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