Abstract:
The lifeboat release mechanism has a hook movably mounted therein. This hook has a concave surface on its lower end. A latch block having a convex surface thereon is also movably mounted therein. In a holding mode, the convex surface of the latch block is laid against the concave surface of the hook. In a release mode, the convex surface is below the concave surface. In a first aspect of the invention, the concave surface extends above and below an axis of rotation of the latch block to prevent an unattended release of the mechanism. In another aspect, the concave surface and the convex surface have a same radius of curvature to prevent localized wear thereon. In a third aspect, the latch lock is rotatable over an angular displacement of 80° between a holding position and a release position, such that the releasing of the mechanism is predictable.

Description:
FIELD OF THE INVENTION 
     This invention pertains to lifeboat release mechanisms, and more particularly it pertains to lifeboat release mechanisms having mating concave and convex parts. 
     BACKGROUND OF THE INVENTION 
     A twin fall davit lifeboat or a totally enclosed motor propelled survival craft is used to evacuate personnel from an offshore oil drilling platform or a marine vessel. This type of lifeboat system has release mechanisms that disengage the lifeboat from the davit lines when the craft reaches or is just above the water. Regulations state that the release mechanisms on a lifeboat must be operable with the full weight of the lifeboat on the davit lines. Although this regulation has been drafted to ensure that a lifeboat will be positively released when the release mechanisms are operated, there has been and continues to be, isolated cases of malfunctions of the release mechanisms, including cases of premature releases at some undesirable distance above the water. 
     Generally, the lifeboat release mechanisms of the prior art have interlocking parts including hooks to which are attached the ropes supporting the lifeboat. These hooks are allowed to pivot in such a way as to release the ropes of the lifeboat upon a rotation thereof from their holding positions. Each hook is held in its holding position by a catch member. In some of the prior art devices, the engagement of the hook with the catch member is very small such that when the catch member is moved even by a slight amount, the hook is released and pivots on itself, thereby releasing the lifeboat line unexpectedly. 
     Examples of lifeboat release mechanisms of the prior art are shown in the following documents:
     U.S. Pat. No. 60,963 issued to James R. Taylor on Jan. 1, 1867;   U.S. Pat. No. 60,964 issued to James R. Taylor on Jan. 1, 1867;   U.S. Pat. No. 60,965 issued to James R. Taylor on Jan. 1, 1867;   U.S. Pat. No. 60,966 issued to James R. Taylor on Jan. 1, 1867;   U.S. Pat. No. 61,279 issued to James R. Taylor on Jan. 15, 1867;   U.S. Pat. No. 61,280 issued to James R. Taylor on Jan. 15, 1867;   U.S. Pat. No. 61,281 issued to James R. Taylor on Jan. 15, 1867;   U.S. Pat. No. 1,030,586 issued to J. Irwin on Jun. 25, 1912;   U.S. Pat. No. 2,618,792 issued to A. Vreugdenhil on Nov. 25, 1952;   U.S. Pat. No. 4,201,410 issued to H. Crawford et al. on May 6, 1980;   U.S. Pat. No. 4,358,146 issued to C. A. Goudey on Nov. 9, 1982;   U.S. Pat. No. 4,610,474 issued to J. Jaatinen on Sep. 9, 1986.   

     In the devices of U.S. Pat. No. 1,030,586 and U.S. Pat. No. 4,358,146, in particular, the catch members are held in a holding position by cams and springs. In another type, as illustrated and described in U.S. Pat. No. 4,201,410, a pair of levers must be pulled in sequence with each other to release the catch member. The device of U.S. Pat. No. 4,610,474 has an hydraulic cylinder which is used to retain a catch member in its holding position. 
     A lifeboat is exposed to sea water and harsh weather conditions. The lifeboat and its release mechanisms are repainted periodically to limit their deterioration by corrosion. During winter, a layer of ice accumulates on every part of a lifeboat and on its release mechanisms. Therefore a release mechanism must be operable when covered with ice, when partly corroded and after having been repainted several times. 
     Because of their exposure to the elements, these lifeboat release mechanisms should not contain small springs, roller bearings, small gears, small levers and pins, sprockets and chains, hydraulic or pneumatic equipment, or other mechanical parts which are susceptible to seize in a corrosive environment or to jam when covered with ice. 
     Another preferred feature of a lifeboat release mechanism is that the engaging surfaces thereof should be as large as possible to prevent wear of its components after several years in service. The engagement surfaces between the latch members and the catch members in the release mechanisms of the prior art are often very small, such as a roller held against a relatively flat surface. A lifeboat suspended to a twin fall davit is often in motion from the force of the wind and the rocking of the vessel to which it is attached. Also, the vibrations of the engine of the vessels and of its propellers are transmitted through the vessel and into the release mechanisms of the lifeboat. These vibrations and the oscillatory motion of the lifeboat eventually wear out the engaging surfaces of the components of the release mechanisms, and where a hard roller bears against a flat surface, a flat spot is formed on the roller, or a notch is formed in the flat surface. It is believed that this type of wear in a lifeboat release mechanism is often the cause of malfunction of the release mechanism. 
     Accordingly, it may be appreciated that there continues to be a need for a new and improved lifeboat release mechanism that has a predictable unlatching movement, that contains no springs or similar small parts and that has large engagement surfaces of its elements to avoid localized wear. 
     SUMMARY OF THE INVENTION 
     The lifeboat release mechanism according to the present invention has a sturdy construction with large engaging surfaces of its elements. The release mechanism is free of small intricate parts susceptible of malfunction when corroded or covered with ice. The unlatching of the release mechanism is effected by turning an actuator with a substantially constant force over a displacement of about one quarter of a turn, thereby providing a predictable release point. 
     In a first aspect of the present invention, there is provided a lifeboat release mechanism comprising a hook having a concave surface on its lower end and a lower tip on this concave surface. A pair of side plates enclose the hook and each side plate has a circular opening there through. A pivot pin extends through the side plates above the circular openings and through the upper end of the hook. The hook is rotatable about that pivot pin from a holding position to a release position. The lifeboat release mechanism also comprises a latch block mounted between the side plates. This latch block has a convex surface thereon facing against a release direction of the lower end of the hook. A pair of bearing discs are mounted in the circular openings of the side plates and are affixed to the latch block. The bearing discs are rotatable in the circular openings about a common axis of rotation. 
     In this first aspect of the present invention, the convex surface of the latch block is mounted against the concave surface of the hook. The concave surface of the hook extends above and below the common axis of rotation of the bearing discs such that a force on the hook is not transferred as a moment on the bearing discs. This feature prevents any unattended unlatching of the release mechanism. 
     In another aspect of the present invention, the concave surface on the hook and the convex surface on the latch block have a same radius of curvature, and a same centre of curvature when the lifeboat release mechanism is in a holding mode. The matched curvatures of both pieces ensure large engaging surfaces between these elements to prevent vibration and oscillation-induced wear of these elements. 
     In yet a further aspect of the present invention, the bearing discs are rotatable to move the latch block from a first position where the convex surface lies against the concave surface for preventing the hook from rotating on the pivot pin, and a second position where the convex surface is below the lower tip of the hook, for allowing a rotation of the hook about the pivot pin. The first position and the second position are about the common axis of rotation of the bearing discs and are separated by an angle of about 80°. 
     Because latches in general, and especially common door latches have door knobs or handles that are rotatable about a 90° angle, and have been like this for as long as one can remember, it is believed that any latching device having a rotary actuator should have a rotation of about one quarter of a turn in order to provide a predictable release point. Therefore the lifeboat release mechanism according to the present invention with its 80° actuator rotation has a release point that is more predictable than some of the release devices of the prior art. 
     This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiment thereof in connection with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One embodiment of the present invention is illustrated in the accompanying drawings, in which like numerals denote like parts throughout the several views, and in which: 
         FIG. 1  is a perspective front and left side view of the lifeboat release mechanism according to the preferred embodiment of the present invention; 
         FIG. 2  is an exploded view the preferred lifeboat release mechanism without the side plates and the safety pin thereof; 
         FIG. 3  is a side view of the preferred lifeboat release mechanism, shown in the holding mode, with the left side plate removed; 
         FIG. 4  is a side view of the preferred lifeboat release mechanism, shown in a released mode, with the left side plate removed; 
         FIG. 5  is an enlarged view of the latch block and the hook heel in an intermediate position between a holding mode and a released mode; 
         FIG. 6  is an enlarged view of the latch block and the hook heel in an unlatching mode; 
         FIG. 7  is an enlarged view of the latch block and the hook heel in a released mode; 
         FIG. 8  is a vectorial representation of the clearance between the latch block and the lower tip of the hook heel. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will be described in details herein one specific embodiment, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and is not intended to limit the invention to the embodiment illustrated and described. 
     The preferred lifeboat release mechanism  20  is illustrated in its entirety in  FIG. 1  while the illustrations of  FIGS. 2-4  are provided to explain the interaction of the various structural elements thereof. 
     The lifeboat release mechanism has a pair of side plates  22 ,  24  that are fastened to a lifeboat by way of a flange  26  on each side plate. Although a pair of holed flanges  26  are suggested to fasten the release mechanism to a lifeboat by bolts (not shown), it will be appreciated that other attachment means can also be used, depending upon the structure of the lifeboat. The side plates  22 ,  24  are held in a spaced apart relationship by a front spacer  28 , and a similar rear spacer  30  which is partly visible in  FIGS. 3 and 4 . Both spacers  28 ,  30  are welded or bolted to the side plates  22 ,  24  as to form with the side plates, a permanent box-like structure. 
     The spacers  28  and  30  are referred to herein above as the front and rear spacers respectively, to facilitate the description of the preferred release mechanism. The same convention is maintained throughout the present disclosure. 
     A hook  32  is mounted between both side plates  22 ,  24  and is pivoted to the side plates on a pivot pin  34  extending through both side plates. The pivot pin  34  is held axially to the side plates by snap rings, collars or otherwise (not shown). The pivot pin  34  extends through the hook  32  on the rear side of the throat  36  of the hook such that an upward force in the throat  36  of the hook causes a moment about the pivot pin  34  to swing the throat  36  of the hook upside down about the pivot pin  34  when the mechanism is released. In use, the davit lines are attached to the hooks  32  as in other conventional lifeboat release mechanisms. Additional holes  38  are provided in the side plates  22 ,  24  to retain a safety rope thereto if desired. 
     The preferred lifeboat release mechanism  20  also has a safety pin  40  extending through both side plates  22 ,  24  and through a hole  42  in the body of the hook  32 . This safety pin  40  is removably mounted through holes  44 , as shown in  FIG. 4 , in the side plates and through the hook. The safety pin  40  has a handle  46  thereon for affording an easy removal thereof prior to unlatching the release mechanism. 
     The preferred lifeboat release mechanism  20  is characterized mainly by its latching elements. These latching elements are comprised of the hook&#39;s heel  50 , a pair of bearing discs  52 ,  54  which are pivoted to the side plates, and a latch block  56  mounted between the bearing discs  52 ,  54 . 
     Each of the bearing discs  52 ,  54  has a circular shoulder  58  thereon, and the side plates  22 ,  24  have circular openings therein to receive these circular shoulders with a free sliding fit, such that the circular shoulders  58  constitute bearing surfaces on which the discs can rotate. Both side plates  22 ,  24  have a same thickness and the thickness of each circular shoulder  58  is slightly more than the thickness of the side plates  22 ,  24 . 
     The latch block  56  is fastened to the bearing discs  52 ,  54  by two bolts  60 , one of which is illustrated in  FIG. 1 , extending though bolt holes  62  through the bearing discs  52 ,  54  and bolt holes  64  through the latch block  56 . The thickness of the latch block  56  is slightly more than the thickness of the hook  32 , such that the hook  32  is free to move between the bearing discs  52 ,  54 . 
     The latch block  56  is further held in a precise position relative to the bearing discs  52 ,  54  by means of a pair of keys  66 , one of which is seen in  FIG. 2 , protruding from the inside surface of the bearing discs  52 ,  54 , and corresponding inside keyways  68  in the sides of the latch block  56 . 
     An outside keyway  70  is machined on the outside surface of one of the bearing discs, and an outside key  72  is mounted in this keyway  70 . A lever  74  or other torque transmission means is fastened to the outside key  72 , to rotate the bearing disc  52  and to operate the release mechanism. In use, the lever  74  is attached to a rod or a rope that extends to a location in the lifeboat that is easily accessible to the occupants of the lifeboat, as in other conventional lifeboat release mechanisms. 
     Referring now to  FIGS. 3-8 , the characteristics of the preferred lifeboat release mechanism  20  will be explained in greater details. 
     The heel  50  of the hook has a concave surface  80  thereon and the latch block  56  has a convex surface  82 . The concave surface  80  of the hook&#39;s heel  50  and the convex surface  82  of the latch block have a same radius of curvature and share a same centre of curvature when the release mechanism is in a latched or holding mode, as illustrated in FIG.  3 . The advantage of this arrangement is that the lifeboat release mechanism  20  can withstand years of vibration and oscillation without having a notch or a flat spot worn out on the engaging parts thereof. 
     The concave surface  80  of the heel  50  has a lower tip  84  that extends slightly below the axis of rotation  86  of the bearing discs  52 ,  54 , as illustrated in  FIGS. 3 ,  5 ,  6  and  7 . This lower tip  84  extending below the axis of rotation  86  prevents a force on the hook from being transmitted as a moment on the latch block  56 . 
     The latch block  56  is fastened to both bearing discs  52 ,  54  such that the axis of rotation  86  of the bearing discs  52 ,  54  is located along a line passing through the midpoint of the convex surface  82 , and the centre of curvature  88  of this convex surface  82 . The axis of rotation  86  of the bearing discs  52 ,  54  is further located at a distance ‘A’ from the centre of curvature  88  of the convex surface  82  as illustrated in FIG.  7 . The distance ‘A’ is longer than the radius of curvature ‘B’ of the latch block  56 , by an offset dimension ‘C’ which corresponds substantially to the extent at which the lower tip  84  of the heel projects below the axis of rotation  86  of the bearing discs  52 ,  54 . 
     It will be appreciated that the unlatching of the release mechanism is effected by rotation of the bearing discs  52 ,  54  and the latch block  56  about the axis of rotation  86  in the direction of angle ‘D’ as illustrated in FIG.  6 . During the rotation of the latch block  56 , the midpoint of the convex surface  82  slides around the tip  84  of the heel  50  to release the hook  32 . The hook  32  is then free to pivot about the pivot pin  34  in a release direction  90  opposite the direction of the angle ‘D’, to release the davit line from the throat  36  thereof. 
     Theoretically, if the offset dimension ‘C’ corresponds exactly to the extent at which the tip  84  of the heel  50  projects below the axis of rotation  86  of the bearing discs  52 ,  54 , the angle ‘D’ of rotation required to release the hook  32  would be exactly one quarter of a turn. However, in practice, it is desirable to incorporate a clearance ‘E’ between the tip  84  of the hook and the convex surface  82  to prevent any binding of these parts and to ensure a failsafe operation of the release mechanism in all operating conditions. On the other hand, the introduction of a clearance as mentioned above reduces the angular displacement ‘D’ required to unlatch the release mechanism. It is believed that an unlatching of the mechanism upon a rotation of the lever  74  that is substantially less than a quarter of a turn would be considered as an unpredictable release. Therefore there is an incentive to maintain the release angle, as mentioned before, as close as possible to one quarter of a turn. 
     It has been found that a clearance ‘E’ should be determined so that an angular displacement ‘D’ to release the hook  32  is about 80° or slightly more. This angular displacement ‘D’ has been found to be advantageous for providing sufficient clearance for a safe operation of the release mechanism while maintaining the release point at a predictable angular location. 
     The preferred method to calculate the clearance ‘E’ between the lower tip  84  of the hook&#39;s heel  50  and the convex surface  82  of the latch block  56 , is by using the expression ‘E’=‘C’ minus (‘C’×Sine 80°), as illustrated in FIG.  8 . 
     The preferred radius of curvature ‘B’ of the convex surface  82  is 2.0 inches. The preferred thickness of the latch block  56  is about 1.61 inches. The preferred offset dimension ‘C’ is about 0.120 inch and the preferred clearance ‘E’ is about 0.002 inch. These dimensions can be extrapolated to manufacture release mechanisms of various sizes. The material of construction of the preferred lifeboat release mechanism is type 316 stainless steel. 
     It will be appreciated that because the convex surface  82  rolls against the lower tip  84  of the hook with a contact point being relatively close to the axis of rotation  86  of the bearing discs  52 ,  54 , the unlatching of the mechanism  20  is effected without effort, and the hook  32  is retained firmly in a same position until the release angle ‘D’ has been reached. 
     As to other manner of usage and operation of the present invention, the same should be apparent from the above description and accompanying drawings, and accordingly further discussion relative to the manner of usage and operation of the invention would be considered repetitious and is not provided. 
     While one embodiment of the present invention has been illustrated and described herein above, it will be appreciated by those skilled in the art that various modifications, alternate constructions and equivalents may be employed without departing from the true spirit and scope of the invention. Therefore, the above description and the illustrations should not be construed as limiting the scope of the invention which is defined by the appended claims.