Abstract:
A sled includes a hull having opposed first and second side walls. First and second strap anchors are mounted on the respective first and second side walls. A center strap anchor is disposed between the first and second strap anchors.

Description:
FIELD OF INVENTION 
   The invention is directed toward sleds, and in particular, to restraint systems for such sleds. 
   BACKGROUND 
   Known sleds, such as that disclosed in Sellers, U.S. Pat. No. 4,666,171, feature a strap extending transversely across the rider&#39;s knees. Such straps prevent the rider from pitching out of the sled. However, they do little to prevent lateral shifting of the rider&#39;s legs. Such lateral shifting is particularly pronounced during tight turns at high speed. 
   The involuntary lateral shift of the rider&#39;s legs during a turn can skew the sled&#39;s weight distribution. This can lead to loss of control, which at high speed, can be dangerous. 
   SUMMARY 
   In one aspect, the invention includes a sled having a hull having opposed first and second side walls. First and second strap anchors are mounted on the respective first and second side walls. A center strap anchor is disposed between the first and second strap anchors. 
   In one embodiment, the sled also includes a strap extending from the first strap anchor to the second strap anchor. This strap passes through the center strap anchor. 
   In another embodiment, the sled includes first and second straps. The first strap extends from the first strap anchor to the center strap anchor and the second strap extends from the center strap anchor to the second strap anchor. 
   The center strap anchor can take a variety of forms. For example, it can include a bar supported by at least one leg extending from a floor of the hull. Or can be shaped to conform to a rider&#39;s thigh. 
   These and other features of the invention will be apparent from the following detailed description and the accompanying figures, in which: 
   These and other features and advantages of the invention will be apparent from the following detailed description and the figures, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 and 2  are top and side views of a hull for a sled; 
       FIG. 3  is a cross-section of the hull shown in  FIGS. 1 and 2 ; 
       FIGS. 4–6  show a configuration for attaching a strap to the hull; 
       FIGS. 7–10  show sleds having variable-length straps; 
       FIG. 11  shows a sled having a strap configured to secure a rider&#39;s calves; and 
       FIGS. 10–14  show sleds having center anchors. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A downhill racing sled suitable for incorporating the features of the invention is described with particularity in Sellers, U.S. Pat. No. 4,666,171, the contents of which are herein incorporated by reference. 
   As shown in  FIGS. 1–3 , the sled includes a one-piece elongated molded hull  10 , preferably of vacuum-molded thermoplastic. The hull  10  has a bow or front-end, which is on the right as viewed in  FIGS. 1 and 2 , and a stern, or rear-end, which is on the left as viewed in  FIGS. 1 and 2 . Between the bow end and the stern end are a pair of optional contoured shin pads  40  on which a rider kneels while riding the sled. 
   The hull  10  presents a generally crescent-shaped profile, best seen in  FIG. 2 . An upper outwardly rolled molded edge of the hull  10  forms continuous railings or gunwales  12  surrounding the hull  10 . The gunwales  12  are raised at the bow to afford handholds and to protect against the intrusion of snow. The bottom of the hull  10  while generally curved in profile as shown in  FIG. 2 , includes certain features that enhance the sled&#39;s performance in deep snow. 
   Between the two runners  14  and  16 , a main central channel  30  extends along a mid-line of the hull  10  from the bow to the stern with progressively increasing depth as shown in  FIGS. 2 and 3 . The inside ribs  20  and  22  define the edges of the channel  30  and are slightly outwardly flared with gradually increasing spacing at both ends of the hull  10 . Inside the hull  10 , the molded channel  30  forms a large longitudinal central rib or keel-like hump  32  running down the center of the hull  10 . Because of the increasing depth of the snow channel  30  toward the rear of the hull  10 , the hump  32  becomes more pronounced toward the rear as shown in phantom in  FIG. 2 . 
   Referring now to  FIG. 4 , side portions of the gunwale  12  are rolled outward to form a lip  56 . This lip  56  curls downward to form a rim portion  58  parallel to the hull  10  and separated therefrom by a gap  60 . An outboard hole  62  through the rim portion  58  is aligned with an inboard hole  64  through the hull  10 . Molded retaining walls  66 A–B, seem in isometric view in  FIG. 5  flank the inboard hole  64  and extend outward from the hull  10 , part way across the gap  60 . 
   A strap  36  has a grommet  68  at each of its two ends, one of which is shown in  FIG. 6 . To attach the strap  36  to the hull  10 , a grommet hole  70  defined by the grommet  60  is aligned with the inboard hole  64 . Then, a threaded ½ inch bolt  72  is passed through the grommet hole  70  and through the inboard hole  64 . The bolt  72  is long enough to extend through the inboard hole  64  and all the way to the outboard hole  62 . Preferably, the bolt  72  extends approximately 3/16 inches beyond the outboard hole  62  to ensure adequate support by the edge of the outboard hole  62 . 
   A nut  74  is then threaded onto the bolt  72  to secure the bolt  72  to the hull  10 . When the nut  74  is fully tightened, it comes to rest snugly between the retaining fins  66 A–B, as shown in  FIG. 8 . The retaining fins  66 A–B thus limit rotation of the nut  74  in response to torque transmitted by the strap  36 . By doing so, the retaining fins  66 A–B reduce the likelihood that the nut  74  will loosen during use. The nut  74 , the bolt  72 , and the walls forming the inboard and outboard holes  62 ,  64  collectively define a strap anchor  65 . 
   Because of its strength, metal is typically used for making the nut  74  and bolt  72 . However, other materials, such as plastic can be used. 
   A shear force exerted on the strap  36  is transmitted to the hull  10  by the bolt  72 . However, the hull  10  supports the bolt  72  at two different points, namely at the edge of the inboard hole  64  and also at the edge of the outboard hole  62 . As a result, the strap-anchoring configuration shown in  FIGS. 4–6  resists the tendency of the bolt  72  to pivot about a single support in response to a shear force. It does so by resisting shear force using shear resistance provided by the hull  10  at two different support points. 
   By concealing the nut  74  and bolt  72  from view, the rim portion  58  of the lip provides the hull  10  with a more attractive and streamlined appearance. This appearance can be enhanced by coloring the end of the bolt  72  or by extending the end of the bolt  72  slightly beyond the rim portion  58  so it can be capped. 
   In addition, by covering the nut  74  and bolt  72 , the rim portion  58  also prevents the nut  74  and bolt  72  from snagging on nearby objects, such as the rider&#39;s clothing. 
   In one embodiment, the strap  36  has a length that varies in response to the force exerted thereon. An example of such a strap  36  is an elastic strap as shown in  FIG. 7 . Another example is a strap  36  having one or more elastic sections  76 A–B, as shown in  FIG. 8 . In this case, the strap  36  has a pair of inelastic grommet sections  78 A–B that accommodate the grommets  68  and a central inelastic section  80  for securing the rider. Each grommet section  78 A–B is connected to the central inelastic section  80  by a corresponding one of the elastic sections  76 A–B. Yet another example, shown in  FIG. 9  is a strap  36  having a pair of inelastic grommet sections  78 A–B joined by a central elastic section  82 . 
   Preferably, the elasticity of the strap  36 , or the elasticity of an elastic section thereof, is such that the strap  36  changes in length by no more than three inches. A strap  36  that is excessively elastic, in which the length changes significantly, will fail to restrain the rider. A strap  36  that has too little elasticity will be uncomfortable in the presence of high g-forces. 
   The elastic sections can be made of a manufactured fiber in which the fiber-forming substance is a long-chain synthetic polymer comprised of at least 85% of a segmented polyurethane. An exemplary fiber having these properties is presently sold under the name SPANDEX™. The elastic sections can also be made of a manufactured elastic fiber sold under the name SPANDURA™. 
   The inelastic sections can be made of a manufactured fiber in which the fiber forming substance is a long-chain synthetic polyamide in which less than 85% of the amide-linkages are attached directly (—CO—NH—) to two aliphatic groups. An exemplary fiber having these properties is presently sold under the name NYLON™. 
   Another embodiment, shown in  FIG. 10 , features an elastic section  76 A in which the elasticity is provided by a spring  84 . The spring  84  is sheathed by a fabric jacket  86  (opened to expose the spring  84  in  FIG. 10 ) to protect the rider&#39;s clothing from being caught by the spring  84  as it expands and contracts. 
   The longitudinal position of the strap anchor  65  can be chosen so that the strap  36  extends across the hull  10  above the shin pads  40 . In this configuration, the strap  36  extends over the rider&#39;s thighs. However, the strap  36  can also be placed astern of the shin pads  40  so that the strap  36  extends over the rider&#39;s upper calves, as shown in  FIG. 11 . In this latter configuration, the strap  36  secures the rider&#39;s calves and thereby frees the rider from having to ride with fully flexed knees at all times. A rider thus freed is able to kneel erect or partially erect in the sled, thereby enabling the rider to shift the center-of-mass vertically by a distance that corresponds to the difference between the rider&#39;s fully erect position and the rider&#39;s fully crouched position. 
   In  FIG. 11 , the strap  36  can be switched between a rear pair of strap anchors  65  and a forward pair of strap anchors  88  that are structurally the same as the rear pair of strap anchors  65  but positioned over the shin pads  40 . The sled shown in  FIG. 11  is thus convertible between the configuration shown in  FIG. 1 , in which the strap  36  secures the rider&#39;s calves, and a configuration in which the strap  36  secures the rider&#39;s thighs. 
   A disadvantage of having a single strap  36  that extends across the hull  10  is that in sharp turns, both of the rider&#39;s legs are apt to shift laterally. This causes the center-of-mass of the combined rider and sled to also shift laterally. This lateral shift during a turn undermines the stability of the turn and, in extreme cases, can capsize the sled. 
   To avoid this difficulty, another embodiment of the sled features a center anchor  90  at the mid-line of the hull  10 . An exemplary center anchor  90 , shown in  FIG. 12 , is a longitudinally extending horizontal bar  92  supported over the hull by a vertically-extending bow leg  94 A and a vertically-extending stern leg  94 B. The bar  92  and the two legs  94 A–B define an aperture  96  through which a strap  36  extending transversely across the hull  10  passes. When the strap  36  is looped through the center anchor  90 , as shown in  FIG. 12 , the rider&#39;s legs are individually secured. This makes it more difficult for the rider&#39;s legs to shift laterally in a sharp turn. 
   In  FIG. 13 , the single strap  36  extending across the hull  10  is replaced by a pair of straps  98 A,  98 B, each one of which extends from a strap anchor  65  to the center anchor  90 . This embodiment enables the rider to individually adjust the straps  98 A,  98 B. 
   In another embodiment, shown in  FIG. 14 , the center anchor  90  is molded and/or padded to more closely fit the rider&#39;s thighs. This embodiment can be configured to accommodate a single strap  36  looping through an aperture in the center anchor  90  or a pair of straps extending in opposite directions from the center anchor  90  to each of the two sides of the hull  10 . 
   The invention has been described in the context of a specific recreational racing sled. However, the various features of the invention can readily be incorporated other types of recreational sleds.