Freedive blades hardness numbers

[Dromilious]

Hi, I would like to ask if anyone knows how the freedive blades manufacturers ,measure their blades harness.For example i went to a store and he told me that the ideal number for me is 1.4 for a specific blade.But i dont know what this 1.4 means. They had many numbers, 1.2-1.5
How this is measured ?

 

[Pinniped72]

I have never heard of such a thing, when you say hardness do you mean how stiff the fins are or do you literally mean how hard the material is, ie how likely it is to get scratched? There is a scale for hardness for everything from coal to diamond but a scale for the stiffness of fins does not exist, as far as I am aware. I wish it did though, it would make fin choice so much easier and accurate. Not much help but that's all I know i'm afraid

 

[Dromilious]

You can see at the bottom of the page what i mean http://www.tsourosmarine.gr/products_en.asp?prodid=3600

 

[Pinniped72]

Interesting, that is obviously referring to the stiffness I would say, I would imagine its an indication of how much dry weight is required to bend the fin a certain distance, I like the idea and would be interested to know how the tests were done, it would be great if such tests were widely used and how the results impacted on use was widely known. It would be more objective than relying on others reviews whose technique may be better or legs stronger

 

[Dromilious]

That's exactrly what i mean.How do they make their measurements and which parameters.I guess it is their own way to categorize their blades .

 

[hteas]

Generally blade stiffness is measured in marketing-speak. Nobody has come up with anything reasonable, despite the fact that it wouldn't be hard to do. They also fail to measure the stiffness of the side ribs, and of the footpocket itself, which make a huge difference in how the fins work. Apparently, it is much more profitable to merely say that they have the perfect combination of power and speed, whatever that is.
To get to an adequate answer, bending of blades, both from that manufacturer and others, would have to be measured in appropriate footpockets, and then get a lot of divers to decide what is stiff, and what is soft.
My early Dessault footpockets had soft ribs, my current Dessaults have a very nice medium stiffness, and my old Omers had ridiculously stiff ribs. Another variation is my Imersion carbons, with very softy footpockets and ribs, but fairly stiff blades. The combination works really well for me.
Where does that leave us? I'm afraid that the equipment manufacturers score. I have purchased early Dessaults (1), current Dessaults (3), Imersions (2), Omer Milleniums (1), Picassos (2), and a few others I no longer recall, along with borrowing a multitude of others.

 

[Dromilious]

I agree with you that the footpockets make a huge difference .So i think each manufacturer has his own way to measure the blades for reference .That's why some of them use specific brands of footpockets with their blades to be more accurate of the blade performance.But of cource this is a matter of taste.

 

[riccardosl]

I'm using c4 footpockets with Skorpio blade with a stifness indicator as 25


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[DRW]

Fin stiffness is traditionally measured using a Durometer reading:

Here is a a page from W. G. Fischer's 1956 US Naval Experimental Diving Unit report Comparative Evaluation of Swim Fins, which can be downloaded from http://www.dtic.mil/dtic/tr/fulltext/u2/780665.pdf:

Note the two penultimate columns in the table comparing 14 different fin models. The two durometer readings measure the pocket and blade hardness respectively in "shores". The final column is also of interest as it equates "stiffness" to the weight in pounds required to bend the fin down to 30 degrees.

Here's a more recent web page screenshot from around 2004:

PALMES KENT SOFT « INITIATION » Elles sont symétriques et bicolores. La voilure a une dureté 80 shores, le chausson 60 shores. Double évacuation eau et sable.
PALMES KENT PLUS « PROGRESSION » Elles sont asymétriques, flottantes et bicolores. La voilure a une dureté de 90 shores et le chaussant 60 shores. Double évacuation eau et sable.
PALMES SHARKS FINS « PERFORMANCE » Elles sont asymétriques, flottantes et bicolores. La voilure a une dureté de 90 shores et le chaussant 50 shores. Evacuation eau et sable.

You can see the Botalo French-medium web page for yourself at http://web.archive.org/web/20041128115603/http://perso.wanadoo.fr/botalo/palmekent.html. The description of each model lists the blade and pocket hardness in shores. The "Performance" fin has the hardest blade of the three (90 shores) and the softest pocket (50 shores).

There is a Wikipedia article entitled "Shore durometer" at https://en.wikipedia.org/wiki/Shore_durometer. There may be other, proprietary, measurements of fin pocket and blade hardness, but the durometer scale named after its inventor Albert Ferdinand Shore appears to have the greatest international recognition. It's a shame that shore durometer readings aren't used more frequently to inform buyers of fins, particularly people contemplating expensive freediving fins, about blade and pocket stiffnesses before purchasing. Many manufacturers and stockists, of course, are equally unforthcoming about the internal dimensions (foot length and width) of fin foot pockets in millimetres, relying overmuch on the blunt and often inaccurate instrument of shoe sizes. We need, and deserve, more transparency in the new world of online retailing.

 

[dforcucci]

Durometer only measures the material and will not tell you much about the stiffness of the blade. Look at the first two rows of data all the way to the right. Both fins had the same durometer with much different stiffness index. It would depend on the density of the material and that might be what the meister blades are referring to although it should be a per unit area measure.

 

[DRW]

Yes, the "Stiffness Index" in the 1956 Fischer navy report equates "stiffness" to the weight in pounds required to bend the fin down to 30 degrees and I can see that will be the key parameter in this case. What is missing from current manufacturers' blade stiffness numbers (Dromilious's 1.2-1.5) is the underlying rationale used to calculate the position of a blade on what sounds like an arcane in-house scale.

 

[Pinniped72]

To make any stiffness tests real world helpful, manufacturers would need to agree on an industry standard test, in theory I cant see why this would be difficult, the previous article proves this is possible but I guess that all the time we are happy to buy fins based on the opinions of others and our own aesthetic requirements, there is no real motivation for manufacturers to go to the expense of setting up a standardised testing procedure? Come on fin manufacturers, its not that difficult