Carbon blade stiffness grading

[Don Solomon]

Hi Guys, i am curious as to the stiffness grading system used by the euro style carbon blades. 1.0 1.1 etc.... i have seen for example 1.4Kgr i have seen 1.4kg. how does this grading system work. I'm trying to understand the Kgr or Kg value. I'm currently using 1.5 deepMaster...what a great fin.

 

[John B Griffith Jr]

Hi Guys, i am curious as to the stiffness grading system used by the euro style carbon blades. 1.0 1.1 etc.... i have seen for example 1.4Kgr i have seen 1.4kg. how does this grading system work. I'm trying to understand the Kgr or Kg value. I'm currently using 1.5 deepMaster...what a great fin.

I own a pair of Seatec "Forza 10" blades. The rating system for these, and my monofins, is in degrees of hardness: SOFT - MEDIUM - HARD. or a corresponding numeric value of stiffness: 1=extra-soft, 2=soft, etc.

I believe, and I may be very wrong, that you are describing the "weight" of the fins, and there may be a direct correlation with the imparted "force" and the perceived "stiffness" of the fins. Force = mass * acceleration, so the stiffness of the blade determines the momentum that can be generated to linearly propel you through the water (acceleration), expressed as Δv. The weight of the blades translates into an external variable.... I'll stop there...that's probably not what you wanted to know . Glad you like the fins!

 

[SeaRow]

I own a pair of Seatec "Forza 10" blades. The rating system for these, and my monofins, is in degrees of hardness: SOFT - MEDIUM - HARD. or a corresponding numeric value of stiffness: 1=extra-soft, 2=soft, etc.

I believe, and I may be very wrong, that you are describing the "weight" of the fins, and there may be a direct correlation with the imparted "force" and the perceived "stiffness" of the fins. Force = mass * acceleration, so the stiffness of the blade determines the momentum that can be generated to linearly propel you through the water (acceleration), expressed as Δv. The weight of the blades translates into an external variable.... I'll stop there...that's probably not what you wanted to know . Glad you like the fins!

I believe this is correct. The manufacturer will weigh the blade (1.1g, etc.) and the amount of resin on the carbon/other is what slows/stiffens the blade. Is this a realistic and cross-comparable value? I don't think so. A soft in one brand vs another is hard to compare, I think. I wish there was a uniform test comparison!
How is there not a way to compare/QC blade to blade?

 

[Don Solomon]

I've been in touch with one of the brands and they replied to me that the Kg value is a force value. i scratched over the internet And basically traces back to a newton as a measurement of force. So i am guessing that the manufactures have a standard test that applies a standard weight or force to the blade edge and then measure its relation to the flex. A 1.0 very soft, will obviously take less force to flex. compared to a 2.2 very hard.

 

[SeaRow]

I've been in touch with one of the brands and they replied to me that the Kg value is a force value. i scratched over the internet And basically traces back to a newton as a measurement of force. So i am guessing that the manufactures have a standard test that applies a standard weight or force to the blade edge and then measure its relation to the flex. A 1.0 very soft, will obviously take less force to flex. compared to a 2.2 very hard.

Neat! I never knew that. Its certainly not advertised well.

 

[Don Solomon]

yeh... but whether the different manufactures will use the same test method is another issue, even though they share the similar grading system. might be easier to use super soft, soft, medium etc....as a grading system.

 

[growingupninja]

I do not think it is possble or wise to use those numbers to judge fin stiffness across multiple brands. Manufacturing processes are different and some fins are soft at the tip and progressively harder (thicker) towards the base, etc. Within a single brand the number may have meaning since most makers use the same basic process for all their fins.

Some brands run 'stiff' and others seem to run 'soft', ie a C4 medium may be noticeably stiffer than a Bluetec medium.

Also the footpocket will have a lot of influence--a stiffer, heavier footpocket will make a blade feel stiffer than a more minimal footpocket.