that most blows sustained by sea kayaks are like sharp hammer blows, and carbon or S-glass handle those pretty well.
Inside Kevlar layers are useful for ww boats that sustain relatively slow, deep distortions, such as getting wrapped against a rock or tree by the current.
Top end slalom racing boat hulls are usually high in carbon for stiffness. But if one buys the same boat laid up for lots of practice sessions and longer life, then Kevlar appears, mainly in the inside of the boat. These practice boat layups are described with words like "Flexi".
As I understand it, Kevlar is about as strong under tension as carbon, but greatly inferior in compression strength. Kevlar in a layup seems to cut down on propagation of cracks. After long searching on the internet, I found an apparently knowledgable source stating that resin adherence to Kevlar is maybe 15% lower than it is to the average for other cloths. Maybe that relates to suggestions that an S/K/S/K layup might be superior in long term resistance to repeated flexing. Interleaving "fresh" glass layers seems to be an old strategy for when trying to keep hard-to-stick fibers in a layup.
Then there was the report that Mad River was obtaining Kevlar with a coating promoting adhesion. Quite possibly Kevlar would do better if such a coating could be used.
Kayak Motor Kit
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