Tech Talk

Composite fin materials comparisons.

We often get asked why carbon fibre outperforms other materials used in making fin blades. To demonstrate the difference in stiffness of various materials and combinations of each we fabricated 5 test strips with equal weights of each material. The photo here shows what each strip is made from. Each strip had an equal amount of weight suspended from it and the picture tells the story.

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Test strip 1. 100% Carbon Fibre produces the least deflection proving the high strength and stiffnes of this material making it ideal for performance freediving fin blades that are not subject to a high degree of abrasion or abuse around rocks etc. The high strength and stiffness of this material means less has to be used to create a very light and responsive fin blade. This in turn makes the blade more likely to be damaged due to thin laminates produced.

Test strip 2. Carbon Fibre outer layers with Kevlar between. This produces slightly more deflection but still performs very well. Bend stress loads are carried in the outside skins of the strip so in this case the Carbon Fibre is doing most of the work while the Kevlar core is subject to mostly shear stress. A combination of Carbon and Glass Fibre works very well when layered this way also.

Test strip 3. Carbon/Kevlar Hybrid fabric has 50% of each fibre woven together to form an even amount of each material. You can see from the photo that this is not an efficient way to combine these materials when compared to test strip 2 which has the same amount of each material combined in a different way. These fabrics are generally used to gain an "averaged" use of the properties of both materials and do not exhibit "ideal" use of either Carbon or Kevlar Fibres. The Kevlar fibres in these fabrics can also be pigmented red or blue.

Test strip 4. 100% Kevlar deflects vastly more than the laminates containing Carbon Fibre demonstrating the much lower stiffness of this material when compared to Carbon. An advantage of Kevlar is its inherent abrasion resistance and it deflect further before failing than Carbon Fibres. These properties make it an ideal material for a fin subject to abuse during rock hopping in rough water. The high cost of the Kevlar and cost of processing it however make it hard to justify choosing this material for a pair of "rock bashing" blades.

Test strip 5. 100% Fibre Glass clearly deflects the most of all materials tested. This is no surprise given it is a much lower cost material than the others. Fibre Glass will deflect greatly before failing. This combined with its low cost make it the ideal material for rock hopping or "hard duty" diving.

There are many more variables to consider when assessing composite materials for fin blades such as resin used, impregnation process used and curing cycles all of which we will look at in future articles.

If anyone wishes to discuss which material is best for your particular style of diving please contacts us we are very happy to discuss any of this with you,

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