I chatted with a salesman who was trying to sell me a new composite NDK. In an effort to upsell, he cautioned me about buying any used composite kayak. His argument was this: hull cracks – not uncommon on used fiberglass models – were a potential opportunity for water to seep in and soak the fiberglass mesh… which would then add weight to the boat, especially when it came time to car-top it afterwards.
Is there anything to this notion? I can’t say as I’ve experienced any weight differential in the older boats I’ve paddled, but he seemed confident when he said it. Any insight appreciated.
I don’t think there is anything to that notion.
I think there is a possibility of some absorption into a composite fiberglass matrix in general. I don’t believe a glass fiber itself can absorb any water. But within the matrix of the composite it might be possible. But kayaks and canoes aren’t typically on the water enough for this to really occur. I can’t say that I’ve felt it in a kayak. A noticeable difference is probably unlikely.
Then there’s the difference between a gelcoat crack and a crack in the composite structural layers. It’s quite common for the structural layer to flex without cracking where the gelcoat does crack. Gelcoat doesn’t waterproof a kayak. The composite structural layers are waterproof. A crack in the gelcoat doesn’t really represent any sort of issue in my experience, other than aesthetics. But that can be very important to a person. Not much different from being bothered by scratches and dents on a car.
If you do have a crack in the structural composite, that is something to address, just in terms of the structural integrity of the kayak. But in my experience, the majority of used kayaks out there don’t have this, and if they do, they sell quite cheap. And I don’t think it’s as difficult as it’s often made out to be to reinforce a small crack with a little cloth and resin.
Overall, I would consider it a misleading sales pitch. Largely false. I’m not saying impossible. But most often improbable.
It is nice to get a new kayak though.
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It seems to me some kayaking legend like Nigel Dennis of NDK maybe maintains that a kayak will gain weight over the years due to water absorption. One of the reasons NDK says to store their kayaks with the hatch covers off is to encourage the inside to dry out completely.
But I think “overblown” is a good description of the salesman’s pitch. It’s possible his basis for the claim is fiberglass hulls that are on the water long-term and/or have bilges that hold water. But that doesn’t apply to kayaks.
The gelcoat, aside from offering color options, is there to protect the glass layers from UV which is destructive to epoxy resin and not, as @CapeFear said, for waterproofing.
When I built my wooden kayak, I actually paddled her once prior to adding the varnish, which serves the same purpose as gelcoat. The epoxy saturated glass was absolutely waterproof, no damage to the wood. Cracks in the epoxy resin, however, will allow water in between the glass layers and that is trouble. Any wood boat owner will tell you that is what damages the boat - water seepage through epoxy cracks that get under the glass and into the wood.
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The salesman’s line is complete BS, as the others have explained. A well-constructed composite layup will have no place where water could penetrate. Fiberglass and the resins used to bind it -polyester, vinylester or epoxy - do not absorb water.
“Spider cracks” are common on composite boats, particularly British boats with thick gelcoat like NDKs and older VCPs. They form because thick gelcoat is less flexible that the composite layup underneath, so when the hull flexes, cracks form. They’re most common around bulkheads and other high stress areas. They’re an eyesore, but structurally harmless. They can be repaired, but it’s generally not worth the effort.