DavidJ , Mar 1, The space between the fibers soaked up the water. And maybe the water the boat sits in dissolved some of the resins. And I have read wetting out kevlar with resin is not easy? Maybe a hydraulic pressure erosion of the bond as hull moves caused water to get behind the kevlar. It is not the resin giving the strength of the kevlar, so maybe an entirely different 'resin' maybe use a polyurethane rubber to embed the kevlar into?
Then put more of same polyurethane on top of the kevlar. Nothing is going to dissolve a laminating resin. There should be no spaces between the fibers What hydraulic pressure erosion could you be talking about??? Polyurethane is an elastomer - flexible- if you want the fibers to provide some strength, the resin needs to be not actually flexible like rubber.
David J - sounds good to me. Oh, ok, I was thinking of blisters, they hydrolyze and dissolve styrene. For all I know that was what happened, how else will water get behind the Kevlar laminate? If the resin saturation was poor, and the hull works, it will suck water into the strands.
I have read of hulls pumping and failing cracking their laminates on another boat survey site.. And hydraulic erosion of cored hulls, pulverizes the hull. So then in a poly it would be fine. And I think if it had been embedded in a poly it would not have cracked loose from the hull and soaked up water. Granted this is just my own opinion. And embedded the seams to make a watertight hull, since it has been fine. I will bow out now and not respond again.
They mentioned that repairs were being made after a scrape with a reef. Maybe the kevlar broke free after doing it's job, protecting the hull in a reef collision. Hard to know exactly what happened. Canracer , Mar 1, The tricky part with composites is that there are many possible combinations of fibres and resins and some combinations work better than others.
Kevlar is particularly tricky. Resin has a hard time to bond to the fibre. It only makes sense to use Kevlar where tensile loads are expected, weight is critical and epoxy resin is used.
Polyester is not going to bond to the fibre. Even in impact or abrasion critical areas glass can be used for a fraction of the cost. Additionally it is possible that the fibres were sized for weaving bullet proof vests and not for laminating. Sizing is a process where the fibres are coated with a thin surface layer to enhance manufacturing processes. Weaving of vests will require different sizing compared to laminating boats.
Unless you know what you are doing stick to glass fibres. Karsten , Mar 1, Orca hull and deck and mast was laid up with high-performance resin - thixotropic, isothalic Cargill poly product with greater elongation and fire resistant qualities.
No sign of any water in the layup at twenty years or since splashed in I put on vinylester resin last time we took it down to bare hull as precaution. Tales of water in kevlar seem to be short on details.
Photos really tell a lot. I did a new hatch with carbon and kevlar. Tough to work with and, done right, very tough. Kojii , Mar 9, You must log in or sign up to reply here. Show Ignored Content. Similar Threads. Maybe a few glass boats. Yet no one asks why knowledgeable boat builders would continue to use Kevlar. Organic chain fibers have various tendencies to soak up water. Polypropelene absorbs hardly any.
Polyester Dacron etc absorbs a little more. Nylon absorbs more still, and stretches some when soaked. Kevlar is I have heard chemically related to Nylon, so it is not surprising if it absorbs water.
But as Eric pointed out, when surrounded with resin, all fibers are limited both in their exposure to moisture, and in their ability to absorb it. Surrounding resin not only keeps moisture from the sides of Kevlar, it also limits water absorption because the Kevlar is prevented from swelling.
If it does swell… Kevlar has been used by builders of slalom racing boats for decades. These boats get cracked and hammered. Their owners, who paid a lot, will not tolerate weight gain. So we are dealing with a suburban legend. Necky marketing I suspect they made a decision to not use kevlar and go for glass and carbon. The implication being that everyone still building with kevlar was behind the times. The resin would need to be removed before water could be absorbed.
Certainly a contact laminators sweat will soak into dry fabric and keep it from resinating, but once the resin is worked into the fabric, that isa the end of the story. There are two misconceptions about Kevlar: 1 It absorbs water false ; 2 Its a great material to build lightweight sea kayaks with also false.
I have found Kevlar fibers are easily exposed in high wear areas of kayak, specifically under ones heals. Kevlar is not a very stiff material compared to carbon or glass.
The best property it adds to a hull is impact resistance. It does this with a realtively low weight. This is good if hitting things can not be avoided. Therefore it is a great material for for lighter weight white water boats or surf kayaks.
When Kevlar is impacted it deflects a lot. Kevlar, not being stiff, does not resist deflection and if hit hard enough will often deflect well beyong the yield limit of gel coats. Therefore you can hit rocks and even possibly jump up and down on your kayak and the Kevlar may not break. However, do not be surprised to see abused or heavily usede Kevlar boats have a lot of gel coat cracks. Another problem with all composites is that the fibers eventually creep microscopically within their resin.
This creeping occurs after repeated flexing from normal use. So a boat that may be stiff enough when new will be less so after a season or two of use.
I have seen this occur more readily and to a significantly higher degree with Kevlar. Actually Kevlar can be very smartly used in a cored hull as a layer on the inside of the core.
But there aren't many production boats that are cored and utilising Kevlar this way. Kevlar is a great material for marketing kayaks. Its really not that expensive, its not rare, the supply more than exceeds the demand. Most folks including nearly every one of you reading this aspire to someday own a Kevlar kayak. You are all being fooled. Its not particularly light at 55 lbs. It is not nearly as fast as it used to be because it has softened quite a bit and is whippy and oil-cans.
It has some cosmetic cracks in places where the flexing was too much for the gel coat to take. The good news is that it still a well designed and well built kayak that will still whoop the big name production kayaks.
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