Dynel-decks, Xynole-bottoms, right?

[Steve Lansdowne]

The practice among Forumites seems to be to use Xynole saturated in expoxy as a bottom protective coating and Dynel with the weave not completely filled for a nonskid deck, yet Defender describes these two fabrics similarly. Anyone want to compare these two fabrics for these two uses?

[fixmyboat]

We got a test board at work somplace ill take a pic if i remeber. Dynell looks denser and more like canvas than dynel on the test patch

[Todd Bradshaw]

As far as I know, they're both plain weaves, both are polyester and both are woven with twisted fibers (look like mini-three-strand rope). Both also soak up lots or resin (2-3 times what fiberglass would) mostly because of that twisted construction. Top of my head, I'm thinking that Dynel may be a bit coarser (bigger yarns and more open weave - maybe a bit heavier, too). In any case, they both offer a lot of abrasion resistance and pretty high tear strength, but don't contribute much hull stiffness or structural beef compared to glass. The case for a tough deck covering is pretty obvious and I suspect the choice of dynel may be more a matter of looking more canvas-like than anything structural. I can't see where it would have any other advantage. For hull sheathing, the true question seems to always be can I live with all the extra weight that either of these fabrics will add, compared to somewhat less protection but a lot less weight with glass? I don't think it will matter much which one is used and suspect that dynel and Xynole may just be different versions of the same basic thing from different manufacturers.
Q - What do you call a boat with a dynel deck and Xynole-covered hull?
A - a submarine

[pipefitter]

Isn't it the dynel that conforms to curves and radiuses better and the xynol is stiffer initially? I also read somewhere that the canvas look of the dynel was genuine enough right down to the dirt it trapped in the weave,even if ever so slightly left looking like canvas. Especially in places where cormorants and pelicans frequented the boat for a resting place.

[George Roberts]

On a pound for pound basis laid fiberglass is tougher than either.

[Steve Lansdowne]

I have used Dynel for a bottom, along with lots of epoxy and microballoons, so I'm familiar with it. I've read that Xynole is good at stretching around corners, etc. I'm not sure whether it is moreso than Dynel.

[Tom Lathrop]

I've used both. As Todd said, they look very much alike and soak up the same amount of resin. Dynel is kind of a beige color and Xynole is white.

If you are looking for a tough abrasion resistant sheath, Dynel, Xynole and polypropylene Vectra are way better than fiberglass. Xynole and Dynel move and fit around edges and corners easily, with Vectra in between those and fiberglass in conformability. In peel strength, Xynole is far better than the others. The Dynel samples I tested had little tensile strength and all ripped apart easily rather than peel from the wood. Epoxy doesn't really stick to any of these materials but does soak into the fibers of Xynole and Dynel so well that they become inseparable.

I ran a series of objective tests years ago on all these materials. For tensile strength (making the wood more rigid) glass is the only one that will do that. Non-woven glass is far better to improve stiffness than the woven cloth which actually increases stiffness less than the same thickness of added wood.. For abrasion resistance, Xynole and Dynel are about even with Vectra next and glass last.

When I need a tough abrasion resistant bottom or topsides, I choose Xynole and fill with epoxy and fairing compound. On a skiff bottom this will ignore dragging over oyster shells on a beach with no damage. Glass is nowhere near as abrasion resistant as Xynole. For areas where there are less things to damage it (shells, docks, pilings, etc), I choose glass because it comes out lighter and easier to finish.

Glass has an unearned reputation for abrasion resistance. 10oz glass cloth in epoxy is only twice as abrasion resistant as the same thickness of epoxy alone. One layer of 6oz Xynole filled with epoxy is 6 times as resistant to abrasion as 10oz glass. On a same thickness basis, Xynole is 2.4 times as resistant to abrasion as glass cloth. These are my results from objective tests on the same machine without human intervention.

I don't use Dynel for anything any more.

[Bill Perkins]

Tom supplied me with his test results awhile ago ,so I used Xynole on my bottom and deck . The deck does look like canvas . By useing 2 different fabrics you'll only increase the amount lost to waste I think .

[Steve Lansdowne]

Thanks for the objective test data. I'm getting the feeling that one reason Xynole/Dynel is so useful for abrasion is that in fact there is 60% more epoxy in the mix than with glass, though I realize that's not the whole story.

[BillyBudd]

There may be another element at play with xynole. Supposedly (source, I think: Reuel Parker's book) xynole will flex vs. fiberglass will fracture if/when the hull slaps into something big and sharp and nasty.

[Tom Lathrop]

That is right Billy. Glass fractures easily and is therefore less protection against impacts.

[boatclassic]

Hi,I'm new to this forum.I'm in the middle of a major restoration of a Fairley Marine"Atalanta 26" designed by Uffa Fox and I am just about to sheath the underwater body with epoxy and Dynel which is why I hijacked this thread.As she is sitting on her keel I intend to use plastic staples to hold the dynel in place.Can I stretch it and staple on all sides and then wet out or is it going to sag like glass does?I forgot to mention that I am living in the wilds of Austria and was unable to find dynel anywhere in Europe.Ended up buying it from Jamestown.I'm using dynel because I used it 30 years ago on a boat I built in Canada and was very impressed with it then.

[George Roberts]

Steve Lansdowne ---

I try very hard not to fight with people, but objective tests are more subjective than objective.

I believe that 16oz of fiberglass plus epoxy weighs as much as 4oz of xynole plus epoxy (something about the fiber density and the weave).

There is some engineering concerning point loads on thin surfaces that might be of interest.

I don't know which type of abrasion test one should use:

1) a flat surface against a flat surface or

2) an irregular surface against a flat surface.

You will get different results.

Yea, objective tests look very subjective.