Wakeboard Release Mechanism

Abstract

Wakeboarding causes a large number of knee injuries, especially to the ACL. These injuries occur from large tensile, compressive and rotational forces on the knees. Rotational and compressive forces cause meniscus tears. Rotation and tensional forces lead to ACL tears. Knee injuries may be prevented by releasing both feet from the board simultaneously at a force lower than the ultimate strength of the ligaments in the knee. This novel device releases both feet within 0.25 of a second at a force under 268 lbs.

Description

TECHNICAL FIELD

This invention pertains to a mechanism that will allow for the near-simultaneous release of both feet from a wakeboard at a preset force.

BACKGROUND ART

Wakeboarding is a sport similar to waterskiing in which riders are pulled behind a motorized boat. However, unlike waterskiing, the objective of wakeboarding is to jump the wake produced by the boat and perform aerial maneuvers. Because riders become airborne, the sport is inherently more dangerous than waterskiing. Knee injuries, such as anterior cruciate ligament (ACL) tears, are common among wakeboarders, but there has not yet been a device aimed at reducing these injuries.

Wakeboards are mechanically simple devices. Because they lack moving parts, they can typically be used in excess of ten years. They are usually made of fiberglass, plastic, foam, or a combination of these materials. When foam is used, it is encased in layers of plastic or fiberglass so that it lasts a long time.

There are several aspects of the design of wakeboards that cause them to be a hazard to the knees. The large surface area of the board causes high forces to be placed on the knees due to water resistance in the event of a crash. During use, the board is perpendicular to the line of motion, which causes high lateral forces to be transmitted to the knees. Wakeboard bindings use stiffer materials than bindings for other water sports, which, while giving wakeboarders greater ankle support, also causes more stress to be transmitted to the knees, increasing the likelihood of knee injury.

Current wakeboards use a design in which the bindings are rigidly attached to the board. This design leads to two scenarios that often cause knee injuries. First, if a rider's bindings are too tight and do not release in the event of a crash, the large tensile forces imparted on the knee are often enough to strain or even tear ligaments in the knee. Second, because a rider's feet are released from their bindings independently of one another, one foot can be released from its binding before the other. If the rider is spinning when he/she hits the water, the rotation of the rider's body weight around the knee of the leg that did not release can cause severe knee injuries due to the large torsional stresses imparted on that knee. The rider's front foot often comes out of its binding first, and the rotational inertia of the rider's upper body causes high torsional stress to be placed on the rider's back knee.

Most prior developments in the wakeboarding industry have been directed towards increasing the performance of wakeboards. There have been relatively few innovations related to the safety of wakeboard design. Knee braces are an option available to wakeboarders, but they are costly and usually only purchased after an initial injury to support a compromised knee. In addition, knee braces protect the knee from buckling, but do not offer protection against tensile forces.

Comparing wakeboarding to the winter sport of snowboarding, snowboarding is less likely to result in knee injuries. This is because in snowboarding, both feet are attached to the board via ratcheting straps that virtually never release, unless something catastrophic occurs. Wakeboarding conditions appear to put wakeboarders at particular risk for ACL injuries. There is an unfilled need for improved safety in wakeboard design.

There are four major ligaments of the knee: the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial collateral ligament (MCL), and the lateral collateral ligament (LCL). These ligaments constrain the motion of the knee and protect against large tensile forces. The lateral meniscus and the medial meniscus protect against compressive stresses.

The ACL limits forward movement of the tibia as well as rotation of the knee. Because both of these types of motion occur often in wakeboarding, the ACL is particularly susceptible to injury. The menisci absorb compressive forces, such as the force from the femur pushing down on the tibia when landing on the water. The menisci are particularly vulnerable when there is rotation accompanied by a compressive force, as often happens during landings.

A wakeboard in use can exert an upward force, pushing the rider's feet away from the board. On a conventional wakeboard, the friction of a foot in a boot exerts a downward force that keeps the foot on the board. When the upward force is greater than the friction of a foot in the boot, the foot is released. However, this is an imprecise method of release, and the force required for release can vary greatly. Often, the force of the friction of the boots is greater than the strength of the knee, which can lead to severe injuries.

Head injuries are also associated with wakeboarding. As the rider leaves the wake produced by the boat, the rider lets the board extend behind the rider's body, holds the position for as long as possible, and then tucks the board beneath the body before landing. However, if the rider does not pull the board underneath the body in time, the large surface area of the board causes it to act like a parachute when it dips beneath the surface of the water, putting tremendous stress on the knees. Furthermore, because the board decelerates so rapidly while the rider's upper body continues to move forward at about 22-25 mph (a common wakeboarding speed), the board can act as a pivot to slam the rider's head into the water, which can cause a concussion.

DISCLOSURE OF THE INVENTION

We have discovered a novel wakeboard binding release mechanism that allows for the near-simultaneous release of both feet from a wakeboard at a preset force. The novel mechanism improves the safety of a wakeboard, and decreases the risk of both knee and head injuries.

A preferred embodiment is made from stainless steel, aluminum, and polycarbonate components, which should last the lifetime of several sets of bindings.

Referring to the embodiment depicted in FIGS. 1 and 2, the bindings each have a plate 2 attached on the bottom. Each plate 2 has a dual beveled edge (upper and lower bevel) 4, 6. Two low-friction pins 8 (fixed to the board) slide over the bevels 4 as the plate 2 is inserted.

In a preferred embodiment, the angle of the lower bevel 6 on the binding plate 2 is greater than the angle of the upper bevel 4, so that the force required to release the plate 2 is greater than the force required to put the plate back in place.

In the most preferred embodiment, a 45-degree incline is used on the top bevel 4 of the binding plate 2. This angle is large enough to push the spring to the side, but not so steep that the binding would release too easily. A 60-degree angle is used for the bottom bevel 6 of the binding plate 2.

Also, in the most preferred embodiment, the plates 2 are narrower than those used in our initial prototype to protect against unexpected release resulting from flexing of the plates.

FIG. 5 depicts the passive set-up of the device. The plates 2 are held in position by springs 12, 14 that maintain force on the pins 8, 10, and thus on the bevel on the upper side 4 of the plate 2. One pin 10 is on the outside and another on the inside 8 of each plate 2. The two pins 8 on the insides of the two plates are coupled by a screw or shaft 16. In a preferred embodiment, the length of the shaft 16 is adjustable. This adjustment is made, for example by a turnbuckle 18. Adjusting the turnbuckle 18 adjusts the amount of force exerted by the springs 12, 14 on the pins 8, 10 and thus on the bevels 4 to keep the plates 2 in position.

If the force imposed on one of the plates 2 exceeds the force holding that plate 2 in position (i.e., when the rider and the wakeboard move in different directions at sufficient velocity), then the plate 2 will be released, as shown in FIG. 6. The pins 8, 10 that hold the plate 2 in place are displaced due to the force from the springs 12, 14. Because the inside pins 8 are coupled, when one inside pin 8 is displaced due to the release of a plate 2, the force on the other inside pin 8 is released and the other plate 2 is also released, almost simultaneously, as shown in FIG. 7. The pins 8, 10 are preferably made from polytetrafluoroethylene or from graphite composite.

A preferred embodiment uses four compression springs 12, 14 mounted in polycarbonate blocks 20, 22 to accomplish the near-simultaneous release of the bindings, as shown in FIGS. 5-7.

There are at least four release mechanisms total, one on the inside and one on the outside of each of the two binding plates 2. The mechanisms on the insides of the two binding plates 2 are coupled to each other, for example by a solid turn-buckle type arrangement 18, so that when one binding plate 2 releases, a rod 16 instantly slides into the gap left by the released binding plate 2 and the pressure is taken off of the central connection 16, which should be free to slide as a single unit. When this happens, pressure on the inside of the other binding plate 2 is released, and the other binding plate 2 also releases. The outer springs 14 are used in case there is a torque on the binding plate 2 that rotates the binding toward the center of the board, in which case the outside of the binding plate 2 would lift and release first, and again the other binding plate 2 would also be released.

A compression spring 12 is sandwiched between each shaft 16 and a bolt with a washer welded on the end to press against the spring 12. In a preferred embodiment, a square shaft and receiver combination is used on the bolt to prevent rotation of the shafts 16 when the turnbuckle 18 twists. The differences between the inner 20 and outer blocks 22 are shown in FIGS. 3 and 4.

In the prototype embodiment, the four blocks 20, 22 were manufactured from polycarbonate. Its deformation under the maximum applied load was in the order of 10⁻³ inches, which is an acceptable deformation based on the results of a stress analysis.

A preferred embodiment employs both aluminum and stainless steel because both are corrosion resistant. Stainless steel is preferred in higher stress areas where extra strength is needed, whereas aluminum is preferred in lower stress areas to reduce the overall weight of the mechanism. Both corrosion resistance and light weight are important characteristics since the board is designed to perform airborne maneuvers and because it spends time in and out of water. The most preferred embodiment uses springs with a corrosion resistant coating, such as zinc.

The invention should lead to a significant decrease in the number and severity of not only knee injuries, but also head injuries sustained while wakeboarding. Head injuries typically occur when the edge of the board catches the water, causing the rider to slam face-first into the water. However, with the novel release mechanism in place, the bindings should release as soon as the board dips beneath the surface, so that the rider maintains more forward momentum and is not slammed into the water.

The same release mechanism disclosed here can also be used for quick release from a snowboard.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a prototype embodiment of the wakeboard release mechanism.

FIG. 2 depicts a cross-section of the footplate and pin.

FIG. 3 depicts the outer release mechanism.

FIG. 4 depicts the inner release mechanism.

FIG. 5 depicts one embodiment of a complete device in accordance with the present invention.

FIG. 6 depicts the initial stage of release of the first footplate from the mechanism.

FIG. 7 depicts the release of the second footplate.

MODES OF PRACTICING THE INVENTION

Noyes et al. The Journal of Bone and Joint Surgery. “Biomechanical Analysis of Human Ligament Grafts Used in Knee-Ligament Repairs and Reconstructions.” 1984. reported measurements finding that the ACL strength of 18 subjects with a mean age of 26 was 388±60 pounds. Based on these measurements and assuming a normal distribution, a release mechanism that imparts no more than 268 pounds of tensile force to the knees would be below the ultimate ACL strength of 97% of a 26 year-old population. Thus we chose 268 pounds as the maximum force for design purposes.

The rider imparts a downward force upon the board through the boots, and the board pushes up on the rider with the same force. The allowed magnitude of this force is controlled by point at which the springs release the feet from the board. In a preferred embodiment, the boots are held in place by 4 release mechanisms that function similarly to spring plungers. The stiffness of the spring controls the release force. In a preferred embodiment, a turnbuckle partially compresses the middle springs, allowing for some adjustment of the spring stiffness, and thus adjustment of the release force.

The preset release force is less than about 1000 pounds, preferably less than about 500 pounds, and most preferably less than about 268 pounds.

FIG. 5 depicts one embodiment of a complete device in accordance with the present invention. At the center is turnbuckle 18. Threaded through turnbuckle 18 are two bars 16, each of which presses against a spring 12 inside a hollow block 20. On the far end of each block 20 is a pin 8. Each pin 8 has a rounded end, which pushes down and holds a footplate 2 in place. The footplates 2 each have a beveled edge, and are designed to hold the boots and feet of a rider. On the far side of each footplate 2 is another hollow block 22, with a spring 14 and a peg 10, which help to stabilize the footplates 2.

FIG. 6 depicts shows the initial stage of release of left footplate 2 for the same embodiment depicted in FIG. 5. An upward force, sufficient to overcome the preset spring force on the left pegs 8 and 10 that had kept left footplate 2 in place, cause the left springs 12 and 14 to compress into left block 18, and the left footplate 2 releases.

FIG. 7 depicts the subsequent release of right footplate 2. Once the left footplate 2 has been released, there is no longer sufficient force on turnbuckle 18 and on right springs 12 and 14 to hold the right footplate 2 in place, and right footplate 2 is thus released very quickly.

Determining release force for a previous design wakeboard:

To determine the force required to release a rider's feet from the bindings of a previous design wakeboard, we used a Jackson Strength Evaluation System. Tow straps anchored a load cell to an immobile, fixed structure on one side and to the test wakeboard on the other side. A second tow strap near a subject's head was anchored to another immobile, fixed structure so that the subject could pull on the tow strap to apply a force to the load cell. Before inserting his feet into the bindings, the subject wet his feet and the bindings to simulate the environment in which wakeboards are used. After inserting his feet into the bindings and tightening them, he pulled as hard as he could on the tow strap, and the results were recorded.

The maximum force applied during this test was 315 pounds, which was not enough to release either foot. It is uncertain how much greater the force would need to release the subject's feet from the bindings. It is clear that the safety of wakeboards will be significantly improved with a release mechanism that requires a smaller force, such as 268 pounds or less, to release the rider from the binding.

Design Considerations

A maximum 268-pound limit for the release value was set. We considered this figure to be a conservative estimate for injury prevention based on the average ACL strength of 388 pounds±60 pounds, as previously discussed. Also, the other ligaments of the knee, such as the LCL and MCL, contribute to the overall tensile strength of the knee. The knee as a whole should withstand a greater force than an isolated ACL. Further, athletes such as wakeboarders are likely to have above-average ligament strength.

It is critical that the bindings for the two feet release virtually simultaneously, so that strong rotational force is never applied to either knee. Adjustability of the minimum release force is an optional but preferred feature, so that beginners and advanced riders can use the same device. Beginners will want the board to release more easily, while more advanced riders will want the board to be more difficult to release so that it doesn't release at inopportune moments, such as when the rider is performing aerial maneuvers. A release force of 50-100 pounds is likely appropriate for a beginner, because beginners rarely become airborne. These beginner release estimates were determined through experiments in which we found that, so long as the bindings were laced up, no matter how loosely, the feet did not pull out from the bindings with a force less than 100 pounds. Fifty pounds was chosen as the lower limit to prevent the bindings from releasing accidentally due to waves and small incidental forces that occur during normal wakeboarding. As the rider progresses, he or she will be able to increase the release force of the bindings to suit ability.

Fabricating the prototype:

The first step in fabricating a prototype embodiment was to retrofit the original bindings of an as-purchased wakeboard so that they were compatible with the novel release mechanism. An aluminum disk approximately one inch thick was machined so that the top and bottom edges had angles of 45 and 60 degrees, respectively. Next, five grooves were cut into the top and bottom surfaces in each quadrant of the disk. A ⅛-inch deep rim was cut into the bottom surface of the disk to help align the individual pieces with the binding plate. Finally, threads were tapped into the pieces, and they were attached to the board using screws. The heads of the screws, as well as the metal inserts in the top surface of the board, were ground down for the bindings to fit flush with the surface of the board.

The next step in the fabrication process was machining the polycarbonate blocks 20, 22. Several incremental cuts were made to create the necessary holes in the polycarbonate blocks 20, 22.

A stainless steel turnbuckle 18 was manufactured, incorporating a one-inch diameter knob 24 so that adjustments could easily be made by the end user, on the spot, without the use of tools.

Rods 16 for the central connection were fabricated from a 5/16-inch thick, square, stainless steel stock piece. One end of the rod was rounded off, and threads were cut into the surface to interface with the turnbuckle 18. A washer was welded to the other end of the rod 16 to push against the springs 12. A receiver with a square hole was machined from aluminum to accept the square section of the rod and prevent rotation if the turnbuckle twisted. For the outer blocks 22, the receivers had a circular, threaded hole in the center to enable adjustment by simply twisting the bolts. The individual components were assembled using basic hardware such as bolts and washers, and the mechanism was attached to the board using wood screws. The whole mechanism added about two pounds to the board, which weighs around 15 pounds with bindings. The mechanism weighed less than 15% of the weight of the board.

Testing the prototype:

Four tests were performed on the prototype embodiment to determine the time between release of the first binding plate 2 and the second binding plate 2, and the force required to release the bindings.

For the speed test, a Sony Super Steady Shot HDR-SR11™ camera was used in a high speed mode that recorded 120 frames per second. There were 5 frames between the time when both binding plates were connected to the board and the time when both binding plates were released, so the total elapsed time was about 0.04 seconds.

We estimated that the maximum allowable release time to prevent injury was probably between about 0.125 seconds and about 0.5 seconds. The actual release time achieved with the prototype, about 0.04 seconds, was substantially faster. The invention allows the two bindings to release nearly simultaneously, so that there is insufficient time for dangerous levels of torsional force to be imparted to the knee due to rotation of the upper body around the knee.

To test the release force of the prototype, a Jackson-strength evaluation system was used to measure the force exerted on the board by a test subject pulling his feet out of the bindings. The system was configured to record only the peak force exerted on the load cell by the human test subject. In actual use, the strongest force should be that just before detachment, the force at which the binding releases from the wakeboard. A human test subject held a pair of handles and pulled himself out of the bindings while lying on the ground. The force at which the bindings released from the board was recorded.

In the initial tests, four different preload settings were used on the springs 12, 14, to vary the resistance to release. Eventually, we had to stop testing because the original turnbuckle 18, which was aluminum, was beginning to strip. The average values measured in tests at different preload settings were 178 pounds (n=19 releases), 118.7 pounds (n=10), 162 pounds (n=8). Only two releases were recorded at the highest preload setting, 202 and 226 pounds, before the turnbuckle 18 stripped.

In a subsequent laboratory test, the release value was 182±6 pounds with over 15 releases tested. After the second lab test, the mechanism was tested on the water. In earlier tests, the mechanism released several times when it should not have, when the binding plates 2 rotated out of position. Therefore, four pins were added (0.25 inch shouldered stainless steel bolts) to the top of the board, using pre-existing threaded inserts on the top surface. The pins fit into holes drilled into the aluminum foot plates of the bindings, and helped inhibit rotation of the bindings. Springs with a spring rate of 508 pounds-per-inch were used in the central connection 12, and springs with a spring rate of 165 pounds-per-inch were used in the outer blocks 14. When tested, the average release force was 222±22 pounds. One release occurred at a force above 268 pounds, namely, 274 lbs, during this trial.

In subsequent field tests following these design adjustments, the board had fewer accidental releases than in the first field test. In the later tests, the binding plates always released together, and the binding plates were stable enough to permit jumping and even inverted aerial maneuvers. The prototype binding plates 2 still released prematurely a few times, evidently due to flexing of the binding plate. To prevent flexing and early release, the binding plate may be made substantially narrower, or it may be reinforced with a supporting material, or it could be formed from a stronger material than that used in the prototype.

The complete disclosures of all references cited in this specification are hereby incorporated by reference, including the complete disclosure of priority application No. 61/417,530. In the event of an otherwise irreconcilable conflict, however, the present specification shall control.

Claims

1. Apparatus for the rapid and essentially simultaneous release of both of a user's boots from a board, wherein the board is a wakeboard or a snowboard; wherein said apparatus comprises:(a) two boots and two plates, wherein said boots are adapted to receive the user's feet, and wherein one of said plates is affixed to the bottom of each of said boots;(b) two pairs of receivers, one pair of said receivers associated with each of said two plates, wherein each of said four receivers is affixed to or is adapted to be affixed to the board; and wherein each of said pairs of receivers is adapted to receive and to engage one of said plates, and thereby to hold one of said boots in proximity to the board;(c) four pins, wherein one of said pins is associated with each of said receivers; and(d) a coupler located directly adjacent to two of said pins, wherein said coupler engages or is adapted to engage both of said adjacent pins, and to impose a force on each of said adjacent pins; wherein the force upon either of said adjacent pins is in a direction generally opposite to the direction of the other said adjacent pin, and wherein the force upon either of said adjacent pins is in a direction generally toward the center of the corresponding said plate;wherein:when in use, said coupler, pins, plates, and receivers cooperate and interact with one another as follows:if only one plate is engaged with said plate's corresponding pair of receivers, then there is little or no force holding said plate in proximity to the board, and said plate and said plate's corresponding boot may be removed from proximity to the board upon the application of no force or a very small force;if both plates are engaged with the corresponding pairs of receivers and pins, then both plates are held in proximity to the board by a substantial force, and said plates and boots may only be released from proximity to the board upon the application of at least a threshold force to at least one of said boots or to at least one of said plates;the threshold force is pre-determined or is set by a user; the threshold force is sufficiently high that the boots do not prematurely release during ordinary, non-injurious use of the board; and the threshold force is sufficiently low that a boot will be released essentially simultaneously upon the application of a force to the boot that could otherwise cause serious injury to a user's knee; andthe release of a first plate from the corresponding first pair of said receivers simultaneously releases the force that said first plate had imposed upon the corresponding first adjacent said pin; and when the force is released from the corresponding first adjacent said pin, the force is also simultaneously released from said coupler and from the second adjacent said pin; and when the force is released from the second adjacent said pin, the force holding the second boot and said second plate to the board is simultaneously released, so that the second boot and said second plate are released from the board essentially simultaneously with the release of the first boot and the first said plate from the board.

2. Apparatus as in claim 1, wherein said coupler comprises a compression spring.

3. Apparatus as in claim 1, wherein the board is a wakeboard.

4. Apparatus as in claim 1, wherein the board is a snowboard.

5. Apparatus as in claim 1, wherein the threshold force is between about 50 pounds and about 300 pounds.

6. Apparatus as in claim 1, wherein the threshold force is between about 100 pounds and about 268 pounds.

7. Apparatus as in claim 1, wherein the threshold force is between about 268 pounds and about 500 pounds.

8. Apparatus as in claim 1, wherein the threshold force is between about 500 pounds and about 1000 pounds.

9. Apparatus as in claim 1, additionally comprising a wakeboard, wherein each of said four receivers is affixed to said wakeboard.

10. Apparatus as in claim 1, additionally comprising a snowboard, wherein each of said four receivers is affixed to said snowboard.