Used for swimming and diving, swim fins substantially increase the surface area of the naked foot, thereby increasing the propulsive force of the legs. If used properly, swim fins can conserve a diver's energy and facilitate underwater movement as powerful extensions of a diver's body. In fact, swim fins can be so effective that arms and hands are not necessarily needed for propulsion when skin or scuba diving. However, most swim fins are inconvenient and impractical for walking. Few things feel as awkward as trying to walk while wearing swim fins due to their extended length. Swim fins are cumbersome and can be potentially dangerous while walking.
To overcome this problem, various swim fins have been proposed which include fins capable of folding or rotating between a swimming mode and a walking mode. For example, U.S. Pat. No. 6,155,898 (Burns) discloses an amphibious shoe-like structure with a fin blade surface that expands in a swimming mode and collapses in a walking mode to rest adjacent to a wearer's instep. U.S. Pat. No. 5,924,902 (Burns) discloses a shoe-like structure with an attached one-piece continuous sole-fin structure and a flexible folding zone which facilitates the folding of the sole-fin structure upward.
U.S. Pat. No. 5,292,272 (Grim) discloses a swim fin having a pivoting fin portion which pivots at the toe of the foot pocket. However, walking is still difficult because the non-collapsible fin blade in the retracted state is positioned at a 90 degree angle relative to the longitudinal axis of the foot which increases resistance when walking or wading in shallow water. Likewise, U.S. Pat. No. 4,981,454 (Klein) discloses a swim fin having a retractable fin portion that pivots near the arch of the foot. This pivoting allows the fully expanded fin portion to rise above the instep of the foot where it is positioned adjacent and parallel to the leg. This prevents an awkward upright blade at the toe of the foot pocket, but the large surface area of the fin portion is still in a cumbersome position which reduces flexibility while walking. U.S. Pat. No. 4,752,259 (Tackett) discloses another embodiment having a retractable fin portion wherein the surface area is bifurcated. The frontal end portion of the fin portion pivots upon itself either over or under the foot to facilitate walking. However, only a portion of the fin portion retracts leaving a substantial length extending longitudinally beyond the user's foot which impedes natural ambulation. U.S. Pat. No. 6,540,574 (Haghizume) also discloses a foldable swim fin having a complex apparatus for permitting rotation of the fin portion at or near the arch of the foot.
In order to avoid the disadvantages of such swim fins, it has been proposed to attach a separate and removable fin portion to the shoe-like structure. For example, U.S. Pat. No. 5,041,039 (Chang) discloses a detachable fin portion secured to the sole of the shoe structure by screw means. Likewise, U.S. Pat. No. 5,766,050 (Maggi) discloses a fin portion with a cup-like structure with internal locking means that fits over the toe area of a shoe-structure and seats thereto. However, in such swim fins, the fin portions must be manually attached when needed and when not in use must still be transported by the user, thereby defeating the purpose of easy convertibility between a swimming mode and walking mode. Still further designs for swim fins have been disclosed in U.S. Pat. No. 5,242,321 (Gil) and U.S. Pat. No. 4,250,584 (Korn) wherein collapsible fin portions are provided for easy and compact transport and storage. However, these styles are still not adaptable for walking, and therefore, cannot be converted between a swimming and walking mode.
There is a need, therefore, for an amphibious shoe, which may be used for walking and swimming, having convenient, relatively inexpensive and secure means for converting between a walking mode and a swimming or diving mode and maintaining the amphibious shoe in the desired mode.