Dynel, Xynol, Glass

[charlesrider]

Many years ago I had a great experience with Dynel as a sheath over the abused cold-molded hull of a Jet 14. Worked like a charm. I wasn't looking for strength, just a fair and abrasion resistant coating over a western red cedar hull.

I don't really know the relative merits/deficits of these fabrics except that Glass offers the least stretch. What are people's opinions about Where, When, and How to use these fabrics?

Chad

[Arnie Eaton]

Dynel has good strength and stretch. There are plans for a sailboat called "Tabu" which calls for Dynel as a covering for the hull and also for the box type mast. Dynel costs more then glass but as I understand will conform better to curves and give more strength as well. It is a type of poly material.

[boatbuilder.org]

Dynel works better as a protective layer over wood. It is not as brittle as glass so does not zipper like glass does. It is also harder to scratch through than a layer of glass, I really do not know if it is a function of the cloth itself or the fact that the Dynel swells a bit giving you a thicker layer of protection or a bit of both. The best application for Dynel is sheathing the hull, decks, pilothouse/cabin roofs, cockpit soles etc. For structural applications like glassing on a keel, glassing bulkheads in etc than a biax tooling cloth scheme is in order.

---Joel---

www.boatbuilder.org

[PAR]

Dynel has close to 3 times and Xynol has maybe 6 times the abrasion resistance of 'glass. Xynol is the far better product, though it's cost reflects this.

[Howard]

Is the abrasion resistence a function of the fabric itself, or from all the epoxy it traps in it's weave? It really does build up a thick coat of epoxy.

Another fabric I hear very little about is Olefin. Defender has it and I ordered a few yards to play with it. It seems to be very tough stuff as well. I would think it would be used as one layer of many, in conjunction with Xynol, glass, etc.

[john_manchester]

The stretchy fibers like polyester are better for puncture resistance as well because they absorb energy and don't fracture like glass. There's a nice summary on the web of a backyard experiment on puncture resistance of various fabrics which you've probably seen ( http://www.oneoceankayaks.com/Abrasion.htm).

And what about structural reinforcement--particularly joints like the chines that will take a beating from trailering? Seems to me glass is better in this application because it should prevent the joints from flexing, or rather do a better job of distributing stress around the joints, so they won't fatigue and eventually fracture. Of course, the glass will fatigue and eventually fracture, so you can't win. I wound up glass-taping my chines on the outside beneath the polyester sheathing (and then of course again inside over the fillets), but I have no idea whether it was at all worth it. Anybody know?

Also the polyester doesn't give the hull much stiffness. Given that polyester soaks up a lot of epoxy, isn't glass the better choice for producing a stiffer, lighter hull?

[charlesrider]

Thanks folks. Pretty cool article provided by John. I draw from all this that my experience was typical when using Dynel as a sheath of plywood, that glass is a much better structural reinforcement because of its stiffness and light weight and continues to be a fantastic material these applications, and that kevlar and carbon are specialized materials that are best used where one of their primary qualities (strength, stiffness, and light weight) are of great interest.

The comment about the heavy wet-out of the spun fabrics was very interesting. I hadn't really noticed it, but when I think about the dynel application I did, it is right on the mark. Not being a kayak builder, I don't mind as much and like the sandability of the thick layup.

As usual, many shades of grey (or white or buff or black in this case).

Chad

[Tom Lathrop]

It depends on what you want the sheath to do. For stiffness, glass is much better than the synthetics like Dynel, Xynole or polypropylene Vectra. For abrasion resistance, these synthetics are far better. Kevlar is the king but very expensive and difficult to use.

I made objective tests of abrasion and peel strength of fabrics several years ago and there is an article of these tests in an old Boatbuilder magazine. A single layer of Xynole is a bit more than 6 times as abrasion resistant than 9oz glass cloth, both saturated and covered with epoxy. On a per thickness basis the difference is about 2.4 times. Vectra and Dynel are similar to Xynole in abrasion.

For peel strength, Xynole is by far the best, Vectra is next and glass is not quite as good as Vectra. Dynel failled all attempts to peel it because it broke at the peel line every time. I have had fir plywood to check through Dynel after years of use but never through any of the others. Based on my experience, I would never use Dynel for anything.

[Greg Luckett]

Where are Dynel, Xynole or polypropylene Vectra materials obtained? I mean where can I purchase them?

Thanks.

[Brad]

Raka

http://www.raka.com/FiberglassCloth.html

[Brad]

Scroll down to about mid page

[Greg Luckett]

Brad,

Thank you.

[Charlie Jones]

Greg- also Defender Industries carries them.