Flipper

Abstract

A flipper is provided. The flipper includes a pocket, a blade and a strengthening structure. The pocket is for accommodating the foot of the user. The blade extends forwards from the pocket, and the strengthening structure is detachably disposed at the blade and extends to reach the front edge of the blade. The flexural strength of the strengthening structure is larger than that of the blade to constrain the swing angle of the blade relative to the pocket. By using the strengthening structure to constrain the swing angle of the blade, the flipper can not only provide a larger propulsion in the down-kicking state, but also decrease the resistance of water in the up-kicking state.

What is claimed is: 
     
         1 . A flipper, comprising:
 a pocket for accommodating a foot of a user;   a blade extending forwards from the pocket; and   a strengthening structure detachably disposed at the blade and extending to reach a front edge of the blade;   wherein a flexural strength of the strengthening structure is greater than that of the blade.   
     
     
         2 . The flipper according to  claim 1 , wherein the strengthening structure is disposed on a bottom surface of the blade. 
     
     
         3 . The flipper according to  claim 1 , wherein the strengthening structure is disposed on a top surface of the blade. 
     
     
         4 . The flipper according to  claim 1 , wherein the strengthening structure is disposed on a top surface and a bottom surface of the blade. 
     
     
         5 . The flipper according to  claim 1 , wherein the strengthening structure extends from two sides of the pocket, along two lateral edges of the blade, towards the front edge of the blade. 
     
     
         6 . The flipper according to  claim 5 , wherein the strengthening structure further extends from the two lateral edges of the blade towards the top surface or the bottom surface of the blade. 
     
     
         7 . The flipper according to  claim 5 , further comprising at least one swing-constraining structure disposed on the two sides of the pocket, wherein the strengthening structure is affixed to the blade via the swing-constraining structure, and the swing-constraining structure make the strengthening structure swing within at least one swing angle with respect to the pocket. 
     
     
         8 . The flipper according to  claim 7 , wherein the at least one swing-constraining structure is two or four swing-constraining structures, and the swing-constraining structures are affixed on the pocket pivotally; each of the two sides of the pocket has a protrusion, and the protrusion is used for constraining the swing angle of the swing-constraining structure with respect to the pocket. 
     
     
         9 . The flipper according to  claim 7 , wherein the swing-constraining structure is formed integrally with the strengthening structure. 
     
     
         10 . The flipper according to  claim 1 , wherein the blade has two blade pieces disposed abreast and extending forwards from the pocket. 
     
     
         11 . A flipper, comprising:
 a pocket for accommodating a foot of a user;   a blade extending forwards from the pocket; and   two strengthening structures detachably disposed at the blade and extending to reach a front edge of the blade, wherein the two strengthening structures are spaced to each other, and a flexural strength of the strengthening structures is greater than that of the blade.