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They are totally different from conventional fins.

• Diminishing resistance and increasing thrust
• Small and light
• Excellent walking mobility before entering the water

A frame and sheet structure which we developed makes them possible. (Patent pending)

Beginners use them easily because of smallness of resistance and experts are satisfied with their thrust.

They become very small when folded and you can attach the fins to your shins before you enter the water, making it possible to safely walk in places with unsure footing such as rocky shorelines.

You can attach them to shoes of various sizes and shapes, such as beach shoes and Crocs, when you use them. (You can’t attach them to soft and thin soles such as flip-flops.)

If anyone would like to give us feedback, please contact us by e-mail at info@setagaya-pd.jp. We will send our product.

It should be noted that we will send them to you from Japan and all shipping charges are paid by us but you are to bear the import duty and all other local expenses at the destination.

Recruiting will last from June 20 until August 20, 2013 and will be held only in the USA.

We will close the list when the number of applicants exceeds 10 people.

We think that the ideal shape of fin is a tail of a creature which can swim very fast as a dolphin or a swordfish.

There are some similar features on fins of these creatures, such as the high aspect ratio, moderate rigidity and elastic and the cross-sectional shape.

As a result of evolution, it may be said that they got the same properties beyond the difference in species.

There is the difference between vertical and horizontal movement, but this is also the same as with tail fin movement. They have been simplified and described in the following diagram.

The diagram represents a dolphin's tail fin movement as seen from the side (from above in the case of swordfish). The dark blue part is caudal fin.

The combination of heave (lateral vibration) and pitch (rotational vibration) in the caudal fin provide progression in the direction of the arrow. The fin doesn't make large flapping rotations, so it is able to effectively produce lifting power and gain thrust while reducing water resistance.

Fins that adopt the shape and movement of a dolphin's caudal fins (fins that incorporate devices that will allow for the same types of movement seen in the diagrams above even when used by humans) actually exist, and we believe that as of the present they are as close as possible to an ideal shape.

But it is a monofin.

This is why we would like to search for this ideal form in bifins (a type of fins that are attached to both feet).

Firstly, we have something like the silhouette in the following diagram

This is common as fins go, but as the user becomes more experienced and seeks greater thrust, the vertical length becomes longer and harder in order to overcome water resistance. However, because these fins have a moderate amount of elasticity they are pliable and effective at generating thrust.

The movement of the fins can be seen in the following diagram. (The dark gray in the schematic seen from the side indicates the fin, while the light gray indicates the leg.) 

The feel is very graceful. Technological advancements have made it possible to develop materials that are rigid yet flexible, allowing for the creation of these wonderful fins.

Still, in order to effectively obtain thrust it is necessary to select a hardness that matches the speed (power) of the leg's movements. If the hardness is not suitable then it can actually have a reverse effect of reducing thrust. (This is believed to be due to the way in which turbulence is generated by the difference in the wave motion of the shape of the fins, as well as differences in the strength of the force pushing water to the rear.)

Also, the most thrust one desires the longer and harder the fins must be, which in turn generates greater resistance and thus a need for more power. This can occasionally cause pain in the toes. 

This led to fins with tips that have incisions in the center and also curve back sharply towards the legs. (The diagram below shows the silhouette of fins with incisions in the middle of the tip.)

It is possible to lower resistance by reducing the surface area and changing the angle of the periphery of the fin's cuts.

However, the decrease in thrust caused by the simultaneous reduction in resistance and lift is impossible to avoid. (Even when the surface area is not reduced, it is believed the change in lift-drag ratio will have an effect.)

Still, on the other hand one can look forward to large movements that shape the flow of the water. This makes it easier to move the fins and keeps the movement of both legs smooth.

The flow of water can be seen in the diagram below. 

This gave us an idea.

Would it be possible to more actively control the flow of water without putting incisions in the fins?

Furthermore, wouldn't it be possible to reduce resistance by preventing the fins themselves from flapping (by keeping the angle of the fins' movements smaller than the angle of the legs' movements) like the way a dolphin's caudal fins moves?

The clue to this can be found in the webbed feet of waterfowl.

The picture below is of a cormorant diving into the sea to catch fish.

Rather than choosing its target while still in the air and then diving, a cormorant instead uses its powerful swimming ability to catch prey in the water.

Waterfowl primarily swim use drag as their main thrust (however, it is believed that the final part of the paddling movement gains thrust due to lift), and their webbing has a feature that folds in order to reduce resistance when the legs are drawn back.

However, we thought that this webbing is something that could actively control the flow of water, and that it would also be possible to actively generate lift with webbing.

What proved necessary for this was a carbon-fiber frame with sufficient rigidity and flexibility as well as a durable nylon sheet.

The upper diagram is a schematic that depicts the way the folding fins we developed look when receiving the flow of water from directly horizontally and an oblique upper angle. The arrows indicate the flow of water.

Depending on the vertical and horizontal whip of the frame, the sheet will bend towards the center of the tip. We believe this focuses the flow of water in the center of the fin and allows it to be pushed to the rear more forcefully.

Furthermore, the angle created by the center portion of the sheet and the frame can be controlled by the whip of the frame when it receives water resistance.

Below is a schematic of the fin's movement as seen from the side. The dark blue diagram is the direction of the center portion of the fin's sheet, while the dotted gray line indicates the tip of the fin's frame, the dark gray indicates the base of the frame, and the light gray represents the leg.

While the angle of the direction of the center of the fin's sheet (dark blue) towards the base of the fin's frame (dark gray) may change, the angle towards the direction of progression (the arrow) is not as large as the leg's movement.

You can think of this as being very similar to the movement of a dolphin's caudal fin depicted above. We believe that this movement makes it possible to effectively generate lift while reducing resistance, and thus about great amounts of thrust.

• The fins consist of rigid frames made of carbon fiber and nylon sheets.
• The fins become very small when folded, so they are easy to carry. You can attach them to shoes of various sizes and shapes, such as beach shoes and Crocs, when you use them. 
• The whip of the carbon frame adjusts the angle of the fin's sheet towards the direction of progression, making it possible to obtain thrust efficiently.
• Water resistance is small, because the surface area of the fins is small.
• This product causes no pain in the toes because they are fixed to the entire foot.
• You can attach the fins to your shins before you enter the water, making it possible to safely walk in places with unsure footing such as rocky shorelines.

We will release this product this summer.

Disadvantages of rubber fins

1. Too bulky to carry around

When packing for a trip, conventional fins are so bulky that one hesitates to take them.

2. Increase in water resistance

Increasing the length and rigidity of fins to increase thrust, it tends to increase water resistance.

3. Causes pain in the toes when swimming

Increasing the rigidity of fins to increase thrust, it tends to cause pain in the toes.

4. Difficulty walking before entering the water

Normal fins are difficult to walk in while wearing them. Even if you wear flip-up ones, it is impossible to walk safely in places with unsure footing.

With a frame & sheet structure, all of the above disadvantages are resolved.

The fins become very small when folded.

Also they are significantly lighter than conventional ones, so they are easy to carry.

The whip of the carbon frame adjusts the angle of the fin's sheet towards the direction of progression, making it possible to not only recreate movement like that of a dolphin's caudal fin but also obtain thrust efficiently.

This product causes no pain because the frame is fixed to the entire foot.

You can attach the fins to your shins before you enter the water, making it possible to safely walk in places with unsure footing such as rocky shorelines.

We will release these fins in Japan this coming summer. Would your company like to have the exclusive rights to sell the product in a country other than Japan? We will also accept offers for in-house manufacturing of the product.

We would like to support activities of academic institutions and NPOs which conduct environmental protection or marine survey. If anyone would like to use our fins in such activities, please contact us by e-mail at the address below. We will send them with no charge. (We haven’t established mass production line yet, so it is difficult that we provide a large number of them.)

It should be noted that we will send them to you from Japan and all shipping charges are paid by us but you are to bear the import duty and all other local expenses at the destination.

info@setagaya-pd.jp

Owner-manager

Setagaya Product Development