• Welcome to the DeeperBlue.com Forums, the largest online community dedicated to Freediving, Scuba Diving and Spearfishing. To gain full access to the DeeperBlue.com Forums you must register for a free account. As a registered member you will be able to:

    • Join over 44,280+ fellow diving enthusiasts from around the world on this forum
    • Participate in and browse from over 516,210+ posts.
    • Communicate privately with other divers from around the world.
    • Post your own photos or view from 7,441+ user submitted images.
    • All this and much more...

    You can gain access to all this absolutely free when you register for an account, so sign up today!

Freedivers getting softer?

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.

Blade hardness you use for CB

  • Hardest I can find

    Votes: 10 14.7%
  • Hard

    Votes: 15 22.1%
  • Medium

    Votes: 31 45.6%
  • Soft

    Votes: 12 17.6%
  • Butter

    Votes: 0 0.0%

  • Total voters


Well-Known Member
Aug 10, 2001
Moving towards softer blades?
Would you guys think that the trend for harder and harder blades is flattening out? It seems to me that today more divers are using responsive (carbon or fiberglass) but softer fins. The target depths are still increasing but fin hardness is decreasing.
My personal experience is that I'd rather be powering a softer blade with slow, controlled dolphin kick than struggle with hard blades (regardless mono or bi). Any input on how this works?

I think that's like cycling.
for same speed, racers like armstrong spinn a lot (100 a minute) but some others guys spinn less (70-80 a minute).

hard fins-less kick
or smooth fins -more kick
It depends on your type of muscles fibers.
  • Like
Reactions: gitano
Have to be careful when talking about hard/soft blades and comparing mono and bi-fins....

Monofins have a much larger surface area, and I think dolphin kicking with a soft monofin will feel like more resistance then fairly stiff bi fin. I use Picasso carbons which are about as stiff as you get with Bi-fins. You can't compare exactly but dolphin kicking with these feels at least as soft as a long distance mono ie Waterway LD1. I've tried a medium distance fin and it feels heaps stiffer, probably too stiff for freediving.

What suits me is stiff Bi-fins, and soft Monofins. I did notice at the Pacific cup that a lot of people were using quite soft carbon Bi-fins. I think you have to chose a fin that's suits your fitness, size & technique. A stiffer fin is probably a bit more efficient at a higher speed. I think someone also mentioned before that if you have a good technique with a monofin, that it will work well with a soft fin. Someone using mostly their legs might prefer a stiffer fin.

Just my thoughts :D


I think that the best stiffness of a monofin can be found after invention of a new kind of footpocket where the foot desn't move in a rubbershoe.
All the power will then go straight from the body into the blade.

When we have this solution we can work on the perfect stiffness and the blades are probably getting slightly softer I think.

Very important is also the angle between the feet and the blade, it has to be made so that the blade is "in line" with the body.

Now I think you have to compensate the blade to beeing stiffer because of that the feet moves 0,5-2 cm up and down when you swim.

I think that the monofin market has very very much potential of improvement compared to for example alpine skiis or montainbikes.....

Right or wrong, this is what i believe in!

Peter Ols
  • Like
Reactions: kirehe
Comming from a fluid analysis type background, there's a question eric posted a while back that I often think about... imagine a dolphin - their bodies are relatively similar to ours (in size and shape) but their tail compared to a monofin is tiny, yet they can reach incredibly fast speeds. Why? I'm sure there's a lot to do with muscles and a little streamlining, but there's still plenty of room for monofin design. Pity I've allready finalised my thesis for this year, or it'd be a good topic :)
dolphin shape

Interesting point about dolphins. I remember watching a documentary about them and the scientists tested their swimming efficiency by having them swim against a strain gauge and record heartrate, respiration, etc. It turns out that they produce the most power for the least amount of work out of all the animals tested. Unfortunately they did not provide a list of animals tested but it still shows that their shape plays a huge part in their tremendous swimming ability. In their case I would say that eventhough they have tails with small surafce area, obviously this is not a detriment because their entire musculature is devoted to swimming.
Dolphin fins

I agree the dolphin is interesting!

I think the most important difference is that a dolphins fin is a part of the body and can be controlled by muscles through the whole stroke.
That means that a dolphin has the right "attack angle" through the whole kick and also there is muscles in the fin that makes them able to change the shape etc.

A monofin is a made of "dead" material and we must compensate this by making it another shape.

I think that the shape is quite good in monofins used in finswimming competitions, the bad link in the construction is in my opinion the attachment to the foot.

Hoping to see new innovations on the monofin market.....
Why you can't swim like a dolphin.

In addition to the obvious hydrodynamic advantages (topedo shape), dolphins use carangiform locomotion. This is characterized by a nearly stiff anterior with one flexible area on each side of the caudal peduncle. The reason the caudal fin is crescent shaped is to optimize propulsion by putting most of the fin's surface area outside the turbulent wake created by the body. This is a very fast means of moving through a liquid medium, but it requires a few adaptations to pull it off (I'll try to keep the jargon limited). First you will need a lot of tightly nested muscle with powerful tendons which extend and insert either on peduncular vertebrae or the caudal fin itself. This allows the peduncle to be oscillated rapidly while keeping the angle of attack of the caudal fin optimized. We are not blessed with this feature. [Comparatively] we have loosely packed muscle, with very little attached to our lower vertebrae. We also have multiple pivot points (with very unequal directional thrusting), and a central pivot instead of the needed posterior pivot. In order to pull off this kind of swimming we would need ultra rigid (strong) leg muscles and very flexible knees, and be able to keep our hips and waist completely stiff. Only this kind of movement would prove beneficial to a fin that is very wide and narrow.

In truth, we swim more like a trout. Trout use Sub-carangiform Locomotion (see photo). Forward flexions start the adjacent water moving to the rear; as it goes back each segment, having a greater amplitude, adds to the acceleration. The last edge of the caudal fin provides the greatest thrust, determining the final acceleration given the water. The broader the span of the caudal fin, the greater the mass of water that will be affected. The fish moves forward as water is accelerated backwards.

I presume that this is why monofins have their current shape and flex.



Blake, R.W. (1983). Fish locomotion. Cambridge university press, Cambridge.

Weihs, D. (1989). Design features and mechanics of axial locomotion in fish. American Zoologist. 29(1): 151
Last edited:
  • Like
Reactions: Erik and loopy
Ted- Great post, thanks for the in depth analysis. When you watch monofinners what do you think could be inproved in terms of both the fin and the actual undulation of the body itself to be more efficient or, or dare I say, "trout"like? I think we often try to emulate dolphins because of their allure and majesty, yet at the same time this might be an error because our physiology for swimming may more closely resemble another animal.
Thanks Ted!!

That was a real good explanation:p

What do you think is of most importance if one want's to develop better monofins?
Peter and Jim,

Thanks for the compliments :). My obsession with fish knows no boundaries.

Those are good questions, but probably better answered by someone who actually uses a monofin :D.

That said, I will share this... I "dolphin kick" frequently with my bifins, and from what I can put together, maximum (most effecient) thrust is the perfect combination of three things: 1. timing of undulations 2. force of the undulations 3. stiffness/size of the fin. If it feels like you are grinding your fin through the water, it is most likely too stiff (or large) and is creating turbulent flow. Turbulence creates a low presure pocket, that sucks the diver back into the area of water he/she just displaced. It is the ultimate enemy of efficient aquatic locomotion. On the other hand, if it feels like you are running in sand, your fin is probably too soft (or small) for you to get the most out of your kick. When all three conditions are harmonious, it doesn't even feel like work.

I'll bring my mono to hockey tomorrow night Ted and you can demonstrate. ;)

My first blades (plastic) were ROCK HARD.

The the technical reasoning I used when buying them was :

"I am a MAN"

I had alot of trouble with my style mainly due to the blades slipping as I kicked.

When I changed to Carbon I was advised to go with the softest blades that C4 made. Alot of guys were buying stiff fins for training and always using the softest for competitions.

I guess the comparison between soft carbon and hard plastic isn't fair, but I'm delighted with the flexibility and power of the new blades. They allow you to swim effortlessly (they curve perfectly with no 'folding') and then powering you along as they recover. It's weird actually.

I am also able to justify the lack of macho stiffness because :

1. They look cool
2. Everyone knows they cost a fortune :D

They also feel fabulous when I dolphin kick. I think Eric once wrote that soft bifins were awful for dolphin, but I find they become a real extension of my body and I don't feel them at all.

I'm not going very deep, but despite their model number (25), they still feel strong at 30 and beyond.

  • Like
Reactions: ivan
If freedivers getting softer why everybody recommend to me a carbon monofin or a monofin with a stiffness as a carbon blade?

Is maybe alastairs comment trye ? Is it lite about macho stiffness?

i'm waiting for a new monofin from Specialfins. carbon blade extra stiff, 65cm long by 85cm wide. it's gonna be a handfull to use but i wanted to try this big and stiff approach, (hmmm sounds like a macho problem actually) always liked stiff monos, and also i love sprinting underwater. if Ted is right about the turbulence causing a preasure pocket, well i won't be able to move with this one ! will let you know how it goes. also, as far as i know dolphins get most of their propulsion from the upward movement of their kick (opposite to us). delphicly, Noa

If you've got the strength and technique, you're sure to be rockin'. If this is your first mono, you may have bitten off more than you can chew. Stiff fins are not the specific cause of excess turbulent drag; any fin has this potential. Turbulent drag increases when the power source (you) isn't strong enough to create the optimal kick. There are other [technique/frequency/angular] factors at work as well, but that one is a biggie.

Good luck to ya. Please share your experience with the forum. That mono looks like quite a piece of technology :p.

Originally posted by noa
[also, as far as i know dolphins get most of their propulsion from the upward movement of their kick (opposite to us). delphicly, Noa [/B]

If this is the case, why don't you swim facing up??????

Would this make you go faster or no difference???

the upbeat and donwbeat

Upbeat- The upbeat has to be viewed primarily as a preparation for powerful downbeat. Most experienced coaches believe that the upbeat can make no direct contribution to forward propulsion, but that it has two alternate functions. First,it prepare for the downbeat. Second,the reaction of the upbeat helps to stabilize body position. The argument is that since the upbeat can make no contribution to body speed, the main concentration should be on raising the leg with a minimun of water resistante. In brief the upbeat cannot help propel the body forward, but it should not hinder by creating unnecessary drag

Donwbeat- The downward movement of the legs is the obvious source of power. Iin whipping downward the legs build up to a fast and powerful backward thrust of the feet. The power of the downbeat is due to the construction of the legs. The legs can straighten with great power; the extensor muscles of the thigths are capable of enormous drive
Ted, no not my first mono, thank god ! still think it might be a bit much for me but the intention is on getting some gear that pushes me to progress. always done that, always worked (often with pain...). will let you know how it goes. in the mean time if you have any swimming/diving technique suggestions for such a fin please send them my way. Thanks for the help. Delphicly, Noa
DeeperBlue.com - The Worlds Largest Community Dedicated To Freediving, Scuba Diving and Spearfishing


ISSN 1469-865X | Copyright © 1996 - 2024 deeperblue.net limited.

DeeperBlue.com is the World's Largest Community dedicated to Freediving, Scuba Diving, Ocean Advocacy and Diving Travel.

We've been dedicated to bringing you the freshest news, features and discussions from around the underwater world since 1996.