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Monofins Vs Bi - fins.

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.

I chose the 'peter' model simply because it's the latest offering; a middleground between the 'karmo' and 'teppo', plus I was curious about the 'wing' construction, even though it probably won't benefit a mono-newbie like me, at least not right now.

My 'peter' medium stiff blade is a good inch shorter than my waterway model 1 medium. However, it's definitely a little softer than my waterway; I can overpower it when I inadvertently kick instead of undulate.

I have no preconceptions as to how the Sebak mono should perform, since it is different from most other monofins in a fundamental way (closed heel vs open heel). If it turns out later that I can still mono-kick with my omer millennium comps better than the Sebak, that's fine; it'll have been a good experiment.

Anyway, it'll be a while before I work out the right posture and stroke for this monofin (the 'spaz period' as Erik Y. put it). I'm sure I'll have to be more flexible overall to account for the foot-flex not present in the Sebak fin, but that's okay too if it means I can spend more time in the water.

Peter S.
day two.

I have tried the fin twice now. Things seem to be fine. The footpocket hurts my right foot under the ball of my foot into my toes.
This could be just getting used to the fin /pocket/ technique or could be the pocket. ( my left foot does not suffer though ) If i remove the fin for 5 minutes and then continue again it hurts much less for the rest of the session.

The more i use the stiff blade the more i like it. Granted i'm no 80m diver but this blade should use no more ( nominal ) air on the way down and should bring me back solidly. I tend not to hang around on the ascent. Perhaps this will change as i become more experienced and the blade will then be too stiff.

I do weigh in at 108 kg and the softer blade ( medium ) for me seems to fold too easily and feel insubstantial after the hard.

As for power transfer onto the blade i have no clue except that in every fin i have used especially for hockey , the stiffness of the sole contributes to the power transfer. Fin stiffeners are even inserted to further stiffen the pocket sole to increase power transfer instead of power loss through flexing.
Perhaps the knee bend is more prominent with stiffer pockets because the foot cannot bend instead ?
And perhaps because in resisting the knee bend,( for the sake of widely accepted technique) the foot is attempting to bend in compensation and is pressing the ball of my foot ( right dominant) into the sole with a cramping result.

Mono size.

The foot pocket on the sebak fin is not the only problem, the blade is too small and too stiff

Eric. The waterway fin was the only other 'acceptable' performance orientated fin you mentioned so :

I have been to the waterway site and whilst i realise that whilst they could be producing larger 'custom' fins, the largest advertised is considerably smaller (70 x 62cm) than the Sebak. My Sekak measures 75cm x 75cm including footpockets.

This is both wider and longer. ( presumably they include footpockets in their measurements.) How do you reconcile this information?
What do you feel is the appropriate size for a mono? ( constant weight )

I ask because i naturally want to believe that i have made a good choice of product.


Any mono might be acceptable, as long as it has a 'normal' mono footpocket, and not bifin footpockets. So, a sebak finswimming mono will do just fine.

Eric Fattah
BC, Canada
still don't get it

Hi Eric,

I don't understand why you feel full foot pockets on a mono aren't as beneficial as open foot pockets. I read your post with the sprinter analogy and I understand that flexibility is important, but how does this differ from bifins.

I have used bifins with both full foot pockets and open foot pockets and I definitley get more efficiently out of a stiff full foot pocket regardless of my kick (dolphin or flutter). The energy from my upper body/legs is transferred to the fins much more efficiently.

Would your argument for open vs. full foot pockets on a mono not apply to bifins also? I expect your opinion must have something to do with the fact that your feet are essentially bound together with a mono, but I can't make sense of this.

Would you mind elaborating.


Ottawa, Canada

First of all, you must remember that anything that I post here is just my opinion. I could be wrong about everything! (Quite likely actually)

I often try to justify my opinion with some sort of argument or explanation, to make it more credible. I have ideas as to why the bifin footpocket doesn't work on the monofin. But, I'm really not sure if my theories about this are right.

In the end, I will fall back on a simpler argument.

Open heel bifin footpockets are still much different than open heel monofin footpockets. If you took an open heel bifin footpocket and put it on a monofin, I bet it still wouldn't work. We must give some credit to those people who came before us, who invented the bifin footpockets (both open heel and closed heel), and those people who invented the monofin footpockets (in this case open heel). Oven the last 20 years, I bet that many people (including myself) tried to deviate from the 'joke-simple' monofin footpocket. If any of them had succeeded, their invention would have become standard, and the monofin world records would have been set with the new footpocket. The finswimmers have had a lot of time to experiment.

Now, we must not make the mistake of assuming that everything is perfect and things cannot be improved. I'm sure both bifin footpockets and monofin footpockets can be improved. The solution, however, (in my opinion), is not to take a footpocket designed for bifins and put it on a monofin. This opinion is backed up by my experience. Not only did the sebak fin not seem to work properly, but I had previously tried a similar idea about 18 months ago when I inserted plexiglass soles into my monofin to 'complete' the heel, so to speak. It felt great! It felt like I had huge power transfer! I was so happy, until I tried a deep dive. My pb in constant weight at the time was 67m, and I tried 53m in VARIABLE weight with the new footpocket, and I blacked out at the end! Then I spent weeks trying to understand the problem, and it started to make sense.

In the end, I encourage you to develop your own opinions. Try every possible footpocket on your mono. Try 27 different monofin shapes and stiffnesses. In the end, you may very well come to the same conclusions that I did (after spending hundreds of hours and thousands of dollars). Or, you might come to completely different conclusions. If you have a new custom mono, with a custom shape, custom stiffness profile, and custom footpocket, I have probably already tried that configuration and I can offer my opinion, but in the end your experience with the same config may differ.

Eric Fattah
BC, Canada

Thanks for your info. It's great to get info and opinions from divers such as yourself who have learned through trial and error over the years. Hopefully I'll have equally valuable info for divers in the future.

Ottawa, Canada
Eric, thanks for your extensive information. I can only agree with Jason; you are a great asset to many less experienced freedivers.

Now, if the full foot pockets dont work perfectly for monofins (to the extent that we can generalize Eric's results to all other monofin swimmers), then is it really so that they are the best option for bifins? Peter from waterway would say no, but some might not take his word for granted since he runs a commercial business. However, there is a lot of data that support him. For instance, the monofin records are beaten with open heels (for both sprints and freedives), and, as Erik pointed out, probably the finswimmers would have used another footpocket if it was found to improve speed/efficiency.

the full foot pocket, though, has one distinct advantage: its comfort. I have yet to try an open heel, but most people appear to agree that full foot pockets are more comfortable.

in the end, we seem not to know enough to make a correct decision. We can, however, take an educated guess on the following:
A) monofins work best with open heels
B) bifins are more comfortable with closed heel, but that may not necessarily be the fastest/most efficient way to swim.

This might be a bit redundant from previous threads, but it's just what I get from the current and past discussions. If I am wrong, please correct me.

The closed heel pocket gives the foot control over torque (twist). A bifin is inherently unstable and the foot must prevent the fin from twisting. This 'torque' is much easier to apply with a full foot pocket. That's why I think bifins with a mono-type open heel would be unstable. However, with a mono, the two feet create a 'plate' with a width so wide that you can apply a huge torque to the mono (even with a floppy open heel footpocket), and the mono (by its aspect ratio) is inherently more stable than a bifin anyway.

So, I think that the full foot pocket probably works better than open heel for bifins.

Eric Fattah
BC, Canada
Lets talk about size.

Eric. I think many of your points are valid, and equally valid is your point that different people may have different outcomes with varying equipment combinations.

Having tried the fins last night again i would moot that the closed heel dissuades one from using what Peter from Waterway calls 'finger' (sic) kicking. As such the power upstroke is (so far) practically non existant for me. I merely place the fin in the correct position for the power downstroke again.

I wonder if this aspect of open vs closed heels - ie. the loss of flexibility in the foot of a closed heel to perform a powered upstroke - is not the basis of your finding that the full pocket mono will propel you less and less efficiently than a good bi - fin. ?

I have absolutely no doubt that in terms of absolute distance achieved with one downstroke only, i will glide further with the full pocket mono than any bi - fin i have ever tried.
As for efficiency, in the same test, at this point i would say the mono will eat more fuel but that could be as a result of my ineptitude in its use owing to my basal position on the learning curve with it at present, as well as my fin's particular stiffness not being designed primarily for efficiency but rather for absolute power transfer. ( on the down stroke :) )

From a prespective of power alone and efficiency aside, I would certainly give credence to an opinion that claimed that an open heel mono will outperform a closed one because of the added advantage of being able to perform a more effective upstroke. It follows also that bi - fins also have a reasonable upstroke when dolphin kicked.

But I cannot see that an open heel fin will defeat a closed heel mono on the downstroke alone. The power transfer from my body to the fin, to the water, in my closed heel mono is absolute.

(On the stiffness issue i am in a point in my experimentation where i believe in going down gently, turning, pausing to collect my thoughts and relax, and then keeping a steady rhythmic but powerful ascent @ .2 or .3 m/s faster than my descent. This probably has its roots in a "better get back before i die" inexperienced philosophy but thats the curve im on. Also i'm heavy and feel i need more power to lift me than someone half my weight and therfore a stiffer fin. Fortunately i have the legs to power my fins and secretly i hope that the controlled increase of power i engage on the ascent does not use more oxygen as i am engaging ATP and anaerobic processes.) Having said that it is my short term goal to slow my dives down from 1.3m/s to 1m/s or therabouts.

Naturally we all realise that everyone expresses an opinion here and that those opinions may be flawed, but as some like yourself have a wealth of experimentation between the shoulder - blades your opinions are highly valued, probably as you are of the few at the cutting edge of experimentation that is willing to share your knowledge and fortunately you have the ability to apply your results and bring across your points in a salient and pertinent manner. As such, opinions like yours are often taken as a starting point for others new experimentation rather than to waste time treading covered ground.

Many thanks
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More comments

Laminar and I both noticed that the giant omer footpockets seems to lower the hydrodynamics of the feet.

When I first put 'insert' soles into my mono ages ago, I was surprised to find that I could no longer sink inverted. I was unable to 'point' the monofin in such a way that it was in the same plane as my body. The tip of the mono would always be pointing away from my body, due to the fact that my heels prevented my toes from pointing in the correct direction. This caused me to do 'forward somersaults' (or forward layouts) as I tried to sink.

With the insert soles, I was getting way more power on the main stroke, no power on the reverse stroke, and at the end of each main stroke the fin (pointing in the wrong direction), caused huge drag which nullified any extra power I got from the good power transfer.

Sebak tried to address this problem by angling the footpocket with respect to the blade. However, as it is, it is not nearly angled enough. The only solution to that would be to basically bond the mono to the bottom of the footpocket, perpendicularly, which means that then your feet would constantly cause huge drag, etc...

Eric Fattah
BC, Canada

I have experimented with full-foot pockets on a monofin - one of my monofins has Sporasub pockets on it at the moment. Here are my thoughts on the difference between this and the original design;

The blade on the full-foot fins bends differently to a normal mono. A normal mono flexes progressively, whereas the full-foot flexes at the tip of the foot pockets. This acts very much like bi-fins, especially sporasub bi-fins where the blade flexes most at the end of the foot. This creates a very efficient single stroke - which the monofin now has - but it stops you from being able to do a smooth kick cycle. I have to kick the fin in a series of individual one-way strokes to make it work. I think that is the fundemental differnce between the two designs - flex point when using mono-pockets is spread over a greater distance and hence allows a more fluid and more efficient transfer of continuous power, whereas the single flex point when using full-foot enable a very efficient single stroke, but stops you from being able to transfer continuous power.


Alun (DBs foremost Welshman!) has a pair of waterway Bi-fins which have mono-pockets - I think he considers them to be duff.....
Waterway bi-fins and stuff

well, i like the fact they have open heel footpockets, and so they seem to be more in-line with my body than most bi-fins. i think this is probably a good thing. (I should point out that I'm not a bi-fin person and haven't used that many, so it's hard for me to compare). I also think that power transfer will always be better with mono-style footpockets, mainly because they fit more snuggly, especially when wearing socks, and because it covers the whole foot.

I only use them as back-up for free-immersion, but I may switch back to the monofin as back-up, despite the fact that it seems to cause more drag.

the main thing I don't like at about my soft/medium Waterway bi-fins is that they're too stiff - that's all, and possibly too short. If they were softer and possibly longer, then I would probably quite like them, but still never as much as a good monofin.

I assume that all finswimming products are made for maximum speed (over certain distances). They're not specifically designed for efficiency, in the sense of maximum distance per unit O2 consumed. This is what we need. it just so happens that the fins designed for maximum speed over long distances seem to meet our demands fairly well.

A couple of other points i thought i'd mention about this stuff...

1. i find it hard to imagine that the ideal fin for surface swimming is identical to the ideal fin for underwater swimming. to me, i see them as very different problems.

2. swimming horizontally is different to swimming vertically, due to the relative position of the centres of buoyancy. swimming vertically is made more complicated by the fact that buoyancy will always change, which means that the optimum stroke is likely to change throughout the dive.

i'm always cautious about taking things from finswimming and applying them directly to freediving. that goes for technique and equipment.

ideal equipment and technique for freediving is always going to be very difficult to solve. it's not just a question of finding the best fin, or the best stroke, it's a question of finding the optimum combination of fin and stroke! not easy!

The original reason for finswimming mono to be without angle is simply that the manufacturer could not do it. All those brownish fins are done from electronics printed circuit board. This material is available in 1m x 1m sheets (russian), also there is danish companies as well. Now the manufacturer cuts a mono shaped part from that sheet, makes the needed tapering, and finally glues the footpockets to it. The manufacturer is NOT able to do an angle. These footpockets must have open heel to allow the swimmers foot bend during the kick from about the center as clearly shown in the picture. But when there is no force used, the blade does not point to "same plane as the swimmers body". When Eric put "inserts" he made the situation even worse.
This kind of open heel footpocket gives only small support when kicking upwards. Bi-fin footpockets makes the upper kick a bit better, unfortunately these footpockets are quite heavy. Maybe next step would be to try to make angled inserts, and additional straps to normal footpockets. Imagine a tiny angled plate under the heel in the picture. By this way the foot is always with an angle. The angle position would be much nearer the heel compared to bi-fin footpockets.

When we think about finswimming monos, we must always realize, that the needs are different compared to a freediver.

Somethink to think about:

1. Many finswimming categories are swimming in the surface. This means the blade is not needed to behave very symmetrically (upkick / downkick)
2. It must be possible to slam the fin to the pool end to make a fast swimmers turn.
3. The finswimmers kick is always powerful, so the bending starts from the swimmers feet.
4. Footpockets can be uncomfortable, finswimmers training is mostly with soft rubberfins, only short sprints with the (uncomfortable) mono.
5. Many of todays finswimmin records are done with heavy (4-5kg) skate style wing monos, which have closed heel and huge angle inside the footpocket (by the way Herbert did 181m with this kind of mono, see http://www.freediving.at/eventfeb_gal_e.html )

About the picture - The foot does not belong to a ex swimmer nor a finswimmer, just a freediver. So, the feet is not very flexible. But the bending of the foot is clearly seen. I want also to point out that in my case, I cannot maintain this angle during up kick, and I think most of us cannot (this bending is done by dragging the blade, with similar force as in normal kick).


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You can order monos directly from Canada through our site
www.finswimming.ca - the're the most world-famous monos.

I think switching to monos is right. For this it's enogh to compare the speed with mono and bifins. It looks like the bi-fins swimmer just doesn't swim at all :)

The problem is that you cannot use scuba gear with mono.

we have a new model - it will be put in the site this days.
It's flying special mono for scindiving or racing.

WaterWay is the world lider in monofins. This new model sells mainly in Europe for finracers and in fact a copy of dolpin tale. So it's a new. For going to depth it's not good.

IMHO for the competitions in freediving Model1 WaterWay is the best.

Another news I have at last in North America WaterWay fiberblades for ScubaPro footpocket. It's a bestseller in Europe.
So it makes possible using WaterWay fins with full footpocket.
Well fiberblades - it's fiberblades and carbon can not be even comparable with them.

So it's the news.

About long monofins (longer hten usual) - WW doesn't look forvard for it. Effectivety is not good.

Hi Teppo!
I'm sorry but manufacturer CAN make the angle. The last model for finracers makes needed angle. For the freedivers we don't have a need to to it so as soft blade automatically takes the right angle and moreover it makes the mono 2 times more expensive with tiny or zero profit.

all the best,
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