Polyester knit fabric

I'm an escapee from way over @ the metal building side.

Has anyone used polyester knit cloth (as in clothing) as a reinforcement for polyester or epoxy resins? I'm experimenting with it. Its stretchiness is what intrigues me, over frames. This was inspired by my Walker Bay 8' disappearing and wanting a replacement.

I don't know diddly about what I'm doing. I've never built a boat out of anything other than aluminum. I do do some basic research before I fly off where I haven't been. I see that polyester thread is pretty strong:

"Polyester is strong but Filament Kevlar Thread is about twice as strong. For example, size 92 polyester as a 14.5 pound tensile strength; the same size Kevlar has a 30 pound tensile strength. Kevlar's downside is that it costs about five times more than polyester."

It's cheap, too. I'm not thinking about making the whole of it with this fabric but just to get shape easily. But then, why not if it's cheaper and works? And hell, am I mad to think that polyester will stick to polyester well?

This seems too obvious to me but I can't find anything here or elsewhere. Of course, lots of 'skin' stuff but nothing about what I'm asking.

Two layers of what I found at Salvation Army (women's top for three bucks, 100% poly, unknown specs of course) builds up a very flexible skin .55" thick. This was using some ratty old laminating resin that I've had for 15 years or longer. Took forever to go off, even with an OD of cat.

 

Well,....
if it's any help, my clothes have at times held some shape pretty well after playing with composites.........
I'm sure some knitted tee material might make the basis to lay up the rest of a boat on, fabric patterned laminations are fairly common in surfboards as an visual aspect, it's not like they would add no strength.
A simple set of frame "molds" in a multichine configureation with conduit/or similar chines & stretch fabric wet out & let set with resin may be a start, still will be plenty of sanding & lam work though, good thing is that fashion comes & goes so you get to sell new patterns every season, fashion industry has some great business modelling............
http://www.popsugar.com.au/fashion/...ing-2015-Fashion-Week-35853898#photo-35853757 I mean , like really, check out the latest in Popsugar range, simply stunning.....
Jeff

 

Usually polyester fabrics are sized (machine finished) and the fibers are less willing to accept goo, compared to Xynole, which is what I'm assuming you're looking to duplicate. Some research into the particular fabric you're working with will tell, though fabrics used in dresses typical have a hard, smooth sizing performed on the fibers, which helps them repel stains and liquid spills. This feature also prevents epoxy penetration into the fiber bundles.

 

Any cloth reinforcement depends upon both the fiber strength and straightness for strength.
A knit cloth will certainly adapt to the shape you are trying to make, but will be significantly weaker in strength and significantly less stiff.
Aside from the issues of sizing (which I believe are potentially a problem) a knit fabric will tend to hold a lot of resin compared to a typical SOF cloth. Resin is not very strong and certainly not stiff compared to the thread.

You will probably (I've not done it except epoxy on my clothes) get a heavy, expensive, weak, and flexible skin on your boat. It might be pretty if you choose the right cloth.

Why not typical SOF polyester cloth? It has been made into aircaft, kayaks, dingys, and sailboats. If you get the un-heat-treated cloth is is rather cheap (don't buy it from an aircraft supply house) which can be draped/ pulled and then heat shrunk easily to match many contours.
In this case you don't actually need a resin. Many paints have been used to make a serviceable coating. However, I have used epoxy to bond the cloth to a wooden frame as a final attachment at the coaming opening on a kayak with no issues. I don't know about polyester resins, but the whole thing is cheap enough you can just do a test.
I have scraps if you want to try.

 

Upchurchmr & Paul,

You both mentioned SOF polyester cloth, so I looked up aircraft coverings. Very early planes were covered with cotton cloth & cellulose nitrate dope to tighten & waterproof the fabric, but Dacron & cellulose acetate butyrate are preferred nowadays. Could SOF kayaks be successfully constructed using cellulose acetate butyrate?

I going to use heat shrink wrapping on the hull of my next skiff after I've saturated the glass cloth with epoxy. I anticipate using less epoxy, as well as having little or no fairing to do. Bottom first, then each side then the transom.

http://en.wikipedia.org/wiki/Shrink_wrap

All the best,

Perry

 

Thanks all, for the replies you've got me thinking and questioning! Here is the results of my initial experiment. One of the goals was that after thinking this through, I didn't want to spend longer than a day in pursuit of a reasonable test.

I drew a hull rather quickly in ProSurf, plotted it out, adhered it to mat board, cut it out and glued the pieces together with hot glue to make the form. I backed it with a scrap of 7/16" OSB for to be a stapling surface. The panels were the simplest way I figured I could make the form. Model is: 1" = 12" the LOA is 90".

The fabric did exactly what I hoped for and even did the transom all in one shot with no folds. I missed my one day limit because the resin took so long to cure. I applied the second layer the next day with more MEKP. After it cured I soaked the model in a bucket to melt the paper mold.

As one can see, the weight of the resin made the cloth contact the frame. This was obvious to me as soon as I stretched the fabric which, of course, gave a concave surface (I wanted that). It did not help that I soaked the first coat way too much. Inconsequential to the test and can easily be rectified because the final mold won't look anything like this test piece and like everything else, there is a learning curve. I have several other questions for later about the final mold.

Anyway, it all worked rather well I thought, but again, I don't know squat about this method.

In a separate post I will respond to the thought provoking feedback thus far.

 

Dacron is polyester cloth.
You certainly could use the aircraft system of coatings, it is intended to be out in the weather and lasts quite a long time. 8-10 years? Perhaps someone actually knowledgeable can give us a time frame. If you want to try the aircraft system get the directions they sell for the Ceconite system. http://www.aircraftspruce.com/catalog/cspages/cecmanual.php
Just remember that Aircraft + Certified = Money, Money.

When I looked at the system it seemed that it would cost $200+ in coatings to get one kayak covered. It would probably do several more.

I find that $30/gal oil based house paint is very good. I sometimes use polyurethane one part varnish (Minwax Helmsman) also $30/ gal which also works well with an entirely different "look".

I don't know where you can get the proper cloth for boats in England.
Contact George Dyson (gdyson@gmail.com) in Washington state, USA for a price list and description. Will shipping make it unreasonable? He also has "ballistic" nylon if you might like to try that - coatings are more limited for a good job.

Last (finally) I'd like to hear the details and progress when you try heat shrink.

 

Great experiment Yofish, the dry stretched model looks great, I wonder the limits of the stretched form & sagging over greater spans on a full size setup once wet out.

Jeff.

 

Jeff, that very thing is what intrigues me and I think I'll know the answer after I give this little rower a try. I don't see why it wouldn't as long as one had enough 'bones' to the mold. I've actually fantasized a 20' skiff done this way. I think it would be cool to do the bottom longitudinal stiffening on waterlines, as the sides are, instead of butts. I envision the edges of the mold being incorporated into the whole: they would be structural scantlings that would be glassed in. Another separate framework would hold those elements in place and removed after enough rigidity was obtained.

This whole thing came out of my inherent laziness. I could be entirely wrong but my reading of how the fabrics that others have mentioned here would not work as a one-shot covering, stem to stern including transom, like this model was done.

I think the ideal would be to spray the first couple of coats of resin to close the apertures in the cloth. The second layer was not stretched like the first but was wetted out from the bottom out and the fabric stretched and stapled as it lay best while wetting. I noticed that the resin 'disappears' in that it's hard to tell where you left off spreading with a brush especially on the first coat. Here is a better pic of the covering. It shows no resin bleed and looks and feels just like cloth only rigid. It appears firmly attached to the first layer. I'm going to see how it sands and mess with some kind of finish coat too.

One other attractive thing is that the material is so cheap. For example, the material in the pic could be sewn together and 26.6 yds would twice cover a 20' skiff frame assuming 5' wide bottom and 30" sides for less than $70.

 

There's some cool potential here, my head would be running towards wet & set to the "fashion print" then maybe an external 4-6oz glass cloth with filler coat & gloss coat surfboard style then some internal chop or whatever required for strength...........
Not that I'm gunna take it up,....... I've got some old surf shirts that might get laminated into board fins one year.......
There's some awesome looking clear finished fabric inlays come up in image search.

Jeff.

 

Its going to fall apart.
But don't let me stop you.

How about this rowboat.
No guessing about the structure.
One experiment at a time is always a good policy.

http://gentrycustomboats.com/RUTHpage.html

 

OOOOOOwww, harsh, agreed that the T material aint gunna be the strongest laminated structure but mixed using some other reinforcments & internal structure should be sweet..........., fabric draped boats have been done before, I think there was an example from the UK that built like this as a "basis"

experiments are good... especially when you can swim

Jeff.

 

These forums are seemingly forever hosting people looking for a cheaper way to build a boat, commonsense tells you that if the cheapie methods did the job properly, they would have been adopted as standard practice, no-one likes spending more money than necessary to get the same utility. Now, how about some old hessian bags to bulk out that laminate.......

 

Now, with all due respect, I think these forums are host to those, like you, who forever make false equivalencies!

No one has really given me pause yet which is not unusual, I'm prone to carrying myself unaided headlong into the wall.

 

Boat builders general are a frugal bunch. This is because there's just not a lot of margin in most projects, so research into less costly methods, materials, etc. is common now and historically.

SOF boats were built with early aircraft covering techniques. In fact, these techniques where adaptations from boat builders, initially.

The only issue I see with this method is the weight and resin/fiber ratios that will result with some materials. Polyester sucks up resin like a French hooker does . . . This is where appropriate sizing for the application can be helpful. Some of the acrylics can be used this way as well (Dynel and similar). The trick is textile engineering, to get a fabric that will absorb enough resin to be effective, but not so much that the fabric quadruples in weight. Ideally, if you can work up fiber strands into tight enough bundles, maybe with sizing techniques or special loom design, so they can accept the necessary amount of goo, but no more, then you've got a product. Of course us cheap boat building ********, will not invest in this level of textile research, but some online effort might yield a fabric, that will come close to a 1:1 resin/fiber ratio.