My 'Pretty Fin' Patent

[Arak Lea]

Foil Embodiment #2

This second foil design (Fig 29) is simpler and less costly. It is shown here without fences but optionally can also exhibit that feature. In this image only the cross-section is shown. The leading edge (Fig 29-A) does not extend forward as much as the design in Image (Fig 28). There are encapsulated plastic insets at A and C.

Up to four materials can be used. These are cast in multiple steps (Fig 31), started by casting D and E as hard plastic, then casting those into C and B and finally cast everything with A. Parts E and D are made of a ridged plastic such as a medium density reinforced polyethylene. These have long tunnels inside to accommodate the axels, and holes that keep the parts locked into their positions. This is required since the material for D and E may not co-bond with synthetic rubbers. A final casting or two could be used to add optional fences.

The depth of the ‘V’ geometry will vary the distribution of bending along the foil.

Some possible ranges in silicone rubbers are;

A - Shore durometer scale A, 30 to 60 (always less than C)
B and C - Shore durometer scale A, 60 to 85 (always more than A)

If the elasticity of the middle section (Fig 31-A), needs to be more abrupt from the ends, a hip can be added, as shown in Image Fig 32. The depth of the hip can be adjusted to better interface with the middle section. This will spread the bendable area wider along the foil toward the hips.

 

[Arak Lea]

Foil Embodiment #3

The inserts are also used in the third design (Fig 22 and Fig 30) with only one elastic material. The inserts are shown in Fig 30-D and E.

Foil Embodiment #4

This fourth foil design is higher performing and much more complex than the prior three designs. Fabricating this design starts by cutting the patterns Fig 33-A, Fig 34-B, Fig 35-D and 35-E into sheets of flexible sheet plastic as shown in the images, then bedding two of them at the center lines shown. One set for each foil. An example material suitable for these patterns is a medium density reinforced polyethylene sheet about .0625in thick.

Sheets Fig 34-A and Fig 35-B are heated along the center lines and folded.

The two folded sheets are inserted into each other and as such provide 6 different distributed zones using only two cross-sections. From top to bottom in the image (Fig 36) the profiles swap from one to the other 5 times, for a total of six sections. The first profile is shown as Fig 36-A combined with C, and the second is Fig 36-B with D.

As shown in the image (Fig 37) the two parts A and B are inserted into each other, with the fingers to the inside and the twelve holes lined up in six pairs. Once they are lined up, they are firmly bolted together though each hole pair with screw posts (Fig 39). The two spacer sheets (Fig 37-C and D) are inserted and aligned to the holes, then also secured with screw posts.

Once firmly attached, the main two parts (Fig 37-A & B), when looking from the side edges, has the general appearance of a stretched infinity symbol (Fig 38-E), using an interweave (Fig 38-A).

Three screw posts are added to holes at the leading edge, close to the left of the assembly in the image Fig 37-A. This serves to restrain and stabilize the curvature at the leading edge. Typical Screw Posts (Fig 39-A, Prior Art) are as shown, a set of two parts, one set are used per hole.

 

[Arak Lea]

A pair of rubber restrictor bands are used in the two holes which are yet still unfilled, these between the interweave and holes at the far left in Fig 37-A. These banding assemblies appear in Fig 40. The assembly is configured as shown in Fig 41. The bands are first inserted through both sides, then stiff wires are inserted to retain the bands.

The bands are threaded through both surface layers of the foil (Fig 41) and restricts the width of the foil, but remain elastic in that use.

Then the next step in assembly, the two axels are inserted, one at the ‘Flex-Nose’ section (Fig 42), one at the ‘Rigid Tail’ section (Fig 42) and held in place with jigs, petroleum jelly is then used to fill all air spaces as a lubricant. Then eventually the entire foil body is put in a mold and filled with an elastic sheath made of catalyst setting silicone. That final layer encapsulates and retains the wires in place, and also as a container bottles the lubricant inside.

This foil, #4, is designed to accomplish a deformation into the required a foil shapes during each power stroke of the fin. The design of this structure is contrived to transfer, through an interwoven mid-section (Fig 42-Hinge Area), the extra material from the inside of the curve (concave at Fig 43-D), via the midsection, over to the outside at the forward ‘Nose’ section (Fig 43-A). And conversely to transfer a deficit from the outside convex curve at mid-section (Fig 43-C) over to the inside at the forward ‘Nose’ section (Fig 43-B). The banded retainers create some guiding limitation so that the nose will curve more and balloon out less (less gap between Fig 43-A and B).

During a power stroke, water pressure will put some force into pressing the surface inside the curve (Fig 43-D) against the spacers, which then press against the convex outside layer (Fig 43-C). They stay in contact since all sheet layers are resisting the bend to some degree. The material properties of thickness, compressibility and stiffness must be carefully selected to allow bending deformation, but with enough rigidity to keep the nose in configuration against that same water pressure (measured distance between A and B).

 

[Arak Lea]

Under water swim-fins can be subject to substantial ambient pressure. That situation requires that no air volumes exist inside the foil body. Any voids require a filler of some type. In addition, the foil must flex and there are moving parts that need lubrication. As previously stated, after assembly of the hard or firm parts into the foil, then the voids are filled. But some highly flexible silicone is also used.

To accomplish the fill, first a preformed dowel, made of silicon in Shore durometer scale A, 15 to 30, is lubricated (as a parting agent) and inserted at Fig 44-K. This will act as a block against leakage during casting. The foil assembly is fit into a partial mold, and some metal shafts used as the axles, are pre-lubricated and inserted (Fig 44-M and N). These are held in position by the mold. Then the void at Fig 44-A (and 44-F) is filled up to the dowel blocker with Silicone at around Shore durometer scale A, 15 to 30, and allowed to catalyze.

The flex area was previously pinned (Fig 44-N) at the tail and will act as a block so that it also can be filled with setting silicone. This is elastic as Shore durometer scale A, 65 to 90 in the void at the tail (Fig 44-J) and allowed to harden.

The foil is then removed from the partial mold. The shafts are left in position inside the foil assembly. Then the midsection is temporarily spread open just enough to inject petroleum jelly into the void at Fig 44-H, via a tube. Also filled with jelly is the void to the right of the blocker at Fig 44-K. Then the section at C is pressed back into a flat position, and the excess jelly is scraped off with a spatula.

Next, the section at G has jelly troweled into that space in the open valley at mid-section (Fig 44-G) until level and even with the sides.

The foil assembly is then placed into a full mold with a cavity having the perimeter shape as shown in Fig 45. Silicone rubber of Shore durometer scale A, 30 to 60 is injected and allowed to harden. Once removed from the mold the foil is ready for final assembly into the other part of the fin having the spars.

Optionally, the final mold for the foil can include a void for a fence as shown at Fig 47-B in the image. Or it can be left fenceless as shown in Fig 46-A. Per the prior discussion, Fig 47-B will be the more efficient design.

 

[Arak Lea]

Foil Embodiment #5

Optional to using sheet plastic, a 3d print can also build up a skeleton of the foil in this fifth design. The images Fig 48 and Fig 49 indicates the difference in cross-section between sheet material and 3d print fabrication.

As was the case with the sheet fabrication the profile (Fig 50-B) is reversed (in Fig 50-E) at regular intervals for a total of six profiles (Fig 50-B and C). In the case of 3d printing, after printing, a router is required to cut slots, shown as left to right voids at Fig 50-D. These are placed between each profile to remove undesired material. This then allows unrestricted sliding motion that duplicates the sliding action of the sheet version.

 

[Arak Lea]

Foil Embodiment #6

A sixth foil design presented in Fig 51 is based on hydraulics. The foil materials are elastic silicone with at least three different durometer values used. The foil contains a network of channels filled with a light oil. The channels collectively form 4 different chambers crosslinked in two pairs.

Each chamber has a different function. Fig 51-A is connected to D. And 51-C is connected to B such that oil can flow between. A change in the curvature of the foil affects the volume of the adjacent chamber local to it. While the chamber Fig 51-A is compressing, Fig 51-C is decompressing, and visa-versa. Fig 51-A works to control the fluid volume in Fig 51-D, and 51-C controls B. As a net result, Fig 51-B will always go more convex while D goes more concave, and visa-versa.

In typical operation there are two cycles that a chamber-pair will experience. Per the image, as a fin moves in a stroke, down in the diagram, pressure pushes on the Fig 51-C side of the foil and it responds by a concave bending. Chamber Fig 51-C becomes shorter, purging some fluid into B, which expands. This bends the leading edge of the foil. At the same time, chamber A, being outside of the curve, Fig 51-A expands in length, creating space and lowering the pressure inside. This allows some fluid to return from its pair-mate which is chamber D. D has been shortening due to the bending at the leading edge, and the excess fluid needs to exit into chamber A.

Since A/C chambers have a larger surface area than B/D, there is more total force when under the pressure of a kick stroke, this overwhelms the forces applied to the smaller surface areas that B/D are subject to. The spring resistance of the foil body works to limit how much the foil bends under an encountered force. Therefore, this controls the foil geometry and thereby how much fluid moves between chambers. The size of the passage way between chambers needs to be large enough to not restrict fluid flow. If pulsing or fluttering were to be a problem, some restriction may become necessary.

 

[Arak Lea]

The cross-connected sections of paired chambers can be adjusted relative to each other. This will change the amount of leverage each has in controlling fluid flow. A larger chamber thickness in B compared to C will gave C more leverage. But in trade this will give B less dimensional change per volume of fluid moved, and comparably less curvature.

If the chambers were each a simple large single volume they might ‘bubble’. A bubble effectively disables the interaction between paired chambers. A complex structure is used to limit this deformation.

Each chamber of the four, are actually a network of channels. The arrangement creates internal ‘attachments’ that restrain the sides to remain closer to their initial thickness. This enables the length dimension to be more central in controlling internal fluid volumes.

In the image Fig 52, there are 4 distinct cross-sections shown that run from leading to trailing edges of the foil. Fig 52-D is a simple end cap or wall, and exists only at the far left and right edges of the foil. The profile shown by Fig 52-B contains the restraining cross-links. The number of cross-over ‘attachments’, and the count of B profiles, can be adjusted to give more finite control of the width dimension along the full length. The image only shows 3 ‘attachment’ in profile Fig 52-B.

Fig 52-A and C are mirror opposites and contain the cross-over channels that effectively pairs major chambers together. The Fig 52-B profiles are used to separate A and C profiles. The B profile provides cross linking voids that allow channels to belong together, effectively making a single larger chamber. B profiles also provide the attachments that hold the thickness of the foil in dimension. Finally, B also provides the blockage walls that isolates the two distinct chamber pairs from each other. This is important since the two pairs are always in an opposite cycle from each other.

 

[Arak Lea]

Scanning across the width of Fig 53, the profiles would start with D. Then sequences of C-B-A-B until the end with a final C-B-A-D profile set. Fig 53-E illustrates use of 13 sections. The actual count is a selection based on trading off between complexity and finite control of the foil surface.

This foil design has at least three materials of different Durometer scale settings. The tail (Fig 54-A) is the stiffest possible at A-90 or above. In Fig 54-E and Fig 56-C are relatively elastic and Fig 54-D and Fig 55-D are somewhat stiff. The D zones need to be able to bend, but stiff enough to limit bulging from intruding into the adjacent and opposite chamber.

This design is a candidate for 3d printing in multiple silicone materials. But until that becomes more practical and common, it can be made with multi-casting and other fabrication methods.

To start two shafts are prepared by lightly lubricating and inserting into silicone sleeves. Then these are placed in a mold and the tail structure at Fig 51-A is cast including the center-line wall (Fig 54-D and Fig 55-D), including the centerline wall forward of the leading axle. This casting will bond to the sleeves.

Then this structure is placed in the next mold where a set of filler forms are cast correlating to the chamber voids.

The center filler is made of a material that will dissolve in a solvent or when heated that does not affect the silicone of the other parts. This material does not bond to the silicone parts. Low density styrene is one that is suitable. Paraffin wax is another possible material.

This composite structure is then placed in a mold and the shell element E is cast. At the same time the shell (Fig 54-E and 55-E) bonds where contacting the existing silicone parts. Next, as noted above, the filler material is now removed. Next the assembly is cleaned removing any residual filler material.

The assembly is placed in a mold and one end-cap is cast on. Then the voids are filled with a suitable fluid. Next it is carefully placed in a final mold and the last end cap is cast on.

The costing processes above would include shaking or vacuum steps to eliminate bubbles and ensure the integrity of the two sets of sealed chamber pairs. The chambers are now fully enclosed and filled with a fluid suitable for hydraulic operation.

 

[Bubblesong]

My recommendation is to talk to a physical therapist that understands how swim exercise with your new fin design affects parts of the feet, knees and legs, for the smoothest, most constant pressure transfer during the entire swim stroke.
Best Wishes!

 

[Arak Lea]

Foil Embodiment #7

The sixth foil mechanism utilizes flexible cable loops. The cables slide inside of plastic sleeves (Fig 57). The sleeves a tube of slippery and flexible material such as Teflon, Nylon or polypropylene. The cable is packed with petroleum jelly inside the tube section as a lubricant and to eliminate air spaces. Prior to packing, the cables ends are tack welded together (Fig 58) and embedded in an epoxy block (Fig 59-E) as shown. The tubes do not need to be embedded inside the block and can be kept free and able to slide freely on the cables. The actual length of the two cable loops are nearly the same but not exactly so as to accommodate a slightly wider path that the outside loop (Fig 59-C) will take compared to the inside loop (Fig 59-D) once they are installed. Three sets of dual loop cable assemblies are required per fin.