Author Topic: Fabrics for lamination  (Read 5601 times)

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jadranko

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Fabrics for lamination
« on: February 07, 2010, 03:29:47 PM »
I would like to start discussion about different fabrics which can be used in this type of boat building.

First why I am will build a boat ? Couse I dont have enough money to buy boat like this.

What I want from that boat ? To last about 30 years +

So which is the best fabric to accomplish that point ?

Glass

Kevlar

Vectran

Aramid

Or maybe some combinations between them in layers ?

Brian.Dixon

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Re: Fabrics for lamination
« Reply #1 on: February 07, 2010, 04:21:42 PM »

The biggest issue that you'll run into when using Kevlar (same thing as Aramid) or Vectran is that they are lower density than the epoxy and tend to float rather than stay put.  It is also much cheaper to use regular fiberglass materials and to put on a second layer if you need more strength or abrasion resistance, e.g. beaching the boat (yes, the Great Alaskan is designed to be beachable).  The think the short and long of it is that you'll have a much much happier time building the boat using fiberglass than any other fiber and it exceeds the strength requirements as well (when built as specified).  I know that while Kevlar/Aramid have excellent abrasion resistance, it also gets 'fuzzy' when abraded and that makes it absorb water.  If the Kevlar is in between layers and your boat is used or stored in freezing temperatures, then the damp Kevlar can cause delamination when the water in it freezes.

That said, there is one application in the boat that I think can benefit from Aramid/Kevlar, and that would be to give the boat better puncture resistance, e.g. waves or swells dropping your hull onto a pointy wash rock for example.  Since Kevlar floats in epoxy and is hard to 'fiberglass' with it, you would be best off vacuum bagging it if you use it.  Another option is to use light (5-oz or lighter) Kevlar in one or more layers to build up the strength that you want.  It's not too difficult to glass flat plywood with light Kevlar, without vacuum bagging, but curved surfaces are very difficult to glass without vacuum bagging (I tried).  In any case, I'm rambling ...the usage that I was referring to would be on the interior of the boat where it's ultra-high tensile strength would be best utilized for preventing puncturing from an impact outside the boat.  I would suggest glassing the forward half of the bottom panel pieces prior to laying them in the bottom panel molds and stitching them up ...while they are flat on the floor.  I would pre-coat the plywood with 2 coats of epoxy, sand and wash, then apply one layer of 5-oz woven Kevlar, then put the bottom panels into their molds and proceed as usual (stitch, build the keel seam, add chine flats, fiberglass inside faces with glass as instructed etc.)

Just my 2-bits...  I wouldn't mind hearing from others who've tried to use alternative materials and how it turned out for them.

Brian


jadranko

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Re: Fabrics for lamination
« Reply #2 on: February 07, 2010, 04:57:42 PM »
What u think about precoat plywood with epoxy then wait for half cure period when epoxy is still sticky, then put on it kevlar or vectran and coat it with epoxy ? ( I found that metod on some forum )

And also to add additional strenght to whole boat to fill the space under tank support floor from aft to bow with composite made of carbon nanotubes and epoxy ? ( that is my idea, I will ask you lots of things, maybe some not so bright  ;D )

 

Brian.Dixon

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Re: Fabrics for lamination
« Reply #3 on: February 07, 2010, 05:13:36 PM »
What u think about precoat plywood with epoxy then wait for half cure period when epoxy is still sticky, then put on it kevlar or vectran and coat it with epoxy ? ( I found that metod on some forum )

And also to add additional strenght to whole boat to fill the space under tank support floor from aft to bow with composite made of carbon nanotubes and epoxy ? ( that is my idea, I will ask you lots of things, maybe some not so bright  ;D )

The "let the epoxy get tacky" approach would likely work, although I wouldn't trust anything on a curved surface without vacuum bagging ...I had great difficulty with that when I tried it and ended up peeling it all back off the boat and going with just glass.  Note that you should not glass and flat surfaces that will be bent into a curve unless it is the inside face.  Trying to bend glassed plywood, glass on the outside of the curve, is difficult but makes little to no difference if on the inside face.

As far as the under-floor idea goes (and 'floor' is actually the right technical term for it), You can fill it with whatever you want, although it's not necessary.  The boat is over-strong as it is, so I wouldn't worry about that.  The stringers are far beyond requirements, so is the bottom panel thickness, and the glued-in decks (and the 'floor') effectively work like a box-girder structure ...very strong.  Personally, I'd save the weight and just leave the area hollow (or filled with polyethylene closed-cell foam).

Brian


paul h

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Re: Fabrics for lamination
« Reply #4 on: March 01, 2010, 05:30:54 PM »
To really take advantage of kevlar and graphite, you need to vacuum bag them and cure the resin in an autoclave.

Having built a tolman skiff and now in the dreaming/planning stages of a Great Alaskan, I can highly advise folks don't try to "improve" the design.  You'll take more time and spend more $, but won't have a better boat.  These boats are easily contructed w/o the use of special tools and techniques, and are very light for their size. 

Ed Snyder

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Re: Fabrics for lamination
« Reply #5 on: April 28, 2010, 01:03:02 AM »
Brian, In your area of town you call for Biaxial to use in the 30 oz ply join layups. Here at the bottom of the world they call some of it Double bias...  the -+45 deg orientation glass strand type....
Is that what you want?
Thunking no, as the pix I've seen look like -+90 deg used... correct?

Following is a quote from a supplier site here in Ozzie.

"Double Bias 265 gsm 1.27m wide E Glass per Metre $11.41
This is usually called Biaxial or +-45 Biaxial by our north American friends. We think double bias is a much clearer name for this cloth. It is 0.35mm thick and a full roll is 100metres long. This cloth is 1.27m wide and would have to be folded to go through the post. A roll can go by Fastway or general freight."
Not waving....... Drowning!

Brian.Dixon

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Re: Fabrics for lamination
« Reply #6 on: April 29, 2010, 12:07:20 AM »
Yes... what I call "biaxial" is +- 45 degrees, 2 mono-layers knitted together, e.g. not woven together like a basket.  Note that when each 'layer' goes over an angle (corner) that it does so much easier than woven ...easy to use biaxial on seams than woven, especially if the seam forms a sharp angle.

Brian