2.5 m 2    
   Soft Rail Width between cables . . . 3 m 
   Scope Ration . . . 2/1 
   Total length of soft rail line . . . 28 m 
   Tow Speed . . . 7.5 m/sec 
   Tow Point . . . 4 m above water level 
   Point where soft rail enters water . . . 8 m aft of launch point 
   Launch speed . . . 0.50 m/sec 
   Payload . . . 2300 kg 
   Drag . . . 22400 kg 
   Dive Force . . . 13200 kg 
   Dive Force/Drag Ratio . . . 0.59 
   Soft Rail tension . . . 26000 kg 
   Payload to Line tension ratio . . . 0.35 
   Additionally, the dive wing  125  has bilateral attachment points for cables  110  formed by cable attachment plates  305 . Each cable attachment plate  305  has a convex bottom surface  317  that may be welded or otherwise attached to the concave side of the dive wing  125 , preferably in an area of the dive wing  125  that is proximate to a corresponding dive wing keel  312 . 
   As shown in  FIGS. 3A and 3B , each cable attachment plate  305  is anvil shaped, having a concave leading edge  316  which joins the convex bottom surface  317 . The concave leading edge  316  extends to join a concave top surface  318 . The concave top surface  318  tapers to join the bottom surface  317  at a trailing edge of the plate  305 . 
   The cable attachment points  310  have throughbores in a region of the plate  305  that is proximate to where the concave leading edge extends to join the concave top surface. Cable attachment hardware, such as anchor shackles  308 , utilize the throughbores at cable attachment points  310  to provide secure fastening of the cables  110  to the dive wing  125 . 
   A drogue attachment plate  320  has a substantially concave top edge  321  that is welded or otherwise attached to the convex side of the dive wing  125 , and is disposed so that it directly opposes the cable attachment plate  305 . A fin-like bottom surface of the drogue attachment plate  320  may have a convex bottom edge  322 , as it extends below the dive wing  125 . An aft section of the bottom edge  322  joins a drogue attachment plate trailing edge  324  that extends at an angle away from the dive wing  125 . 
   The top edge  321  of the drogue attachment plate  320  extends downward from an upper trailing edge  303  of the dive wing  125  to join the trailing edge  324  of drogue attachment plate  320 . Proximate and parallel to the trailing edge of the drogue attachment plate  320  are a plurality of throughbores  326 , which are provided as attachment points for drogue attachment hardware. 
   The cables  110  are preferably one to two inches in diameter, and may be composed of strands of a durable synthetic polymer, e.g. nylon. Each cable  110  may be custom designed to withstand suitable tensions for any given payload. Braided ropes are preferable because of their resistance to twisting. Synthetic ropes with low elastic elongation do not have severe snap reaction when broken under high loads, enhancing the safety of the launch. Each of these ropes can be easily spliced by experienced personnel on board the launch vessel. 
   Higher strength synthetic ropes have nearly twenty years of working history in fishing fleets and have properties of high strength, high abrasion resistance and low weight, and thus are preferable for use as cables  110 . In particular, the high molecular weight polyethylene ropes marketed under the trade names of Spectra® and Dynema® are suitable for use in the launch and recovery system  105 . 
   Typical rope properties for use as cables  110  preferably include an ultrahigh molecular weight (UHMW) polyethylene composition having a specific gravity of 0.98, a percent stretch at 30% break load of 0.96%, a diameter of fifty-two millimeters, a breaking strength of 186,000 kg, and a weight per length of 162 kg/100 m. 
   Alternatively, the cables  110  may be composed of flexible and resilient stranded wire having similar properties to the aforementioned. A payload to line tension ratio may range up to approximately 0.35. The angle of attack of the cables  110  with respect to the water may range from approximately 30° (scope ratio of 2:1) for the steepest angle to approximately 5° (scope ratio of 11:1) for a shallower angle. 
   The length of lower rigging  127  to the length of upper rigging  126  may preferably approximate a ratio of 0.90. It should be noted that lower rigging  127  comprises a combination of cable tie off to the dive wing  125  and drogue tie off to dive wing  125  at bottom leading edge  142  of drogue  130 . Upper rigging  126  ties off to cable  110  at a point anterior to the dive wing  125  and ties off to top of lateral nets  140  of the drogue  130 . 
   Speed of the ship  103  generates drag on the drogue  130  and dive wing  125 , which develop high tension in the cables  110 . The cables  110  extend a distance dependent upon the launch height above water and the drogue depth while sloping downward behind the ship  103 . In some instances where the cable angle is insufficient for a gravity launch, a secondary drogue device can be used to assist the deployment process. The watercraft  120  is held on the cables  110  by a sling carriage  115 , which is removably attached to, and is capable of riding on, the taut cables  110 . 
   As shown in  FIG. 4 , the sling carriage  115  includes resilient, or alternatively, rigid longitudinal frame members  405 , anterior alignment bar  410 , and a netted or strapped structure  420  that holds the watercraft  120  by friction between the netted structure  420  and the watercraft  120 . Guide rollers  415  having slide bores form a removable attachment to the cables  110 , and are disposed at the corners of the sling carriage  115 . 
   Optionally, the watercraft  120  may be held in place by capture rollers (not shown) disposed longitudinally along the sides of the sling carriage  115 . Deployment of the watercraft  120  is achieved by releasing the sling carriage  115 , which carries the watercraft  120  along the cables  110  and into the water behind the ship  103 . The sling carriage  115  continues underwater where it reaches stops disposed on the cables  110 . Thus, the watercraft  120  is automatically free of the sling carriage  115  when the watercraft  120  hits the water, thereby completing the launch process. According to the present invention, when the payload drop is from four meters above the water, payload trajectory speed may range from approximately twenty meters per second to approximately twelve meters per second, depending upon the payload weight, which may range from under 1,000 kg to over 20,000 kg. 
   Recovery of the watercraft  120  from the water is accomplished by capturing a ball and recovery line  111  that is passed through a guide in the alignment bar  410  of sling carriage  115  and allowed to play out thirty to fifty feet beyond the sling carriage. The end of line  111  is attached to a buoy. The crew of the watercraft  120  retrieve the end of the line  111  from the buoy and secure the captured line to the bow of watercraft  120  at a tow hook  121 . Winch  102  pulls in the watercraft while aligning the watercraft  120  with the sling carriage  115  by means of the guide in alignment bar  410 . The watercraft is pulled back aboard the sling carriage  115 , and line  111  is winched to pull both sling carriage  115  and watercraft  120  back aboard ship  103 . The split drum winches then pull cables  110 , dive wing  125  and drogue  130  back aboard ship  103 . 
   It is within the scope of the present invention that the various aforementioned dimensions and performance limitations of elements of the launch recovery system  105  may be modified by using simulation and analysis software such as, for example, the Numerical Engineering and Modeling of Ocean Systems (NEMOS) published at Illinois Institute of Technology (IIT). 
   Other modeling software allowing for dynamic and non-linear element formulation, large deformations, fluid loading that includes the capability to simulate superimposed waves, current gradient, current shear, and having the capability to subject elements to pressure, wave and current loading may be utilized. 
   It is to be understood that the present invention is not limited to the embodiment described above, but encompasses any and all embodiments within the scope of the following claims.