Custom-made high-performance diving fins

[FinnFin]

I’ve been free-diving for well over a decade, also at an international competitive level, and I never found a set of fins that I would have been happy with. All the fins I bought and tried had many recurring problems e.g.:

• Why are the fins either efficient OR comfortable? What is preventing the fins from being efficient AND comfortable at the same time? My cycling shoes are achieving this, so it should not be an impossible combination.
• Why do I generate most of the power in the front/down-kick, even though I have large muscle groups available also to the back/up-kick (hamstring, glutes, lower back)?
• Why do the fins have so many weak links eroding the power transfer efficiency e.g. stretching foot pocket upper cover or compressible diving sock?
• Why is no-one making fins that would have sufficient angle between foot pocket and fin blade to prevent my knees from bending in glide and free fall?
• Why is the buoyancy correction built into the fins using compressible materials, e.g. cell foam? Wouldn’t some pressure-resistant material reduce the risk of the fin breaking under pressure and provide consistent fin performance in different depths?
• Why are the fin blades not using the same shapes, proportions, geometries and bending properties as Nature’s apex predators? Surely there must be reasons why millions of years’ worth of trial-and-error evolution has led to the designs we see in the Nature?
• Why do I need to buy a new set of foot pockets with every new dive fin? Why cannot I just attach my favourite foot pocket to whatever fin blade I feel like using for a given dive?
• Why are my diving fins so heavy? I tried attaching neutrally buoyant ankle weights to see if higher weight at fins makes the diving better, but the exact opposite happened. So, could lighter fins then make the diving better?

After thinking about this problem, I concluded that the best way to approach this problem would be to start from the diver, and more specifically an individual cast taken from her/his foot, and build a fin around the foot that fits perfectly and comfortably, and then proceed to solve the other recurring problems one at a time.

Since no other company seemed to be working on solving these issues by starting from the foot pocket, I set up a company of my own for this: www.finnfin.fi.

I would love to hear what you think of the concept and approach:

• Have these problems bothered you?
• What else would you like to have fixed in diving fins?

 

[REVAN]

I think I addressed many of your issues with my stereo fins. They worked very well, but I didn't think that I could effectively manufacture and sell them at competitive prices. Plus, I find I prefer monofins most of the time, and wanted to focus on the mono.

Let's see if I can link from a different thread:

How many others watching this thread are interested in the Pilot SR-1 fins?
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It looks like the pictures are there in link form only. Click the arrow in the header to see the original post with pictures.

Anyway, that's an interesting foot pocket design you have. Is your fin targeted toward freedivers or scuba divers? Is this early prototype development, or functionally representative equipment that is close to production hardware? What price point are you targeting?

 

[FinnFin]

I think I addressed many of your issues with my stereo fins. They worked very well, but I didn't think that I could effectively manufacture and sell them at competitive prices. Plus, I find I prefer monofins most of the time, and wanted to focus on the mono.

Let's see if I can link from a different thread:


It looks like the pictures are there in link form only. Click the arrow in the header to see the original post with pictures.

Anyway, that's an interesting foot pocket design you have. Is your fin targeted toward freedivers or scuba divers? Is this early prototype development, or functionally representative equipment that is close to production hardware? What price point are you targeting?

I tested the possibility to use ready-made cycling shoes as well in the early stage, as that would have made the product development SO much easier, but they had some fundamental problems:

• They are not buoyant: especially in long glides with kick-and-glide - type of swimming they started sinking heavily, and in free fall I had more difficulties in keeping myself in a vertical position. According to my tests, the foot pocket is the best place to compensate the sinking of the legs, as the buoyancy built into the foot pocket also compensates the angular torque of the sinking legs (=you don't turn upright at the end of the glide). Furthermore, building buoyancy into the fin (e.g. by the commonly seen monofin 'wings') completely destroyed the fin blades' performance by increasing the weight and hysteresis loss, and was possible only using compressible materials.
  
• They are optimized for a force that is towards to a different direction, i.e. towards the sole of the shoe, whereas in diving the biggest force is towards the upper cover of the shoe. This causes the cycling shoes to have a risk of breaking when max force is repeatedly applied to a direction they are not built for. When developing the product I also tested similar small ratchet buckles as are being used in cycling shoes, but they did not have the needed strength to deal with the strong kicking force, so I ended up using a heavy-duty ratchet buckle instead.
  
• Cycling shoes are built to hold the ankle in a straight angle (walking position), so holding ankles extended to a diving position caused blisters arount the achilles heel as the skin is very thin there.
• They soak water, and beceme very heavy.
• They use materials that are not intended to be used in sea water, and some corroding parts e.g. threads and closure elements (buckles, Boa dials etc. ) are permanently attached to the shoe and cannot be replaced when they break.

For these and many other reasons I needed to scrap the idea of using ready-made cycling shoes, and needed to take the long route of making also the foot pocket from scratch.

These products I show in the web page (www.finnfin.fi) are already functional production hardware. This version is hands down the best set of diving fins I have ever used. When I dive with these fins I need to constantly look down at the fins to confirm to myself that I am using stereo fins, as the speed and power I get from them is something I am used to getting from a monofin. The second reason to looking down is to check that I am actually wearing fins, because they fit so well that I don't even notice where the leg ends and fin begins, and they weigh so little that the kicking feels almose suspiciously effortless.

The price for these fins is above many other fins: 800EUR for foot pockets +200EUR per set of fin blades. This is caused by the needed extra materials and logistics for making the custom mold of divers' feet, and the many, many difficult and time-consuming process steps for making the product by custom lamination of high-end materials e.g. carbon fibre. But if you look at it from a different angle it can actually be viewed as a bargain : one set of high-end competition-level fins costs typically in the ballpark of 500-600EUR per set, so buying 2 sets of these fins (e.g. stereo + mono) can make these more expensive than buying from FinnFin. And you would be getting a long stack of innovations and benefits built into the products that few other companies (if any) can provide.

I'm targeting free diving, scuba and snorkelling divers, as in all those disciplines I've been interested in having ergonomic, efficient and adjustable diving fins. The design has some limitations, especially for scuba divers, as my design cannot be used with a dry suit, and as the blades that are oriented to the direction of the diver makes reverse kicks difficult (unless the diver orders the foot pocket with a smaller angle correction).

 

[REVAN]

Thanks for the quick reply. It looks like a cool and ambitious project, and I hope it goes well for you. Making a custom foot pocket is difficult, and I applaud your efforts in this area.

Some knowledge I have learned over time (the hard way):

Many scuba divers are more interested in how well a fin works for swimming backward than they are interested in how effective it is for swimming forward. It seems like a dumb position to hold, but that is the thinking held by a lot of scuba heads. They also care a lot about having durable fins that are good for walking around on a boat, and it looks like this may be challenging with your fins (mine were not that great for walking in either). Many of them also seem to have a mental cutoff that no fin should cost more than $200, and if that $200 fin isn't good enough, then the solution should be to buy a $4000 DPV. That's a big price deadband, IMO. But, you can expect to hear that from many scuba divers. It would be good to have your counterpoint argument ready to respond if you are going to market your fins to scuba divers.

Snorkelers just want cheap fins.

Freedivers will need to be convinced that the efficiency of the fins are competitive with the long blades and monofins that they are used to using. This is difficult, because a fin's efficiency is almost impossible to measure. If you come up with a good solution, I'd like to know about it.

 

[J Campbell]

It would be nice to see a video of these fins in action.

 

[Kizz92]

Re opening this old topic.. ive made my own design carbon fin blades, but just wondering if people use a template to cut the foot end to suit foot pockets or do you just guess it?