Benefits over typical diving fins

Typical diving fins:

Efficient OR comfortable

Efficiency and comfort have been a rare combination (red) in diving fins for a long time

FinnFin benefit:

Efficient AND comfortable

Custom-made for each leg’s 3D-shapes according to individual molds

Distributes pressure over a wide area

Even today, highly efficient competition-level diving fins continue to be very unergonomic, causing the pressure to concentrate into small and painful pressure points (red)

Typical diving fins:

Ankle can over-extend

If the diver has flexible ankles (green), then kicking with a powerful fin (red) can cause the ankle to over-extend into a position that human anatomy cannot tolerate

Over-extension can cause both acute pain and long-term injuries

FinnFin benefit:

Ankle protected from over-extension

Ankle lock can be attached optionally to the fin when needed

Protects the ankle from over-extension

Typical diving fins:

Power dominantly from down-kick

The fin bends and creates forward thrust dominantly in the front/down-kick (green)

Minimal bending and thrust is generated in the back/up-kick (red)

FinnFin benefit:

Power also from up-kick

Stiff foot pocket sole provides leverage when using calf muscle in up/back-kick

Ankle lock can be attached optionally to the fin when needed

Powerful back-side muscles (hamstring, glutes, lower back) can be used in up-kick with no work needed from calf muscle

Large unused muscle groups

Human body has powerful muscle groups that could produce power also to the up/back-kick (green)

Working agains own muscles

Transferring these muscles’ power into the fin blade requires a large effort from calf muscle to keep the ankle from pivoting (red)

Typical diving fins:

Power transfer losses

Typical diving fins lose much of the power generated by the diver before it is transformed into forward thrust:

Foot pocket material (rubber, plastic) stretches in the kick, causing a power transfer loss
The foot shakes in the poorly fitting foot pocket before beginning the power transfer
Diving sock squeezes and thus consumes the energy that could have been used for propulsion

The ankle bends and stretches, which consumes the available range of motion that could have been used for power generation

FinnFin benefit:

Seamless power transfer

Foot pocket material (e.g. carbon and Kevlar fibers) does not stretch

Custom fit ensures that the foot does not shake in the foot pocket, and there is no need to wear a squeezing diving sock

Stiff sole and the optional ankle lock increase the range of motion where power can be generated

Typical diving fins:

Drag in glide phase

In the glide phase between kicks, the hydrodynamic drag guides the fin blade to be parallel with the diver’s direction (green)

If the diver’s ankles are not flexible enough, this causes a bend in the knees (red), which in turn increases the diver’s drag

Additionally, in long glides the legs and fins can begin to sink which further increases drag

FinnFin benefit:

Less drag between kicks

Foot pockets have angles that orient the fin blade to be parallel with the diver’s direction

These angles are custom-made for each leg separately to ensure they are sufficient and balanced

The angles are made with buoyant and pressure-resistant (over 200m) material which help reduce the drag also in longer glides

Some high-end fins have built-in buoyancy and angle correction (green) that seeks to mitigate the sinking of the fin in glide phase and the bending of the knees

However, these angles are often too small, don’t account for flexibility differences across ankles, and are made from compressible material (e.g. cell foam) that subjects them to breaking under deep dive’s pressure

Typical diving fins:

Inefficient fin blade

Kick phase

In the kick phase, a fin generates forward thrust when the fin blade is bent into an efficient angle of attack (~45 degrees)

Most fins use only a small fraction of their overall length in this efficient angle (green)

Often the end of the blade bends too much, and does not generate thrust efficiently (yellow)

Even worse, the start of the blade bends too little, and only moves water at a 90-degree angle fompared to the diver’s direction (red). This consumes energy, but does not generate thrust.

FinnFin benefit:

Efficient fin blade in all phases of the kick cycle

Correct length and progression of stiffness to

Account for a wide range of kicking force from relaxed kick to full strength
Minimize the amount of insufficiently bending fin

High lateral stiffness to keep the fin stabile and balanced

End phase

In the end phase of each kick, the fin blade needs to release the energy that has been stored in the bending of the fin. This requires the fin blade to have low energy release loss (hysteresis).

Most fin blades use materials that have high hysteresis loss, e.g. rubber and plastic, that are never used in other high-end applications where low hysteresis loss is required, e.g. archery

Custom-laminated, aerospace-grade carbon fibre

Low energy release loss (hysteresis)
Low weight (~180 g/fin)
Stiff and strong attachment point to foot pocket

Glide phase

In the end lide phase between kicks the fin blade needs to create as little drag as possible. This drag is mostly dependent on the shape (geometry) of the fin blade.

Most current fin blades’ front- and tail-end shapes don’t use the best practice shapes of Nature’s best divers, e.g. sperm whales

Efficient shape using the same geometries as Nature’s best divers

Thin and correctly angled front end to cut through water in glide phase
Tail end shape for guiding the thrust into propulsion

Typical diving fins:

Unstandardized and fixed fins

In most current fins all parts are permanently attached to each other

There are no standards for comparing e.g. foot sizes or fin stiffness or bending characteristics

Often the diver does not know if the fin is good or not before (s)he has already bought it

Divers wanting to find one set of good fins, or right fin for different dives need to buy multiple fins

This resuires the divers to buy again also the parts that they are already comfortable with, e.g. foot pockets
Furthermore, divers cannot combine the fins’ best parts, e.g. best foot pocket to best fin blade

FinnFin benefit:

Right fin for different dives

Exchangeable fin blades, even from stereo to monofin to meet the different needs of individual dives

Use the same foot pocket for different dives

Optionally attachable ankle lock

Typical diving fins:

Multiple compromises in construction

Typical diving fins are very heavy even when they contain no advanced features, such as buoyancy and angle compensation

Sub-optimal materials and constructions used to achieve low cost and mass production speed

FinnFin benefit:

Made for high-performance diving

Pressure-resistant and buoyant angle material which is specified to tolerate over 500m depth’s pressure enables consistent performance under depth as on surface

High-end material e.g. carbon and Kevlar fibers

Low overall weight
Made variably stiff (e.g. foot pocket sole), compliant (e.g. foot pocket upper) or flexible (e.g. fin blade) depending on the need

Fixtures and attachment points made from stainless steel

Heavy-duty velcro- and ratchet straps that can be operated easily in water even when wearing gloves

Materials and designs that have been selected for marine conditions: moisture, pressure, salt, UV-radiation