Abstract:
A water craft includes a tow tower including a tower loop raised and lowered by two linear actuators. The tower loop is firmly supported in the raised position by the linear actuators to provide a proper attachment for towing enthusiasts, and is lowered to allow the water craft to be stored in a normal height garage structure. The linear actuators are unique designs with large shaft diameter, short stroke, and high overlap between the shaft and actuator body, and in particular include novel compressible bumpers to create a compressive jam-lock counterforce at full extension to effectively jam-lock the linear actuator and prevent back creep.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to water sport towing attachments and in particular to a water sport towing attachment which may be lowered automatically using linear actuators. 
   Water sports often involve towing a water sports enthusiast behind a water craft. In some instances, a preferred tow point is high and near the center of the water craft. Unfortunately, a permanent structure of sufficient height will generally interfere with storing the water craft in a residential garage. Known towers extend vertically to between approximately five feet and ten feet above the floor of the water crafts. Folding towers are known which allow the towers to be folded manually, but are difficult to handle. For example, U.S. Pat. No. 6,666,159 for “Water Sport Towing Apparatus,” discloses a tow tower which may be manually pivoted forward against a forward deck of the water craft to provide a lower profile for passing under bridges or into a boat house. While this addresses the height issue, it is often difficult to manually lower the tower of the &#39;159 patent. The &#39;159 patent is herein incorporated by reference in its entirety. 
   Although not directed to lowering a towing tower, U.S. Pat. No. 7,234,408 for “Water Sport Tow Attachment With Recoil,” discloses a tower supported by pneumatic or hydraulic cylinders. The &#39;408 patent uses the cylinders to provide a recoil action in the tower to allow enthusiasts to use stored compressive energy in the cylinders to achieve better jumps and the like. Although the &#39;408 patent does not disclose also using the cylinders to lower the tower for storing the boat in a garage, such lowering might be achieved without significant modifications. However, a tower supported by pneumatic or hydraulic cylinders presents an unacceptable risk of injury if a pneumatic or hydraulic leak or line breakage occurs. Because of the location of the tower, it is likely that the tower would slam down on occupants of the boat. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention addresses the above and other needs by providing a water craft which includes a tow tower raised and lowered by two linear actuators. The tow tower is firmly supported in the raised position by the linear actuators to provide a proper attachment for towing enthusiasts, and is lowered to allow the water craft to be stored in a normal height garage structure. The linear actuators are unique designs with large shaft diameter, short stroke, and high overlap between the shaft and actuator body, and in particular include novel compressible bumpers to create a compressive counterforce at full extension to effectively jam-lock the linear actuator and prevent back creep. 
   In accordance with one aspect of the invention, there is provided a water craft and tow tower. The water craft has a bow, a mid section, and a stern. The tow tower includes a tower support structure firmly attached to the water craft and residing near the mid section of the water craft and a tower loop pivotally attached to the tower support structure by tower pivots and forming a “U” shaped loop, an open end of the “U” to the bow of the water craft. Two lockable linear actuators pivotally attached between the tower support structure and the tower loop, the linear actuators having a retracted position, wherein the tower loop is lowered and in an extended position wherein the tower loop is raised, and wherein the linear actuators jam-lock in the fully extended position until the linear actuators are reversed. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
       FIG. 1A  is a side view of a water craft with a tower loop of a tow tower according to the present invention in a raised position. 
       FIG. 1B  is a side view of the water craft on a trailer with the tower loop of the tow tower according to the present invention in a lowered position. 
       FIG. 2  is a top view of the water craft and tow tower. 
       FIG. 3A  is side view of the tow tower only. 
       FIG. 3B  is a top view of the tow tower only. 
       FIG. 4  is a side view of a linear actuator according to the present invention for raising and lowering the tower loop. 
       FIG. 5A  is a cross-sectional view of the linear actuator taken along line  5 - 5  of  FIG. 4  with an actuator piston in an extended position. 
       FIG. 5B  is a cross-sectional view of the linear actuator taken along line  5 - 5  of  FIG. 4  with the actuator piston in a retracted position. 
       FIG. 6  is a cross-sectional view of an actuator body according to the present invention taken along line  5 - 5  of  FIG. 4  of the linear actuator. 
       FIG. 7  is a cross-sectional view of the actuator piston taken along line  5 - 5  of  FIG. 4 . 
       FIG. 8A  is a cross-sectional view of a second embodiment of the linear actuator taken along line  5 - 5  of  FIG. 4  with an actuator piston in an extended position. 
       FIG. 8B  is a cross-sectional view of the second linear actuator taken along line  5 - 5  of  FIG. 4  with the actuator piston in a retracted position. 
       FIG. 9  is a cross-sectional view of a second embodiment actuator body of the second linear actuator according to the present invention taken along line  5 - 5  of  FIG. 4  of the second linear actuator. 
       FIG. 10  is a partial cross-sectional view of the second actuator body according with a rubber bumper included in an actuator body bushing according to the present invention taken along line  5 - 5  of  FIG. 4  of the linear actuator. 
       FIG. 11  is a partial cross-sectional view of the second actuator body according with a spring included in an actuator body bushing according to the present invention taken along line  5 - 5  of  FIG. 4  of the linear actuator. 
       FIG. 12  is a screw cap of the linear actuator according to the present invention. 
       FIG. 13  is a cross-sectional view taken along line  13 - 13  of  FIG. 12  of the screw cap showing a screw cap bearing according to the present invention. 
   

   Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
   A side view of a water craft  10  with a tower loop  18  of a tow tower  11  according to the present invention is shown in a raised position in  FIG. 1A  and a side view of the water craft  10  on a trailer  28  with the tower loop  18  of the tow tower  11  according to the present invention in a lowered position is shown in  FIG. 1B . The water craft  10  includes a bow  10   a , and mid section  10   b , a stern  10   c , a deck  12 , and a seating area  15 . The tow tower  11  comprises the tower loop  18  and a tower support structure  14  supporting the tower loop  18 . The tower loop  18  is connected to the tower support structure  14  by tower pivots  16  and raised and lowered by linear actuators  20  pivotally connected between the tower support structure  14  and the tower loop  18 . The tower support structure  14  preferably outlines a windshield  13  of the water craft  10  to provide an aesthetic appearance (also see a top view in  FIG. 2 ). 
   The linear actuators  20  are electrically operated preferably using 12 volt Direct Current (DC) power and are preferably controlled using a momentary Double Pole Double Throw (DPDT) switch whereby a user watches the tower loop  18  raise or lower, and releases the DPDT switch when the tower loop  18  is fully raised or fully lowered. The overall height to the water craft  10  and tow tower  11  is reduced by a height H when the linear actuators  20  are fully retracted. The height H is preferably between approximately three feet and approximately five feet and the linear actuators  20  are connected between the tower support structure  14  and the tower loop  18  so that approximately ten inches of linear actuators  20  raises and lowers the tower loop  18 . 
   A top view of the water craft  10  and tow tower  11  is shown in  FIG. 2 . The water craft  10  has a port (or left) side  10   d  and a starboard (or right) side  10   e . The tower support structure  14  includes forward braces  14   a  extending upwards and rearward from the deck  12  approximately leading the leading edge  13   a  (see  FIG. 1A ) of the windshield  13 , and rear braces  14   b  connected to the forward braces and extending rearward and downward to the deck  12  thus forming a four point support structure firmly attached to the water craft  10 . In some instance, backing plates may be used to strengthen the attachment of the tower support structure  14  to the deck  13 . 
   The linear actuators  20  reside at about a 45 degree angle above the horizontal and tilted back when the tower loop  18  is raised, and recline to about a five degree to ten degree angle above the horizontal when the tower loop is lowered. 
   For further clarification, a side view of the tow tower  11  only is shown in  FIG. 3A  and a top view of the tow tower  11  only is shown in  FIG. 3B . 
   A prototype of the tow tower  11  was constructed using known linear actuators. Unfortunately, such known linear actuators were not suitable because they either flexed at full extension, or gradually backed off when subjected to jarring loads experienced by the tower pool  18 . The linear actuator  20  of the present invention was developed to overcome these issues. 
   A side view of the linear actuator  20  according to the present invention for raising and lowering the tower loop  18  is shown in  FIG. 4 . A cross-sectional view of the linear actuator  20  taken along line  5 - 5  of  FIG. 4  with an actuator piston  40  in an extended position is shown in  FIG. 5A  and a cross-sectional view of the linear actuator  20  taken along line  5 - 5  of  FIG. 4  with the actuator piston in a retracted position is shown in  FIG. 5B . A cross-sectional view of the actuator body  30  of the linear actuator  20  taken along line  5 - 5  of  FIG. 4  is shown in  FIG. 6  and a cross-sectional view of the actuator piston  40  taken along line  5 - 5  of  FIG. 4  is shown in  FIG. 7 . For safe operation, the tow tower  11  must be elevated by apparatus which securely holds the tower loop  18  and does not include a failure mode wherein the tower loop  18  may drop rapidly into the seating area  15 . Therefore, hydraulic or pneumatic apparatus for raising the tower loop  18  is not acceptable because a line failure may allow rapid and unexpected lowering of the tower loop  18 . Further, although an electro mechanical apparatus such as a common linear actuator is not likely to allow the tower loop  18  to fall rapidly, the jarring forces exerted on the tower loop  18  while towing an enthusiast tends to result in a gradual lowering the tower loop  18 , which is not acceptable by the enthusiast. 
   The linear actuators  20  according to the present invention include an actuator body  30  and an electric actuator motor  32  residing in a base  30   a  of the actuator body  30 . A rotating externally threaded actuator screw  34  resides in the actuator body  30  and is mechanically connected to the actuator motor  32 , which actuator motor  32  turns the actuator screw  34 . An actuator piston  40  extends from the actuator body  30  and is extendable and retractable from the actuator body  30 . An actuator piston nut  44  is fixed to an inside end  45  of the actuator piston  40  and includes internal threads which threadably engage external threads on the actuator screw for extending and retracting the actuator piston  40 . An actuator piston bushing  42  is fixed to the inside end of the actuator piston  40  to slide on an inside wall  31  of the actuator body  30  and an actuator body bushing  36  is fixed to an actuator body mouth  30   b  opposite the base  30   a , which actuator body bushing  36  includes an inside surface allowing sliding of the actuator piston  40 . An actuator body end cap  48  resides at the base  30   a  of the actuator body and includes a mouth for pivotally attaching to the tower support structure  14 . An actuator piston end cap  46  is attached to the actuator piston  40  opposite the inside end  45  of the actuator piston  40  for pivotally connecting to the tower loop  18 . 
   To address the known issues, the linear actuators  20  according to the present invention include a novel jam-locking feature which prevents a gradual lowering of the tower loop  18  during use. Specifically, the linear actuators  20  include a screw cap  38  which is jammed against the actuator piston nut  44  at full extension of the actuator piston  40 , where at least one of the screw cap  38  and the actuator piston nut  44  having a compressible portion compressed between the screw cap  38  and the actuator piston nut  44  at full extension of the linear actuators  20 , to provide sufficient residual force on the engagement of threads on an actuator screw  34  with the actuator piston nut  44  to prevent the actuator screw  34  from gradually turning and lowering the tower loop  18 . Preferably, the screw cap  38  is made from plastic or is metal with plastic on a surface which contacts the actuator screw nut  44  at full extension of the actuator piston. 
   An overlap distance D between the actuator piston bushing  42  and a forward edge  36 ′ of the actuator body bushing  36  is provided for strength. The distance D is preferably at least five inches and more preferably approximately seven inches. 
   A cross-sectional view of a second embodiment of the linear actuator  20   a  taken along line  5 - 5  of  FIG. 4  with the actuator piston  40  in an extended position is shown in  FIG. 8A , a cross-sectional view of the second linear actuator  20   a  taken along line  5 - 5  of  FIG. 4  with the actuator piston  40  in a retracted position is shown in  FIG. 8B , and a cross-sectional view of a second embodiment actuator body  30 ′ of the second linear actuator  20   a  according to the present invention taken along line  5 - 5  of  FIG. 4  of the second linear actuator is shown in  FIG. 9 . The first linear actuator  20  works well in most instances, but in some instances, the screw cap  38  may wear and result in changes of the friction between the screw cap  38  and the actuator piston nut  44 . In these instances, the release from a fully raised position may not be even, and the tower loop  18  may be twisted. To avoid wear, the second actuator  20   b  replaces the screw cap  38  with an extended actuator body bushing  36   a . At full extension, the extended actuator body bushing  36   a  contacts the actuator piston bushing  42  and some compression results, creating the residual force on the engagement of threads on an actuator screw  34  with the actuator piston nut  44 . Because the extended actuator body bushing  36   a  does not turn, it does not wear and cause changes to tower loop  18  lowering. 
   A partial cross-sectional view of the second actuator body  30 ′ with a two part actuator body bushing  36   c  including a rubber bumper  52  for contact with the actuator piston bushing  42  according to the present invention taken along line  5 - 5  of  FIG. 4  is shown in  FIG. 11 . The rubber bumper  52  is selected to compress to provide a preferred force on the engagement of threads on an actuator screw  34  with the actuator piston nut  44 . 
   A partial cross-sectional view of the second actuator body  30 ′ with a two part actuator body bushing  36   c  and a spring  50  separating the two parts according to the present invention taken along line  5 - 5  of  FIG. 4  is shown in  FIG. 11 . The spring  50  is selected to provide a preferred force on the engagement of threads on an actuator screw  34  with the actuator piston nut  44 . Additionally, a switch  54  may be provided in the linear actuator  20  to cut power to the actuator motor  32  when the linear actuator  20  reaches full extension. 
   A second screw cap  38   a  of the linear actuator  20  according to the present invention is shown in  FIG. 12  and a cross-sectional view of the screw cap  38   a  taken along line  13 - 13  of  FIG. 12  showing a screw cap bearing  56  according to the present invention is shown in  FIG. 13 . The use of a cap screw  38   a  with a bearing  56  reduces or prevents wear of the cap screw  38   a  and thereby provides consistent lowering of the tower loop  18 . 
   The actuator body  30  and the actuator piston  40  are preferably made from aluminum and preferably anodized. The bushings are preferably made from Delrin® plastic material. 
   While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.