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Xynole polyester vs. fiberglass


john_manchester
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I'm building a PS22 which calls for 10 oz. fiberglass OR polyester. Parker advocates using Xynole polyester cloth (from Defender) for sheathing instead of fiberglass in "The Sharpie Book". Consensus on the web seems to be that the polyester cloth gives superior abrasion resistance and a higher strength/weight ratio to fiberglass. Defender only sells 4 oz. polyester cloth. It's a little cheaper than 10 oz. fiberglass, will take less resin to wet out and fill, and is supposed to be easier to work with.

In the spirit of not letting the perfect be the enemy of the good, is 4 oz. polyester cloth a reasonable alternative to 10 oz. fiberglass?

If so, would it be advisable to double-up on just the bottom?

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John...there was a pretty good discussion on plywood strength, coatings, glassing, etc.. on the Messing about design forum, which most of these readers frequent:

http://www.messing-about.com/forum/viewtopic.php?t=2736

And this site always a good one to remember:

http://www.oneoceankayaks.com/Abrasion.htm#synanch

He shows what happens with the various clothes get "whacked" as will happen under use.

I am playing around with a sample piece of luan, working with verious epoxies, cloths, fillers, paints, etc. One scrap has some Xynole cloth. What you will notice about it is that it doesn't "suck down" to the wood like glass cloth or tape does. It stands tall and proud. Meaning it's going to require lots of epoxy to simply wet it out and even more to fill the weave and fair. You will wind up with a very thick coat of epoxy on the surface. It is also very tough stuff when finished, although not bulletproof. I have put it on the bottom tip of two rudders and when they ground, it gets deeply scuffed just like fiberglass does.

And as per the System 3 Epoxy book, they remind us that the purpose of the glass cloth is not structural to the hull, but structural to the epoxy coating. If you are laying down one layer of cloth only, all you do by using heavier cloth is making a thicker coating that will be harder to fair and add weight to the boat. If that is your goal, then use the heavier cloth.

If you start adding 2, 3 or even more layers of cloth, you may eventually start getting structural benefits from the glass, but I think that it takes a lot of layers to get there.

Howard

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My limited testing has shown Dynel to have about 3 times the abrasion resistance of 'glass and Xynole about 5, maybe 6 times the abrasion resistance of similar weight 'glass cloth.

Xynole is lighter weight and doesn't float like 'glass can, it's also easier to make it conform to compound shapes. It's a little different to use and to wet out if you're use to ''glass, but is a good product. The 4 oz will perform as well if not a bit better on your bottom.

You'd need considerable more bulk to gain a real strength advantage in multiple layers of fabric on the bottom of your boat. The plywood is providing that for you. You just need the abrasion resistance, which a single skinning will give you.

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