Patent Publication Number: US-9427626-B2

Title: Swimming device with retractable fins

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of a provisional patent application: 
     Ser. No. 62/032,576 filed on Aug. 3, 2014 
     Ser. No. 62/036,597 filed on Aug. 12, 2014 
    
    
     FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     SEQUENCE LISTING OR PROGRAM 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is in the area of Swimming Devices. 
     2. Description of Related Art 
     Currently, prevalent Swimming Devices include a set of two Fins made of resilient material which have foot pockets or shoes as means of wearing them on the user&#39;s feet. The conventional swimming Fins currently in wide use are not suited for walking and are not ideal for swimming. It is almost impossible to walk freely with the Fins worn on the feet without stumbling. Thus, swimmers have to walk without them on the beach and to wear them near the water line. When in shallow water, swimmers have still to continue walking hitting underwater rocks and stumbling. Fins have large planar sections which are used to push the water in order to propel the swimmer. Since the orientation of the planar sections is approximately parallel to the soles of feet when fins are worn, the conventional fins create a substantial drag while swimming because the orientation of the feet soles and of the planar sections during swimming is not parallel to the water flow. In addition, the wide planar sections of the fins are mutually colliding while swimming. In order to prevent Fins&#39; mutual collisions, the swimmers need to keep the legs wide apart, which is inconvenient posture both in swimming and in walking. 
     Several inventions attempted to solve the problem of walking while wearing fins, most of them proposed similar arrangements of retracting fins by turning them upwards in front or behind the calves. Each fin is pivoted on two hinges installed on the left and right sides of the foot and can be turned upwards for walking. When the fins are leveled in front of the feet they can be used for swimming. Such are the inventions of U.S. Pat. No. 5,108,327 to Klein, U.S. Pat. No. D561,862 of Moyal, U.S. Pat. No. 6,672,920 B2 to Wilson, U.S. Pat. No. 3,315,286 to Brion, and U.S. Pat. No. 3,268,927 to Makowitz. Other inventions propose other retracting solutions such as in U.S. Pat. No. 5,924,902 and U.S. Pat. No. 6,155,898 to Burns et al. which proposed a small retractable fin up front as an extension of the sole, or U.S. Pat. No. 8,678,870 B2 to Johnson, which propose a very complex structure worn on the feet and calves to carry the fins. Other inventions involve flexible folding in U.S. Pat. No. 2,903,719 to Wozencraft et al. or in U.S. Pat. No. 5,593,333 to Johnson which folds part of the fin under the foot. However, all the inventions mentioned above do not eliminate the problems of mutual Fins&#39; collisions and of substantial drag while swimming. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The conventional swimming Fins currently in wide use, are not suited for walking and are not ideal for swimming. It is almost impossible to walk freely with the Fins worn on the feet without stumbling because Fins tend to collide with the ground and with one another. Since the Fins have wide planar sections with orientations which are approximately parallel to the soles of the swimmer&#39;s feet, they exhibit a significant drag in the water because the orientation of the feet&#39;s soles during swimming is not parallel to the direction of water flow. Our Swimming Device with Retractable Fins (SDRF) offers satisfactory solutions to these problems. First, the SDRF enables unhindered walking when retracted. Second, the SDRF has much less drag in the water since the wide sections of the retractable Fins are substantially parallel to the water flow during swimming. Third, changing SDRF positions from walking to swimming or vice versa is quick and can be performed easily on land or in water. Fourth, SDRFs can be easily detached from the swimming shoes or reattached to the swimming shoes. 
     The SDRF was designed entirely differently from all the other devices with retractable Fins in order to achieve all these advantages which require adjusting the fins in diagonal orientations which are not possible with the conventional approaches. In the SDRF structure, the Fins have slanted axes of rotation which are connected to the rear sides of user&#39;s swimming shoes. This arrangement enables to rotate (i.e. tilt) and lock the Fins diagonally in opposite directions away from each other both in swimming and in walking positions. The space created by the tilting prevents mutual Fin collisions while swimming and also during walking. In addition, the Fins&#39; axes of rotation are also slightly slanted with respect to the horizontal direction of the user&#39;s soles. Slanting poses the Fins diagonally, leaning backwards with respect to the calves while in the walking position and leaning forwards while in the swimming position. Slanting has two advantages. The diagonal backwards leaning prevents Fin collisions with the calves while walking. The forwards leaning poses the Fins in more streamlined position with respect to the water flow, which results with less drag during swimming. The SDRF has a positioning mechanism which enables the user to easily change locked Fin positions simply by pulling the positioning members and rotating the Fins. The SDRF is also equipped with latching mechanisms which enable easy detaching of the Fins from the shoes simply by pulling at the latches. The latching mechanisms also allow quick reattachment of the Fins to the rear side of the swimming shoes simply by mounting and pushing the Fins towards the shoes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the SDRF is presented in  FIGS. 1-23 . However, this embodiment represents only one variation derived from the Swimming Device with Retractable Fins (SDRF) invention. 
         FIG. 1  describes the user with a SDRF in walking positions in which the Fins are folded in upwards Tilted orientations and enable walking. 
         FIG. 2  describes the user with a SDRF in swimming position in which the Fins are in downwards orientations and enable swimming. 
         FIG. 3  illustrates the rear view of a swimmer with a SDRF in Tilted walking positions in which the left leg Fin is Tilted to the left and the right leg Fin is Tilted to the right. It is obvious that the Tilted upwards positions provide a wider inner spacing between the Fins which enable unhindered walking. 
         FIG. 4  is a 3D isometric drawing of a disassembled left leg Fin&#39;s mechanism with all its parts. 
         FIG. 5  is a cross section side view of  FIG. 6  which illustrates a front view of the left leg part of the SDRF in an upwards-walking position that enables walking. 
         FIG. 7  is a cross section side view of  FIG. 8  which illustrates a front view of the left leg part of the SDRF in downwards-swimming position that enables swimming. 
         FIG. 9  is a cross section side view of the SDRF&#39;s shoe view which is presented in  FIG. 10 . 
         FIG. 11  describes 3 views of the left member for the left leg part of the SDRF. 
         FIG. 12  is an enlargement of  FIG. 4  which depicts a 3D isometric drawing of a disassembled left leg part of the SDRF with all its parts. 
         FIG. 13  is a front view of the latch and 
         FIG. 14  is a cross section side view of the latch in  FIG. 13 . 
         FIGS. 15-18  describe step by step the action of the latching mechanism by which the Fin is fastened to the shoe. 
         FIG. 19  presents 3 views of the round bar which is used for latching the Fin to the shoe. 
         FIG. 20  is a front view of the right leg part of the SDRF in an upwards—walking position that enables walking. 
         FIG. 21  illustrates a front view of the right leg part of the SDRF in downwards—swimming position which enables swimming. 
         FIG. 22  depicts a 3D isometric drawing of a disassembled right leg part of the SDRF with all its parts. 
         FIG. 23  Describes the Slant and Tilt angles with respect to the left shoe&#39;s sole. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 23  Describes the Slant and Tilt angles with respect to the left shoe&#39;s sole. The angle between the left Shoe&#39;s vertical axis  2 H and the left Fin&#39;s axis of symmetry  1 E is defined as the left Tilt angle of the left Fin  1 A. The left/right Shoe&#39;s vertical axis  2 H/R 2 H is a line pointing upwards (Z axis and its parallel axis Z′ in  FIG. 23 ), which is perpendicular to the plane of the soles of the corresponding left/right shoes  2 K/R 2 K. The left Slant angle is the angle between the left vertical axis  2 H and the left Fin&#39;s axis of rotation  2 J. Similarly, the right Slant (not drawn in  FIG. 23 ) angle is the angle between the right vertical axis R 2 H and the right Fin&#39;s axis of rotation R 2 J. 
       FIG. 1  describes the user with SDRF in upwards-walking position in which the Fins  1 A and R 1 A are in upwards orientations and enable walking. The left leg Fin  1 A and the right leg Fin R 1 A are rotatably attached to the rear sides of the swimmer left shoe  2 A and right shoe R 2 A respectively. The Fins and are in an upwards-walking position and they are positioned behind the swimmer&#39;s calves. Also drawn is the tilt Angle2 i.e. the angle between the left shoe vertical axis  211  and the left Fin&#39;s axis of symmetry  1 E. 
     In the walking position the Fins&#39; longitudinal axes of mirror symmetry are slightly Tilted with respect to the user&#39;s calves. These tilted orientations, which are described in  FIGS. 1 and 3  are designed to enable walking without obstruction i.e. without mutual collisions of the Fins, with the ground or with the calves. In the upwards position, the left leg Fin  1 A is Tilted to the left by Angle2 (as illustrated in  FIGS. 3 and 6, 8 ) and the right leg Fin R 1 A is Tilted to the right by Angle2. Thus the left and right Tilt angles are equal to Angle2 which is measured between the left/right Fin&#39;s axes of symmetry  1 E/R 1 E and the left/right vertical axes  2 H/R 2 H. The left/right axes of rotation  2 J/R 2 J of the left leg and right leg Fins are also slanted backwards by Angle1+90 with respect to the left/right Shoes&#39; vertical axis  2 H/R 2 H (as illustrated in  FIGS. 5, 7 and 23 ). The left/right Slant is actually measured between the left/right axes of rotation  2 J/R 2 J and the left/right vertical axes  2 H/R 2 H which are perpendicular to the left/right soles&#39; planes thus, the official Slant is actually 90+Angle1. The right leg Fin R 1 A is a mirror image of the left leg Fin  1 A (as shown in  FIGS. 20, 21 and 22 ). It means that all the features of the right leg Fin R 1 A correspond to symmetric features of the left leg Fin  1 A wherein the line of symmetry is the vertical axis at the midpoint between the shoes  2 A, R 2 A. Thus, in the upwards position, the right leg Fin R 1 A is Tilted to the right by Angle2 and also Slanted backwards by Angle1+90 with respect to the vertical axis of the right shoe R 2 H. Hence, in the upwards position, the two Fins  1 A, R 1 A are Tilted outwards in symmetric angles (Angle2) that prevent the Fins  1 A, R 1 A from hitting one the other while walking. Left and right Fins&#39; axes of rotation  2 J/R 2 J are also slanted backwards by Angle1+90 with respect to the left/right shoe vertical axes  2 H/R 2 H which enables walking without the Fins hitting the user&#39;s calves from behind. In one embodiment we approximate both angles Angle1 and Angle2 to be in the range between 5 to 30 degrees. However, these angles could have other values as well. 
       FIG. 2  describes the user with SDRF in downwards-swimming position in which the Fins  1 A, R 1 A are in downwards orientations and enable swimming. When the user wants to use the SDRFs for swimming the user unfolds each Fin by rotating it around its shaft by 180−2·Angle2 degrees. This rotates the left leg Fin  1 A into a downwards orientation in which the left Fin axis of symmetry  1 E is Slanted to the left by Angle2 with respect to the left shoe vertical axis  2 H pointing downwards, which coincides with straight extension of the left calf (as illustrated in  FIGS. 2 and 8 ). The right leg Fin also is rotated into a downwards orientation in which the right leg Fin is Tilted to the right by Angle2 with respect to the right shoe vertical axis R 2 H pointing downwards, which coincides with straight extension of the right calf (as illustrated in  FIGS. 2 and 21 ). Thus, in the downwards position, the Fins are Slanted outwards in such angles that prevent the Fins from mutual collision while swimming. 
     While in downwards-swimming position, both Fins are also Slanted forwards by Angle1 with respect to the left/right shoes&#39; vertical axis  2 H/R 2 H pointing downwards, which coincide with the straight line extensions of the calves. This forwards Slanted orientation is ideal for swimming because swimmers tend to turn their feet slightly backwards when they swim to reduce the drag of their feet in the water. Turning the feet backwards approximately cancels the Slant forwards by Angle1 as measured between left/right vertical axes  2 H/R 2 H and the left/right Fins&#39; axes of symmetry  1 E/R 1 E and the Fins are oriented in the direction of the swimming water flow and have minimal drag on the swimmer. In this aspect, the Fins&#39; orientations in the SDRF have significant swimming advantage over the traditional prevalent Fins which are mounted with orientations of their planar wide sections which are extensions of the swimmer&#39;s feet soles. Since the feet soles orientations with respect to the calves have quite large differences, the traditional Fins exhibit large drag on the swimming water flow compared to the SDRF. 
       FIG. 3  illustrates the rear view of a swimmer with the left leg Fin  1 A and the right leg Fin R 1 A in upwards-walking positions in which the left leg Fin  1 A is Tilted to the left by Angle2 which is the angle between left shoe&#39;s vertical axis  2 H and left fin axis of symmetry  1 E. The right leg Fin R 1 A is Tilted to the right by Angle2 which is the angle between right shoe&#39;s vertical axis R 2 H and right Fin&#39;s axis of symmetry R 1 E. From  FIG. 3 , it is obvious that the Tilted upwards positions provide a wider inner spacing between the Fins which enables the user to walk without causing Fins collision. 
       FIG. 4  is a 3D isometric drawing of a disassembled left leg part of the SDRF with all its parts.  FIG. 12  is an enlargement of  FIG. 4 .  FIG. 22  is a 3D isometric drawing of a disassembled right leg part of the SDRF. Due to the mirror image symmetry between the left leg part of the SDRF and the right leg part of the SDRF, the right leg part of the SDRF has the same parts and features as of the left leg part of the SDRF except that their shapes are mirror images of the left leg part of the SDRF. All the parts and features of the right leg part of the SDRF have the same alphanumeric codes as the codes of the left leg part of the SDRF but with added R in front of each code. 
     Referring to  FIGS. 4 and 12 , the base  1 B of the left Fin  1 A has a left bearing  1 C which fits the left shaft  2 C connected to the left heel  2 B of the shoe  2 A. Thus, the left Fin  1 A can be turned around the left shaft  2 C. The left bearing  1 C has 3 left recesses:  1 D 1 ,  1 D 2 ,  1 D 3  which are used to lock the angular position the left Fin  1 A with respect to the left shoe  2 A. The SDRF has a left member  3 A with two positioning pins i.e. left protrusions  3 C 1 ,  3 C 2  which are inserted into the left Fin&#39;s left recesses at different angular positions—as will be elaborated in following paragraphs. The left member  3 A has a polygonal left bar  3 F which fits a left polygonal cavity  2 D in the left shaft  2 C. The left polygonal cavity  2 D allows the left member  3 A to move along the left shaft  2 C axis but not to rotate around it. Thus, the left round bar  4 A has a fixed angular orientation with respect to the left shoe  2 A. The left member  3 A has a left inner square cavity  3 B which houses a left round bar  4 A with a left square head  4 C which fits the left inner square cavity  3 B. The left round bar  4 A also has a left notch  4 B and an left ending ramp  4 D at its very end, which are used to latch the left round bar to the left shoe&#39;s heel  2 B as will explained later. The left compression spring  5 A also resides in the left inner square cavity  3 B and is installed enveloping the left round bar  4 A. The left strip  8 A is screwed to the left member  3 A using left member screws  8 B, which are screwed into left member holes  3 E in order to lock the left round bar  4 A inside the left inner square cavity  3 B. The left shoe&#39;s heel  2 B houses the left latch  6 A in a left tunnel  2 E. The left latch  6 A has a left opening ramp  6 B at the right hand side of the left center opening  6 C and a left spring hole  6 D which is used to anchor the left extension spring  7 A (also housed in the left tunnel  2 E). The other end of left extension spring  7 A is anchored to the left extension spring screw  7 B which is screwed into left shoe&#39;s hole  2 G (visible only in  FIG. 10 ). As already mentioned,  FIG. 22  which illustrates the corresponding blow up of the positioning and latching mechanisms of the right fin R 1 A has the same description as in this paragraph except that all the alphanumeric codes of the corresponding right hand parts have the letter R in front: 
     Referring to  FIG. 22 , the base R 1 B of the right Fin R 1 A has a bearing R 1 C which fits the shaft  2 C connected to the right heel R 2 B of the right shoe R 2 A. Thus, the right Fin R 1 A can be turned around the right shaft R 2 C. The right bearing R 1 C has 3 pin recesses: R 1 D 1 , R 1 D 2 , R 1 D 3  which are used to lock the angular position the right Fin R 1 A with respect to the right shoe R 2 A. The SDRF has a right member R 3 A with two positioning pins i.e. right protrusions R 3 C 1 , R 3 C 2  which are inserted into the Fin&#39;s pin recesses at different angular positions—as will be elaborated in following paragraphs. The right member R 3 A has a polygonal right bar R 3 F which fits a right polygonal cavity R 2 D in the right shaft R 2 C. The right polygonal cavity R 2 D allows the right member R 3 A to move along the right shaft R 2 C axis but not to rotate around it. Thus, the right round bar R 4 A has a fixed angular orientation with respect to the right shoe R 2 A. The right member R 3 A has a right inner square cavity R 3 B which houses a right round bar R 4 A with a right square head R 4 C which fits the right inner square cavity R 3 B. The right round bar R 4 A also has a right notch R 4 B and a right ending ramp R 4 D at its very end, which are used to latch the right round bar to the right shoe&#39;s heel  2 B as will explained later. The left compression right spring R 5 A also resides in the right inner square cavity R 3 B and is installed enveloping the right round bar R 4 A. The right strip R 8 A is screwed to the right member R 3 A using right member screws R 8 B screwed into right member holes R 3 E in order to lock the right round bar R 4 A inside the right inner square cavity R 3 B. The right shoe&#39;s heel R 2 B houses the right latch R 6 A in a right tunnel R 2 E. The right latch R 6 A has a right opening ramp R 6 B at the left hand side of the right center opening R 6 C and a right spring hole R 6 D which is used to anchor the right extension spring R 7 A (also housed in the right tunnel R 2 E). The other end of the right extension spring R 7 A is anchored to the right extension spring screw R 7 B which is screwed into right shoe&#39;s hole R 2 G (visible only in  FIG. 10 ). 
       FIGS. 5, 6, 7 and 8  describe the Fin positioning mechanism of the left leg part of the SDRF. The positioning mechanism of the right leg Fin which is described in  FIGS. 20, 21 and 22 , has the same part and feature alphanumeric codes preceded with an R. The left Fin  1 A has a left bearing  1 C which is mounted on a cylindrical left shaft  2 C which is attached to the left heel  2 B. The cylindrical left bearing  1 C is located at the left Fin&#39;s basis  1 B. The left bearing  1 C has three left recesses:  1 D 1 ,  1 D 2 ,  1 D 3  around its circumference which are used for the left Fin&#39;s positioning. Left recess number  1   1 D 1  is positioned upwards at the left fin axis of symmetry. Left recess number  2   1 D 2  is positioned downwards with 180−2*Angle2 degrees spaced in counterclockwise direction from the left axis of symmetry. Wherein Angle2 is equal to the left tilt angle and also to the right tilt angle. Left recess number  3  is located at 180+2*Angle2 degrees spaced in counterclockwise direction from the left axis of symmetry. The set of left walking recesses includes left recess number  1   1 D 1  and left recess number  2   1 D 2 . The set of left swimming recesses includes left recess number  1   1 D 1  and left recess number  3   1 D 3 . It means that at left walking position the left protrusion number  1  i.e.  3 C 1  is inserted in left recess number  1  i.e.  1 D 1  and left protrusion number  2  i.e.  3 C 2  is inserted in left recess number  2  i.e.  1 D 2 . Whereas, at left swimming position the left protrusion number  1  i.e.  3 C 1  is inserted in left recess number  3  i.e.  1 D 3  and left protrusion number  2  i.e.  3 C 2  is inserted in left recess number  1  i.e.  1 D 1 . 
       FIGS. 20, 21 and 22  describe the Fin positioning mechanism of the right leg part of the SDRF. The right Fin  1 A has a right bearing  1 C which is mounted on a cylindrical right shaft  2 C which is attached to the right heel  2 B. The cylindrical right bearing  1 C is located at the right Fin&#39;s basis  1 B. The right bearing  1 C has three right recesses:  1 D 1 ,  1 D 2 ,  1 D 3  around its circumference which are used for the right Fin&#39;s positioning. Right recess number  1   1 D 1  is positioned upwards at the right fin axis of symmetry. Right recess number  2   1 D 2  is positioned downwards with 180−2*Angle2 degrees spaced in counterclockwise direction from the right axis of symmetry. Right recess number  3  is located at 180+2*Angle2 degrees spaced in counterclockwise direction from the right axis of symmetry. The set of right walking recesses includes right recess number  1   1 D 1  and right recess number  2   1 D 2 . The set of right swimming recesses includes right recess number  1   1 D 1  and right recess number  3   1 D 3 . It means that at right walking position the right protrusion number  1  i.e.  3 C 1  is inserted in right recess number  1  i.e.  1 D 1  and right protrusion number  2  i.e.  3 C 2  is inserted in right recess number  2  i.e.  1 D 2 . Whereas, at right swimming position the right protrusion number  1  i.e.  3 C 1  is inserted in right recess number  3  i.e.  1 D 3  and right protrusion number  2  i.e.  3 C 2  is inserted in right recess number  1  i.e.  1 D 1 . 
     The cylindrical axes of the left and the right shoes ( 2 C and R 2 C respectively) which are attached to the shoes&#39; heels ( 2 B, R 2 B respectively) have polygonal cavities ( 2 D, R 2 D respectively) which house respective left and right members ( 3 A, R 3 A) with fitting polygonal bars ( 3 F, R 3 F respectively). These members also have two protrusions ( 3 C 1 ,  3 C 2  left protrusions for the left member and R 3 C 1 , R 3 C 2  right protrusions for the right member). The left fin  1 A has 3 left recesses ( 1 D 1 ,  1 D 2 ,  1 D 3 ) and the right fin R 1 A has right recesses (R 1 D 1 , R 1 D 2 , R 1 D 3 ). Due to the fitting left and right polygonal bars ( 3 F, R 3 F respectively) of the corresponding left and right members ( 3 A, R 3 A) the orientations of the left and right members are fixed with respect to the left and right shoes ( 2 A, R 2 A respectively). Thus, when the protrusions are inserted into the recesses, the orientations of the left and right Fins ( 1 A, R 1 A respectively) are also locked with respect to the corresponding left and right shoes ( 2 A, R 2 A). 
       FIGS. 5, 6  describe the SDRF of the left leg Fin in upwards-walking position. When the left protrusion  3 C 1  is inserted into the left recess  1 D 1  of the left Fin and the left protrusion  3 C 2  is inserted into the left recess  1 D 2 , as illustrated in  FIG. 6 , the left Fin is locked in the upwards-walking position which allows walking. Since left recess  1 D 1  is Tilted at Angle2 with respect to the vertical axis of the shoe  211 , the left leg Fin is locked at Tilted orientation at Angle2 to the left with respect to the left calf. Tilting the left leg Fin to the left and the right leg Fin to the right i.e. outwards, prevents mutual collision of the Fins when the user walks with them. 
       FIGS. 20 and 21  describe the SDRF of the right leg. The right leg Fin is a mirror image of the left leg Fin&#39;s SDRF. Thus all the angles in the right leg SDRF have the same values as in the left leg SDRF and the right leg Fin is Tilted at Angle2 to the right enabling walking without collision with the left leg Fin. When the right protrusion R 3 C 1  is inserted into the right recess R 1 D 1  of the right Fin R 1 A and the right protrusion R 3 C 2  is inserted into the right recess R 1 D 2 , as illustrated in  FIG. 20 , the right leg Fin is locked in the upwards-walking position which allows walking. Since locking pin R 1 D 1  is Tilted at Angle2 to the right with respect to the vertical axis of the shoe, the right Fin is locked at Tilted orientation at Angle2 to the right with respect to the right calf. Tilting the right leg Fin to the right i.e. outwards, prevents mutual collision of the Fins when the user walks with them. 
       FIGS. 7 and 8  describe the left leg SDRF at a downwards-swimming position when the left protrusion  3 C 1  is inserted into the left recess  1 D 3  of the left Fin and left protrusion  3 C 2  is inserted into the left recess  1 D 1 , the left Fin  1 A is locked in the downwards-swimming position which allows swimming. Since left protrusion  3 C 2  is Tilted at Angle2 downwards to the left with respect to the downwards vertical axis of the left shoe, the left leg Fin is locked at Tilted orientation at Angle2 downwards to the left.  FIGS. 6 and 8  describe the SDRF of the left shoe in upwards and downwards orientations respectively. 
       FIG. 21  describes the right leg SDRF at downwards position at which the right leg Fin R 1 A is Tilted at Angle2 downwards to the right enabling swimming without collision with the left leg Fin. The downwards position of the right leg Fin is achieved when the right protrusion R 3 C 1  is inserted into the right recess R 1 D 3  of the right Fin R 1 A and right protrusion R 3 C 2  is inserted into the right recess R 1 D 1 , then the right Fin R 1 A is locked in the downwards-swimming position which allows swimming. Since right protrusion R 3 C 2  is Tilted downwards to the right at Angle2 with respect to the downwards vertical axis of the shoe, the right leg Fin is locked at Tilted orientation at Angle2 downwards to the right. Since the left leg Fin is Tilted to the left by Angle2 at downwards position and the right leg is Tilted to the right by Angle2 at downwards position, the Fins are spaced apart such as to avoid mutual collision at swimming. 
       FIGS. 6, 8  describe the angular positions of the left part of the SDRF. To fit the Slanted rotation angles the left Fin&#39;s protrusions  1 C 1 ,  1 C 2  are spaced at angular displacement of 180−2*Angle2=180−Angle4 degrees. Similarly, the left leg Fin&#39;s recesses pairs:  1 D 1 ,  1 D 2  and  1 D 1 ,  1 D 3  also have angular displacements of 180−Angle2 degrees. This leaves the angular displacement between  1 D 2  and  1 D 3  to be 4*Angle2=Angle3+Angle4. Measuring in counterclockwise direction from the left Fin&#39;s upwards axis of symmetry, the angular locations of the left Fin&#39;s recesses which are measured in counterclockwise direction, are  1 D 1  at zero degrees,  1 D 2  at 180−2*Angle2=180−Angle4 degrees and  1 D 3  at 180+Angle4 degrees. 
       FIGS. 20, 21  describe the angular positions of the right part of the SDRF. For fitting the Slanted rotation angles, the right leg Fin&#39;s protrusions R 1 C 1 , R 1 C 2  are spaced at angular displacement of 180−2*Angle2=180−Angle4 degrees measured in clockwise direction. The right leg Fin&#39;s recesses pairs R 1 D 1 , R 1 D 2  and R 1 D 1 , R 1 D 3  also have angular displacements of 180−2*Angle2 degrees. This leaves the angular displacement between R 1 D 2  and R 1 D 3  to be 4*Angle2=Angle3+Angle4. Measuring in clockwise direction from the right leg Fin&#39;s upwards axis of symmetry, the angular locations of the right leg Fin&#39;s recesses are R 1 D 1  at zero degrees, R 1 D 2  at 180−2*Angle2=180−Angle4 degrees and R 1 D 3  at 180+Angle4 degrees. 
       FIGS. 4, 5, 6, 7, 8, 12, 20, 21 and 22  describe the positioning and locking mechanisms of the left and right parts of the SDRF. The left and right members ( 3 A, R 3 A respectively) have left and right polygonal bars ( 3 F, R 3 F respectively) which are inserted into the respective polygonal cavities  2 D, R 2 D centered at the axes of the left and the right shafts i.e.  2 C and R 2 C respectively. Due to the polygonal cavities, the locking members cannot turn around the respective cylindrical shafts&#39; axes  2 J, R 2 J but can move along the axes  2 J, R 2 J of the left and right shafts  2 C and R 2 C respectively. The left and right members  3 A, R 3 A respectively also have left and right inner square cavities  3 B, R 3 B respectively which house left and right round bars  4 A, R 4 A respectively with left and right square heads  4 C, R 4 C which fit the left and right inner cavities  3 B, R 3 B respectively. The left and right round bars  4 A, R 4 A of the left and right parts of the SDRF are fastened to the left and right shoes&#39; heels  2 B, R 2 B respectively with corresponding left and right latches  6 A, R 6 A. As illustrated in  FIGS. 5 and 7 , the left and right round bars  4 A, R 4 A are enveloped by left and right compression springs  5 A, R 5 A inside the left and right inner cavities  3 B, R 3 B respectively. The left and right springs  5 A, R 5 A are partially compressed and therefore tend to push the left and right members  3 A, R 3 A towards the corresponding left and right shoes&#39; heels  2 B, R 2 B which in turn push the left and right protrusion pairs:  1 C 1 ,  1 C 2  and R 1 C 1 , R 1 C 2  into their corresponding left and right Fin&#39;s recesses. The left and right springs  5 A, R 5 A also push the corresponding left and right Fins  1 A, R 1 A towards the corresponding left and right shoes&#39; heels  2 B, R 2 B and hold the left and right Fins in place. When the user wishes to change the orientation of a Fin from upwards-walking to downwards-swimming or vice versa, the user can pull against the spring bias the Fin&#39;s member away from the shoe. Pulling the member extracts the protrusions from their recesses, unlocks the Fin and allows the user to switch the Fin&#39;s orientation by turning the unlocked Fin. The pair of left and right member holes  3 D, R 3 D in the corresponding left and right members  3 A, R 3 A are designed to enable one to tie string loops to the locking members for the purpose of pulling them for switching Fin orientations. 
       FIGS. 9 and 10  describe the front view and cross section side view of the left and right shoes  2 A, R 2 A which have identical shapes. The left and right heels  2 B, R 2 B (which do not include the soles  2 K, R 2 K) are connected to the left and right shafts  2 C, R 2 C respectively which have left and right polygonal cavities  2 D, R 2 D respectively. The left and right shoe holes  2 F, R 2 F are fitted for the left and right round bars  4 A, R 4 A respectively. The left and right tunnels  2 E, R 2 E within the left and right heels  2 B, R 2 B are designed to house the left and right latches  6 A, R 6 A respectively. The left and right extension spring anchoring holes  2 G, R 2 G are for the left and right anchoring screws  7 B, R 7 B respectively which anchor one end of the left and right extension springs  7 A, R 7 A.  FIGS. 5, 7, and 9  also depict Angle1 which is the Slant angle backwards of the Fins when they are in upwards-walking positions. 
       FIG. 11  illustrates 3 views of the left member  3 A. The left member has two left protrusions  3 C 1 ,  3 C 2  which are inserted into fitting left recesses of the left Fin and lock the left Fin&#39;s angular position with respect to the left shoe  2 A. The left member  3 A has a left inner square cavity  3 B which holds the left round bar  4 A and the left compression spring  5 A. The two left strip holes  3 E are for the left strip screws  8 B which hold the left strip  8 A. The two left member holes  3 D are for tying a string which could help in pulling the left member when one wants to rotate the left Fin from one position to the other position. 
       FIG. 13  is a front view of the left latch  6 A also of right latch R 6 A which has identical shape.  FIG. 14  is a cross section side view of the left and right latch in  FIG. 13 . The left and right shoes&#39; rear sides  2 B, R 2 B house the left and right latches  6 A, R 6 A in the left and right tunnels  2 E, R 2 E respectively. The left and right latches  6 A, R 6 A have corresponding left and right opening ramps  6 B, R 6 B at one end of their respective left and right center openings  6 C, R 6 C. The left and right latches  6 A, R 6 A also have left and right latch anchoring holes  6 D, R 6 D which are used to anchor the left and right extension springs  7 A, R 7 A respectively. The left and right extension springs  7 A, R 7 A are also housed in left and right tunnels  2 E, R 2 E respectively. The other ends of left and right extension springs  7 A, R 7 A are anchored to the left and right extension springs anchoring screws  7 B, R 7 B respectively which are screwed into left and right anchoring holes  2 G, R 2 G respectively (holes  2 G, R 2 G are visible only in  FIG. 10 ). Left and right latch holes  6 E, R 6 E are used to tie strings which help in pulling the left and right latches in order to detach the left and right Fins from the left and right shoes respectively. 
       FIGS. 15-18  describe step by step the action of the latching mechanism by which the left and right Fins are fastened to the left and right shoes. Since Latch  6 A is identical to latch R 6 A we describe in  FIGS. 13-15  only the left latch  6 A. In  FIG. 15  the left ramp  4 D of the left round bar  4 A is not yet touching the left latch&#39;s opening ramp  6 B. In  FIG. 16 , the left round bar advances to the right and the left ending ramp  4 D of the left round bar  4 A is sliding on the left latch&#39;s opening ramp  6 B. This causes the left latch  6 A to slide downwards. In  FIG. 17  the left round bar advances even more to the right and the left ending ramp  4 D of the left round bar  4 A was sliding on the left latch&#39;s opening ramp  6 B to its maximal extent. This causes the left latch  6 A to slide maximally downwards until the left round bar can pass through the left latch&#39;s center opening  6 C. In  FIG. 18  the left latch  6 A springs back into the left round bar&#39;s left notch  4 B and the left round bar is now latched i.e. locked into its forward position. 
       FIG. 19  presents 3 views of the left and right round bars  4 A, R 4 A which are used for latching the left and right Fins  1 A, R 1 A to the left and right shoes  2 A, R 2 A respectively. The left and right round bars have left and right notches  4 B, R 4 B respectively for latching, The left and right ending ramps  4 D, R 4 D which are used to slide on the left and right latches&#39; opening ramps and left and right square heads  4 C, R 4 C which fit the left and right inner square cavities  3 B, R 3 B of the left and right members  3 A, R 3 A respectively. 
     The user can also detach or attach the Fins to the shoes. This is a valuable SDRF feature which enables to separate the Fins from the shoes for more compact packing or carrying. When the left and right Fins  1 A, R 1 A are attached to the left and right shoes  2 A, R 2 A respectively, they are held by their corresponding left and right round bars  4 A, R 4 A which are fastened to the left and right shoes&#39; heels  2 B, R 2 B by left and right latches  6 A, R 6 A respectively. When the left and right Fins are latched, the left and right latches opening ramps  6 B, R 6 B are inserted into the left and right notches  4 B, R 4 B respectively. The steps of latching are describes in  FIGS. 15-18 . The left and right latches  6 A, R 6 A slide inside left and right tunnels  2 E, R 2 E and they are pulled towards the left and right heels&#39;  2 B, R 2 B centers by left and right extension springs  7 A, R 7 A respectively. The left and right latches  6 A, R 6 A have Slanted left and right opening ramp surfaces  6 B, R 6 B which fit the left and right ending ramp surfaces  4 D, R 4 D at the tip of the left and right round bars  4 A, R 4 A. 
     When the user wants to attach the left and right Fins to the left and right shoes, the user pushes their left and right round bars  4 A, R 4 A towards their respective left and right latches  6 A, R 6 A. This can be done simply by pushing the left and right members  3 A, R 3 A towards the shoes&#39; left and right rear ends  2 B, R 2 B respectively. The left and right round bars  4 A, R 4 A are also being pushed since the left and right round bars are locked inside their left and right inner cavities  3 B, R 3 B respectively by left and right strips  8 A, R 8 A which are fastened to the top of the locking members by left and right strip screws  8 B, R 8 B respectively. Pushing the left and right round bars&#39; ending ramps onto the left and right latches&#39; opening ramps causes the left and right latches to slide backwards against the left and right extension springs&#39;  7 A, R 7 A biases. As the left and right latches are being pushed backwards the left and right round bars are moving forwards until the left and right latches  6 A, R 6 A are fully retracted and allow the left and right round bars to slide through the left and right latches&#39; center openings  6 C, R 6 C. This moves forwards the corresponding left and right round bars&#39; notches  4 B, R 4 B until they reach the tips of the left and right latches&#39; opening ramps. At that point the left and right latches  6 A, R 6 A are pulled back by their respective left and right extension springs  7 A, R 7 A respectively into the left and right round bar&#39;s notches  4 B, R 4 B respectively latching them to the shoes&#39; left and right rear ends  2 B, R 2 B respectively. The whole latching process is illustrated by  FIGS. 13-18 . 
     When the user wants to detach the Fins from the shoes, the user can pull the left and right latches  6 A, R 6 A by pulling at their left and right tips  6 E, R 6 E. This pulls out the left and right opening ramps  6 B, R 6 B from the left and right round bar&#39;s notches  4 B, R 4 B thereby releasing the left and right round bars  4 A, R 4 A from the left and right shoes. 
     The SDRF includes two Fin mechanisms. However, the left leg Fin mechanism is an exact mirror image of the right leg Fin mechanism. So swimmer worn SDRF has two Fin Mechanisms which are symmetrical with the center vertical line between the legs as the axis of mirror symmetry. The SDRF can be adjusted for swimming or for walking. One embodiment ( FIG. 4 ) of a left leg Fin mechanism includes a Fin  1 A which is mounted on a cylindrical shaft  2 C connected to the user&#39;s shoe&#39;s heel  2 B and can be rotated into a walking position or into a swimming position. When the Fins are in walking position, they are in upwards orientation (pointing upwards) and the SDRFs enable the user to walk freely. When the Fins are set in swimming position, they are in downwards orientation (pointing downwards) and the SDRF enable the user to swim efficiently with minimal drag. 
     In the walking position the Fins&#39; longitudinal axes of symmetry ( 1 E in  FIGS. 4,5,6,7,8,20,21 ) are pointing upwards but with slight Slant and Tilt angles. We define Slant as the angle between the axis of Fin&#39;s rotation ( 2 J in  FIGS. 5,7,9 and 23 ) and the vertical axis i.e. the normal to the shoe&#39;s sole&#39;s plane ( 2 H in  FIGS. 5,7,9 and 23 ). We define the left Tilt angle as the angle of rotation on the axis of left Fin&#39;s rotation  2 J measuring it in counterclockwise direction between the vertical axis i.e. the normal to shoe&#39;s sole&#39;s plane  211  and the Fin&#39;s axis of symmetry ( 1 E in  FIGS. 4,5, 6, 7, 8, 23  and R 1 E in  20 , 21  for the right leg Fin) when the axis points towards the viewer. Thus, when the Slant angle is 90 degrees the Fin is pointing vertically. When the Slant angle is slightly greater than 90 degrees the Fin is pointing slightly backwards. The Slanted orientations, which are described in  FIGS. 1 and 3  are slightly greater than 90 degrees i.e. Slant=90+Angle1 and are designed to enable walking without hitting the calves. Also, in the upwards walking position, the left leg Fin is Tilted to the left by Tilt=Angle2 (as illustrated in  FIGS. 3 and 6 ) and the right leg Fin is tilted to the right by Tilt=Angle2. The right leg Fin is a mirror image of the left leg Fin (as shown in  FIGS. 20,21 and 22  for the right leg Fin and in  FIGS. 4, 6, 8 and 12  for the left leg Fin). It means that all the features of the right leg Fin correspond to symmetric features of the left leg Fin wherein the axis of mirror symmetry is the vertical axis passing at the center point between the left and right shoes. Thus, in the upwards—walking position, the right leg Fin is Tilted to the right by Angle2 and also Slanted backwards by Angle1 with respect to the right calf and the left leg Fin is slanted backwards by Angle1 and Tilted to the left by Angle2. Hence, in the walking position, the Fins are Tilted outwards in symmetric angles (Angle2) that prevent the Fins from hitting one the other while walking. Both Fins are also Slanted backwards by Angle1 which enables walking without the Fins hitting the calves from behind. In one embodiment we approximate both angles to be in the range between 5 to 30 degrees. However, these angles could have other values as well. 
     When the user wants to use the SDRFs for swimming the user unfolds each Fin by rotating it around its shaft by 180−2·Angle2 degrees. This rotates the left leg Fin  1 A into a downwards orientation in which the left leg Fin is Tilted to the left by 180·Angle2 which means that the left leg Fin is at Angle2 to the left with respect to straight extension of the left calf (as illustrated in  FIGS. 2 and 8 ). The right leg Fin also is rotated into a downwards orientation in which the right leg Fin is Tilted to the right by 180·Angle2 which is equal to a Tilt to the right of Angle2 with respect to straight extension of the right calf (as illustrated in  FIGS. 2 and 21 ). Thus, in the downwards position, the Fins are Tilted outwards by Angle2 to prevent the Fins from hitting one the other while swimming. 
     While in downwards—swimming position, both Fins are also Slanted forwards by Angle1 with respect to the straight extensions of the calves. This forwards Slanted orientation is ideal for swimming because swimmers tend to turn their feet slightly backwards when they swim to reduce the drag of their feet in the water. Turning the feet backwards approximately cancels the Slant forwards by Angle1 of the Fins&#39; longitudinal axes of symmetry and the Fins are oriented in the direction of the swimming water flow and have minimal drag on the swimmer. In this aspect, the Fins&#39; orientations in the SDRFs have significant swimming advantage over the traditional prevalent Fins which are mounted at orientations which are straight extensions of the swimmer&#39;s feet soles. Since the feet soles angles with respect to the calves have quite large differences, the traditional Fins exhibit a large drag on the swimming motion flow compared to the SDRFs. 
     The Fins&#39; positioning mechanisms of the SDRFs is described as follows (referring here to the left leg Fin described in  FIGS. 4, 5, 6, 7, 8, and 12 , the right leg Fin which is described in  FIGS. 20, 21 and 22  has the same feature alphanumeric codes preceded with an R). Each Fin has a bearing  1 C which is mounted on a cylindrical shaft  2 C which is attached to the shoe&#39;s heel  2 B. The cylindrical bearing  1 C is located at the Fin&#39;s basis  1 B. The bearing has three recesses:  1 D 1 ,  1 D 2 ,  1 D 3  around its circumference which are used for the Fin&#39;s positioning. Recess1 of the left leg Fin  1 D 1  and recess1 of the right leg Fin R 1 D 1  are positioned upwards at the Fins&#39; axes of symmetry  1 E and R 1 E respectively. Recess2 of the left leg Fin ( 1 D 2 ) is positioned downwards with Angle3=2·Angle2 spaced to the left from the downwards axis of symmetry of the Fin. Recess number  2  of the right leg Fin (R 1 D 2 ) is positioned downwards with Angle3 spaced to the right from the downwards axis of symmetry of the right leg Fin. Recess number  3  ( 1 D 3 ) of the left leg Fin is positioned downwards with Angle4=2·Angle2 spaced to the right from the Fin&#39;s axis of symmetry downwards. With mirror symmetry, recess number  3  of the right leg Fin (R 1 D 3 ) is positioned downwards with Angle4 spaced to the left from the Fin&#39;s axis of symmetry downwards. 
     The cylindrical axes of the left and the right shoes ( 2 C and R 2 C respectively) which are attached to the shoes&#39; heels ( 2 B, R 2 B respectively) have polygonal cavities ( 2 D, R 2 D respectively) which house respective left and right members ( 3 A, R 3 A) with fitting polygonal bars ( 3 F, R 3 F). The left member and right member also have two positioning pins each ( 3 C 1 ,  3 C 2  for the left member and R 3 C 1 , R 3 C 2  for the right member). These positioning pins which fit all 3 recesses ( 1 D 1 ,  1 D 2 ,  1 D 3 ) of the left leg Fin and (R 1 D 1 , R 1 D 2 , R 1 D 3 ) of the right leg Fin. Due to the fitting polygonal bars ( 3 F, R 3 F) of the locking members ( 3 A, R 3 A) the orientations of the left and right members is fixed with respect to the left and right shoes ( 2 A, R 2 A). Thus, when the positioning pins are inserted into the recesses, the orientations of the left leg and right leg Fins ( 1 A, R 1 A) are also locked with respect to the corresponding left and right shoes ( 2 A, R 2 A). 
     When the pin  3 C 1  is inserted into the recess  1 D 1  of the left leg Fin and the pin  3 C 2  is inserted into the recess  1 D 2 , as illustrated in  FIG. 6 , the left leg Fin is locked in the walking position which allows walking. Since locking pin  1 D 1  is Tilted at Angle2 with respect to the vertical axis of the shoe, the left leg Fin is locked at Tilted orientation at Angle2 to the left with respect to the left calf (the left leg calf orientation is considered as coinciding with the normal to the left shoe&#39;s sole  2 H). Tilting the left leg Fin to the left and the right leg Fin to the right i.e. outwards, prevents collision of the Fins when the user walks with them.  FIGS. 4, 5, 6, 7 and 8  describe the SDRF of the left leg Fin and  FIGS. 20, 21 and 22  describe the SDRF of the right leg Fin. 
     The SDRF of the right leg Fin (described in  FIGS. 20,21 and 22 ) is a mirror image of the left leg Fin&#39;s SDRF. Thus all the angles in the right leg SDRF have the same values as in the left leg SDRF and the right leg Fin is Tilted at Angle2 to the right enabling walking without collision with the left leg Fin. When the pin R 3 C 1  is inserted into the recess R 1 D 1  of the right leg Fin and the pin R 3 C 2  is inserted into the recess R 1 D 2 , as illustrated in  FIG. 20 , the right leg Fin is locked in the upwards-walking position which allows walking. Since locking pin R 1 D 1  is Tilted at Angle2 with respect to the vertical axis of the shoe, the right leg Fin is locked at Tilted orientation at Angle2 to the right with respect to the right calf. Tilting the right leg Fin to the right i.e. outwards, prevents collision of the Fins when the user walks with them. 
     When the pin  3 C 1  is inserted into the recess  1 D 3  of the left leg Fin and pin  3 C 2  is inserted into the recess  1 D 1 , the left leg Fin is locked in the downwards—swimming position which allows swimming. Since locking pin  3 C 2  is Tilted at Angle2 downwards with respect to the downwards vertical axis of the shoe, the left leg Fin is locked at Tilted orientation at Angle2 downwards to the left.  FIGS. 6 and 8  describe the SDRF of the left shoe in upwards and downwards orientations respectively. 
     At the swimming position, the SDRF of the right shoe is a mirror image of the left shoe&#39;s SDRF. Thus all the angles in the right leg SDRF have the same values as in the left leg SDRF and the right leg Fin is Tilted at Angle2 downwards to the right enabling swimming without collision with the left leg Fin. When the pin R 3 C 1  is inserted into the recess R 1 D 3  of the right leg Fin and pin R 3 C 2  is inserted into the recess R 1 D 1 , the right leg Fin is locked in the downwards position which allows swimming. Since locking pin R 3 C 2  is Tilted downwards to the right at Angle2 with respect to the downwards vertical axis of the shoe, the right leg Fin is locked at Tilted orientation at Angle2 downwards to the right.  FIGS. 20 and 21  describe the SDRF of the right shoe in upwards and downwards orientations respectively.  FIG. 22  describes in 3D isometric drawing of a disassembled right leg SDRF with all its parts. 
     To fit the Tilted rotation angles the left leg Fin&#39;s positioning pins  1 C 1 ,  1 C 2  are spaced at angular displacement of 180−2·Angle2=180 Angle4 degrees. Similarly, the left leg Fin&#39;s recess pairs  1 D 1 ,  1 D 2  and  1 D 1 ,  1 D 3  also have angular displacements of 180−2·Angle2 degrees. This leaves the angular displacement between  1 D 2  and  1 D 3  to be 4·Angle2=Angle3 Angle4. Measuring in counterclockwise direction from the left leg Fin&#39;s upwards axis of symmetry  1 E, the angular locations of the left leg Fin&#39;s recesses are  1 D 1  at zero degrees,  1 D 2  at 180−2·Angle2=180 Angle4 degrees and  1 D 3  at 180+Angle4 degrees. 
     Similarly, for fitting the Tilted rotation angles, the right leg Fin&#39;s positioning pins R 1 C 1 , R 1 C 2  are spaced at angular displacement of 180−2·Angle2=180 Angle4 degrees. The right leg Fin&#39;s recess pairs R 1 D 1 , R 1 D 2  and R 1 D 1 , R 1 D 3  also have angular displacements of 180−2·Angle2 degrees. This leaves the angular displacement between R 1 D 2  and R 1 D 3  to be 4·Angle2=Angle3 Angle4. Measuring in clockwise direction from the right leg Fin&#39;s upwards axis of symmetry R 1 E, the angular locations of the right leg Fin&#39;s recesses are R 1 D 1  at zero degrees, R 1 D 2  at 180−2·Angle2−180 Angle4 degrees and R 1 D 3  at 180+Angle4 degrees. 
     With reference to  FIGS. 4, 5, 6, 7, 8, 12, 13-18 and 22 , the left and right locking members ( 3 A, R 3 A respectively) have polygonal bars ( 3 F, R 3 F) which are inserted into the polygonal cavities  2 D, R 2 D centered at the axes of the left and the right cylindrical shafts:  2 C and R 2 C respectively. Due to the polygonal cavities  2 D, R 2 D, the left and right members  3 A, R 3 A cannot turn around the cylindrical shafts&#39; axes  2 J, R 2 J but can move along the these axes. The left and right members  3 A, R 3 A also have inner square cavities  3 B, R 3 B which house round bars  4 A, R 4 A respectively with square heads  4 C, R 4 C respectively which fit the inner cavities  3 B, R 3 B. The round bars  4 A, R 4 A are fastened to the shoes&#39; heels  2 B, R 2 B respectively with corresponding latches  6 A, R 6 A. As illustrated in  FIGS. 5 and 7 , the round bars  4 A, R 4 A are enveloped by compression springs  5 A, R 5 A inside the inner cavities  3 B, R 3 B respectively. The springs  5 A, R 5 A are partially compressed and therefore tend to push the left and right members  3 A, R 3 A towards the shoes&#39; heels  2 B, R 2 B respectively, which in turn push the positioning pins pairs  1 C 1 ,  1 C 2  and R 1 C 1 , R 1 C 2  into their corresponding Fin&#39;s recesses. The springs  5 A, R 5 A also push the Fins towards the shoes&#39; heels and thus hold the Fins in place. When the user wishes to change the orientation of a Fin from upwards to downwards or vice versa, the user can pull the members away from the shoes against the springs biases. Pulling the left and right members extracts the positioning pins from their recesses, unlocks the Fin and allows the user to switch the Fin&#39;s orientation by turning the unlocked Fin. The pair of holes  3 D, R 3 D in the corresponding left and right members  3 A, R 3 A are designed to enable one to tie a string loop to the locking member for the purpose of pulling it for switching Fin orientations. 
     The user can also detach or attach the Fins to the shoes. This is a valuable SDRF feature which enables to separate the Fins from the shoes for more compact packing or carrying. When the Fins  1 A, R 1 A are attached to the shoe  2 A, R 2 A they are held by the round bars  4 A, R 4 A which are fastened to the shoes&#39; soles  2 B, R 2 B by latches  6 A, R 6 A respectively. The latches  6 A, R 6 A slide inside their corresponding tunnels  2 E, R 2 E and they are pulled towards the heels&#39;  2 B, R 2 B centers by extension springs  7 A, R 7 A respectively. The latches  6 A, R 6 A have Slanted ramp surfaces  6 B, R 6 B which fit the ramp surfaces  4 D, R 4 D at the tips of the round bars  4 A, R 4 A respectively. 
     When the user wants to attach the Fins to the shoes, the user pushes their round bars  4 A towards their latches  6 A, R 6 A. This can be done simply by pushing the left and right members  3 A, R 3 A towards the shoes&#39; heels  2 B, R 2 B. The round bars  4 A, R 4 A are also being pushed since the round bars are locked inside their inner cavities  3 B, R 3 B by their corresponding strips  8 A, R 8 A which are fastened to the top of the members by screws  8 B, R 8 B. Pushing the round bars&#39; ramps  4 D, R 4 D onto the corresponding latches&#39; ramps  6 B, R 6 B causes the latches  6 A, R 6 A to slide backwards against the extension springs&#39;  7 A, R 7 A biases. As the latches are being pushed backwards the round bars are moving forwards until the latches are fully retracted and allow the round bar to slide through the corresponding latches&#39; openings  6 C, R 6 C. This moves forwards the round bars&#39; notches  4 B, R 4 B until they reach the tips of the latches&#39; ramps. At that point the latches  6 A, R 6 A are pulled back by their respective extension springs  7 A, R 7 A into the round bar&#39;s notches  4 B, R 4 B latching them to the shoes&#39; heels  2 B, R 2 B. The whole latching process is illustrated by  FIGS. 13-18 . 
     When the user wants to detach the Fins from the shoes, the user can pull the latches  6 A, R 6 A by pulling at their corresponding tips  6 E, R 6 E. This pulls out the ramps  6 B, R 6 B from the round bar&#39;s corresponding notches  4 B, R 4 B thus releasing the corresponding round bars  4 A, R 4 A and their corresponding left and right Fins  1 A, R 1 A from the corresponding shoes  2 A, R 2 A.