How strong is...

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Captain_John

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2 ounce mat? I am experimenting on my boat stringers and have glassed in some two by's with 2 ounce mat and am considering goin' over it with cloth, but it seems REALLY strong!

Now, I know this will NEVER fly and it is only for the experience and floatability, but I want it done correctly.

Can one expect structural stability with a two ounce mat or should it be recoated with a fabric to be certain?

What is the deal with this stuff? I am kinda enjoying it, but DON'T TELL ANYONE!!!

:gig: CJ
 

Topaz

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As I understand it, composites are much stronger when the fibers are as straight as possible, to the point that I've seen it recommended to use multiple plies of unidirectional cloth in high-stress areas instead of bidirectional cloth, because in the latter one set of fibers cross above and below the other, resulting in an s-shaped curve to that set of fibers.

Fiberglass mat has the fibers curled and twisted in all sorts of directions, so I imagine that, pound for pound (or for a given thickness), it wouldn't be as strong as properly laid-up UNI cloth, or even BID. I imagine it would be great for forming around corners or curves in low-stress areas, though, especially where you might want to build up some thickness.
 

Captain_John

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Yup, yop, yup... I gotcha...

That makes sense to me!

Twenty five years ago the builder only did matting there and it lasted so long. I suppose an additional layer might be overkill. I am going shopping today for other materials and will see what they have to offer. I still need to remain thin as there are many compund curves involved. Either that or I lay it up in pieces...

Thanks!

:D CJ
 

wsimpso1

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Captain John,

2 oz matt is really thin, but if that was what the original builder used, and it lasted a long time, it is probably a good bet again. At 2 oz, it is mostly holding the water out of the stringers and the joint to the main structure.

Since you are inquiring about strength, if it was an airplane longeron, I would apply two BID cut on the bias so that the fibers would run at +/- 45 degrees to the stringers. Between the main structure and a reinforcing structure like a stringer or a longeron, you need shear strength, which +/- 45 degrees gives you the best of, and need conformability, which +/-45 degrees also gives you. You also need a fillet between the main structure and the stringer or the glass will not follow the curve and will just peel off later.

If you do not want to use Rutan's book for direction on this, the Gougeon Brothers book on Wooden Boat Building is The Bible on this topic. It is so standard that you can get it from many libraries...

Good luck, and be careful, next thing you know, you might have the urge to build a plastic airplane...

Billski
 

Captain_John

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Thank Billski,

I chose to use multiple layers because that is the way I am. Elsewhere (the bilge pump pad) I used the cloth because it is mounted directly to the lower hull. Some wiggling goin on down there.

On the deck I am using at least two layers of mat on the main deck over 5/8" plywood. On the edges I will use 2" and 4" cloth.

Maybe a Compair 6 or a Sportsman 2+2 on floats next time around? Who knows!?!

:gig: CJ
 

Captain_John

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Update:

From a metal guy, this stuff REALLY stinks!!!

I am soooo glad I have a detatched garage!

The new deck project is coming out GREAT!

I have a layer of 2 ounce mat all over the deck and at least one layer of BID cloth at all edges! One more layer of the mat in the alternate direction and I will be ready for paint!

It is gonna be like having a new boat!!!

:ban: CJ
 

wsimpso1

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Captain_John,

So, what resin system are you working with that stinks so much? If it is an epoxy, I want to know what it is so I can avoid it.

I had assumed that since you were writing about this on an airplane thread, you were using airplane materials. Since it stinks, I am suspicious that you are working with polyester resin bought at the chandelry, hardware store or autoparts store, which gives off a strong aroma of styrene.

Most boats are made with and repaired with polyester resins. Polyester has relatively low strength, low toughness, and it shrinks as it cures, and then keeps on curing forever, so it keeps on shrinking and that allows the weave of fabrics to "print through" after a time. Since it produces a lesser strength coomposite, the reinforcement can be mat and you will need more of everything to produce a strong enough struture, and by then, matt is strong enough. High strength cloth does you little good if the resin won't carry it.

In airplane structures, we really can not get away with polyester resins, except in fairings and the like. Van's and the conventional manufacturers use polyester resins for many fairings and the like.

Many folks repairing polyester boats and the like use West System epoxy. Epoxy and vinylester resin systems allow exploitation of the strength and stiffness of the fiber reinforcements. Epoxy (and the less used vinylester) is also the way that wooden boats and airplanes are built and an increasing number of high performance sail- and power-boats are epoxy based composites.

And the epoxies that I use (Gougeon Brothers' Proset and West System) are pretty low odor. While I definitely would not make big use of them in the house, I will do small jobs inside and even my aroma-sensitive wife does not comment on the smell. She would with polyester though...

Billski
 

Captain_John

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Billski, yes... I am using the cheap stuff from the boatyard. It is polyester and gasses off ALOT of odor. Even more than my dog!!!

:gig:

It was only $20 per gallon, so I am not expecting superior performance. If I get another 20 years out of this boat I will be pleased!

When it comes to doing the plane, I plan on using an epoxy resin, probably West System.

:whistle: CJ
 
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